Optical glass and optical element

Abstract

Disclosed is an optical glass which is a SiO2-TiO2-Nb2O5-based glass, contains 10% by mass or more of SiO2, contains 11.0% by mass or less of Na2O, K2O, and Cs2O in total [Na2O+K2O+Cs2O], and has a specific gravity and a refractive index nd that satisfy the following formula (1). nd ≥ 0.2 × specific gravity + 1.18··· (1).

Description

TECHNICAL FIELD

[0001] The present application relates to an optical glass and an optical element. BACKGROUND

[0002] In recent years, along with the progress of AR (Augmented Reality) technology, as an AR device, a display device such as a goggle type or a glasses type has been developed. For example, for a goggle type display device, a lens having a high refractive index and a low specific gravity is required, and the demand for a glass that can be applied to such a lens is increasing.

[0003] High refractive index optical glasses are disclosed in Patent Documents 1 to 4. However, when used as a lens for an AR device, there is a problem that the specific gravity is too large with respect to the refractive index.

[0004] Therefore, an optical glass having a high refractive index while having a reduced specific gravity is required.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: Japanese Patent No. 5766002

[0008] Patent Document 2: Japanese Patent No. 5734587

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2016-88759

[0010] Patent Document 4: Japanese Patent Application Laid-Open No. 2019-34874 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] The present application has been made in view of such circumstances, and aims to provide an optical glass having a high refractive index and a low specific gravity, and an optical element.

[0013] MEANS OF SOLVING THE PROBLEM

[0014] The gist of the present application is as follows.

[0015] (1) An optical glass which is a SiO2-TiO2-Nb2O5-based glass, wherein,

[0016] the content of SiO2 is 10 mass% or more,

[0017] the total content of Na2O, K2O and Cs2O [Na2O + K2O + Cs2O] is 11.0 mass% or less,

[0018] the specific gravity of the optical glass and the refractive index nd satisfy the following formula (1):

[0019] nd≥ 0.2 x specific gravity + 1.18... (1).

[0020] (2) An optical glass, wherein,

[0021] the content of SiO2 is 1 to 50 mass%,

[0022] the content of TiO2 is 1 to 50 mass%,

[0023] the content of BaO is 0 to 16.38 mass%,

[0024] the content of Nb2O5 is 1 to 50 mass%,

[0025] the total content of Li2O, Na2O, K2O and Cs2O [Li2O + Na2O + K2O + Cs2O] is 0.1 to 20 mass%,

[0026] the total content of La2O3, Gd2O3 and Y2O3 [La2O3 + Gd2O3 + Y2O3] is 0 to 10 mass%,

[0027] the total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 45 to 65 mass%,

[0028] the mass ratio of the content of TiO2 to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2 + Nb2O5)] is 0.3 or more,

[0029] the mass ratio of the content of Li2O to the total content of Li2O, Na2O, K2O and Cs2O [Li2O / (Li2O + Na2O + K2O + Cs2O)] is 0.1 to 1,

[0030] the Abbe number vd of the optical glass is 25 or less,

[0031] the refractive index nd of the optical glass is 1.86 or more.

[0032] (3) An optical glass, wherein,

[0033] the content of SiO2 is 1 to 50 mass%,

[0034] the content of TiO2 is 1 to 50 mass%,

[0035] the content of Nb2O5 is 1 to 50 mass%,

[0036] the content of Na2O is 0 to 8 mass%,

[0037] The content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 40 to 80 mass%,

[0038] The mass ratio of the content of TiO2 to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2 + Nb2O5)] is 0.3 or more,

[0039] The optical glass has a refractive index nd of 1.88 or more,

[0040] The optical glass has a ratio of the refractive index nd to the specific gravity [refractive index nd / specific gravity] of 0.50 or more.

[0041] (4) The optical glass according to (3), wherein

[0042] The content of BaO is less than 16.0 mass%.

[0043] (5) An optical glass, wherein

[0044] The mass ratio of the content of Li2O to the total content of glass components other than SiO2, B2O3, P2O5, and GeO2 [Li2O / {100 - (SiO2 + B2O3 + P2O5 + GeO2)}] is 0.02 or more,

[0045] The mass ratio of the content of TiO2 to the total content of TiO2, Nb2O5, WO3, ZrO2, SrO, BaO, ZnO, La2O3, Gd2O3, Y2O3, Ta2O5, and Bi2O3 [TiO2 / (TiO2 + Nb2O5 + WO3 + ZrO2 + SrO + BaO + ZnO + La2O3 + Gd2O3 + Y2O3 + Ta2O5 + Bi2O3)] is 0.40 or more,

[0046] The optical glass has a refractive index nd of 1.86 or more.

[0047] (6) An optical member made of the optical glass according to any one of (1) to (5).

[0048] (7) A light guide plate made of the optical glass according to any one of (1) to (5).

[0049] (8) The light guide plate according to (7), which has a diffraction grating on a surface thereof.

[0050] (9) An image display device comprising:

[0051] an image display element, and

[0052] a light guide plate that guides light emitted from the image display element,

[0053] wherein the light guide plate is made of the optical glass described in any one of (1) to (5).

[0054] Effects of the Invention

[0055] According to the present application, it is possible to provide an optical glass and an optical element having a high refractive index and a low specific gravity. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 is a coordinate diagram obtained by plotting the optical glass of Example 1 and the optical glasses disclosed in Examples of Patent Documents 1 to 4 with the refractive index nd as the vertical axis and the specific gravity as the horizontal axis.

[0057] Figure 2 is a view showing the configuration of a head-mounted display using the light guide plate as one embodiment of the present application.

[0058] Figure 3 is a side view schematically showing the configuration of a head-mounted display using the light guide plate as one embodiment of the present application.

[0059] Figure 4 is a coordinate diagram obtained by plotting the optical glass of Example 4 and the optical glasses disclosed in Examples of Patent Documents 1 to 4 with the mass ratio [Li2O / {100-(SiO2+B2O3+P2O5+GeO2)}] as the vertical axis and the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] as the horizontal axis.

[0060] Figure 5 is a coordinate diagram obtained by plotting the optical glass of Example 4 and the optical glasses disclosed in Examples of Patent Documents 1 to 4 with the ratio [refractive index nd / specific gravity] of the refractive index nd and the specific gravity as the vertical axis and the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] as the horizontal axis.

[0061] Figure 6 is a photograph of the glass sample obtained in Comparative Example 1.

[0062] Figure 7 is a photograph of the glass sample obtained in Comparative Example 2.

[0063] Figure 8 is a photograph of the glass sample obtained in Comparative Example 4.

[0064] Figure 9 is a photograph of a glass sample obtained in Comparative Example 5.

[0065] Figure 10 is a photograph of a glass sample obtained in Comparative Example 6.

[0066] Figure 11 is a photograph of a glass sample obtained in Comparative Example 7. DETAILED DESCRIPTION

[0067] In the present application and the present specification, the glass composition is expressed on an oxide basis unless otherwise specified. Here, the "glass composition on an oxide basis" means a glass composition obtained by converting the entirety of the substances that are decomposed when the glass raw materials are melted and exist in the glass in the form of oxides. The total content of all the glass components expressed on an oxide basis (Sb (Sb203) and Ce (Ce02) added as fining agents are excluded) is set to 100 mass%. Each glass component is expressed as Si02, Ti02, etc. according to custom. Unless otherwise specified, the content and the total content of the glass components are on a mass basis, and "%" means "mass%".

[0068] The content of the glass component can be quantified by a publicly known method, for example, inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), or the like. In the present specification and the present application, the content of a constituent component of 0% means that the constituent component is substantially not contained, and the component can be contained at an unavoidable impurity level.

[0069] Hereinafter, the present application will be described in a first embodiment, a second embodiment, a third embodiment, and a fourth embodiment.

[0070] First Embodiment

[0071] The optical glass of the first embodiment is a Si02-Ti02-Nb205 glass, in which

[0072] The content of Si02is 10 mass% or more,

[0073] The total content of Na20, K20, and Cs20 [Na20 + K20 + Cs20] is 11.0 mass% or less,

[0074] The specific gravity and the refractive index ndsatisfy the following formula (1),

[0075] nd≥ 0.2 x specific gravity + 1.18 (1).

[0076] The optical glass of the first embodiment is a SiO2-TiO2-Nb2O5-based glass. That is, it contains SiO2, TiO2, and Nb2O5 as glass components. By being a SiO2-TiO2-Nb2O5-based glass, it is possible to suppress a decrease in strength and chemical durability.

[0077] In the optical glass of the first embodiment, the content of SiO2 is 10% or more. The lower limit of the content of SiO2 is preferably 12%, and is more preferably in the order of 15%, 18%, and 20%. In addition, the upper limit of the content of SiO2 is preferably 40%, and is more preferably in the order of 38%, 35%, 33%, and 30%.

[0078] SiO2 is a network-forming component of glass. By setting the content of SiO2 to the above range, it is possible to improve the thermal stability, chemical durability, and weather resistance of the glass, and to increase the viscosity of the molten glass. On the other hand, if the content of SiO2 is too high, there is a risk that the refractive index of the glass will decrease and the desired optical properties will not be obtained.

[0079] In the optical glass of the first embodiment, the total content of Na2O, K2O, and Cs2O [Na2O + K2O + Cs2O] is 11.0% or less. The upper limit of this total content is preferably 10.0%, and is more preferably in the order of 9.0%, 8.0%, 7.0%, and 6.0%. In addition, the lower limit of this total content is preferably 0%.

[0080] By setting the total content [Na2O + K2O + Cs2O] to the above range, it is possible to maintain the thermal stability of the glass and to maintain the refractive index at a high level.

[0081] In the optical glass of the first embodiment, the refractive index nd and the specific gravity satisfy the following formula (1). It is preferable to satisfy the following formula (2), and it is more preferable to satisfy the following formula (3). By making the refractive index nd and the specific gravity satisfy the following formula, it is possible to obtain an optical glass in which the refractive index is high and the specific gravity is relatively low.

[0082] nd ≥ 0.2 × specific gravity + 1.18... (1)

[0083] nd ≥ 0.2 × specific gravity + 1.19... (2)

[0084] nd ≥ 0.2 × specific gravity + 1.20... (3)

[0085] For the content, ratio, and properties of the glass components other than the above in the optical glass of the first embodiment, non-limiting examples are shown below.

[0086] In the optical glass of the first embodiment, the upper limit of the content of P2O5 is preferably 10%, and more preferably in the order of 8%, 5%, 3%. The content of P2O5 can also be 0%.

[0087] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the content of P2O5 is preferably set to the above range.

[0088] In the optical glass of the first embodiment, the upper limit of the content of B2O3 is preferably 10%, and more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of B2O3 is preferably 0%, and more preferably in the order of 0.5%, 0.8%, 1.0%.

[0089] B2O3 is a network-forming component of glass. B2O3 has the effect of improving the thermal stability of glass, but when the content of B2O3 is too high, there is a risk of a decrease in the refractive index. Therefore, the content of B2O3 is preferably set to the above range.

[0090] In the optical glass of the first embodiment, the upper limit of the content of Al2O3 is preferably 10%, and more preferably in the order of 8%, 5%, 3%. The content of Al2O3 can also be 0%.

[0091] Al2O3 has the effect of improving chemical durability, but when the content of Al2O3 is too high, there is a risk of a decrease in the melting properties of glass. Therefore, the content of Al2O3 is preferably set to the above range.

[0092] In the optical glass of the first embodiment, the lower limit of the total content of SiO2 and Al2O3 [SiO2 + Al2O3] is preferably 10%, and more preferably in the order of 13%, 15%, 18%, 20%. In addition, the upper limit of the total content is preferably 50%, and more preferably in the order of 45%, 40%, 35%, 30%.

[0093] In order to improve the thermal stability of glass, the total content [SiO2 + Al2O3] is preferably set to the above range.

[0094] In the optical glass of the first embodiment, the lower limit of the mass ratio of the content of B2O3 to the total content of SiO2 and Al2O3 [B2O3 / (SiO2 + Al2O3)] is preferably 0.01, and more preferably in the order of 0.02, 0.03, 0.04. The upper limit of the mass ratio is preferably 0.20, and more preferably in the order of 0.18, 0.15, 0.13, 0.10.

[0095] From the viewpoint of improving chemical durability and thermal stability, the mass ratio [B2O3 / (SiO2 + Al2O3)] is preferably set to the above range.

[0096] In the optical glass of the first embodiment, the lower limit of the total content of B2O3 and P2O5 [B2O3 + P2O5] is preferably 0.5%, further more preferably in the order of 0.8%, 1.0%. In addition, the upper limit of the total content is preferably 10%, further more preferably in the order of 8%, 5%, 3%.

[0097] From the viewpoint of improving chemical durability and thermal stability, the total content [B2O3 + P2O5] is preferably set to the above range.

[0098] In the optical glass of the first embodiment, the lower limit of the total content of B2O3 and SiO2 [B2O3 + SiO2] is preferably 10%, further more preferably in the order of 15%, 18%, 20%. In addition, the upper limit of the total content is preferably 50%, further more preferably in the order of 45%, 40%, 35%.

[0099] In order to obtain an optical glass with a high refractive index, the total content [B2O3 + SiO2] is preferably set to the above range.

[0100] In the optical glass of the first embodiment, the lower limit of the content of ZrO2 is preferably 0%, further more preferably in the order of 0.1%, 0.5%, 1.0%. In addition, the upper limit of the content of ZrO2 is preferably 10%, further more preferably in the order of 8%, 5%, 3%. The content of ZrO2 can also be 0%.

[0101] ZrO2 is a component that contributes to high refractive index. On the other hand, when the content of ZrO2 is too much, thermal stability decreases, and in addition, there is a risk of increasing specific gravity. Therefore, the content of ZrO2 is preferably set to the above range.

[0102] In the optical glass of the first embodiment, the lower limit of the content of TiO2 is preferably 10%, further more preferably in the order of 13%, 15%, 18%, 20%. In addition, the upper limit of the content of TiO2 is preferably 50%, further more preferably in the order of 45%, 40%, 35%.

[0103] TiO2 is a component that contributes to high refractive index, and has the effect of improving glass stability. In addition, it is possible to increase the refractive index without causing an increase in specific gravity. On the other hand, when the content of TiO2 is too much, there is a risk of decreasing thermal stability. Therefore, the content of TiO2 is preferably set to the above range.

[0104] In the optical glass of the first embodiment, the lower limit of the content of Nb2O5 is preferably 10%, further more preferably in the order of 13%, 15%. In addition, the upper limit of the content of Nb2O5 is preferably 50%, further more preferably in the order of 45%, 40%, 35%.

[0105] Nb2O5is a component that contributes to high refractive index, and has an effect of improving glass stability. On the other hand, when the content of Nb2O5is too much, there is a risk of increasing specific gravity, and there is a risk of decreasing thermal stability. Therefore, the content of Nb2O5is preferably set to the above range.

[0106] In the optical glass of the first embodiment, the lower limit of the total content of TiO2and Nb2O5[TiO2+ Nb2O5] is preferably 20%, and further more preferably in the order of 25%, 30%, 35%. In addition, the upper limit of the total content is preferably 70%, and further more preferably in the order of 65%, 60%, 55%.

[0107] TiO2and Nb2O5are components that contribute to high refractive index. Therefore, in order to obtain a glass having desired optical properties, the total content of TiO2and Nb2O5is preferably set to the above range.

[0108] In the optical glass of the first embodiment, the lower limit of the mass ratio of the content of TiO2to the total content of TiO2and Nb2O5[TiO2 / (TiO2+ Nb2O5)] is preferably 0.20, and further more preferably in the order of 0.25, 0.30, 0.35. The upper limit of the mass ratio is preferably 0.80, and further more preferably in the order of 0.75, 0.70, 0.65.

[0109] In order to obtain an optical glass having high refractive index and reduced specific gravity, the mass ratio [TiO2 / (TiO2+ Nb2O5)] is preferably set to the above range.

[0110] In the optical glass of the first embodiment, the upper limit of the content of WO3is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The content of WO3may also be 0%.

[0111] WO3is a component that contributes to high refractive index. On the other hand, when the content of WO3is too much, there is a risk of decreasing thermal stability and increasing specific gravity, and there is a risk of increasing coloring of the glass and decreasing transmittance. Therefore, the content of WO3is preferably set to the above range.

[0112] In the optical glass of the first embodiment, the upper limit of the content of Bi2O3is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of Bi2O3is preferably 0%. The content of Bi2O3may also be 0%.

[0113] Bi2O3is contained in an appropriate amount to improve the thermal stability of the glass. In addition, it is a component that contributes to high refractive index. On the other hand, if the content of Bi2O3is too high, the specific gravity increases. In addition, the coloring of the glass increases. Therefore, the content of Bi2O3is preferably set to the above range.

[0114] In the optical glass of the first embodiment, the upper limit of the total content of TiO2, Nb2O5, WO3, and Bi2O3 [TiO2+Nb2O5+WO3+Bi2O3] is preferably 80%, further more preferably in the order of 70%, 60%. In addition, the lower limit of the total content is preferably 20%, further more preferably in the order of 25%, 30%, 35%.

[0115] TiO2, Nb2O5, WO3, and Bi2O3 are all components that contribute to high refractive index. Therefore, the total content [TiO2+Nb2O5+WO3+Bi2O3] is preferably set to the above range.

[0116] In the optical glass of the first embodiment, the lower limit of the content of Li2O is preferably 0.0%, further more preferably in the order of 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%. The upper limit of the content of Li2O is preferably 10%, further more preferably in the order of 9%, 8%, 7%, 6%, 5%.

[0117] Li2O is a component that contributes to low specific gravity, and in addition, among alkali metals, it is a component that particularly contributes to high refractive index. On the other hand, if the content of Li2O is too high, there is a risk that the thermal stability will decrease. Therefore, the content of Li2O is preferably set to the above range.

[0118] In the optical glass of the first embodiment, the upper limit of the content of Na2O is preferably 10%, further more preferably in the order of 9%, 8%, 7%. The lower limit of the content of Na2O is preferably 0%, further more preferably in the order of 0.5%, 1.0%, 1.5%, 2.0%.

[0119] In the optical glass of the first embodiment, the upper limit of the content of K2O is preferably 10%, further more preferably in the order of 8%, 5%. The lower limit of the content of K2O is preferably 0%, further more preferably in the order of 0.5%, 1.0%, 1.5%, 2.0%. The content of K2O can also be 0%.

[0120] Na2O and K2O have the effect of improving the melting property of the glass. On the other hand, if the content of each of them is too high, there is a risk that the refractive index will decrease, and in addition, there is a risk that the thermal stability will decrease. Therefore, the content of each of Na2O and K2O is preferably set to the above range.

[0121] In the optical glass of the first embodiment, the upper limit of the content of Cs2O is preferably 5%, and further more preferably in the order of 3%, 1%. The lower limit of the content of Cs2O is preferably 0%.

[0122] Cs2O has an effect of improving the thermal stability of the glass, but when the content thereof is increased, chemical durability and weather resistance are reduced. Therefore, the content of Cs2O is preferably set to the above range.

[0123] In the optical glass of the first embodiment, the lower limit of the mass ratio [Li2O / (Li2O+Na2O+K2O)] of the content of Li2O to the total content of Li2O, Na2O, and K2O is preferably 0.00, and further more preferably in the order of 0.10, 0.15, 0.20, 0.25. The upper limit of the mass ratio is preferably 1.00, and further more preferably in the order of 0.80, 0.75, 0.70, 0.65.

[0124] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O)] is preferably set to the above range.

[0125] In the optical glass of the first embodiment, the lower limit of the mass ratio [Li2O / (Li2O+Na2O+K2O+Cs2O)] of the content of Li2O to the total content of Li2O, Na2O, K2O, and Cs2O is preferably 0.10, and further more preferably in the order of 0.15, 0.20, 0.25. The upper limit of the mass ratio is preferably 1.00, and further more preferably in the order of 0.80, 0.75, 0.70, 0.65.

[0126] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O+Cs2O)] is preferably set to the above range.

[0127] In the optical glass of the first embodiment, the lower limit of the total content [Li2O+Na2O+K2O+Cs2O] of Li2O, Na2O, K2O, and Cs2O is preferably 1.5%, and further more preferably in the order of 2%, 4%, 6%. The upper limit of the total content is preferably 15%, and further more preferably in the order of 13%, 10%.

[0128] In order to obtain an optical glass having excellent meltability, the total content [Li2O+Na2O+K2O+Cs2O] is preferably set to the above range.

[0129] In the optical glass of the first embodiment, the upper limit of the content of MgO is preferably 20%, and further more preferably in the order of 15%, 10%, 5%. In addition, the lower limit of the content of MgO is preferably 0%.

[0130] In the optical glass of the first embodiment, the lower limit of the content of CaO is preferably 1%, and further more preferably in the order of 3%, 5%, 8%. The upper limit of the content of CaO is preferably 20%, and further more preferably in the order of 18%, 15%, 13%.

[0131] MgO and CaO have an effect of improving the melting property of the glass. On the other hand, when the content of each of them is too much, there is a risk that the thermal stability decreases. Therefore, each of the contents of MgO and CaO is preferably set to the above range.

[0132] In the optical glass of the first embodiment, the upper limit of the content of SrO is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of SrO is preferably 0%.

[0133] SrO has an effect of improving the melting property of the glass and increasing the refractive index. On the other hand, when the content of SrO is too much, there is a risk that the thermal stability decreases and the specific gravity increases. Therefore, the content of SrO is preferably set to the above range.

[0134] In the optical glass of the first embodiment, the upper limit of the content of BaO is preferably 20%, and further more preferably in the order of 17%, 15%, 13%, 10%. In addition, the lower limit of the content of BaO is preferably 0%.

[0135] BaO has an effect of improving the melting property of the glass and increasing the refractive index. On the other hand, when the content of BaO is too much, there is a risk that the thermal stability decreases and the specific gravity increases. Therefore, the content of BaO is preferably set to the above range.

[0136] In the optical glass of the first embodiment, the upper limit of the content of ZnO is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of ZnO is preferably 0%.

[0137] ZnO is a glass component that has an effect of improving the thermal stability of the glass. However, when the content of ZnO is too much, the specific gravity increases. Therefore, from the viewpoint of improving the thermal stability of the glass and maintaining the desired optical properties, the content of ZnO is preferably set to the above range.

[0138] In the optical glass of the first embodiment, the upper limit of the total content of MgO, CaO, SrO, BaO, and ZnO [MgO + CaO + SrO + BaO + ZnO] is preferably 40%, and further more preferably in the order of 35%, 30%, 25%. In addition, the lower limit of the total content is preferably 3%, and further more preferably in the order of 5%, 8%, 10%. From the viewpoint of suppressing the increase in the specific gravity and maintaining the thermal stability without hindering the increase in the dispersion, the total content is preferably set to the above range.

[0139] In the optical glass of the first embodiment, the upper limit of the content of Ta2O5 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of Ta2O5 is preferably 0%.

[0140] Ta2O5 is a component that contributes to high refractive index. In addition, it is a glass component that has an effect of improving the thermal stability of the glass, and is a component that lowers Pg, F. On the other hand, when the content of Ta2O5 is increased, the thermal stability of the glass is decreased, and melting residue of the glass raw material is easily generated when the glass is melted. In addition, the specific gravity is increased. Therefore, the content of Ta2O5 is preferably set to the above range.

[0141] In the optical glass of the first embodiment, the upper limit of the content of La2O3 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of La2O3 is preferably 0%.

[0142] La2O3 is a component that contributes to high refractive index. On the other hand, when the content of La2O3 is increased, the specific gravity is increased, and the thermal stability of the glass is decreased. Therefore, from the viewpoint of suppressing the increase in the specific gravity and the decrease in the thermal stability of the glass, the content of La2O3 is preferably set to the above range.

[0143] In the optical glass of the first embodiment, the upper limit of the content of Y2O3 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of Y2O3 is preferably 0%.

[0144] Y2O3 is a component that contributes to high refractive index. On the other hand, when the content of Y2O3 is excessively increased, the thermal stability of the glass is decreased, and the glass becomes easily devitrified in the manufacturing. Therefore, from the viewpoint of suppressing the decrease in the thermal stability of the glass, the content of Y2O3 is preferably set to the above range.

[0145] In the optical glass of the first embodiment, the content of Sc2O3 is preferably 2% or less. In addition, the lower limit of the content of Sc2O3 is preferably 0%.

[0146] In the optical glass of the first embodiment, the content of HfO2 is preferably 2% or less. In addition, the lower limit of the content of HfO2 is preferably 0%.

[0147] Sc2O3 and HfO2 have an effect of increasing the high dispersion of the glass, but are expensive components. Therefore, each content of Sc2O3 and HfO2 is preferably set to the above range.

[0148] In the optical glass of the first embodiment, the content of Lu2O3 is preferably 2% or less. In addition, the lower limit of the content of Lu2O3 is preferably 0%.

[0149] Lu2O3 has an effect of increasing the high dispersion of the glass, but since it has a large molecular weight, it is also a glass component that increases the specific gravity of the glass. Therefore, the content of Lu2O3 is preferably set to the above range.

[0150] In the optical glass of the first embodiment, the content of GeO2 is preferably 2% or less. In addition, the lower limit of the content of GeO2 is preferably 0%.

[0151] GeO2 has an effect of increasing the high dispersion of the glass, but among the glass components that are generally used, it is a particularly expensive component. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, the content of GeO2 is preferably set to the above range.

[0152] In the optical glass of the first embodiment, the upper limit of the content of Gd2O3 is preferably 3.0%, and more preferably 2.0%. In addition, the lower limit of the content of Gd2O3 is preferably 0%.

[0153] Gd2O3 is a component that contributes to the increase in the refractive index. On the other hand, when the content of Gd2O3 is too large, the thermal stability of the glass decreases. In addition, when the content of Gd2O3 is too large, the specific gravity of the glass increases, which is not preferable. Therefore, from the viewpoint of maintaining the thermal stability of the glass while suppressing the increase in the specific gravity, the content of Gd2O3 is preferably set to the above range.

[0154] In the optical glass of the first embodiment, the content of Yb2O3 is preferably 2% or less. In addition, the lower limit of the content of Yb2O3 is preferably 0%.

[0155] Yb2O3 has a large molecular weight compared to La2O3, Gd2O3, and Y2O3, and therefore, it can cause an increase in the specific gravity of the glass. When the specific gravity of the glass increases, the mass of the optical element increases. Therefore, it is preferable to reduce the content of Yb2O3 to suppress the increase in the specific gravity of the glass.

[0156] In addition, when the content of Yb2O3 is too large, the thermal stability of the glass decreases. From the viewpoint of preventing the decrease in the thermal stability of the glass and suppressing the increase in the specific gravity, the content of Yb2O3 is preferably set to the above range.

[0157] In the optical glass of the first embodiment, the upper limit of the total content of La2O3, Gd2O3, and Y2O3 [La2O3 + Gd2O3 + Y2O3] is preferably 10%, and more preferably in the order of 8%, 5%, and 3%. The lower limit of the total content is 0%. The total content can also be 0%.

[0158] From the viewpoint of suppressing an increase in specific gravity and maintaining thermal stability, the total content [La2O3+ Gd2O3+ Y2O3] is preferably set to the above range.

[0159] In the optical glass of the first embodiment, the lower limit of the mass ratio [Li2O / {100 - (SiO2+ B2O3+ P2O5+ GeO2)}] of the content of Li2O to the total content of glass components other than SiO2, B2O3, P2O5, and GeO2 is preferably 0.00, and further more preferably in the order of 0.02, 0.03, 0.04, 0.05, 0.06. The upper limit of the mass ratio is preferably 0.20, and further more preferably in the order of 0.15, 0.13, 0.10.

[0160] Note that the total content of all glass components is set to 100 mass%. Thus, the total content of glass components other than SiO2, B2O3, P2O5, and GeO2 is expressed as [100 - (SiO2+ B2O3+ P2O5+ GeO2)]. From the viewpoint of obtaining an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / {100 - (SiO2+ B2O3+ P2O5+ GeO2)}] is preferably set to the above range.

[0161] In the optical glass of the first embodiment, the lower limit of the mass ratio [TiO2 / (TiO2+ Nb2O5+ WO3+ ZrO2+ SrO+ BaO+ ZnO+ La2O3+ Gd2O3+ Y2O3+ Ta2O5+ Bi2O3)] of the content of TiO2 to the total content of TiO2, Nb2O5, WO3, ZrO2, SrO, BaO, ZnO, La2O3, Gd2O3, Y2O3, Ta2O5, and Bi2O3 is preferably 0.40, and further more preferably in the order of 0.42, 0.44, 0.46, 0.48, 0.50. The upper limit of the mass ratio is preferably 0.80, and further more preferably in the order of 0.75, 0.70, 0.65.

[0162] From the viewpoint of increasing the refractive index while suppressing an increase in specific gravity, the mass ratio [TiO2 / (TiO2+ Nb2O5+ WO3+ ZrO2+ SrO+ BaO+ ZnO+ La2O3+ Gd2O3+ Y2O3+ Ta2O5+ Bi2O3)] is preferably set to the above range.

[0163] The optical glass of the first embodiment is preferably composed mainly of the above glass components, i.e., Li20, Ti02as essential components, Si02, P205, B203, Al203, Zr02, Nb205, W03, Bi203, Na20, K20, Cs20, MgO, CaO, SrO, BaO, ZnO, Ta205, La203, Y203, Sc203, Hf02, Lu203, Ge02, Gd203, and Yb203as optional components, and the total content of the above glass components is preferably 95% or more, more preferably 98% or more, further preferably 99% or more, and still further preferably 99.5% or more.

[0164] Note that the optical glass of the first embodiment is preferably composed substantially of the above glass components, but can contain other components within a range not impairing the effects of the present application. Also, in the present application, the presence of unavoidable impurities is not excluded.

[0165] (Other components)

[0166] Pb, As, Cd, Tl, Be, and Se are toxic. Therefore, it is particularly preferable that the optical glass of the first embodiment not contain these elements as glass components. The content of each of the above elements, converted to an oxide, is preferably less than 0.5%, further more preferably less than 0.1%, still further more preferably less than 0.05%, and yet further more preferably less than 0.01%, in this order.

[0167] U, Th, and Ra are radioactive elements. Therefore, it is particularly preferable that the optical glass of the first embodiment not contain these elements as glass components. The content of each of the above elements, converted to an oxide, is preferably less than 0.5%, further more preferably less than 0.1%, still further more preferably less than 0.05%, and yet further more preferably less than 0.01%, in this order.

[0168] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm cause an increase in coloring of the glass and can become a source of fluorescence. Therefore, it is particularly preferable that the optical glass of the first embodiment not contain these elements as glass components. The content of each of the above elements, converted to an oxide, is preferably less than 0.5%, further more preferably less than 0.1%, still further more preferably less than 0.05%, and yet further more preferably less than 0.01%, in this order.

[0169] Sb (Sb203) and Ce (Ce02) are elements that can be added optionally as fining agents. Of these, Sb (Sb203) is a fining agent that has a large fining effect. Ce (Ce02) has a smaller fining effect than Sb (Sb203). If Ce (Ce02) is added in a large amount, there is a tendency for the coloring of the glass to become strong.

[0170] Note that in the present specification, the contents of Sb (Sb203) and Ce (Ce02) are expressed as external addition ratios, and are not included in the total content of all glass components expressed on an oxide basis. That is, in the present specification, the total content of all glass components other than Sb (Sb203) and Ce (Ce02) is taken as 100 mass%.

[0171] The content of Sb203is expressed as an external addition ratio. That is, in the optical glass of the first embodiment, the content of Sb203when the total content of all glass components other than Sb203and Ce02is taken as 100 mass% is preferably 1 mass% or less, and is further preferably 0.1 mass% or less, 0.05 mass% or less, or 0.03 mass% or less in this order. The content of Sb203may also be 0 mass%.

[0172] The content of Ce02is also expressed as an external addition ratio. That is, in the optical glass of the first embodiment, the content of Ce02when the total content of all glass components other than Ce02and Sb203is taken as 100 mass% is preferably 2 mass% or less, and is further preferably 1 mass% or less, 0.5 mass% or less, or 0.1 mass% or less in this order. The content of Ce02may also be 0 mass%. By taking the content of Ce02in the above range, the fining property of the glass can be improved.

[0173] (Properties of the glass)

[0174] <Abbe number vD>

[0175] In the optical glass of the first embodiment, the Abbe number vDis preferably 15 to 30. The Abbe number vDmay be 18 to 25, or 20 to 24. By taking the Abbe number vDin the above range, a glass having a desired dispersion property can be obtained. The Abbe number vDcan be controlled by adjusting the contents of Ti02, Nb205, W03, and Bi203, which are glass components that contribute to high dispersion.

[0176] <Refractive index nD>

[0177] In the optical glass of the first embodiment, the lower limit of the refractive index nDis 1.86. The lower limit of the refractive index nDmay also be taken as 1.87, 1.88, 1.89, or 1.90. In addition, the upper limit of the refractive index nDmay be taken as 2.20, and further, as 2.15, 2.10, or 2.05. The refractive index can be controlled by adjusting the contents of Ti02, Nb205, W03, Bi203, Zr02, La203, Gd203, Y203, and Ta205, which are glass components that contribute to high refractive index.

[0178] <Specific gravity of the glass>

[0179] The optical glass of the first embodiment is a high refractive index glass, but its specific gravity is not large. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. On the other hand, if the specific gravity is too small, the thermal stability will be reduced.

[0180] Therefore, in the optical glass of the first embodiment, the specific gravity is preferably 4.2 or less, and more preferably 4.0 or less, 3.8 or less, 3.6 or less, and 3.4 or less in this order.

[0181] The specific gravity can be controlled by adjusting the content of each glass component. In particular, by adjusting the content of Li2O and TiO2, the specific gravity can be reduced while maintaining a high refractive index.

[0182] In the optical glass of the first embodiment, the ratio of the refractive index nd to the specific gravity [refractive index nd / specific gravity] is preferably 0.50 or greater, more preferably 0.52 or greater, and even more preferably 0.54 or greater. By setting the ratio [refractive index nd / specific gravity] within the above range, an optical glass having a high refractive index and a relatively low specific gravity can be obtained.

[0183] <Glass transition temperature Tg>

[0184] In the optical glass of the first embodiment, the upper limit of the glass transition temperature Tg is preferably 690°C, more preferably 680°C, 660°C, 650°C, 630°C, and 600°C in this order. The lower limit of the glass transition temperature Tg is not particularly limited, but is usually 500°C, preferably 550°C.

[0185] The glass transition temperature Tg can be controlled by adjusting the total content of alkali metals.

[0186] By ensuring that the upper limit of the glass transition temperature Tg satisfies the above conditions, increases in the molding temperature and annealing temperature during re-hot pressing of the glass can be suppressed, thereby reducing thermal damage to re-hot pressing equipment and annealing equipment.

[0187] By making the lower limit of the glass transition temperature Tg satisfy the above-mentioned conditions, it is easy to maintain good re-hot press moldability and thermal stability of the glass while maintaining desired Abbe number and refractive index.

[0188] <Light Transmittance of Glass>

[0189] The light transmittance of the optical glass of the first embodiment can be evaluated based on the coloration degrees λ80, λ70, and λ5.

[0190] For a glass sample having a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance was measured in a wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance reached 80% was set as λ80, the wavelength at which the external transmittance reached 70% was set as λ70, and the wavelength at which the external transmittance reached 5% was set as λ5.

[0191] The λ80 of the optical glass of the first embodiment is preferably 700 nm or less, more preferably 650 nm or less, and further preferably 600 nm or less.

[0192] The λ70 is preferably 600 nm or less, more preferably 550 nm or less, and further preferably 500 nm or less.

[0193] The λ5 is preferably 500 nm or less, more preferably 450 nm or less, and further preferably 400 nm or less.

[0194] (Production of Optical Glass)

[0195] The optical glass of the first embodiment is produced by adjusting the glass raw material to achieve the above given composition, and using the adjusted glass raw material, according to a publicly known glass production method. For example, a plurality of compounds are adjusted, and mixed sufficiently to produce a batch raw material. The batch raw material is put into a quartz crucible or a platinum crucible to perform rough melt. The melt obtained by the rough melt is rapidly cooled and pulverized to produce a crushed glass. The crushed glass is further put into a platinum crucible to perform heating and remelt to obtain a molten glass. After performing fining and homogenization, the molten glass is shaped and slowly cooled to obtain the optical glass. The shaping and slow cooling of the molten glass can be performed by a publicly known method.

[0196] Note that the compound used when adjusting the batch raw material is not particularly limited as long as it can introduce the desired glass component into the glass and achieve the desired content, and as such a compound, oxides, carbonates, nitrates, hydroxides, fluorides, and the like can be cited.

[0197] (Production of Optical Element and the Like)

[0198] When an optical element is produced using the optical glass of the first embodiment, a publicly known method can be employed. For example, in the production of the optical glass described above, the molten glass is injected into a mold to be shaped into a plate shape, and a glass raw material formed of the optical glass of the present application is produced. The obtained glass raw material is appropriately cut, ground, and polished to produce a chip having a size and a shape suitable for press molding. The chip is heated and softened, and press molding (reheat press) is performed by a publicly known method to produce an optical element blank having a shape similar to that of the optical element. The optical element blank is annealed, and grinding and polishing are performed by a publicly known method to produce the optical element.

[0199] According to the use purpose, an antireflection film, a total reflection film, or the like can be coated on the optical functional surface of the manufactured optical member.

[0200] According to one embodiment of the present application, an optical member made of the above-described optical glass can be provided. As the type of the optical member, a lens such as a plane lens, a spherical lens, an aspherical lens, a prism, a diffraction grating, a light guide plate, and the like can be exemplified. As the shape of the lens, various shapes such as a lenticular lens, a plano-convex lens, a biconcave lens, a plano-concave lens, a convex meniscus lens, a concave meniscus lens, and the like can be exemplified. As the use of the light guide plate, a display device such as an augmented reality (AR) display type of eyewear-type device, a mixed reality (MR) display type of eyewear-type device, and the like can be exemplified. Such a light guide plate is a plate-shaped glass mountable to a frame of an eyewear-type device, and is formed of the above-described optical glass. If necessary, a diffraction grating for changing the traveling direction of light that can propagate by repeatedly performing total reflection inside the light guide plate can be formed on the surface of the light guide plate. The diffraction grating can be formed by a known method. When the eyewear-type device having the above-described light guide plate is worn, light propagated inside the light guide plate is incident to the pupil, and thus a function of the augmented reality (AR) display, the mixed reality (MR) display can be exhibited. Such an eyewear-type device is disclosed in, for example, Japanese Patent Application Laid-Open No. 2017-534352, and the like. Note that the light guide plate can be manufactured by a known method. The optical member can be manufactured by a method including a process of processing a glass molded body made of the above-described optical glass. As the processing, cutting, cutting, rough grinding, fine grinding, polishing, and the like can be exemplified. When such processing is performed, by using the above-described glass, breakage can be reduced, and thus a high-quality optical member can be stably provided.

[0201] (Image display device)

[0202] Hereinafter, a light guide plate according to one embodiment of the present application and an image display device using the light guide plate will be described in detail with reference to the drawings. Note that the same reference numerals are used throughout the drawings to designate the same or similar portions, and the description thereof will not be repeated.

[0203] Figure 2 is a view illustrating a configuration of a head-mounted display 1 (hereinafter, referred to as "HMD 1") using a light guide plate 10 according to one embodiment of the present application, Figure 2 (a) is a front side perspective view of the HMD 1, Figure 2 (b) is a back side perspective view of the HMD 1. As Figure 2 (a) and Figure 2(b) As shown, a spectacle frame 2 worn on the head of a user has a front surface portion on which a spectacle lens 3 is mounted. A backlight 4 for illuminating an image is mounted on a mounting portion 2a of the spectacle frame 2. A signal processing device 5 for reflecting an image and a speaker 6 for reproducing sound are provided on leg portions of the spectacle frame 2. An FPC (Flexible Printed Circuits) 7 constituting a wiring from a circuit of the signal processing device 5 is wired along the spectacle frame 2. A display element unit (for example, a liquid crystal display element) 20 is wired to the center positions of the eyes of the user by the FPC 7, and is held in a manner such that the substantially central portion of the display element unit 20 is disposed on the optical axis of the backlight 4. The display element unit 20 is fixed in opposition to a light guide plate 10 in a manner such that the substantially central portion of the display element unit 20 is located on the light guide plate 10. Further, HOEs (Holographic Optical Elements) 32R, 32L (first optical elements) are fixedly adhered to a first surface 10a of the light guide plate 10 at positions in front of the eyes of the user. HOEs 52R, 52L are laminated on a second surface 10b of the light guide plate 10 at positions in opposition to the display element unit 20 with the light guide plate 10 interposed therebetween.

[0204] Figure 3 is a side view schematically showing the configuration of the HMD 1 as one embodiment of the present application. Note that in Figure 3 , only the main portion of the image display device is shown for the sake of clarity of the drawing, and the illustration of the spectacle frame 2 and the like is omitted. As shown in Figure 3 , the HMD 1 has a structure symmetrical to the left and right with a center line X interposed therebetween, which links the center of the image display element 24 and the center of the light guide plate 10. Further, light of each wavelength incident on the light guide plate 10 from the image display element 24 is divided into two portions and guided to the right eye and the left eye of the user, respectively, as will be described later. The optical paths of the light of each wavelength guided to each eye are also substantially symmetrical to the left and right with the center line X interposed therebetween.

[0205] As shown in Figure 3 , the backlight 4 has a laser light source 21, a diffusion optical system 22, and a microlens array 23. The display element unit 20 is an image generation unit having an image display element 24, which is driven, for example, in a field sequential manner. The laser light source 21 has laser light sources corresponding to each of R (wavelength 436 nm), G (wavelength 546 nm), and B (wavelength 633 nm), which sequentially irradiate light of each wavelength at high speed. The light of each wavelength is incident on the diffusion optical system 22 and the microlens array 23, is converted into uniform parallel light beams having high directivity without unevenness in light quantity, and is perpendicularly incident on the display panel surface of the image display element 24.

[0206] The image display element 24 is, for example, a transmissive liquid crystal (LCDT-LCOS) panel driven in a field sequential manner. The image display element 24 applies modulation corresponding to the image signal generated by the image engine (not shown) of the signal processing device 5 to the light of each wavelength. The light of each wavelength modulated by the pixels of the effective area of ​​the image display element 24 is incident on the light guide plate 10 with a given beam cross section (approximately the same shape as the effective area). It should be noted that the image display element 24 can also be replaced by a display element of other types, such as a DMD (digital micromirror device), a reflective liquid crystal (LCOS) panel, a MEMS (micro electro mechanical system), an organic EL (electro-luminescence), an inorganic EL, etc.

[0207] It should be noted that the display element unit 20 is not limited to a field sequential display element, and can also be an image generating unit of a synchronous display element (a display element having a predetermined arrangement of RGB color filters on the front surface of the light exiting surface). In this case, a white light source can be used as the light source, for example.

[0208] like Figure 3 As shown, the light of each wavelength modulated by the image display element 24 is incident on the inside of the light guide plate 10 in sequence from the first surface 10a. HOE52R and 52L (the second optical element) are stacked on the second surface 10b of the light guide plate 10. HOE52R and 52L are, for example, volume phase type HOEs with a rectangular reflective shape, which have a structure in which three sheets of photosensitive polymers with interference fringes corresponding to the wavelengths of R, G, and B are stacked. That is, HOE52R and 52L are constructed in a manner that has a wavelength selection function of diffracting the light of each wavelength of R, G, and B and transmitting the light of other wavelengths.

[0209] It should be noted that HOEs 32R and 32L are also reflective volume phase HOEs, and have the same layer structure as HOEs 52R and 52L. For example, the pitch of the interference fringe patterns of HOEs 32R and 32L and 52R and 52L can be substantially the same.

[0210] HOEs 52R and 52L are stacked together with their centers aligned and their interference fringe patterns reversed by 180 degrees. In this stacked state, they are tightly fixed to the second surface 10b of the light guide plate 10 by adhesive or other means, with their centers aligned with the centerline X. Light of various wavelengths modulated by the image display element 24 is sequentially incident on the HOEs 52R and 52L via the light guide plate 10.

[0211] For the HOEs 52R, 52L, in order to guide the light of each wavelength which has entered in turn to the right eye, left eye, respectively, a given angle is imparted and diffraction is performed. The light of each wavelength which has been diffracted by the HOEs 52R, 52L is repeatedly totally reflected at the interface between the light guide plate 10 and the air, propagates inside the light guide plate 10, and is incident to the HOEs 32R, 32L. Here, the HOEs 52R, 52L impart the same diffraction angle to the light of each wavelength. Therefore, the light of all wavelengths which have entered the light guide plate 10 at approximately the same position (or which have been emitted from approximately the same coordinates within the effective area of the image display element 24 according to other aspects) propagates in approximately the same optical path inside the light guide plate 10, and is incident to approximately the same position on the HOEs 32R, 32L. According to another aspect, the HOEs 52R, 52L diffract the light of each wavelength of RGB in such a manner that the pixel positional relationship of the image displayed within the effective area of the image display element 24 is faithfully reproduced on the HOEs 32R, 32L.

[0212] As such, in one embodiment of the present application, the HOEs 52R, 52L diffract the light of all wavelengths which have been emitted from approximately the same coordinates within the effective area of the image display element 24 to approximately the same position on the HOEs 32R, 32L, respectively. Alternatively, the HOEs 52R, 52L can be configured so that the diffraction can be performed in such a manner that the light of all wavelengths which would have formed the same pixel if they had been offset relative to each other within the effective area of the image display element 24 is incident to approximately the same position on the HOEs 32R, 32L.

[0213] The light of each wavelength which has been incident to the HOEs 32R, 32L is diffracted by the HOEs 32R, 32L, and is emitted in turn to the outside substantially perpendicularly from the second face 10b of the light guide plate 10. As such, the light of each wavelength which has been emitted as substantially parallel light is imaged as a virtual image I of the image generated by the image display element 24 on the retina of the right eye, the retina of the left eye of the user, respectively. In addition, the HOEs 32R, 32L can be imparted with a capacitor function so that the user can observe the virtual image I of the magnified image. That is, the light which has been incident to the peripheral area of the HOEs 32R, 32L can be emitted so as to form an angle in such a manner as to approach the center of the pupil, and imaged on the retina of the user. Alternatively, in order for the user to observe the virtual image I of the magnified image, the HOEs 52R, 52L can diffract the light of each wavelength of RGB in such a manner that the pixel positional relationship on the HOEs 32R, 32L becomes a magnified similar shape relative to the pixel positional relationship of the image displayed within the effective area of the image display element 24 within the effective area.

[0214] The higher the refractive index, the shorter the air-equivalent optical path length of light advancing within the light guide plate 10, and therefore, by using the optical glass of the present embodiment, which has a high refractive index, it is possible to increase the apparent viewing angle with respect to the width of the image display element 24. Further, although the refractive index is high, the specific gravity is suppressed to a low level, and therefore, it is possible to provide a light guide plate that is light but that achieves the above-described effects.

[0215] Note that the light guide plate of one embodiment of the present application can be used for a see-through transmission-type head-mounted display, a non-transmission-type head-mounted display, or the like.

[0216] These head-mounted displays are excellent in immersion due to the wide viewing angle because the light guide plate is made of the optical glass of the present embodiment, which has a high refractive index and a low specific gravity, and are suitable as image display devices used in combination with information terminals, used for providing AR (Augmented Reality) or the like, or used for providing movie appreciation, games, VR (Virtual Reality), or the like.

[0217] The above description has been given with the head-mounted display as an example, but the above-described light guide plate can be attached to other image display devices.

[0218] Second Embodiment

[0219] In the optical glass of the second embodiment,

[0220] The content of SiO2is 1 to 50 mass%,

[0221] The content of TiO2is 1 to 50 mass%,

[0222] The content of BaO is 0 to 16.38 mass%,

[0223] The content of Nb2O5is 1 to 50 mass%,

[0224] The total content of Li2O, Na2O, K2O, and Cs2O [Li2O + Na2O + K2O + Cs2O] is 0.1 to 20 mass%,

[0225] The total content of La2O3, Gd2O3, and Y2O3 [La2O3 + Gd2O3 + Y2O3] is 0 to 10 mass%,

[0226] The total content of TiO2and Nb2O5[TiO2+ Nb2O5] is 45 to 65 mass%,

[0227] The mass ratio of the content of TiO2to the total content of TiO2and Nb2O5[TiO2 / (TiO2+ Nb2O5)] is 0.3 or more,

[0228] The mass ratio of the content of Li2O to the total content of Li2O, Na2O, K2O, and Cs2O [Li2O / (Li2O+Na2O+K2O+Cs2O)] is 0.1 to 1,

[0229] The Abbe number vd of the optical glass is 25 or less,

[0230] The refractive index nd of the optical glass is 1.86 or more.

[0231] In the optical glass of the second embodiment, the content of SiO2 is 1 to 50%. The lower limit of the content of SiO2 is preferably 10%, and is more preferably in the order of 12%, 15%, 18%, and 20%. In addition, the upper limit of the content of SiO2 is preferably 40%, and is more preferably in the order of 38%, 35%, and 33%.

[0232] SiO2 is a network-forming component of the glass. By setting the content of SiO2 to the above range, the thermal stability, chemical durability, and weather resistance of the glass can be improved, and the viscosity of the molten glass can be increased. On the other hand, when the content of SiO2 is too high, there is a risk that the refractive index of the glass decreases and the desired optical properties cannot be obtained.

[0233] In the optical glass of the second embodiment, the content of TiO2 is 1 to 50%. The lower limit of the content of TiO2 is preferably 10%, and is more preferably in the order of 13%, 15%, 18%, and 20%. In addition, the upper limit of the content of TiO2 is preferably 45%, and is more preferably in the order of 40% and 35%.

[0234] By setting the content of TiO2 to the above range, the refractive index is increased, and the stability of the glass can be improved. In addition, the refractive index can be increased without increasing the specific gravity. On the other hand, when the content of TiO2 is too high, there is a risk that the thermal stability decreases.

[0235] In the optical glass of the second embodiment, the content of BaO is 0 to 16.38%. The upper limit of the content of BaO is preferably 15%, and is more preferably in the order of 13% and 10%. In addition, the lower limit of the content of BaO is preferably 0%.

[0236] By setting the content of BaO to the above range, the melting property of the glass can be improved, and the refractive index can be increased. On the other hand, when the content of BaO is too high, there is a risk that the thermal stability decreases and the specific gravity increases.

[0237] In the optical glass of the second embodiment, the content of Nb2O5 is 1 to 50%. The lower limit of the content of Nb2O5 is preferably 10%, and further more preferably in the order of 13%, 15%. In addition, the upper limit of the content of Nb2O5 is preferably 50%, and further more preferably in the order of 45%, 40%, 35%.

[0238] By setting the content of Nb2O5 to the above range, the refractive index can be increased, and the stability of the glass can be improved. On the other hand, when the content of Nb2O5 is too much, there is a risk of increasing the specific gravity, and there is a risk of reducing the thermal stability.

[0239] In the optical glass of the second embodiment, the total content of Li2O, Na2O, K2O, and Cs2O [Li2O + Na2O + K2O + Cs2O] is 0.1 to 20%. The lower limit of the total content is preferably 1.5%, and further more preferably in the order of 2%, 4%, 6%. The upper limit of the total content is preferably 15%, and further more preferably in the order of 13%, 10%.

[0240] By setting the total content [Li2O + Na2O + K2O + Cs2O] to the above range, an optical glass having excellent meltability can be obtained.

[0241] In the optical glass of the second embodiment, the total content of La2O3, Gd2O3, and Y2O3 [La2O3 + Gd2O3 + Y2O3] is 0 to 10%. The upper limit of the total content is preferably 8%, and further more preferably in the order of 5%, 3%. The lower limit of the total content is 0%. The total content can also be 0%.

[0242] From the viewpoint of suppressing an increase in the specific gravity and maintaining the thermal stability, the total content [La2O3 + Gd2O3 + Y2O3] is preferably set to the above range.

[0243] In the optical glass of the second embodiment, the total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 45 to 65%. The lower limit of the total content is preferably 20%, and further more preferably in the order of 25%, 30%, 35%. In addition, the upper limit of the total content is preferably 63%, and further more preferably in the order of 61%, 59%, 57%.

[0244] By setting the total content [TiO2 + Nb2O5] to the above range, the refractive index can be increased, and a glass having desired optical properties can be obtained.

[0245] In the optical glass of the second embodiment, the mass ratio [TiO2 / (TiO2+Nb2O5)] of the content of TiO2 to the total content of TiO2 and Nb2O5 is 0.3 or more. The lower limit of the mass ratio is preferably 0.35, and further more preferably 0.40, 0.45 in this order. The upper limit of the mass ratio is preferably 0.80, and further more preferably 0.75, 0.70, 0.65 in this order.

[0246] By setting the mass ratio [TiO2 / (TiO2+Nb2O5)] to the above range, an optical glass having a high refractive index and a reduced specific gravity can be obtained.

[0247] In the optical glass of the second embodiment, the mass ratio [Li2O / (Li2O+Na2O+K2O+Cs2O)] of the content of Li2O to the total content of Li2O, Na2O, K2O and Cs2O is 0.1 to 1. The lower limit of the mass ratio is preferably 0.15, and further more preferably 0.20, 0.25 in this order. The upper limit of the mass ratio is preferably 0.80, and further more preferably 0.75, 0.70, 0.65 in this order.

[0248] By setting the mass ratio [Li2O / (Li2O+Na2O+K2O+Cs2O)] to the above range, an optical glass having a high refractive index and a reduced specific gravity can be obtained.

[0249] <Abbe number vD>

[0250] In the optical glass of the second embodiment, the Abbe number vD is 25 or less. The Abbe number vD can be 15 to 25, 18 to 25, or 20 to 24. By setting the Abbe number vD to the above range, a glass having a desired dispersion can be obtained. The Abbe number vD can be controlled by adjusting the contents of TiO2, Nb2O5, WO3 and Bi2O3, which are glass components contributing to high dispersion.

[0251] <Refractive index nD>

[0252] In the optical glass of the second embodiment, the refractive index nD is 1.86 or more. The lower limit of the refractive index nD can be set to 1.87, and further to 1.88, 1.89, or 1.90. In addition, the upper limit of the refractive index nD can be set to 2.20, and further to 2.15, 2.10, or 2.05. The refractive index can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, Bi2O3, ZrO2, La2O3, Gd2O3, Y2O3 and Ta2O5, which are glass components contributing to high refractive index.

[0253] The content, ratio, and characteristics of glass components other than the above in the optical glass of the second embodiment are shown below as non-limiting examples.

[0254] In the optical glass of the second embodiment, the upper limit of the content of P2O5 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The content of P2O5 can also be 0%.

[0255] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the content of P2O5 is preferably set to the above range.

[0256] In the optical glass of the second embodiment, the upper limit of the content of B2O3 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of B2O3 is preferably 0%, and further more preferably in the order of 0.5%, 0.8%, 1.0%.

[0257] B2O3 is a network-forming component of glass. B2O3 has the effect of improving the thermal stability of glass, but when the content of B2O3 is too high, there is a risk of a decrease in the refractive index. Therefore, the content of B2O3 is preferably set to the above range.

[0258] In the optical glass of the second embodiment, the upper limit of the content of Al2O3 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The content of Al2O3 can also be 0%.

[0259] Al2O3 has the effect of improving chemical durability, but when the content of Al2O3 is too high, there is a risk of deterioration in the melting properties of the glass. Therefore, the content of Al2O3 is preferably set to the above range.

[0260] In the optical glass of the second embodiment, the lower limit of the total content of SiO2 and Al2O3 [SiO2 + Al2O3] is preferably 10%, and further more preferably in the order of 13%, 15%, 18%, 20%. In addition, the upper limit of the total content is preferably 50%, and further more preferably in the order of 45%, 40%, 35%, 30%.

[0261] In order to improve the thermal stability of the glass, the total content [SiO2 + Al2O3] is preferably set to the above range.

[0262] In the optical glass of the second embodiment, the lower limit of the mass ratio of the content of B2O3 to the total content of SiO2 and Al2O3 [B2O3 / (SiO2 + Al2O3)] is preferably 0.01, and further more preferably in the order of 0.02, 0.03, 0.04. The upper limit of the mass ratio is preferably 0.20, and further more preferably in the order of 0.18, 0.15, 0.13, 0.10.

[0263] From the viewpoint of improving chemical durability and thermal stability, the mass ratio [B2O3 / (SiO2+ Al2O3)] is preferably set to the above range.

[0264] In the optical glass of the second embodiment, the lower limit of the total content of B2O3 and P2O5 [B2O3+ P2O5] is preferably 0.5%, and more preferably in the order of 0.8%, 1.0%. In addition, the upper limit of the total content is preferably 10%, and more preferably in the order of 8%, 5%, 3%.

[0265] From the viewpoint of improving chemical durability and thermal stability, the total content [B2O3+ P2O5] is preferably set to the above range.

[0266] In the optical glass of the second embodiment, the lower limit of the total content of B2O3 and SiO2 [B2O3+ SiO2] is preferably 10%, and more preferably in the order of 15%, 18%, 20%. In addition, the upper limit of the total content is preferably 50%, and more preferably in the order of 45%, 40%, 35%.

[0267] In order to obtain an optical glass having a high refractive index, the total content [B2O3+ SiO2] is preferably set to the above range.

[0268] In the optical glass of the second embodiment, the lower limit of the content of ZrO2 is preferably 0%, and more preferably in the order of 0.1%, 0.5%, 1.0%. In addition, the upper limit of the content of ZrO2 is preferably 10%, and more preferably in the order of 8%, 5%, 3%. The content of ZrO2 can also be 0%.

[0269] ZrO2 is a component that contributes to high refractive index. On the other hand, when the content of ZrO2 is too much, thermal stability decreases, and in addition, there is a risk of increasing specific gravity. Therefore, the content of ZrO2 is preferably set to the above range.

[0270] In the optical glass of the second embodiment, the upper limit of the content of WO3 is preferably 10%, and more preferably in the order of 8%, 5%, 3%. The content of WO3 can also be 0%.

[0271] WO3 is a component that contributes to high refractive index. On the other hand, when the content of WO3 is too much, there is a risk of decreasing thermal stability and increasing specific gravity, and there is a risk of increasing coloring of the glass and decreasing transmittance. Therefore, the content of WO3 is preferably set to the above range.

[0272] In the optical glass of the second embodiment, the upper limit of the content of Bi2O3 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of Bi2O3 is preferably 0%. The content of Bi2O3 can also be 0%.

[0273] Bi2O3 has the effect of improving the thermal stability of the glass by being contained in an appropriate amount. In addition, it is a component that contributes to the increase in the refractive index. On the other hand, when the content of Bi2O3 is too much, the specific gravity increases. In addition, the coloring of the glass increases. Therefore, the content of Bi2O3 is preferably set to the above range.

[0274] In the optical glass of the second embodiment, the upper limit of the total content [TiO2 + Nb2O5 + WO3 + Bi2O3] of TiO2, Nb2O5, WO3, and Bi2O3 is preferably 80%, and further more preferably in the order of 70%, 60%. In addition, the lower limit of the total content is preferably 20%, and further more preferably in the order of 25%, 30%, 35%.

[0275] TiO2, Nb2O5, WO3, and Bi2O3 are all components that contribute to the increase in the refractive index. Therefore, the total content [TiO2 + Nb2O5 + WO3 + Bi2O3] is preferably set to the above range.

[0276] In the optical glass of the second embodiment, the lower limit of the content of Li2O is preferably 0.1%, and further more preferably in the order of 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%. The upper limit of the content of Li2O is preferably 10%, and further more preferably in the order of 9%, 8%, 7%, 6%, 5%.

[0277] Li2O is a component that contributes to the decrease in the specific gravity, and in addition, among alkali metals, it is a component that particularly contributes to the increase in the refractive index. On the other hand, when the content of Li2O is too much, there is a risk that the thermal stability decreases. Therefore, the content of Li2O is preferably set to the above range.

[0278] In the optical glass of the second embodiment, the upper limit of the content of Na2O is preferably 10%, and further more preferably in the order of 9%, 8%, 7%. The lower limit of the content of Na2O is preferably 0%, and further more preferably in the order of 0.5%, 1.0%, 1.5%, 2.0%.

[0279] In the optical glass of the second embodiment, the upper limit of the content of K2O is preferably 10%, and further more preferably in the order of 8%, 5%. The lower limit of the content of K2O is preferably 0%, and further more preferably in the order of 0.5%, 1.0%, 1.5%, 2.0%. The content of K2O can also be 0%.

[0280] Na2O and K2O have an effect of improving the melting property of the glass. On the other hand, when the content of each of them is excessive, there is a risk of lowering the refractive index, and in addition, there is a risk of lowering the thermal stability. Therefore, the content of each of Na2O and K2O is preferably set to the above range.

[0281] In the optical glass of the second embodiment, the upper limit of the content of Cs2O is preferably 5%, and further more preferably in the order of 3%, 1%. The lower limit of the content of Cs2O is preferably 0%.

[0282] Cs2O has an effect of improving the thermal stability of the glass, but when the content of each of them is excessive, the chemical durability and weather resistance are lowered. Therefore, the content of Cs2O is preferably set to the above range.

[0283] In the optical glass of the second embodiment, the lower limit of the mass ratio [Li2O / (Li2O+Na2O+K2O)] of the content of Li2O to the total content of Li2O, Na2O and K2O is preferably 0.10, and further more preferably in the order of 0.15, 0.20, 0.25. The upper limit of the mass ratio is preferably 1.00, and further more preferably in the order of 0.80, 0.75, 0.70, 0.65.

[0284] In order to obtain an optical glass having a high refractive index and a low specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O)] is preferably set to the above range.

[0285] In the optical glass of the second embodiment, the lower limit of the total content [Na2O+K2O+Cs2O] of Na2O, K2O and Cs2O is preferably 0%. The upper limit of the total content is preferably 11.0%, and further more preferably in the order of 10.0%, 9.0%, 8.0%, 7.0%, 6.0%.

[0286] In order to maintain the refractive index at a high level while maintaining the thermal stability of the glass, the total content [Na2O+K2O+Cs2O] is preferably set to the above range.

[0287] In the optical glass of the second embodiment, the upper limit of the content of MgO is preferably 20%, and further more preferably in the order of 15%, 10%, 5%. In addition, the lower limit of the content of MgO is preferably 0%.

[0288] In the optical glass of the second embodiment, the lower limit of the content of CaO is preferably 1%, and further more preferably in the order of 3%, 5%, 8%. The upper limit of the content of CaO is preferably 20%, and further more preferably in the order of 18%, 15%, 13%.

[0289] MgO and CaO have an effect of improving the melting property of the glass. On the other hand, when the content of each of them is too much, there is a risk that the thermal stability is reduced. Therefore, the content of each of MgO and CaO is preferably set to the above range.

[0290] In the optical glass of the second embodiment, the upper limit of the content of SrO is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of SrO is preferably 0%.

[0291] SrO has an effect of improving the melting property of the glass and increasing the refractive index. On the other hand, when the content of SrO is too much, there is a risk that the thermal stability is reduced and the specific gravity is increased. Therefore, the content of SrO is preferably set to the above range.

[0292] In the optical glass of the second embodiment, the upper limit of the content of ZnO is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of ZnO is preferably 0%.

[0293] ZnO is a glass component having an effect of improving the thermal stability of the glass. However, when the content of ZnO is too much, the specific gravity is increased. Therefore, from the viewpoint of improving the thermal stability of the glass and maintaining the desired optical properties, the content of ZnO is preferably set to the above range.

[0294] In the optical glass of the second embodiment, the upper limit of the total content of MgO, CaO, SrO, BaO, and ZnO [MgO + CaO + SrO + BaO + ZnO] is preferably 40%, and further more preferably in the order of 35%, 30%, 25%. In addition, the lower limit of the total content is preferably 3%, and further more preferably in the order of 5%, 8%, 10%. From the viewpoint of suppressing the increase in the specific gravity and maintaining the thermal stability without hindering the high dispersion, the total content is preferably set to the above range.

[0295] In the optical glass of the second embodiment, the upper limit of the content of Ta2O5 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of Ta2O5 is preferably 0%.

[0296] Ta2O5 is a component that contributes to the high refractive index. In addition, it is a glass component having an effect of improving the thermal stability of the glass, and is also a component that reduces Pg,F. On the other hand, when the content of Ta2O5 is too much, the thermal stability of the glass is reduced, and the melting residue of the glass raw material is likely to occur when the glass is melted. In addition, the specific gravity is increased. Therefore, the content of Ta2O5 is preferably set to the above range.

[0297] In the optical glass of the second embodiment, the upper limit of the content of La2O3 is preferably 10%, and more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of La2O3 is preferably 0%.

[0298] La2O3 is a component that contributes to high refractive index. On the other hand, when the content of La2O3 is increased, the specific gravity increases, and the thermal stability of the glass decreases. Therefore, from the viewpoint of suppressing the increase in the specific gravity and the decrease in the thermal stability of the glass, the content of La2O3 is preferably set to the above range.

[0299] In the optical glass of the second embodiment, the upper limit of the content of Y2O3 is preferably 10%, and more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of Y2O3 is preferably 0%.

[0300] Y2O3 is a component that contributes to high refractive index. On the other hand, when the content of Y2O3 is excessively increased, the thermal stability of the glass decreases, and the glass becomes likely to devitrify during production. Therefore, from the viewpoint of suppressing the decrease in the thermal stability of the glass, the content of Y2O3 is preferably set to the above range.

[0301] In the optical glass of the second embodiment, the content of Sc2O3 is preferably 2% or less. In addition, the lower limit of the content of Sc2O3 is preferably 0%.

[0302] In the optical glass of the second embodiment, the content of HfO2 is preferably 2% or less. In addition, the lower limit of the content of HfO2 is preferably 0%.

[0303] Sc2O3 and HfO2 have an effect of increasing the high dispersion of the glass, but are expensive components. Therefore, the content of each of Sc2O3 and HfO2 is preferably set to the above range.

[0304] In the optical glass of the second embodiment, the content of Lu2O3 is preferably 2% or less. In addition, the lower limit of the content of Lu2O3 is preferably 0%.

[0305] Lu2O3 has an effect of increasing the high dispersion of the glass, but is also a glass component that increases the specific gravity of the glass because of a large molecular weight. Therefore, the content of Lu2O3 is preferably set to the above range.

[0306] In the optical glass of the second embodiment, the content of GeO2 is preferably 2% or less. In addition, the lower limit of the content of GeO2 is preferably 0%.

[0307] GeO2 has an effect of increasing the high dispersion of the glass, but is an especially expensive component among the glass components that are generally used. Therefore, from the viewpoint of reducing the production cost of the glass, the content of GeO2 is preferably set to the above range.

[0308] In the optical glass of the second embodiment, the upper limit of the content of Gd2O3 is preferably 3.0%, more preferably 2.0%. In addition, the lower limit of the content of Gd2O3 is preferably 0%.

[0309] Gd2O3 is a component that contributes to a higher refractive index. On the other hand, excessive Gd2O3 content reduces the thermal stability of the glass. Furthermore, excessive Gd2O3 content increases the specific gravity of the glass, which is not preferred. Therefore, to maintain good thermal stability of the glass while suppressing an increase in specific gravity, the Gd2O3 content is preferably within the above-mentioned range.

[0310] In the optical glass of the second embodiment, the content of Yb2O3 is preferably 2% or less. The lower limit of the content of Yb2O3 is preferably 0%.

[0311] Yb2O3 has a higher molecular weight than La2O3, Gd2O3, and Y2O3, leading to an increase in the specific gravity of the glass. When the specific gravity of the glass increases, the weight of the optical element increases. Therefore, it is preferable to reduce the Yb2O3 content to suppress the increase in the specific gravity of the glass.

[0312] In addition, when the content of Yb2O3 is too much, the thermal stability of the glass decreases. From the viewpoint of preventing the decrease in the thermal stability of the glass and suppressing the increase in specific gravity, the content of Yb2O3 is preferably set to the above range.

[0313] In the optical glass of the second embodiment, the mass ratio of the Li₂O content to the total content of the glass components other than SiO₂, B₂O₃, P₂O₅, and GeO₂ [Li₂O / {100-(SiO₂+B₂O₃+P₂O₅+GeO₂)}] is preferably 0.02, more preferably 0.03, 0.04, 0.05, and 0.06, in this order. The upper limit of this mass ratio is preferably 0.20, more preferably 0.15, 0.13, and 0.10, in this order.

[0314] It should be noted that the total content of all glass components is set to 100% by mass. Therefore, the total content of glass components other than SiO2, B2O3, P2O5 and GeO2 is expressed as [100-(SiO2+B2O3+P2O5+GeO2)]. From the viewpoint of obtaining an optical glass with a high refractive index and a reduced specific gravity, the mass ratio [Li2O / {100-(SiO2+B2O3+P2O5+GeO2)}] is preferably set to the above range.

[0315] In the optical glass of the second embodiment, the lower limit of the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] of the content of TiO2and the total content of TiO2, Nb2O5, WO3, ZrO2, SrO, BaO, ZnO, La2O3, Gd2O3, Y2O3, Ta2O5, and Bi2O3is preferably 0.40, and more preferably in the order of 0.42, 0.44, 0.46, 0.48, 0.50. The upper limit of the mass ratio is preferably 0.80, and more preferably in the order of 0.75, 0.70, 0.65.

[0316] From the viewpoint of increasing the refractive index while suppressing an increase in specific gravity, the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] is preferably set to the above range.

[0317] The optical glass of the second embodiment is preferably composed mainly of the above glass components, i.e., SiO2, TiO2, Nb2O5as essential components, and BaO, P2O5, B2O3, Al2O3, ZrO2, WO3, Bi2O3, Li2O, Na2O, K2O, Cs2O, MgO, CaO, SrO, ZnO, Ta2O5, La2O3, Y2O3, Sc2O3, HfO2, Lu2O3, GeO2, Gd2O3, and Yb2O3as optional components, and the total content of the above glass components is preferably 95% or more, more preferably 98% or more, further preferably 99% or more, and more further preferably 99.5% or more.

[0318] Note that the optical glass of the second embodiment is preferably composed substantially of the above glass components, but can contain other components within a range that does not hinder the effects of the present application. In addition, in the present application, the presence of unavoidable impurities is not excluded.

[0319] (Other components)

[0320] Pb, As, Cd, Tl, Be, and Se are toxic. Therefore, it is particularly preferable that the optical glass of the second embodiment not contain these elements as glass components. The content of each of the above elements, converted to an oxide, is preferably less than 0.5%, and more preferably in the order of less than 0.1%, less than 0.05%, and less than 0.01%.

[0321] U, Th, Ra are radioactive elements. Therefore, it is particularly preferable that the optical glass of the second embodiment does not contain these elements as glass components. The content of each of the above elements, converted into oxides, is preferably less than 0.5%, further preferably less than 0.1%, less than 0.05%, less than 0.01% in this order.

[0322] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm cause an increase in coloring of the glass and can become a source of fluorescence generation. Therefore, it is particularly preferable that the optical glass of the second embodiment does not contain these elements as glass components. The content of each of the above elements, converted into oxides, is preferably less than 0.5%, further preferably less than 0.1%, less than 0.05%, less than 0.01% in this order.

[0323] Sb (Sb2O3), Ce (CeO2) are optional elements added to function as fining agents. Among them, Sb (Sb2O3) is a fining agent with a large fining effect. Ce (CeO2) has a small fining effect compared to Sb (Sb2O3). If Ce (CeO2) is added in a large amount, there is a tendency for the coloring of the glass to become strong.

[0324] Note that, in the present specification, the content of Sb (Sb2O3) and Ce (CeO2) is expressed as an externally added proportion and is not included in the total content of all glass components expressed on an oxide basis. That is, in the present specification, the total content of all glass components other than Sb (Sb2O3) and Ce (CeO2) is taken as 100 mass%.

[0325] The content of Sb2O3 is expressed as an externally added proportion. That is, in the optical glass of the second embodiment, the content of Sb2O3 when the total content of all glass components other than Sb2O3 and CeO2 is taken as 100 mass% is preferably 1 mass% or less, further preferably 0.1 mass% or less, 0.05 mass% or less, 0.03 mass% or less in this order. The content of Sb2O3 can also be 0 mass%.

[0326] The content of CeO2 is also expressed as an externally added proportion. That is, in the optical glass of the second embodiment, the content of CeO2 when the total content of all glass components other than CeO2 and Sb2O3 is taken as 100 mass% is preferably 2 mass% or less, further preferably 1 mass% or less, 0.5 mass% or less, 0.1 mass% or less in this order. The content of CeO2 can also be 0 mass%. By taking the content of CeO2 to be within the above range, the fining property of the glass can be improved.

[0327] (Properties of the glass)

[0328] <Specific gravity of glass>

[0329] The optical glass of the second embodiment is a high refractive index glass, but the specific gravity is not large. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. On the other hand, if the specific gravity is too small, the thermal stability can be reduced.

[0330] Therefore, in the optical glass of the second embodiment, the specific gravity is preferably 4.2 or less, and further more preferably 4.0 or less, 3.8 or less, 3.6 or less, 3.4 or less in this order.

[0331] The specific gravity can be controlled by adjusting the content of each glass component. In particular, by adjusting the content of Li20 and Ti02, the specific gravity can be reduced while maintaining a high refractive index.

[0332] Note that, in the optical glass of the second embodiment, the refractive index nd and the specific gravity preferably satisfy the following equation (1), more preferably satisfy the following equation (2), and further preferably satisfy the following equation (3). By making the refractive index nd and the specific gravity satisfy the following equations, an optical glass having a high refractive index and a relatively reduced specific gravity can be obtained.

[0333] nd≥ 0.2 x specific gravity + 1.18 ··· (1)

[0334] nd≥ 0.2 x specific gravity + 1.19 ··· (2)

[0335] nd≥ 0.2 x specific gravity + 1.20 ··· (3)

[0336] In addition, in the optical glass of the second embodiment, the ratio of the refractive index nd to the specific gravity [refractive index nd / specific gravity] is preferably 0.50 or more, more preferably 0.52 or more, and further preferably 0.54 or more. By setting the ratio [refractive index nd / specific gravity] to the above range, an optical glass having a high refractive index and a relatively reduced specific gravity can be obtained.

[0337] <Glass transition temperature Tg>

[0338] In the optical glass of the second embodiment, the upper limit of the glass transition temperature Tg is preferably 680°C, and further more preferably 670°C, 660°C, 650°C, 630°C, 600°C in this order. The lower limit of the glass transition temperature Tg is not particularly limited, and is usually 500°C, and is preferably 550°C.

[0339] The glass transition temperature Tg can be controlled by adjusting the total content of alkali metals.

[0340] By satisfying the above condition for the upper limit of the glass transition temperature Tg, the molding temperature and the annealing temperature of the glass at the time of reheat press molding can be suppressed from increasing, and the damage to the equipment for reheat press molding and the annealing equipment can be reduced.

[0341] By satisfying the above condition for the lower limit of the glass transition temperature Tg, the reheat press moldability and the thermal stability of the glass can be favorably maintained while the desired Abbe number and the refractive index are maintained.

[0342] <Light transmittance of glass>

[0343] The light transmittance of the optical glass of the second embodiment can be evaluated in terms of the coloration degrees λ80, λ70, and λ5.

[0344] For a glass sample having a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance is measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance reaches 80% is set as λ80, the wavelength at which the external transmittance reaches 70% is set as λ70, and the wavelength at which the external transmittance reaches 5% is set as λ5.

[0345] The λ80 of the optical glass of the second embodiment is preferably 700 nm or less, more preferably 650 nm or less, and further preferably 600 nm or less.

[0346] The λ70 is preferably 600 nm or less, more preferably 550 nm or less, and further preferably 500 nm or less.

[0347] The λ5 is preferably 500 nm or less, more preferably 450 nm or less, and further preferably 400 nm or less.

[0348] <Manufacture of optical glass>

[0349] The optical glass of the second embodiment is prepared by adjusting the glass raw materials so as to achieve the above given composition, and is produced using the adjusted glass raw materials according to a publicly known glass production method. For example, a plurality of compounds are adjusted, and are sufficiently mixed to produce batch raw materials. The batch raw materials are put into a quartz crucible or a platinum crucible, and are subjected to rough melt. The melt obtained by the rough melt is rapidly cooled and pulverized to produce crushed glass. The crushed glass is further put into a platinum crucible, and is subjected to heating and remelt to obtain a molten glass. After the molten glass is subjected to fining and homogenization, the molten glass is shaped, and is subjected to slow cooling to obtain the optical glass. The shaping and the slow cooling of the molten glass can be performed according to a publicly known method.

[0350] It should be noted that as long as the desired glass components can be introduced into the glass and the desired content is achieved, there is no particular limitation on the compounds used in preparing the batch raw materials. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, fluorides, and the like.

[0351] (Manufacturing of optical components, etc.)

[0352] When using the optical glass of the second embodiment to produce an optical element, a known method can be used. For example, in the manufacture of the above-mentioned optical glass, molten glass is poured into a mold and formed into a plate-like shape to produce a glass material formed from the optical glass of the present invention. The obtained glass material is appropriately cut, ground, and polished to produce fragments of a size and shape suitable for press molding. The fragments are heated and softened, and press molded (re-hot pressed) by a known method to produce an optical element blank having a shape similar to that of the optical element. The optical element blank is annealed, and then ground and polished by a known method to produce an optical element.

[0353] Depending on the intended use, the optical functional surface of the produced optical element may be coated with an anti-reflection film, a total reflection film, or the like.

[0354] According to one embodiment of the present invention, an optical element made of the above-mentioned optical glass can be provided. As the type of optical element, lenses such as plane lenses, spherical lenses, aspherical lenses, prisms, diffraction gratings, light guide plates, etc. can be exemplified. As the shape of the lens, various shapes such as biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses can be exemplified. As the use of the light guide plate, display devices such as glasses-type devices of augmented reality (AR) display type and glasses-type devices of mixed reality (MR) display type can be exemplified. Such a light guide plate is a plate-shaped glass that can be mounted on the frame of the glasses-type device and is formed of the above-mentioned optical glass. As needed, a diffraction grating can also be formed on the surface of the light guide plate, which is used to change the direction of travel of light that can be repeatedly reflected and propagated inside the light guide plate. The diffraction grating can be formed by a known method. When wearing a glasses-type device with the above-mentioned light guide plate, the light propagated inside the light guide plate is incident on the pupil, thereby showing the functions of augmented reality (AR) display and mixed reality (MR) display. Such eyeglass-type devices are disclosed, for example, in Japanese Patent Publication No. 2017-534352. It should be noted that the light guide plate can be manufactured by a known method. The optical element can be manufactured by a method comprising a step of processing a glass molded body made of the above-mentioned optical glass. Examples of processing include cutting, chipping, rough grinding, fine grinding, and polishing. When performing such processing, the use of the above-mentioned glass can reduce breakage, thereby making it possible to stably provide high-quality optical elements.

[0355] (Image Display Device)

[0356] For the image display device of the second embodiment, the same as the first embodiment can be provided.

[0357] Third Embodiment

[0358] In the optical glass of the third embodiment,

[0359] The content of SiO2is 1 to 50 mass%,

[0360] The content of TiO2is 1 to 50 mass%,

[0361] The content of Nb2O5is 1 to 50 mass%,

[0362] The content of Na2O is 0 to 8 mass%,

[0363] The total content of TiO2and Nb2O5[TiO2+ Nb2O5] is 40 to 80 mass%,

[0364] The mass ratio of the content of TiO2to the total content of TiO2and Nb2O5[TiO2 / (TiO2+ Nb2O5)] is 0.3 or more,

[0365] The refractive index ndof the optical glass is 1.88 or more,

[0366] The ratio of the refractive index ndto the specific gravity [refractive index nd / specific gravity] of the optical glass is 0.50 or more.

[0367] In the optical glass of the third embodiment, the content of SiO2is 1 to 50%. The lower limit of the content of SiO2is preferably 10%, and further more preferably in the order of 12%, 15%, 18%, and 20%. In addition, the upper limit of the content of SiO2is preferably 40%, and further more preferably in the order of 38%, 35%, 33%, and 30%.

[0368] SiO2is a network-forming component of the glass. By setting the content of SiO2to the above range, the thermal stability, chemical durability, and weather resistance of the glass can be improved, and the viscosity of the molten glass can be increased. On the other hand, if the content of SiO2is too much, the refractive index of the glass can be reduced, and the desired optical properties can not be obtained.

[0369] In the optical glass of the third embodiment, the content of TiO2is 1 to 50%. The lower limit of the content of TiO2is preferably 10%, and further more preferably in the order of 13%, 15%, 18%, and 20%. In addition, the upper limit of the content of TiO2is preferably 50%, and further more preferably in the order of 45%, 40%, and 35%.

[0370] By setting the content of TiO2 to the above range, the refractive index is increased, and the stability of the glass can be improved. In addition, the refractive index can be increased without causing an increase in specific gravity. On the other hand, when the content of TiO2 is too much, there is a risk that the thermal stability is reduced.

[0371] In the optical glass of the third embodiment, the content of Nb2O5 is 1 to 50%. The lower limit of the content of Nb2O5 is preferably 10%, and further more preferably in the order of 13%, 15%. In addition, the upper limit of the content of Nb2O5 is preferably 50%, and further more preferably in the order of 45%, 40%, 35%.

[0372] By setting the content of Nb2O5 to the above range, the refractive index can be increased, and the stability of the glass can be improved. On the other hand, when the content of Nb2O5 is too much, there is a risk that the specific gravity is increased, and in addition, there is a risk that the thermal stability is reduced.

[0373] In the optical glass of the third embodiment, the content of Na2O is 0 to 8%. The lower limit of the content of Na2O is preferably 0.5%, and further more preferably in the order of 1.0%, 1.5%, 2.0%. In addition, the upper limit of the content of Na2O is preferably 7%, and further more preferably in the order of 6.5%, 5.5%, 4.5%.

[0374] By setting the content of Na2O to the above range, the melting property of the glass can be improved. On the other hand, when the content of Na2O is too much, there is a risk that the refractive index is reduced, and in addition, there is a risk that the thermal stability is reduced.

[0375] In the optical glass of the third embodiment, the total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 40 to 80%. The lower limit of the total content is preferably 42%, and further more preferably in the order of 44%, 46%, 48%. In addition, the upper limit of the total content is preferably 70%, and further more preferably in the order of 65%, 60%, 55%.

[0376] By setting the total content [TiO2 + Nb2O5] to the above range, the refractive index can be increased, and a glass having desired optical properties can be obtained.

[0377] In the optical glass of the third embodiment, the mass ratio of the content of TiO2 to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2 + Nb2O5)] is 0.3 or more. The lower limit of the mass ratio is preferably 0.35, and further more preferably in the order of 0.40, 0.45. The upper limit of the mass ratio is preferably 0.80, and further more preferably in the order of 0.75, 0.70, 0.65.

[0378] By setting the mass ratio [TiO2 / (TiO2+Nb2O5)] to the above range, an optical glass having a high refractive index and a reduced specific gravity can be obtained.

[0379] In the optical glass of the third embodiment, the refractive index nd is 1.88 or more. The lower limit of the refractive index nd can be set to 1.89, or can be set to 1.90. In addition, the upper limit of the refractive index nd can be set to 2.20, and further can be set to 2.15, 2.10, or 2.05. The refractive index can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, Bi2O3, ZrO2, La2O3, Gd2O3, Y2O3, and Ta2O5, which are glass components contributing to high refractive index.

[0380] In addition, in the optical glass of the third embodiment, the ratio [refractive index nd / specific gravity] of the refractive index nd to the specific gravity is 0.50 or more. It is preferable to be 0.52 or more, and more preferable to be 0.54 or more. By setting the ratio [refractive index nd / specific gravity] to the above range, an optical glass having a high refractive index and a relatively reduced specific gravity can be obtained.

[0381] For the contents, ratios, and characteristics of the glass components other than the above in the optical glass of the third embodiment, non-limiting examples are shown below.

[0382] In the optical glass of the third embodiment, the upper limit of the content of P2O5 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The content of P2O5 can also be 0%.

[0383] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the content of P2O5 is preferably set to the above range.

[0384] In the optical glass of the third embodiment, the upper limit of the content of B2O3 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of B2O3 is preferably 0%, and further more preferably in the order of 0.5%, 0.8%, 1.0%.

[0385] B2O3 is a network-forming component of glass. B2O3 has the effect of improving the thermal stability of glass, but when the content of B2O3 is too much, there is a risk of a decrease in the refractive index. Therefore, the content of B2O3 is preferably set to the above range.

[0386] In the optical glass of the third embodiment, the upper limit of the content of Al2O3 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The content of Al2O3 can also be 0%.

[0387] Al2O3 has an effect of improving chemical durability, but when the content of Al2O3 is too much, there is a risk that the melting property of the glass becomes poor. Therefore, the content of Al2O3 is preferably set to the above range.

[0388] In the optical glass of the third embodiment, the lower limit of the total content of SiO2 and Al2O3 [SiO2 + Al2O3] is preferably 10%, and further more preferably in the order of 13%, 15%, 18%, and 20%. In addition, the upper limit of the total content is preferably 50%, and further more preferably in the order of 45%, 40%, and 35%.

[0389] In order to improve the thermal stability of the glass, the total content [SiO2 + Al2O3] is preferably set to the above range.

[0390] In the optical glass of the third embodiment, the lower limit of the mass ratio of the content of B2O3 to the total content of SiO2 and Al2O3 [B2O3 / (SiO2 + Al2O3)] is preferably 0.01, and further more preferably in the order of 0.02, 0.03, and 0.04. The upper limit of the mass ratio is preferably 0.20, and further more preferably in the order of 0.18, 0.15, 0.13, and 0.10.

[0391] From the viewpoint of improving chemical durability and thermal stability, the mass ratio [B2O3 / (SiO2 + Al2O3)] is preferably set to the above range.

[0392] In the optical glass of the third embodiment, the lower limit of the total content of B2O3 and P2O5 [B2O3 + P2O5] is preferably 0.5%, and further more preferably in the order of 0.8% and 1.0%. In addition, the upper limit of the total content is preferably 10%, and further more preferably in the order of 8%, 5%, and 3%.

[0393] From the viewpoint of improving chemical durability and thermal stability, the total content [B2O3 + P2O5] is preferably set to the above range.

[0394] In the optical glass of the third embodiment, the lower limit of the total content of B2O3 and SiO2 [B2O3 + SiO2] is preferably 10%, and further more preferably in the order of 15%, 18%, and 20%. In addition, the upper limit of the total content is preferably 50%, and further more preferably in the order of 45%, 40%, and 35%.

[0395] In order to obtain an optical glass having a high refractive index, the total content [B2O3 + SiO2] is preferably set to the above range.

[0396] In the optical glass of the third embodiment, the lower limit of the content of Zr02is preferably 0%, and further more preferably in the order of 0.1%, 0.5%, 1.0%. In addition, the upper limit of the content of Zr02is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The content of Zr02may also be 0%.

[0397] Zr02is a component that contributes to high refractive index. On the other hand, when the content of Zr02is too much, the thermal stability decreases, and in addition, there is a risk of an increase in specific gravity. Therefore, the content of Zr02is preferably set to the above range.

[0398] In the optical glass of the third embodiment, the upper limit of the content of W03is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The content of W03may also be 0%.

[0399] W03is a component that contributes to high refractive index. On the other hand, when the content of W03is too much, there is a risk of a decrease in thermal stability, an increase in specific gravity, and a risk of an increase in coloring of the glass and a decrease in transmittance. Therefore, the content of W03is preferably set to the above range.

[0400] In the optical glass of the third embodiment, the upper limit of the content of Bi203is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of Bi203is preferably 0%. The content of Bi203may also be 0%.

[0401] Bi203has the effect of improving the thermal stability of the glass by being contained in an appropriate amount. In addition, it is a component that contributes to high refractive index. On the other hand, when the content of Bi203is too much, the specific gravity increases. In addition, the coloring of the glass increases. Therefore, the content of Bi203is preferably set to the above range.

[0402] In the optical glass of the third embodiment, the upper limit of the total content of Ti02, Nb205, W03, and Bi203[Ti02+Nb205+ W03+ Bi203] is preferably 80%, and further more preferably in the order of 70%, 60%. In addition, the lower limit of the total content is preferably 20%, and further more preferably in the order of 25%, 30%, 35%.

[0403] Ti02, Nb205, W03, and Bi203are all components that contribute to high refractive index. Therefore, the total content [Ti02+Nb205+ W03+ Bi203] is preferably set to the above range.

[0404] In the optical glass of the third embodiment, the lower limit of the content of Li20 is preferably 0.0%, and further more preferably in the order of 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%. The upper limit of the content of Li20 is preferably 10%, and further more preferably in the order of 9%, 8%, 7%, 6%, 5%.

[0405] Li20 is a component that contributes to low specific gravity, and among alkali metals, is a component that particularly contributes to high refractive index. On the other hand, when the content of Li20 is too much, there is a risk of reduction in thermal stability. Therefore, the content of Li20 is preferably set to the above range.

[0406] In the optical glass of the third embodiment, the upper limit of the content of K20 is preferably 10%, and further more preferably in the order of 8%, 5%. The lower limit of the content of K20 is preferably 0%, and further more preferably in the order of 0.5%, 1.0%, 1.5%, 2.0%. The content of K20 can also be 0%.

[0407] K20 has an effect of improving the melting property of the glass. On the other hand, when the content of K20 is too much, there is a risk of reduction in refractive index, and in addition, there is a risk of reduction in thermal stability. Therefore, the content of K20 is preferably set to the above range.

[0408] In the optical glass of the third embodiment, the upper limit of the content of Cs20 is preferably 5%, and further more preferably in the order of 3%, 1%. The lower limit of the content of Cs20 is preferably 0%.

[0409] Cs20 has an effect of improving the thermal stability of the glass, but when the content thereof is too much, chemical durability and weather resistance are reduced. Therefore, the content of Cs20 is preferably set to the above range.

[0410] In the optical glass of the third embodiment, the lower limit of the mass ratio [Li20 / (Li20+Na20+K20)] of the content of Li20 to the total content of Li20, Na20, and K20 is preferably 0.00, and further more preferably in the order of 0.10, 0.15, 0.20, 0.25. The upper limit of the mass ratio is preferably 1.00, and further more preferably in the order of 0.80, 0.75, 0.70, 0.65.

[0411] In order to obtain an optical glass that has a high refractive index and a reduced specific gravity, the mass ratio [Li20 / (Li20+Na20+K20)] is preferably set to the above range.

[0412] In the optical glass of the third embodiment, the lower limit of the total content of Na2O, K2O, and Cs2O [Na2O + K2O + Cs2O] is preferably 0%. The upper limit of the total content is preferably 11.0%, and more preferably in the order of 10.0%, 9.0%, 8.0%, 7.0%, 6.0%.

[0413] In order to maintain the refractive index at a high level while maintaining the thermal stability of the glass, the total content [Na2O + K2O + Cs2O] is preferably set to the above range.

[0414] In the optical glass of the third embodiment, the lower limit of the total content of Li2O, Na2O, K2O, and Cs2O [Li2O + Na2O + K2O + Cs2O] is preferably 1.5%, and more preferably in the order of 2%, 4%, 6%. The upper limit of the total content is preferably 15%, and more preferably in the order of 13%, 10%.

[0415] In order to obtain an optical glass having excellent meltability, the total content [Li2O + Na2O + K2O + Cs2O] is preferably set to the above range.

[0416] In the optical glass of the third embodiment, the lower limit of the mass ratio of the content of Li2O to the total content of Li2O, Na2O, K2O, and Cs2O [Li2O / (Li2O + Na2O + K2O + Cs2O)] is preferably 0.00, and more preferably in the order of 0.10, 0.15, 0.20, 0.25. The upper limit of the mass ratio is preferably 1.00, and more preferably in the order of 0.80, 0.75, 0.70, 0.65.

[0417] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O + Na2O + K2O + Cs2O)] is preferably set to the above range.

[0418] In the optical glass of the third embodiment, the upper limit of the content of MgO is preferably 20%, and more preferably in the order of 15%, 10%, 5%. In addition, the lower limit of the content of MgO is preferably 0%.

[0419] In the optical glass of the third embodiment, the lower limit of the content of CaO is preferably 1%, and more preferably in the order of 3%, 5%, 8%. The upper limit of the content of CaO is preferably 20%, and more preferably in the order of 18%, 15%, 13%.

[0420] MgO and CaO have the effect of improving the meltability of the glass. On the other hand, when the contents thereof are excessive, there is a risk that the thermal stability will decrease. Therefore, each of the contents of MgO and CaO is preferably set to the above range.

[0421] In the optical glass of the third embodiment, the upper limit of the SrO content is preferably 10%, and more preferably 8%, 5%, and 3% in this order. The lower limit of the SrO content is preferably 0%.

[0422] SrO improves the meltability of glass and increases its refractive index. On the other hand, excessive SrO content can lead to decreased thermal stability and increased specific gravity. Therefore, the SrO content is preferably within the above range.

[0423] In the optical glass of the third embodiment, the BaO content is preferably 20% or less, more preferably 17% or less, less than 16.0%, 15% or less, 13% or less, and 10% or less in this order. The lower limit of the BaO content is preferably 0%.

[0424] By setting the BaO content within the above range, the meltability of the glass can be improved and the refractive index can be increased. On the other hand, if the BaO content is too high, there is a risk of reduced thermal stability and increased specific gravity.

[0425] In the optical glass of the third embodiment, the upper limit of the ZnO content is preferably 10%, and more preferably 8%, 5%, and 3% in this order. The lower limit of the ZnO content is preferably 0%.

[0426] ZnO is a glass component that improves the thermal stability of glass. However, excessive ZnO content increases the specific gravity. Therefore, from the perspective of improving the thermal stability of glass and maintaining the desired optical properties, the ZnO content is preferably within the above range.

[0427] In the optical glass of the third embodiment, the upper limit of the total content of MgO, CaO, SrO, BaO, and ZnO (MgO + CaO + SrO + BaO + ZnO) is preferably 40%, more preferably 35%, 30%, and 25%, in that order. Furthermore, the lower limit of this total content is preferably 3%, more preferably 5%, 8%, and 10%, in that order. The total content is preferably within the above range from the perspective of suppressing an increase in specific gravity and maintaining thermal stability without hindering high dispersion.

[0428] In the optical glass of the third embodiment, the upper limit of the content of Ta2O5 is preferably 10%, and more preferably 8%, 5%, and 3% in this order. In addition, the lower limit of the content of Ta2O5 is preferably 0%.

[0429] Ta2O5is a component that contributes to high refractive index. In addition, it is a glass component that has an effect of improving the thermal stability of the glass, and is also a component that lowers Pg, F. On the other hand, when the content of Ta2O5is increased, the thermal stability of the glass decreases, and melting residue of the glass raw material is likely to occur when the glass is melted. In addition, the specific gravity increases. Therefore, the content of Ta2O5is preferably set to the above range.

[0430] In the optical glass of the third embodiment, the upper limit of the content of La2O3is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of La2O3is preferably 0%.

[0431] La2O3is a component that contributes to high refractive index. On the other hand, when the content of La2O3is increased, the specific gravity increases, and the thermal stability of the glass decreases. Therefore, from the viewpoint of suppressing the increase in the specific gravity and the decrease in the thermal stability of the glass, the content of La2O3is preferably set to the above range.

[0432] In the optical glass of the third embodiment, the upper limit of the content of Y2O3is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of Y2O3is preferably 0%.

[0433] Y2O3is a component that contributes to high refractive index. On the other hand, when the content of Y2O3is excessively increased, the thermal stability of the glass decreases, and the glass becomes likely to devitrify during manufacturing. Therefore, from the viewpoint of suppressing the decrease in the thermal stability of the glass, the content of Y2O3is preferably set to the above range.

[0434] In the optical glass of the third embodiment, the content of Sc2O3is preferably 2% or less. In addition, the lower limit of the content of Sc2O3is preferably 0%.

[0435] In the optical glass of the third embodiment, the content of HfO2is preferably 2% or less. In addition, the lower limit of the content of HfO2is preferably 0%.

[0436] Sc2O3and HfO2have an effect of increasing the high dispersion of the glass, but are expensive components. Therefore, each content of Sc2O3and HfO2is preferably set to the above range.

[0437] In the optical glass of the third embodiment, the content of Lu2O3is preferably 2% or less. In addition, the lower limit of the content of Lu2O3is preferably 0%.

[0438] Lu2O3has an effect of increasing the high dispersion of the glass, but is also a glass component that increases the specific gravity of the glass because of the large molecular weight. Therefore, the content of Lu2O3is preferably set to the above range.

[0439] In the optical glass of the third embodiment, the content of GeO2is preferably 2% or less. In addition, the lower limit of the content of GeO2is preferably 0%.

[0440] GeO2has an effect of increasing the high dispersion of the glass, but is an especially expensive component in the glass components generally used. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, the content of GeO2is preferably set to the above range.

[0441] In the optical glass of the third embodiment, the upper limit of the content of Gd2O3is preferably 3.0%, and more preferably 2.0%. In addition, the lower limit of the content of Gd2O3is preferably 0%.

[0442] Gd2O3is a component that contributes to the increase in the refractive index. On the other hand, when the content of Gd2O3becomes excessive, the thermal stability of the glass decreases. In addition, when the content of Gd2O3becomes excessive, the specific gravity of the glass increases, which is not preferable. Therefore, from the viewpoint of maintaining the thermal stability of the glass well while suppressing the increase in the specific gravity, the content of Gd2O3is preferably set to the above range.

[0443] In the optical glass of the third embodiment, the content of Yb2O3is preferably 2% or less. In addition, the lower limit of the content of Yb2O3is preferably 0%.

[0444] Yb2O3has a larger molecular weight than La2O3, Gd2O3, and Y2O3, and therefore, can cause the specific gravity of the glass to increase. When the specific gravity of the glass increases, the mass of the optical element increases. Therefore, it is preferable to reduce the content of Yb2O3to suppress the increase in the specific gravity of the glass.

[0445] In addition, when the content of Yb2O3is excessive, the thermal stability of the glass decreases. From the viewpoint of preventing the decrease in the thermal stability of the glass and suppressing the increase in the specific gravity, the content of Yb2O3is preferably set to the above range.

[0446] In the optical glass of the third embodiment, the upper limit of the total content of La2O3, Gd2O3, and Y2O3 [La2O3+ Gd2O3+ Y2O3] is preferably 10%, and more preferably in the order of 8%, 5%, and 3%. The lower limit of the total content is 0%. The total content can also be 0%.

[0447] From the viewpoint of suppressing the increase in the specific gravity and maintaining the thermal stability well, the total content [La2O3+ Gd2O3+ Y2O3] is preferably set to the above range.

[0448] In the optical glass of the third embodiment, the lower limit of the mass ratio of the content of Li20 to the total content of glass components other than Si02, B203, P205, and Ge02 [Li20 / {100 - (Si02+ B203+ P205+ Ge02)}] is preferably 0.00, and further more preferably in the order of 0.02, 0.03, 0.04, 0.05, 0.06. The upper limit of the mass ratio is preferably 0.20, and further more preferably in the order of 0.15, 0.13, 0.10.

[0449] Note that the total content of all glass components is set to 100 mass%. Therefore, the total content of glass components other than Si02, B203, P205, and Ge02 is expressed as [100 - (Si02+ B203+ P205+ Ge02)]. From the viewpoint of obtaining an optical glass having a high refractive index and a reduced specific gravity, the mass ratio of Li20 to [100 - (Si02+ B203+ P205+ Ge02)] is preferably set to the above range.

[0450] In the optical glass of the third embodiment, the lower limit of the mass ratio of the content of Ti02 to the total content of Ti02, Nb205, W03, Zr02, SrO, BaO, ZnO, La203, Gd203, Y203, Ta205, and Bi203 [Ti02 / (Ti02+ Nb205+ W03+ Zr02+ SrO+ BaO+ ZnO+ La203+ Gd203+ Y203+ Ta205+ Bi203)] is preferably 0.40, and further more preferably in the order of 0.42, 0.44, 0.46, 0.48, 0.50. The upper limit of the mass ratio is preferably 0.80, and further more preferably in the order of 0.75, 0.70, 0.65.

[0451] From the viewpoint of increasing the refractive index while suppressing an increase in the specific gravity, the mass ratio of Ti02 to [Ti02+ Nb205+ W03+ Zr02+ SrO+ BaO+ ZnO+ La203+ Gd203+ Y203+ Ta205+ Bi203] is preferably set to the above range.

[0452] The optical glass of the third embodiment is preferably composed mainly of the above glass components, i.e., SiO2, TiO2, Nb2O5, as essential components, and Na2O, P2O5, B2O3, Al2O3, ZrO2, WO3, Bi2O3, Li2O, K2O, Cs2O, MgO, CaO, SrO, BaO, ZnO, Ta2O5, La2O3, Y2O3, Sc2O3, HfO2, Lu2O3, GeO2, Gd2O3, and Yb2O3, as optional components, and the total content of the above glass components is preferably 95% or more, more preferably 98% or more, further preferably 99% or more, and still further preferably 99.5% or more.

[0453] Note that the optical glass of the third embodiment is preferably composed substantially of the above glass components, but can contain other components within a range not impairing the effects of the present application. Also, in the present application, the presence of unavoidable impurities is not excluded.

[0454] (Other components)

[0455] Pb, As, Cd, Tl, Be, and Se are toxic. Therefore, it is particularly preferable that the optical glass of the third embodiment not contain these elements as glass components. The content of each of the above elements, converted to an oxide, is preferably less than 0.5%, further more preferably less than 0.1%, still further more preferably less than 0.05%, and yet further more preferably less than 0.01%, in this order.

[0456] U, Th, and Ra are radioactive elements. Therefore, it is particularly preferable that the optical glass of the third embodiment not contain these elements as glass components. The content of each of the above elements, converted to an oxide, is preferably less than 0.5%, further more preferably less than 0.1%, still further more preferably less than 0.05%, and yet further more preferably less than 0.01%, in this order.

[0457] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm cause an increase in the coloring of the glass and can become a source of fluorescence. Therefore, it is particularly preferable that the optical glass of the third embodiment not contain these elements as glass components. The content of each of the above elements, converted to an oxide, is preferably less than 0.5%, further more preferably less than 0.1%, still further more preferably less than 0.05%, and yet further more preferably less than 0.01%, in this order.

[0458] Sb (Sb2O3) and Ce (CeO2) are elements that can be added optionally as fining agents. Of these, Sb (Sb2O3) is a fining agent that has a large fining effect. Ce (CeO2) has a smaller fining effect than Sb (Sb2O3). If Ce (CeO2) is added in a large amount, there is a tendency for the coloring of the glass to become strong.

[0459] Note that in the present specification, the contents of Sb (Sb2O3) and Ce (CeO2) are expressed as external addition ratios, and are not included in the total content of all glass components expressed on an oxide basis. That is, in the present specification, the total content of all glass components other than Sb (Sb2O3) and Ce (CeO2) is taken as 100 mass%.

[0460] The content of Sb2O3 is expressed as an external addition ratio. That is, in the optical glass of the third embodiment, the content of Sb2O3 when the total content of all glass components other than Sb2O3 and CeO2 is taken as 100 mass% is preferably 1 mass% or less, and is further preferably 0.1 mass% or less, 0.05 mass% or less, 0.03 mass% or less in this order. The content of Sb2O3 can also be 0 mass%.

[0461] The content of CeO2 is also expressed as an external addition ratio. That is, in the optical glass of the third embodiment, the content of CeO2 when the total content of all glass components other than CeO2 and Sb2O3 is taken as 100 mass% is preferably 2 mass% or less, and is further preferably 1 mass% or less, 0.5 mass% or less, 0.1 mass% or less in this order. The content of CeO2 can also be 0 mass%. By setting the content of CeO2 to the above range, the fining property of the glass can be improved.

[0462] (Properties of the glass)

[0463] <Abbe number vD>

[0464] In the optical glass of the third embodiment, the Abbe number vD is preferably 15 to 30. The Abbe number vD can be 18 to 25, or 20 to 24. By setting the Abbe number vD to the above range, a glass having a desired dispersion property can be obtained. The Abbe number vD can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, and Bi2O3, which are glass components that contribute to high dispersion.

[0465] <Specific gravity of the glass>

[0466] The optical glass of the third embodiment is a high refractive index glass, but the specific gravity is not large. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. On the other hand, if the specific gravity is too small, the thermal stability can be reduced.

[0467] Therefore, in the optical glass of the third embodiment, the specific gravity is preferably 4.2 or less, and is further preferably 4.0 or less, 3.8 or less, 3.6 or less, 3.4 or less in this order.

[0468] The specific gravity can be controlled by adjusting the contents of the respective glass components. In particular, by adjusting the contents of Li2O and TiO2, it is possible to reduce the specific gravity while maintaining a high refractive index.

[0469] Note that in the optical glass of the third embodiment, the refractive index nd and the specific gravity preferably satisfy the following equation (1), more preferably satisfy the following equation (2), and further preferably satisfy the following equation (3). By causing the refractive index nd and the specific gravity to satisfy the following equations, it is possible to obtain an optical glass that has a high refractive index and, in comparison, a reduced specific gravity.

[0470] nd ≥ 0.2 x specific gravity + 1.18 (1)

[0471] nd ≥ 0.2 x specific gravity + 1.19 (2)

[0472] nd ≥ 0.2 x specific gravity + 1.20 (3)

[0473] <Glass transition temperature Tg>

[0474] In the optical glass of the third embodiment, the upper limit of the glass transition temperature Tg is preferably 690°C, and further more preferably in the order of 680°C, 660°C, 650°C, 630°C, 600°C. The lower limit of the glass transition temperature Tg is not particularly limited, and is typically 500°C, and is preferably 550°C.

[0475] The glass transition temperature Tg can be controlled by adjusting the total content of the alkali metals.

[0476] By causing the upper limit of the glass transition temperature Tg to satisfy the above condition, it is possible to suppress the increase in the molding temperature and the annealing temperature of the glass at the time of reheat press molding, and to reduce the damage to the equipment for reheat press molding and the annealing equipment.

[0477] By causing the lower limit of the glass transition temperature Tg to satisfy the above condition, it is possible to easily maintain the reheat press moldability and the thermal stability of the glass while maintaining the desired Abbe number and refractive index.

[0478] <Transmittance of glass>

[0479] The transmittance of the optical glass of the third embodiment can be evaluated in terms of the coloration degrees λ80, λ70, and λ5.

[0480] For a glass sample having a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance was measured in the wavelength range of 200 to 700 nm, and the wavelength at which the external transmittance reached 80% was set as λ80, the wavelength at which the external transmittance reached 70% was set as λ70, and the wavelength at which the external transmittance reached 5% was set as λ5.

[0481] The λ80 of the optical glass of the third embodiment is preferably 700 nm or less, more preferably 650 nm or less, and further preferably 600 nm or less.

[0482] The λ70 is preferably 600 nm or less, more preferably 550 nm or less, and further preferably 500 nm or less.

[0483] The λ5 is preferably 500 nm or less, more preferably 450 nm or less, and further preferably 400 nm or less.

[0484] (Manufacture of optical glass)

[0485] The optical glass of the third embodiment is prepared by adjusting the glass raw material so as to achieve the above given composition, and by using the adjusted glass raw material, according to a publicly known glass manufacturing method. For example, a plurality of compounds are adjusted, and mixed sufficiently to prepare a batch raw material. The batch raw material is put into a quartz crucible or a platinum crucible, and rough melt is performed. The melt obtained by the rough melt is rapidly cooled and pulverized to prepare a crushed glass. The crushed glass is further put into a platinum crucible, heated, and remelted to obtain a molten glass. After refining and homogenization are performed, the molten glass is shaped, and slowly cooled to obtain the optical glass. The shaping and the slow cooling of the molten glass can be performed by a publicly known method.

[0486] Note that the compound used when the batch raw material is adjusted is not particularly limited as long as the desired glass component can be introduced into the glass and reach the desired content, and as such a compound, oxides, carbonates, nitrates, hydroxides, fluorides, and the like can be cited.

[0487] (Manufacture of optical elements and the like)

[0488] When the optical glass of the third embodiment is used to manufacture an optical element, a publicly known method can be employed. For example, in the manufacture of the optical glass described above, the molten glass is injected into a mold to be shaped into a plate shape, and a glass material formed of the optical glass of the present application is manufactured. The obtained glass material is appropriately cut, ground, and polished, and a fragment having a size and a shape suitable for press molding is manufactured. The fragment is heated and softened, and press molding (reheat press) is performed by a publicly known method, and an optical element blank having a shape similar to that of the optical element is manufactured. The optical element blank is annealed, and ground and polished by a publicly known method to manufacture the optical element.

[0489] Depending on the purpose of use, an antireflection film, a total reflection film, or the like can be coated on the optical functional surface of the manufactured optical element.

[0490] According to one embodiment of the present application, an optical element made of the above-described optical glass can be provided. As a kind of optical element, a lens such as a plane lens, a spherical lens, an aspherical lens, a prism, a diffraction grating, a light guide plate, and the like can be exemplified. As a shape of the lens, various shapes such as a lenticular lens, a plano-convex lens, a biconcave lens, a plano-concave lens, a convex meniscus lens, a concave meniscus lens, and the like can be exemplified. As a use of the light guide plate, a display device such as an augmented reality (AR) display type of eyeglass-type device, a mixed reality (MR) display type of eyeglass-type device, and the like can be exemplified. Such a light guide plate is a plate-shaped glass mountable to a frame of an eyeglass-type device, and is formed of the above-described optical glass. If necessary, a diffraction grating for changing a traveling direction of light that can propagate by repeatedly performing total reflection inside the light guide plate can be formed on a surface of the light guide plate. The diffraction grating can be formed by a known method. When the eyeglass-type device having the above-described light guide plate is worn, light propagated inside the light guide plate is incident to a pupil, and thus a function of the augmented reality (AR) display, the mixed reality (MR) display can be exhibited. Such an eyeglass-type device is disclosed in, for example, Japanese Patent Application Laid-Open No. 2017-534352, and the like. Note that the light guide plate can be manufactured by a known method. The optical element can be manufactured by a method including a process of processing a glass molded body made of the above-described optical glass. As the processing, cutting, cutting, rough grinding, fine grinding, polishing, and the like can be exemplified. When such processing is performed, by using the above-described glass, breakage can be reduced, and thus a high-quality optical element can be stably provided.

[0491] (Image display device)

[0492] For the image display device of the third embodiment, the same as the first embodiment can be provided.

[0493] Fourth Embodiment

[0494] In the optical glass of the fourth embodiment,

[0495] The content of Li2O and the mass ratio of the total content of glass components other than SiO2, B2O3, P2O5, and GeO2 [Li2O / {100-(SiO2+B2O3+P2O5+GeO2)}] are 0.02 or more,

[0496] The content of TiO2 and the mass ratio of the total content of TiO2, Nb2O5, WO3, ZrO2, SrO, BaO, ZnO, La2O3, Gd2O3, Y2O3, Ta2O5, and Bi2O3 [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] are 0.40 or more,

[0497] The optical glass has a refractive index nd of 1.86 or more.

[0498] In the optical glass of the 4th embodiment, the mass ratio of the content of Li2O to the total content of glass components other than SiO2, B2O3, P2O5, and GeO2 [Li2O / {100-(SiO2+B2O3+P2O5+GeO2)}] is 0.02 or more. The lower limit of this mass ratio is preferably 0.03, and further more preferably in the order of 0.04, 0.05, 0.06. The upper limit of this mass ratio is preferably 0.20, and further more preferably in the order of 0.15, 0.13, 0.10.

[0499] Note that the total content of all glass components is set to 100 mass%. Therefore, the total content of glass components other than SiO2, B2O3, P2O5, and GeO2 is expressed as [100-(SiO2+B2O3+P2O5+GeO2)]. By setting the mass ratio [Li2O / {100-(SiO2+B2O3+P2O5+GeO2)}] to the above range, an optical glass having a high refractive index and a reduced specific gravity can be obtained.

[0500] In the optical glass of the 4th embodiment, the mass ratio of the content of TiO2 to the total content of TiO2, Nb2O5, WO3, ZrO2, SrO, BaO, ZnO, La2O3, Gd2O3, Y2O3, Ta2O5, and Bi2O3 [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] is 0.40 or more. The lower limit of this mass ratio is preferably 0.42, and further more preferably in the order of 0.44, 0.46, 0.48, 0.50. The upper limit of this mass ratio is preferably 0.80, and further more preferably in the order of 0.75, 0.70, 0.65.

[0501] By setting the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] to the above range, it is possible to increase the refractive index while suppressing an increase in the specific gravity.

[0502] For the content of glass components in the optical glass of the 4th embodiment, and the ratio of components other than the above, non-limiting examples are shown below.

[0503] In the optical glass of the fourth embodiment, the lower limit of the content of SiO2 is preferably 10%, and further more preferably in the order of 12%, 15%, 18%, 20%. In addition, the upper limit of the content of SiO2 is preferably 40%, and further more preferably in the order of 38%, 35%, 33%, 30%.

[0504] SiO2 is a network-forming component of glass, and can improve the thermal stability, chemical durability, and weather resistance of the glass. In order to increase the viscosity of the molten glass, the content of SiO2 is preferably in the above range. If the content of SiO2 is too high, the refractive index of the glass decreases, and the desired optical properties cannot be obtained.

[0505] In the optical glass of the fourth embodiment, the upper limit of the content of P2O5 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The content of P2O5 can also be 0%.

[0506] In order to obtain an optical glass having a high refractive index and a low specific gravity, the content of P2O5 is preferably in the above range.

[0507] In the optical glass of the fourth embodiment, the upper limit of the content of B2O3 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of B2O3 is preferably 0%, and further more preferably in the order of 0.5%, 0.8%, 1.0%.

[0508] B2O3 is a network-forming component of glass. B2O3 has the effect of improving the thermal stability of the glass, but if the content of B2O3 is too high, the refractive index decreases. Therefore, the content of B2O3 is preferably in the above range.

[0509] In the optical glass of the fourth embodiment, the upper limit of the content of Al2O3 is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The content of Al2O3 can also be 0%.

[0510] Al2O3 has the effect of improving the chemical durability, but if the content of Al2O3 is too high, the meltability of the glass deteriorates. Therefore, the content of Al2O3 is preferably in the above range.

[0511] In the optical glass of the fourth embodiment, the lower limit of the total content of SiO2 and Al2O3 [SiO2 + Al2O3] is preferably 10%, and further more preferably in the order of 13%, 15%, 18%, 20%. In addition, the upper limit of the total content is preferably 50%, and further more preferably in the order of 45%, 40%, 35%, 30%.

[0512] In order to improve the thermal stability of the glass, the total content [SiO2 + Al2O3] is preferably in the above range.

[0513] In the optical glass of the fourth embodiment, the lower limit of the mass ratio [B2O3 / (SiO2+ Al2O3)] of the content of B2O3 to the total content of SiO2 and Al2O3 is preferably 0.01, and more preferably 0.02, 0.03, 0.04 in this order. The upper limit of the mass ratio is preferably 0.20, and more preferably 0.18, 0.15, 0.13, 0.10 in this order.

[0514] The mass ratio [B2O3 / (SiO2+ Al2O3)] is preferably set to the above range from the viewpoint of improving chemical durability and thermal stability.

[0515] In the optical glass of the fourth embodiment, the lower limit of the total content [B2O3+ P2O5] of B2O3 and P2O5 is preferably 0.5%, and more preferably 0.8%, 1.0% in this order. In addition, the upper limit of the total content is preferably 10%, and more preferably 8%, 5%, 3% in this order.

[0516] The total content [B2O3+ P2O5] is preferably set to the above range from the viewpoint of improving chemical durability and thermal stability.

[0517] In the optical glass of the fourth embodiment, the lower limit of the total content [B2O3+ SiO2] of B2O3 and SiO2 is preferably 10%, and more preferably 15%, 18%, 20% in this order. In addition, the upper limit of the total content is preferably 50%, and more preferably 45%, 40%, 35% in this order.

[0518] The total content [B2O3+ SiO2] is preferably set to the above range in order to obtain an optical glass having a high refractive index.

[0519] In the optical glass of the fourth embodiment, the lower limit of the content of ZrO2 is preferably 0%, and more preferably 0.1%, 0.5%, 1.0% in this order. In addition, the upper limit of the content of ZrO2 is preferably 10%, and more preferably 8%, 5%, 3% in this order. The content of ZrO2 can also be 0%.

[0520] ZrO2 is a component that contributes to high refractive index. On the other hand, when the content of ZrO2 is too much, thermal stability decreases, and in addition, there is a risk of increasing specific gravity. Therefore, the content of ZrO2 is preferably set to the above range.

[0521] In the optical glass of the fourth embodiment, the lower limit of the content of TiO2 is preferably 10%, and more preferably 13%, 15%, 18%, 20% in this order. In addition, the upper limit of the content of TiO2 is preferably 50%, and more preferably 45%, 40%, 35% in this order.

[0522] TiO2is a component that contributes to high refractive index, and has an effect of improving the stability of the glass. In addition, it is possible to increase the refractive index without causing an increase in specific gravity. On the other hand, when the content of TiO2is too much, there is a risk of a decrease in thermal stability. Therefore, the content of TiO2is preferably set to the above range.

[0523] In the optical glass of the 4th embodiment, the lower limit of the content of Nb2O5is preferably 10%, and further more preferably in the order of 13%, 15%. In addition, the upper limit of the content of Nb2O5is preferably 50%, and further more preferably in the order of 45%, 40%, 35%.

[0524] Nb2O5is a component that contributes to high refractive index, and has an effect of improving the stability of the glass. On the other hand, when the content of Nb2O5is too much, there is a risk of an increase in specific gravity, and in addition, there is a risk of a decrease in thermal stability. Therefore, the content of Nb2O5is preferably set to the above range.

[0525] In the optical glass of the 4th embodiment, the lower limit of the total content of TiO2and Nb2O5[TiO2+Nb2O5] is preferably 20%, and further more preferably in the order of 25%, 30%, 35%. In addition, the upper limit of the total content is preferably 70%, and further more preferably in the order of 65%, 60%, 55%.

[0526] TiO2and Nb2O5are components that contribute to high refractive index. Therefore, in order to obtain a glass having desired optical properties, the total content of TiO2and Nb2O5is preferably set to the above range.

[0527] In the optical glass of the 4th embodiment, the lower limit of the mass ratio of the content of TiO2to the total content of TiO2and Nb2O5[TiO2 / (TiO2+Nb2O5)] is preferably 0.20, and further more preferably in the order of 0.25, 0.30, 0.35. The upper limit of the mass ratio is preferably 0.80, and further more preferably in the order of 0.75, 0.70, 0.65.

[0528] In order to obtain an optical glass that has a high refractive index and a reduced specific gravity, the mass ratio [TiO2 / (TiO2+Nb2O5)] is preferably set to the above range.

[0529] In the optical glass of the 4th embodiment, the upper limit of the content of WO3is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The content of WO3may also be 0%.

[0530] WO3is a component that contributes to high refractive index. On the other hand, when the content of WO3is too much, there is a risk of decrease in thermal stability, increase in specific gravity, and increase in coloring of the glass and decrease in transmittance. Therefore, the content of WO3is preferably set to the above range.

[0531] In the optical glass of the 4th embodiment, the upper limit of the content of Bi2O3is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of Bi2O3is preferably 0%. The content of Bi2O3may also be 0%.

[0532] Bi2O3has the effect of improving the thermal stability of the glass by being contained in an appropriate amount. In addition, it is a component that contributes to high refractive index. On the other hand, when the content of Bi2O3is too much, the specific gravity increases. In addition, the coloring of the glass increases. Therefore, the content of Bi2O3is preferably set to the above range.

[0533] In the optical glass of the 4th embodiment, the upper limit of the total content of TiO2, Nb2O5, WO3, and Bi2O3[TiO2+Nb2O5+WO3+Bi2O3] is preferably 80%, and further more preferably in the order of 70%, 60%. In addition, the lower limit of the total content is preferably 20%, and further more preferably in the order of 25%, 30%, 35%.

[0534] TiO2, Nb2O5, WO3, and Bi2O3are all components that contribute to high refractive index. Therefore, the total content [TiO2+Nb2O5+WO3+Bi2O3] is preferably set to the above range.

[0535] In the optical glass of the 4th embodiment, the lower limit of the content of Li2O is preferably 0.1%, and further more preferably in the order of 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%. The upper limit of the content of Li2O is preferably 10%, and further more preferably in the order of 9%, 8%, 7%, 6%, 5%.

[0536] Li2O is a component that contributes to low specific gravity, and in addition, among alkali metals, it is a component that particularly contributes to high refractive index. On the other hand, when the content of Li2O is too much, there is a risk of decrease in thermal stability. Therefore, the content of Li2O is preferably set to the above range.

[0537] In the optical glass of the 4th embodiment, the upper limit of the content of Na2O is preferably 10%, and further more preferably in the order of 9%, 8%, 7%. The lower limit of the content of Na2O is preferably 0%, and further more preferably in the order of 0.5%, 1.0%, 1.5%, 2.0%.

[0538] In the optical glass of the fourth embodiment, the upper limit of the content of K2O is preferably 10%, further more preferably in the order of 8%, 5%. The lower limit of the content of K2O is preferably 0%, further more preferably in the order of 0.5%, 1.0%, 1.5%, 2.0%. The content of K2O can also be 0%.

[0539] Na2O and K2O have an effect of improving the meltability of the glass. On the other hand, when the content thereof is too much, there is a risk of lowering the refractive index, and in addition, there is a risk of lowering the thermal stability. Therefore, each content of Na2O and K2O is preferably set to the above range.

[0540] In the optical glass of the fourth embodiment, the upper limit of the content of Cs2O is preferably 5%, further more preferably in the order of 3%, 1%. The lower limit of the content of Cs2O is preferably 0%.

[0541] Cs2O has an effect of improving the thermal stability of the glass, but when the content thereof is too much, the chemical durability, weather resistance is lowered. Therefore, the content of Cs2O is preferably set to the above range.

[0542] In the optical glass of the fourth embodiment, the lower limit of the mass ratio [Li2O / (Li2O+Na2O+K2O)] of the content of Li2O to the total content of Li2O, Na2O, and K2O is preferably 0.10, further more preferably in the order of 0.15, 0.20, 0.25. The upper limit of the mass ratio is preferably 1.00, further more preferably in the order of 0.80, 0.75, 0.70, 0.65.

[0543] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O)] is preferably set to the above range.

[0544] In the optical glass of the fourth embodiment, the lower limit of the mass ratio [Li2O / (Li2O+Na2O+K2O+Cs2O)] of the content of Li2O to the total content of Li2O, Na2O, K2O, and Cs2O is preferably 0.10, further more preferably in the order of 0.15, 0.20, 0.25. The upper limit of the mass ratio is preferably 1.00, further more preferably in the order of 0.80, 0.75, 0.70, 0.65.

[0545] In order to obtain an optical glass having a high refractive index and a reduced specific gravity, the mass ratio [Li2O / (Li2O+Na2O+K2O+Cs2O)] is preferably set to the above range.

[0546] In the optical glass of the 4th embodiment, the lower limit of the total content of Na2O, K2O, and Cs2O [Na2O + K2O + Cs2O] is preferably 0%. The upper limit of the total content is preferably 11.0%, and more preferably in the order of 10.0%, 9.0%, 8.0%, 7.0%, 6.0%.

[0547] In order to maintain the refractive index at a high level while maintaining the thermal stability of the glass, the total content [Na2O + K2O + Cs2O] is preferably set to the above range.

[0548] In the optical glass of the 4th embodiment, the lower limit of the total content of Li2O, Na2O, K2O, and Cs2O [Li2O + Na2O + K2O + Cs2O] is preferably 1.5%, and more preferably in the order of 2%, 4%, 6%. The upper limit of the total content is preferably 15%, and more preferably in the order of 13%, 10%.

[0549] In order to obtain an optical glass having excellent meltability, the total content [Li2O + Na2O + K2O + Cs2O] is preferably set to the above range.

[0550] In the optical glass of the 4th embodiment, the upper limit of the content of MgO is preferably 20%, and more preferably in the order of 15%, 10%, 5%. In addition, the lower limit of the content of MgO is preferably 0%.

[0551] In the optical glass of the 4th embodiment, the lower limit of the content of CaO is preferably 1%, and more preferably in the order of 3%, 5%, 8%. The upper limit of the content of CaO is preferably 20%, and more preferably in the order of 18%, 15%, 13%.

[0552] MgO and CaO have the effect of improving the meltability of the glass. On the other hand, when the content of each of them is too much, there is a risk that the thermal stability will decrease. Therefore, the content of each of MgO and CaO is preferably set to the above range.

[0553] In the optical glass of the 4th embodiment, the upper limit of the content of SrO is preferably 10%, and more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of SrO is preferably 0%.

[0554] SrO has the effect of improving the meltability of the glass and increasing the refractive index. On the other hand, when the content of SrO is too much, there is a risk that the thermal stability will decrease and the specific gravity will increase. Therefore, the content of SrO is preferably set to the above range.

[0555] In the optical glass of the fourth embodiment, the upper limit of the BaO content is preferably 20%, and more preferably in the order of 17%, 15%, 13%, and 10%. The lower limit of the BaO content is preferably 0%.

[0556] BaO improves the meltability of glass and increases its refractive index. On the other hand, excessive BaO content can lead to decreased thermal stability and increased specific gravity. Therefore, the BaO content is preferably within the above range.

[0557] In the optical glass of the fourth embodiment, the upper limit of the ZnO content is preferably 10%, and more preferably 8%, 5%, and 3% in this order. The lower limit of the ZnO content is preferably 0%.

[0558] ZnO is a glass component that improves the thermal stability of glass. However, excessive ZnO content increases the specific gravity. Therefore, from the perspective of improving the thermal stability of glass and maintaining the desired optical properties, the ZnO content is preferably within the above range.

[0559] In the optical glass of the fourth embodiment, the upper limit of the total content of MgO, CaO, SrO, BaO, and ZnO (MgO + CaO + SrO + BaO + ZnO) is preferably 40%, more preferably 35%, 30%, and 25%, in that order. Furthermore, the lower limit of this total content is preferably 3%, more preferably 5%, 8%, and 10%, in that order. The total content is preferably within the above range from the perspective of suppressing an increase in specific gravity and maintaining thermal stability without hindering high dispersion.

[0560] In the optical glass of the fourth embodiment, the upper limit of the content of Ta2O5 is preferably 10%, and more preferably 8%, 5%, and 3% in this order. In addition, the lower limit of the content of Ta2O5 is preferably 0%.

[0561] Ta2O5 contributes to a higher refractive index. It also improves the thermal stability of glass and reduces Pg and F. However, increasing the Ta2O5 content reduces the thermal stability of the glass, making it more likely that molten glass residue will remain when the glass is melted. Furthermore, the specific gravity increases. Therefore, the Ta2O5 content is preferably within the above range.

[0562] In the optical glass of the fourth embodiment, the upper limit of the content of La2O3 is preferably 10%, and more preferably 8%, 5%, and 3% in this order. The lower limit of the content of La2O3 is preferably 0%.

[0563] La2O3is a component that contributes to high refractive index. On the other hand, when the content of La2O3is increased, the specific gravity increases and the thermal stability of the glass decreases. Therefore, from the viewpoint of suppressing the increase in the specific gravity and the decrease in the thermal stability of the glass, the content of La2O3is preferably set to the above range.

[0564] In the optical glass of the fourth embodiment, the upper limit of the content of Y2O3is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. In addition, the lower limit of the content of Y2O3is preferably 0%.

[0565] Y2O3is a component that contributes to high refractive index. On the other hand, when the content of Y2O3is excessively increased, the thermal stability of the glass decreases and the glass becomes apt to devitrify in the manufacturing. Therefore, from the viewpoint of suppressing the decrease in the thermal stability of the glass, the content of Y2O3is preferably set to the above range.

[0566] In the optical glass of the fourth embodiment, the content of Sc2O3is preferably 2% or less. In addition, the lower limit of the content of Sc2O3is preferably 0%.

[0567] In the optical glass of the fourth embodiment, the content of HfO2is preferably 2% or less. In addition, the lower limit of the content of HfO2is preferably 0%.

[0568] Sc2O3and HfO2have an effect of increasing the high dispersion of the glass, but are expensive components. Therefore, the content of each of Sc2O3and HfO2is preferably set to the above range.

[0569] In the optical glass of the fourth embodiment, the content of Lu2O3is preferably 2% or less. In addition, the lower limit of the content of Lu2O3is preferably 0%.

[0570] Lu2O3has an effect of increasing the high dispersion of the glass, but is also a glass component that increases the specific gravity of the glass because of the large molecular weight. Therefore, the content of Lu2O3is preferably set to the above range.

[0571] In the optical glass of the fourth embodiment, the content of GeO2is preferably 2% or less. In addition, the lower limit of the content of GeO2is preferably 0%.

[0572] GeO2has an effect of increasing the high dispersion of the glass, but is an especially expensive component among the commonly used glass components. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, the content of GeO2is preferably set to the above range.

[0573] In the optical glass of the fourth embodiment, the upper limit of the content of Gd2O3is preferably 3.0%, and more preferably 2.0%. In addition, the lower limit of the content of Gd2O3is preferably 0%.

[0574] Gd2O3is a component that contributes to high refractive index. On the other hand, when the content of Gd2O3becomes excessive, the thermal stability of the glass decreases. In addition, when the content of Gd2O3becomes excessive, the specific gravity of the glass increases, which is not preferable. Therefore, from the viewpoint of maintaining the thermal stability of the glass well while suppressing the increase in the specific gravity, the content of Gd2O3is preferably set to the above range.

[0575] In the optical glass of the 4th embodiment, the content of Yb2O3is preferably 2% or less. In addition, the lower limit of the content of Yb2O3is preferably 0%.

[0576] Yb2O3has a large molecular weight compared to La2O3, Gd2O3, and Y2O3, and therefore, can cause an increase in the specific gravity of the glass. When the specific gravity of the glass increases, the mass of the optical member increases. Therefore, it is preferable to reduce the content of Yb2O3to suppress the increase in the specific gravity of the glass.

[0577] In addition, when the content of Yb2O3is excessive, the thermal stability of the glass decreases. From the viewpoint of preventing the decrease in the thermal stability of the glass and suppressing the increase in the specific gravity, the content of Yb2O3is preferably set to the above range.

[0578] In the optical glass of the 4th embodiment, the upper limit of the total content of La2O3, Gd2O3, and Y2O3 [La2O3+ Gd2O3+ Y2O3] is preferably 10%, and further more preferably in the order of 8%, 5%, 3%. The lower limit of the total content is 0%. The total content can also be 0%.

[0579] From the viewpoint of suppressing the increase in the specific gravity and maintaining the thermal stability well, the total content [La2O3+ Gd2O3+ Y2O3] is preferably set to the above range.

[0580] The optical glass of the 4th embodiment is preferably mainly composed of the above glass components, i.e., Li2O as an essential component, TiO2, SiO2, P2O5, B2O3, Al2O3, ZrO2, Nb2O5, WO3, Bi2O3, Na2O, K2O, Cs2O, MgO, CaO, SrO, BaO, ZnO, Ta2O5, La2O3, Y2O3, Sc2O3, HfO2, Lu2O3, GeO2, Gd2O3, and Yb2O3as optional components, and the total content of the above glass components is preferably 95% or more, more preferably 98% or more, further preferably 99% or more, and more further preferably 99.5% or more.

[0581] Note that the optical glass of the fourth embodiment is preferably composed of the above glass components, but can contain other components within a range not impairing the effects of the present application. Also, in the present application, the presence of unavoidable impurities is not excluded.

[0582] (Other components)

[0583] Pb, As, Cd, Tl, Be, and Se are toxic. Therefore, it is particularly preferable that the optical glass of the fourth embodiment not contain these elements as glass components. The content of each of the above elements, converted to an oxide, is preferably less than 0.5%, further more preferably less than 0.1%, still more preferably less than 0.05%, and yet more preferably less than 0.01%, in this order.

[0584] U, Th, and Ra are radioactive elements. Therefore, it is particularly preferable that the optical glass of the fourth embodiment not contain these elements as glass components. The content of each of the above elements, converted to an oxide, is preferably less than 0.5%, further more preferably less than 0.1%, still more preferably less than 0.05%, and yet more preferably less than 0.01%, in this order.

[0585] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm cause an increase in the coloring of the glass and can become a source of fluorescence. Therefore, it is particularly preferable that the optical glass of the fourth embodiment not contain these elements as glass components. The content of each of the above elements, converted to an oxide, is preferably less than 0.5%, further more preferably less than 0.1%, still more preferably less than 0.05%, and yet more preferably less than 0.01%, in this order.

[0586] Sb (Sb2O3) and Ce (CeO2) are optional elements that function as fining agents. Of these, Sb (Sb2O3) is a fining agent that has a large fining effect. Ce (CeO2) has a smaller fining effect than Sb (Sb2O3). If Ce (CeO2) is added in a large amount, there is a tendency for the coloring of the glass to become strong.

[0587] Note that in the present specification, the content of Sb (Sb2O3) and Ce (CeO2) is expressed as the externally added proportion and is not included in the total content of the glass components expressed on an oxide basis. That is, in the present specification, the total content of all the glass components other than Sb (Sb2O3) and Ce (CeO2) is taken as 100 mass%.

[0588] The content of Sb2O3 is expressed as an externally added proportion. That is, in the optical glass of the fourth embodiment, the content of Sb2O3 is preferably 1% by mass or less, further preferably in the order of 0.1% by mass or less, 0.05% by mass or less, 0.03% by mass or less, when the total content of all glass components other than Sb2O3 and CeO2 is taken as 100% by mass. The content of Sb2O3 can also be 0% by mass.

[0589] The content of CeO2 is also expressed as an externally added proportion. That is, in the optical glass of the fourth embodiment, the content of CeO2 is preferably 2% by mass or less, further more preferably in the order of 1% by mass or less, 0.5% by mass or less, 0.1% by mass or less, when the total content of all glass components other than CeO2 and Sb2O3 is taken as 100% by mass. The content of CeO2 can also be 0% by mass. By setting the content of CeO2 to the above range, the fining property of the glass can be improved.

[0590] (Properties of the glass)

[0591] <Abbe number vD>

[0592] In the optical glass of the fourth embodiment, the Abbe number vD is preferably 15 to 30. The Abbe number vD can be 18 to 25, or 20 to 24. By setting the Abbe number vD to the above range, a glass having a desired dispersion property can be obtained. The Abbe number vD can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, and Bi2O3, which are glass components that contribute to high dispersion.

[0593] <Refractive index nD>

[0594] In the optical glass of the fourth embodiment, the lower limit of the refractive index nD is 1.86. The lower limit of the refractive index nD can also be set to 1.87, 1.88, 1.89, or 1.90. In addition, the upper limit of the refractive index nD can be set to 2.20, and further to 2.15, 2.10, or 2.05. The refractive index can be controlled by adjusting the contents of TiO2, Nb2O5, WO3, Bi2O3, ZrO2, La2O3, Gd2O3, Y2O3, and Ta2O5, which are glass components that contribute to high refractive index.

[0595] <Specific gravity of the glass>

[0596] The optical glass of the fourth embodiment is a high refractive index glass, but the specific gravity is not large. If the specific gravity of the glass can be reduced, the weight of the lens can be reduced. On the other hand, if the specific gravity is too small, the thermal stability can be reduced.

[0597] Therefore, in the optical glass of the fourth embodiment, the specific gravity is preferably 4.2 or less, and more preferably 4.0 or less, 3.8 or less, 3.6 or less, or 3.4 or less in this order.

[0598] The specific gravity can be controlled by adjusting the contents of the respective glass components. In particular, by adjusting the contents of Li20 and Ti02, it is possible to reduce the specific gravity while maintaining a high refractive index.

[0599] Note that, in the optical glass of the fourth embodiment, the refractive index nd and the specific gravity preferably satisfy the following equation (1), more preferably satisfy the following equation (2), and further preferably satisfy the following equation (3). By causing the refractive index nd and the specific gravity to satisfy the following equations, it is possible to obtain an optical glass having a high refractive index and, at the same time, a reduced specific gravity.

[0600] nd≥ 0.2 x specific gravity + 1.18 (1)

[0601] nd≥ 0.2 x specific gravity + 1.20 (2)

[0602] nd≥ 0.2 x specific gravity + 1.22 (3)

[0603] In addition, in the optical glass of the fourth embodiment, the ratio of the refractive index nd to the specific gravity [refractive index nd / specific gravity] is preferably 0.50 or more, more preferably 0.52 or more, and further preferably 0.54 or more. By setting the ratio [refractive index nd / specific gravity] to the above range, it is possible to obtain an optical glass having a high refractive index and, at the same time, a reduced specific gravity.

[0604] <Glass transition temperature Tg>

[0605] In the optical glass of the fourth embodiment, the upper limit of the glass transition temperature Tg is preferably 660°C, and more preferably 650°C, 630°C, or 600°C in this order. The lower limit of the glass transition temperature Tg is not particularly limited, and is typically 500°C, and is preferably 550°C.

[0606] The glass transition temperature Tg can be controlled by adjusting the total content of alkali metals.

[0607] By causing the upper limit of the glass transition temperature Tg to satisfy the above condition, it is possible to suppress an increase in the molding temperature and the annealing temperature of the glass at the time of reheat pressing, and to reduce the damage of the heat to the equipment for reheat pressing molding and the annealing equipment.

[0608] By causing the lower limit of the glass transition temperature Tg to satisfy the above condition, it is possible to easily maintain the reheat pressing moldability and the thermal stability of the glass while maintaining the desired Abbe number and the refractive index.

[0609] <Transmittance of glass>

[0610] The light transmittance of the optical glass of the fourth embodiment can be evaluated based on the coloration degrees λ80, λ70, and λ5.

[0611] For a glass sample with a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance is measured within the wavelength range of 200 to 700 nm, with the wavelength at which the external transmittance reaches 80% being set as λ80, the wavelength at which the external transmittance reaches 70% being set as λ70, and the wavelength at which the external transmittance reaches 5% being set as λ5.

[0612] The λ80 of the optical glass of the first embodiment is preferably 700 nm or less, more preferably 650 nm or less, and even more preferably 600 nm or less.

[0613] λ70 is preferably 600 nm or less, more preferably 550 nm or less, and even more preferably 500 nm or less.

[0614] λ5 is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less.

[0615] (Manufacture of optical glass)

[0616] The optical glass of the fourth embodiment is prepared by mixing glass raw materials in a manner to achieve the above-mentioned given composition, and then using the prepared glass raw materials to produce the optical glass according to a known glass manufacturing method. For example, a plurality of compounds are mixed and thoroughly mixed to produce a batch of raw materials, which are then placed in a quartz crucible or a platinum crucible for rough melting. The melt obtained by the rough melting is rapidly cooled and crushed to produce cullet. The cullet is further placed in a platinum crucible for heating and remelting to produce molten glass. After further clarification and homogenization, the molten glass is formed and slowly cooled to produce the optical glass. The forming and slow cooling of the molten glass can be carried out by known methods.

[0617] It should be noted that as long as the desired glass components can be introduced into the glass and the desired content is achieved, there is no particular limitation on the compounds used in preparing the batch raw materials. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, fluorides, and the like.

[0618] (Manufacturing of optical components, etc.)

[0619] When the optical glass of the fourth embodiment is used to produce an optical element, a publicly known method can be employed. For example, in the production of the optical glass described above, molten glass is injected into a mold to be shaped into a plate, and a glass material formed of the optical glass of the present application is produced. The resulting glass material is appropriately cut, ground, and polished, and pieces of a size and shape suitable for press molding are produced. The pieces are heated and softened, and press molding (reheat press) is performed by a publicly known method to produce an optical element blank having a shape close to that of the optical element. The optical element blank is annealed, and grinding and polishing are performed by a publicly known method to produce the optical element.

[0620] Depending on the purpose of use, an antireflection film, a total reflection film, or the like can be coated on the optical functional surface of the produced optical element.

[0621] According to one embodiment of the present application, an optical element produced from the optical glass described above can be provided. As the type of optical element, a lens such as a plane lens, a spherical lens, an aspherical lens, a prism, a diffraction grating, a light guide plate, and the like can be exemplified. As the shape of the lens, various shapes such as a lenticular lens, a plano-convex lens, a lenticular lens, a plano-concave lens, a convex meniscus lens, a concave meniscus lens, and the like can be exemplified. As the use of the light guide plate, a display device such as an augmented reality (AR) display type eyewear-type device, a mixed reality (MR) display type eyewear-type device, and the like can be exemplified. Such a light guide plate is a plate-shaped glass mountable to a frame of an eyewear-type device, and is formed of the optical glass described above. If necessary, a diffraction grating for changing the traveling direction of light that can repeatedly be totally reflected inside the light guide plate can be formed on the surface of the light guide plate. The diffraction grating can be formed by a publicly known method. When the eyewear-type device having the light guide plate described above is worn, light that has propagated inside the light guide plate is incident to the pupil, and thus the function of the augmented reality (AR) display, the mixed reality (MR) display can be exhibited. Such an eyewear-type device is disclosed in, for example, Japanese Patent Application Laid-Open No. 2017-534352, and the like. Note that the light guide plate can be produced by a publicly known method. The optical element can be produced by a method including a process of processing a glass molded body produced from the optical glass described above. As the processing, cutting, machining, rough grinding, fine grinding, polishing, and the like can be exemplified. When such processing is performed, by using the glass described above, breakage can be reduced, and thus a high-quality optical element can be stably provided.

[0622] (Image display device)

[0623] For the image display device of the fourth embodiment, the same as the first embodiment can be provided.

[0624] Embodiment

[0625] The present application will be described in more detail below with reference to embodiments. However, the present application is not limited to the embodiments shown in the embodiments.

[0626] Note that Example 1 corresponds to the first embodiment, Example 2 corresponds to the second embodiment, Example 3 corresponds to the third embodiment, and Example 4 corresponds to the fourth embodiment.

[0627] Example 1

[0628] (Example 1-1)

[0629] Glass samples having the glass compositions shown in Table 1-1(1), 1-1(2), 1-1(3), 1-1(4) were produced in the following order, and various evaluations were performed.

[0630] [Production of optical glass]

[0631] First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials so as to obtain an optical glass having the glass composition shown in Table 1-1(1), 1-1(2), 1-1(3), 1-1(4). The raw materials were weighed and prepared so as to obtain the respective compositions, and the raw materials were thoroughly mixed. The thus obtained prepared raw materials (batch raw materials) were put into a platinum crucible, heated at 1350°C to 1400°C for 2 hours to produce a molten glass, and stirred to homogenize. After clarification, the molten glass was cast into a mold preheated to an appropriate temperature. The cast glass was heat-treated at the glass transition temperature Tg for 30 minutes, and naturally cooled in a furnace to room temperature, whereby a glass sample was obtained.

[0632] [Confirmation of glass component composition]

[0633] The content of each glass component was measured by inductively coupled plasma emission spectrometry (ICP-AES) for the obtained glass sample, and it was confirmed that the respective compositions shown in Table 1-1(1), 1-1(2), 1-1(3), 1-1(4) were obtained.

[0634] [Measurement of optical properties]

[0635] After further annealing the obtained glass sample at the glass transition temperature Tg for about 30 minutes to about 2 hours, the sample was cooled to room temperature at a cooling rate of -30°C / hour in a furnace, whereby an annealed sample was obtained. The refractive indices nd, ng, nF, and nc, the Abbe number vd, the specific gravity, the glass transition temperature Tg, λ80, λ70, and λ5 were measured for the obtained annealed sample. The results are shown in Table 1-2(1), 1-2(2), 1-2(3), 1-2(4).

[0636] (i) Refractive indices nd, ng, nF, nc, and Abbe number vd

[0637] For the above annealed samples, the refractive indices nd, ng, nF, nC were determined by the refractive index measurement method of JIS standard JIS B 7071-1, and Abbe number vdwas calculated based on the following formula.

[0638] vd= (nd- 1) / (nF- nC)

[0639] (ii) Specific gravity

[0640] The specific gravity was determined by the Archimedes method.

[0641] (iii) Glass transition temperature Tg

[0642] The glass transition temperature Tg was determined using a differential scanning calorimetry device (DSC 3300 SA) manufactured by NETZSCH JAPAN Corporation at a temperature increase rate of 10°C / min.

[0643] (iv) λ80, λ70, and λ5

[0644] For an annealed sample having a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance was determined in the range of wavelengths of 200 to 700 nm. The wavelength at which the external transmittance reached 80% was set as λ80, the wavelength at which the external transmittance reached 70% was set as λ70, and the wavelength at which the external transmittance reached 5% was set as λ5.

[0645] [Table 1-1 (1)]

[0646] Table 1-1 (1)

[0647]

[0648]

[0649] [Table 1-1 (2)]

[0650] Table 1-1 (2)

[0651]

[0652]

[0653] [Table 1-1 (3)]

[0654] Table 1-1 (3)

[0655]

[0656] [Table 1-1 (4)]

[0657] Table 1-1 (4)

[0658]

[0659] [Table 1-2(1)]

[0660] Table 1-2 (1)

[0661]

[0662] [Table 1-2(2)]

[0663] Table 1-2 (2)

[0664]

[0665] [Table 1-2(3)]

[0666] Table 1-2 (3)

[0667]

[0668] [Table 1-2(4)]

[0669] Table 1-2 (4)

[0670]

[0671] (Example 1-2)

[0672] The optical glasses (Nos. 1-1 to 1-105) produced in Example 1-1 were compared with the optical glasses disclosed in the examples of Patent Documents 1 to 4. In a graph in which the refractive index ndis taken as the vertical axis and the specific gravity is taken as the horizontal axis, the optical glasses of Example 1-1 and the optical glasses disclosed in the examples of Patent Documents 1 to 4 were plotted. The results are shown in Figure 1 .

[0673] As shown in Figure 1 , the optical glasses of Example 1-1 and the optical glasses disclosed in the examples of Patent Documents 1 to 4 were distinguished by a straight line of nd= 0.2 x specific gravity + 1.18.

[0674] That is, it was found that the optical glasses of the present application were clearly distinguished from the optical glasses disclosed in the examples of Patent Documents 1 to 4 by a straight line of nd= 0.2 x specific gravity + 1.18, and exhibited superior effects with a smaller ratio with respect to the same refractive index nd.

[0675] (Example 1-3)

[0676] Each of the optical glasses produced in Example 1-1 was used to produce a lens blank by a known method, and various lenses were produced by processing the lens blank by a known method such as polishing.

[0677] The optical lenses produced were various lenses such as a piano lens, a biconvex lens, a biconcave lens, a plano-convex lens, a plano-concave lens, a concave meniscus lens, and a convex meniscus lens.

[0678] The various lenses can correct secondary chromatic aberration well by being combined with lenses made of other kinds of optical glass.

[0679] In addition, since the specific gravity of the glass is low, the weight of each lens is smaller than that of a lens having the same optical characteristics and size, and is suitable as a material for an AR display device or an MR display device of the eyewear type or the glasses type. Similarly, a prism was produced using each of the various optical glasses produced in Example 1-1.

[0680] (Example 1-4)

[0681] Each of the optical glasses produced in Example 1-1 was processed into a rectangular thin plate having a length of 50 mm, a width of 20 mm, and a thickness of 1.0 mm, and a light guide plate was obtained. The light guide plate was disposed in a head-mounted display 1 as shown in FIG. 1. Figure 2

[0682] For the head-mounted display thus obtained, the results of evaluating the image at the position of the eye point were that an image of high brightness and high contrast could be observed at a wide viewing angle.

[0683] Example 2

[0684] (Example 2-1)

[0685] Glass samples having the glass compositions shown in Table 2-1(1), 2-1(2), 2-1(3), 2-1(4), 2-2(1), 2-2(2), 2-2(3), and 2-2(4) were produced in the following order, and various evaluations were performed.

[0686] [Production of Optical Glass]

[0687] ​First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials so that the glass composition of the resulting optical glass would be each of the compositions shown in Tables 2-1(1), 2-1(2), 2-1(3), 2-1(4), 2-2(1), 2-2(2), 2-2(3), and 2-2(4). The raw materials were weighed in such a manner as to achieve each of the compositions shown in Tables 2-1(1), 2-1(2), 2-1(3), 2-1(4), 2-2(1), 2-2(2), 2-2(3), and 2-2(4) and were mixed. The thus obtained mixed raw materials (batch raw materials) were put into a platinum crucible and heated at 1350°C to 1400°C for 2 hours to produce a molten glass. The molten glass was stirred to homogenize it, was clarified, and was cast into a mold preheated to an appropriate temperature. The cast glass was heat-treated at a temperature near the glass transition temperature Tg for 30 minutes and was naturally cooled in a furnace to room temperature, whereby a glass sample was obtained.

[0688] [Confirmation of the composition of the glass]

[0689] The content of each glass component was measured by inductively coupled plasma emission spectrometry (ICP-AES) for the obtained glass sample, and it was confirmed that the composition was each of the compositions shown in Tables 2-1(1), 2-1(2), 2-1(3), 2-1(4), 2-2(1), 2-2(2), 2-2(3), and 2-2(4).

[0690] [Measurement of optical properties]

[0691] The obtained glass sample was further subjected to an annealing treatment at a temperature near the glass transition temperature Tg for about 30 minutes to about 2 hours, was cooled to room temperature at a temperature decrease rate of -30°C / hour in a furnace, and an annealed sample was obtained. The refractive indices nd, ng, nF, and nC, the Abbe number vd, the specific gravity, the glass transition temperature Tg, λ80, λ70, and λ5 were measured for the obtained annealed sample. The results are shown in Tables 2-3(1), 2-3(2), 2-3(3), and 2-3(4).

[0692] (i) Refractive indices nd, ng, nF, nC, and Abbe number vd

[0693] The refractive indices nd, ng, nF, and nC were measured by the refractive index measurement method of JIS standard JIS B 7071-1 for the above annealed sample, and the Abbe number vd was calculated based on the following equation.

[0694] vd = (nd - 1) / (nF - nC)

[0695] (ii) Specific gravity

[0696] The specific gravity was measured by the Archimedes method.

[0697] (iii) Glass transition temperature Tg

[0698] The glass transition temperature Tg was measured using a differential scanning calorimeter (DSC 3300SA) manufactured by NETZSCH JAPAN, at a temperature increase rate of 10°C / min.

[0699] (iv) λ80, λ70 and λ5

[0700] The spectral transmittance was measured in the wavelength range of 200 to 700 nm for the annealed sample having a thickness of 10.0 mm ± 0.1 mm. The wavelength at which the external transmittance reached 80% was set as λ80, the wavelength at which the external transmittance reached 70% was set as λ70, and the wavelength at which the external transmittance reached 5% was set as λ5.

[0701] [Table 2-1 (1)]

[0702] Table 2-1 (1)

[0703]

[0704] [Table 2-1 (2)]

[0705] Table 2-1 (2)

[0706]

[0707] [Table 2-1 (3)]

[0708] Table 2-1 (3)

[0709]

[0710] [Table 2-1 (4)]

[0711] Table 2-1 (4)

[0712]

[0713] [Table 2-2 (1)]

[0714] Table 2-2 (1)

[0715]

[0716] [Table 2-2 (2)]

[0717] Table 2-2 (2)

[0718]

[0719] [Table 2-2 (3)]

[0720] Table 2-2 (3)

[0721]

[0722] [Table 2-2(4)]

[0723] Table 2-2 (4)

[0724]

[0725] [Table 2-3(1)]

[0726] Table 2-3 (1)

[0727]

[0728] [Table 2-3(2)]

[0729] Table 2-3 (2)

[0730]

[0731] [Table 2-3(3)]

[0732] Table 2-3 (3)

[0733]

[0734] [Table 2-3(4)]

[0735] Table 2-3 (4)

[0736]

[0737] (Example 2-2)

[0738] Using each optical glass produced in Example 2-1, lens blanks were produced by a known method, and the lens blanks were processed by a known method such as polishing to produce various lenses.

[0739] The optical lenses produced include various lenses such as plane lenses, biconvex lenses, biconcave lenses, plano-convex lenses, plano-concave lenses, concave meniscus lenses, and convex meniscus lenses.

[0740] By combining various lenses with lenses made of other types of optical glass, secondary chromatic aberration can be effectively corrected.

[0741] In addition, due to the low specific gravity of glass, each lens weighs less than lenses with comparable optical properties and size, making it suitable as a material for goggle-type or eyeglass-type AR display devices or MR display devices. Similarly, prisms were made using the various optical glasses produced in Example 2-1.

[0742] (Example 2-3)

[0743] Each of the optical glasses produced in Example 2-1 was processed into a rectangular thin plate shape of 50 mm in length, 20 mm in width, and 1.0 mm in thickness, to obtain a light guide plate. The light guide plate was disposed in the head-mounted display 1 illustrated in Fig. 1. Figure 2

[0744] As a result of evaluating the image at the position of the eye point for the head-mounted display thus obtained, an image of high luminance and high contrast was observed at a wide viewing angle.

[0745] Example 3

[0746] (Example 3-1)

[0747] Glass samples having the glass compositions illustrated in Table 3-1(1), 3-1(2), 3-1(3), and 3-1(4) were produced in the following order, and various evaluations were performed.

[0748] [Production of Optical Glass]

[0749] First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials so as to obtain an optical glass having the glass composition of each of the compositions illustrated in Table 3-1(1), 3-1(2), 3-1(3), and 3-1(4). The raw materials were weighed and prepared so as to obtain the above-described raw materials, and the raw materials were sufficiently mixed. The thus obtained prepared raw materials (batch raw materials) were put into a platinum crucible, and heated at 1350°C to 1400°C for 2 hours to produce a molten glass. The molten glass was stirred to homogenize, and after being clarified, the molten glass was cast into a mold preheated to an appropriate temperature. The glass after casting was heat-treated at the glass transition temperature Tg for 30 minutes, and naturally cooled in a furnace to room temperature, whereby a glass sample was obtained.

[0750] [Confirmation of Glass Component Composition]

[0751] The content of each of the glass components of the obtained glass sample was measured by inductively coupled plasma emission spectrometry (ICP-AES), and it was confirmed that the composition was each of the compositions illustrated in Table 3-1(1), 3-1(2), 3-1(3), and 3-1(4).

[0752] [Measurement of Optical Properties]

[0753] ​After the obtained glass sample was further subjected to annealing treatment at the vicinity of the glass transition temperature Tg for about 30 minutes to about 2 hours, the annealed sample was obtained by cooling in the furnace at a temperature lowering rate of -30°C / hour to room temperature. The refractive indices nd, ng, nF and nC, Abbe number vd, specific gravity, glass transition temperature Tg, λ80, λ70 and λ5 were measured for the obtained annealed sample. The results are shown in Tables 3-2(l), 3-2(2), 3-2(3), 3-2(4).

[0754] (i) Refractive indices nd, ng, nF, nC and Abbe number vd

[0755] For the above-mentioned annealed sample, the refractive indices nd, ng, nF, nC were measured by the refractive index measurement method of JIS standard JIS B 7071-1, and the Abbe number vd was calculated based on the following formula.

[0756] vd = (nd - 1) / (nF - nC)

[0757] (ii) Specific gravity

[0758] The specific gravity was measured by the Archimedes method.

[0759] (iii) Glass transition temperature Tg

[0760] The glass transition temperature Tg was measured using a differential scanning calorimetry apparatus (DSC3300SA) manufactured by NETZSCH JAPAN Corporation at a temperature raising rate of 10°C / minute.

[0761] (iv) λ80, λ70 and λ5

[0762] For the annealed sample having a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance was measured in the range of wavelengths of 200 to 700 nm. The wavelength at which the external transmittance reached 80% was set as λ80, the wavelength at which the external transmittance reached 70% was set as λ70, and the wavelength at which the external transmittance reached 5% was set as λ5.

[0763] [Table 3-1(l)]

[0764] Table 3-1 (1)

[0765]

[0766] [Table 3-1(2)]

[0767] Table 3-1 (2)

[0768]

[0769] [Table 3-1(3)]

[0770] Table 3-1 (3)

[0771]

[0772] [Table 3-1 (4)]

[0773] Table 3-1 (4)

[0774]

[0775] [Table 3-2 (1)]

[0776] Table 3-2 (1)

[0777]

[0778] [Table 3-2 (2)]

[0779] Table 3-2 (2)

[0780]

[0781] [Table 3-2 (3)]

[0782] Table 3-2 (3)

[0783]

[0784] [Table 3-2 (4)]

[0785] Table 3-2 (4)

[0786]

[0787] (Example 3-2)

[0788] Using each optical glass produced in Example 3-1, a lens blank was produced by a publicly known method, and the lens blank was processed by a publicly known method such as polishing, and various lenses were produced.

[0789] The optical lenses produced were various lenses such as a piano lens, a double convex lens, a double concave lens, a plano-convex lens, a plano-concave lens, a concave meniscus lens, and a convex meniscus lens.

[0790] The various lenses can correct secondary chromatic aberration well by being combined with lenses made of other kinds of optical glasses.

[0791] In addition, since the specific gravity of the glass is low, the weight of each lens is smaller than that of a lens having the same optical characteristics and size, and is suitable as a material for an AR display device or an MR display device of the goggle type or the eyeglass type. Similarly, a prism was produced using each optical glass produced in Example 3-1.

[0792] (Example 3-3)

[0793] Each optical glass produced in Example 3-1 was processed into a rectangular thin plate shape of 50 mm in length, 20 mm in width, and 1.0 mm in thickness, and a light guide plate was obtained. The light guide plate was disposed in a head-mounted display 1 as shown in FIG. 1. Figure 2

[0794] For the thus obtained head-mounted display, the results of evaluating the image at the position of the eye point were that an image of high brightness and high contrast could be observed at a wide viewing angle.

[0795] Example 4

[0796] (Example 4-1)

[0797] Glass samples having the glass compositions shown in Table 4-1(1), 4-1(2), 4-1(3), 4-1(4), 4-2(1), 4-2(2), 4-2(3), and 4-2(4) were produced in the following order, and various evaluations were performed.

[0798] [Production of Optical Glass]

[0799] First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass were prepared as raw materials so that the glass composition of the obtained optical glass would be each of the compositions shown in Table 4-1(1), 4-1(2), 4-1(3), 4-1(4), 4-2(1), 4-2(2), 4-2(3), and 4-2(4). The above raw materials were weighed and prepared so as to achieve each of the above compositions, and the raw materials were thoroughly mixed. The thus obtained prepared raw materials (batch raw materials) were put into a platinum crucible, heated at 1350°C to 1400°C for 2 hours to produce a molten glass, and stirred to achieve homogenization. After clarification, the molten glass was cast into a mold preheated to an appropriate temperature. The cast glass was heat-treated at the glass transition temperature Tg for 30 minutes, and naturally cooled in the furnace to room temperature, whereby a glass sample was obtained.

[0800] [Confirmation of Glass Component Composition]

[0801] ​For the obtained glass samples, the content of each glass component was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), and it was confirmed that each composition shown in Table 4-1 (1), 4-1 (2), 4-1 (3), 4-1 (4), 4-2 (1), 4-2 (2), 4-2 (3), 4-2 (4) was obtained.

[0802] [Measurement of optical properties]

[0803] For the obtained glass samples, further annealing treatment was performed for about 30 minutes to about 2 hours in the vicinity of the glass transition temperature Tg, and then the samples were cooled to room temperature in the furnace at a cooling rate of -30°C / hour, to obtain annealed samples. The refractive indices nd, ng, nF, and nC, the Abbe number vd, the specific gravity, the glass transition temperature Tg, λ80, λ70, and λ5 were measured for the obtained annealed samples. The results are shown in Tables 4-3 (1), 4-3 (2), 4-3 (3), 4-3 (4).

[0804] (i) Refractive indices nd, ng, nF, nC, and Abbe number vd

[0805] For the above annealed samples, the refractive indices nd, ng, nF, and nC were measured by the refractive index measurement method of JIS standard JIS B 7071-1, and the Abbe number vd was calculated based on the following formula.

[0806] vd = (nd - 1) / (nF - nC)

[0807] (ii) Specific gravity

[0808] The specific gravity was measured by the Archimedes method.

[0809] (iii) Glass transition temperature Tg

[0810] The glass transition temperature Tg was measured using a differential scanning calorimetry device (DSC3300SA) manufactured by NETZSCH JAPAN Corporation, at a temperature increase rate of 10°C / min.

[0811] (iv) λ80, λ70, and λ5

[0812] For the annealed samples having a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance was measured in the wavelength range of 200 to 700 nm. The wavelength at which the external transmittance reached 80% was set as λ80, the wavelength at which the external transmittance reached 70% was set as λ70, and the wavelength at which the external transmittance reached 5% was set as λ5.

[0813] [Table 4-1 (1)]

[0814] Table 4-1 (1)

[0815]

[0816] [table 4-1 (2)]

[0817] Table 4-1 (2)

[0818]

[0819] [table 4-1 (3)]

[0820] Table 4-1 (3)

[0821]

[0822] [table 4-1 (4)]

[0823] Table 4-1 (4)

[0824]

[0825] [table 4-2 (1)]

[0826] Table 4-2 (1)

[0827]

[0828] [table 4-2 (2)]

[0829] Table 4-2 (2)

[0830]

[0831] [table 4-2 (3)]

[0832] Table 4-2 (3)

[0833]

[0834] [table 4-2 (4)]

[0835] Table 4-2 (4)

[0836]

[0837] [table 4-3 (1)]

[0838] Table 4-3 (1)

[0839]

[0840]

[0841] [table 4-3 (2)]

[0842] Table 4-3 (2)

[0843] [Table 4-3 (3)]

[0844] Table 4-3 (3)

[0845]

[0846] [Table 4-3 (4)]

[0847] Table 4-3 (4)

[0848]

[0849] (Example 4-2)

[0850] The optical glasses (Nos. 4-1 to 4-97) produced in Example 4-1 were compared with the optical glasses disclosed in the examples of Patent Documents 1 to 4. First, the optical glasses of Example 4-1 and the optical glasses disclosed in the examples of Patent Documents 1 to 4 were plotted in a coordinate graph with the mass ratio [Li20 / {100 - (Si02+ B203+ P205+ Ge02)}] as the vertical axis and the mass ratio [Ti02 / (Ti02+ Nb205+ W03+ Zr02+ SrO + BaO + ZnO + La203+ Gd203+ Y203+ Ta205+ Bi203)] as the horizontal axis. The results are shown in FIG. 4-1. Figure 4 .

[0851] Next, the optical glasses of Example 4-1 (Nos. 4-1 to 4-97) and the optical glasses disclosed in the examples of Patent Documents 1 to 4 were plotted in a coordinate graph with the ratio of the refractive index ndto the specific gravity [refractive index nd / specific gravity] as the vertical axis and the mass ratio [Ti02 / (Ti02+ Nb205+ W03+ Zr02+ SrO + BaO + ZnO + La203+ Gd203+ Y203+ Ta205+ Bi203)] as the horizontal axis. Note that the larger the value of the ratio [refractive index nd / specific gravity] as the vertical axis, the higher the refractive index and the lower the specific gravity. The results are shown in FIG. 4-2. Figure 5 ,

[0852] As Figure 4As shown in the figure, the optical glass of Example 4-1 is distinguished from the optical glasses disclosed in the examples of Patent Documents 1 to 4 with a line where the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+ZrO2+SrO+BaO+ZnO+La2O3+Gd2O3+Y2O3+Ta2O5+Bi2O3)] as the horizontal axis reaches 0.40 and a line where the mass ratio [Li2O / {100-(SiO2+B2O3+P2O5+GeO2)}] as the vertical axis reaches 0.02 as the boundary.

[0853] Further, as shown in the figure, with respect to the ratio [refractive index nd / density] as the vertical axis, the optical glass of Example 4-1 shows a value higher than the optical glasses disclosed in the examples of Patent Documents 1 to 4. Figure 5

[0854] That is, it is known that the optical glass of Example 4-1 can be clearly distinguished from the optical glasses disclosed in the examples of Patent Documents 1 to 4 on the basis of the composition, and shows an excellent effect of the ratio [refractive index nd / density] being large.

[0855] (Example 4-3)

[0856] Using each of the optical glasses produced in Example 4-1, a lens blank was produced by a publicly known method, and the lens blank was processed by a publicly known method such as polishing, and various lenses were produced.

[0857] The optical lenses produced were various lenses such as a piano lens, a lenticular lens, a biconcave lens, a plano-convex lens, a plano-concave lens, a concave meniscus lens, and a convex meniscus lens.

[0858] The various lenses can correct secondary chromatic aberration well by being combined with lenses made of other kinds of optical glasses.

[0859] Further, since the density of the glass is low, the weight of each lens is smaller than that of a lens having the same optical characteristics and size, and is suitable as a material for an AR display device or an MR display device of the eyewear type or the glasses type. Similarly, prisms were produced using each of the various optical glasses produced in Example 4-1.

[0860] (Example 4-4)

[0861] Each of the optical glasses produced in Example 4-1 was processed into a rectangular thin plate shape of 50 mm in length, 20 mm in width, and 1.0 mm in thickness, and a light guide plate was obtained. This light guide plate was provided to the head-mounted display 1 shown in the figure. Figure 2

[0862] With respect to the head-mounted display thus obtained, the result of evaluating the image at the position of the eye point was that an image of high brightness and high contrast could be observed at a wide viewing angle.​​

[0863] Comparative Example

[0864] Glass samples having the glass compositions shown in Table 5(1) were prepared in the following procedure and various evaluations were performed. Comparative Examples 1 to 7 each have the same composition as the glass disclosed in the literature shown below.

[0865] Comparative Example 1: Physics and Chemistry of Glasses, vol. 12, p. 93, 1971

[0866] Comparative Example 2: J. Non-Crystalline Solids, vol. 107, p. 244, 1989

[0867] Comparative Example 3: J. American Ceramic Soc., vol. 73, p. 2743, 1990

[0868] Comparative Example 4: Applied Optics, vol. 29, p. 3126, 1990

[0869] Comparative Example 5: Applied Optics, vol. 29, p. 3126, 1990

[0870] Comparative Example 6: Japanese Patent Application Laid-Open No. 2003-252646

[0871] Comparative Example 7: J. American Ceramic Soc., vol. 94, p. 2086, 2011

[0872] [Manufacturing of optical glass]

[0873] First, oxides, hydroxides, carbonates, and nitrates corresponding to the constituent components of the glass are prepared as raw materials. The raw materials are weighed and blended so that the glass composition of the optical glass obtained reaches the compositions shown in Table 5 (1), and the raw materials are thoroughly mixed. The blended raw materials (batch raw materials) thus obtained are placed in a platinum crucible and heated at 1350°C to 1400°C for 2 hours to form molten glass. The glass is stirred for homogenization. After clarification, the molten glass is cast into a mold preheated to an appropriate temperature. The cast glass is heat treated at around the glass transition temperature Tg for 30 minutes and naturally cooled to room temperature in a furnace to obtain a glass sample.

[0874] [Confirmation of glass composition]

[0875] For the obtained glass samples, the content of each glass component was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), and it was confirmed that each composition was as shown in Table 5 (1).

[0876] [Measurement of optical properties]

[0877] For the obtained glass samples, further annealing treatment was performed for about 30 minutes to about 2 hours in the vicinity of the glass transition temperature Tg, and then the samples were cooled to room temperature in the furnace at a cooling rate of -30°C / hour, to obtain annealed samples. The refractive index ndand specific gravity of the obtained annealed samples were measured. The results are shown in Table 5 (2).

[0878] (i) Refractive index nd

[0879] For the above-mentioned annealed samples, the refractive index ndwas measured by the refractive index measurement method of JIS standard JIS B 7071-1.

[0880] (ii) Specific gravity

[0881] The specific gravity was measured by the Archimedes method.

[0882] [Observation of glass]

[0883] The obtained glass samples were observed. In Comparative Examples 1 to 7, devitrification occurred in part or in whole, and glass that could be applied to optical glass could not be obtained. Photographs of the glass samples obtained in Comparative Examples 1, 2, 4 to 7 are shown in Figures 6 to 11 .

[0884] [Table 5 (1)]

[0885] Table 5 (1)

[0886]

[0887] [Table 5 (2)]

[0888] Table 5 (2)

[0889]

[0890] It should be understood that the embodiments disclosed herein are all exemplary and do not constitute a limitation. The scope of the present application is defined by the claims, not the above description, and is intended to include all modifications within the meaning and range of equivalents of the claims.

[0891] For example, by performing the composition adjustment described in the specification on the above-described exemplified glass composition, an optical glass according to one embodiment of the present application can be produced.

[0892] In addition, two or more of the matters exemplified in the specification or described as preferred ranges can be combined arbitrarily, of course.

Claims

1. An optical glass, which is a SiO2-TiO2-Nb2O5 glass, wherein: The content of SiO2 is 10% by mass or more, The content of TiO2 is 10% by mass or more, The content of Nb2O5 is 35% by mass or less, The content of P2O5 is 10% by mass or less, The total content of Na2O, K2O and Cs2O [Na2O+K2O+Cs2O] is 5.04 mass % or more and 11.0 mass % or less, The mass ratio of the content of TiO2 to the total content of TiO2 and Nb2O5 [TiO2 / (TiO2+Nb2O5)] is 0.30 or more, The optical glass has a refractive index nd of 1.89424 or greater, an Abbe number vd of 20 to 30, and a specific gravity of 4.2 or less. The specific gravity and refractive index nd of the optical glass satisfy the following formula (1): nd≥0.2×specific gravity+1.18···(1).

2. An optical element made of the optical glass according to claim 1.

3. A light guide plate made of the optical glass according to claim 1. The light guide plate according to claim 3 , having a diffraction grating on its surface.

5. An image display device comprising: Image display element, and a light guide plate for guiding light emitted from the image display element, wherein The light guide plate is made of the optical glass according to claim 1.

Images