Optical glass, optical element blanks and optical elements

Abstract

To provide optical glass and an optical element with high refractive indexes and relatively low specific gravities.SOLUTION: An optical glass has a refractive index nd of 1.950 or more, P2O5 content of 10.0-40.0 mass%, TiO2 content of 5.0-40.0 mass%, Nb2O5 content of 20.0-60.0 mass%, Bi2O3 content of 20.0 mass% or less, with the total content of Al2O3 and SiO2 [Al2O3+SiO2] of 2.0 mass% or less, the total content of Li2O, Na2O and K2O [Li2O+Na2O+K2O] of 5.0 mass% or less, and the total content of ZnO, SrO and BaO [ZnO+SrO+BaO] of 0.01-12.0 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to optical glass, optical element blanks, and optical elements.

Background Art

[0002] In recent years, with the development of AR (augmented reality) technology, display devices such as goggle-type or glasses-type have been developed as AR devices. For example, goggle-type display devices require lenses with a high refractive index and a low specific gravity, and the demand for glass applicable to such lenses is increasing.

[0003] Patent Documents 1 to 4 disclose optical glasses containing Ti and Nb as optical glasses with a high refractive index. However, from their compositions, it is estimated that these optical glasses have too large a specific gravity with respect to the refractive index to be adopted as lenses for AR devices.

[0004] Therefore, there is a demand for optical glasses with a reduced specific gravity while maintaining a high refractive index.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] In view of such a situation, the present invention is made, and an object thereof is to provide an optical glass and an optical element having a high refractive index and a relatively low specific gravity. [Means for solving the problem]

[0007] The gist of this invention is as follows: (1) The refractive index nd is 1.950 or greater, The P2O5 content is 10.0 to 40.0% by mass. The TiO2 content is 5.0 to 40.0% by mass. The Nb2O5 content is 20.0 to 60.0% by mass. The Bi2O3 content is 20.0% by mass or less. The total content of Al2O3 and SiO2 [Al2O3+SiO2] is 2.0% by mass or less. The total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is 5.0% by mass or less. Optical glass with a total content of ZnO, SrO, and BaO [ZnO+SrO+BaO] of 0.01 to 12.0% by mass. (2) An optical element blank made of the optical glass described in (1) above. (3) An optical element made of the optical glass described in (1) above. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide optical glass and optical elements with a high refractive index and relatively low specific gravity. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows the configuration of a head-mounted display using a light guide plate, which is one embodiment of the present invention. [Figure 2] Figure 2 is a schematic side view showing the configuration of a head-mounted display using a light guide plate, which is one embodiment of the present invention. [Modes for carrying out the invention]

[0010] In this invention and specification, glass composition is expressed on an oxide basis unless otherwise specified. Here, "glass composition on an oxide basis" refers to the glass composition obtained by calculating it as if all glass raw materials were decomposed during melting and existed as oxides in the glass. The total content of all glass components expressed on an oxide basis (excluding Sb (Sb2O3), Ce (CeO2), and Sn (SnO2) added as clarifying agents) is 100% by mass. Each glass component is written as SiO2, TiO2, etc., following convention. The content and total content of glass components are on a mass basis unless otherwise specified, and "%" means "mass%".

[0011] The content of glass components can be quantified by known methods, such as inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Furthermore, in this specification and the present invention, a component content of 0% means that the component is substantially absent, and it is permissible for the component to be present at an unavoidable impurity level.

[0012] In this specification, unless otherwise specified, refractive index refers to the refractive index nd at the helium d-line (wavelength 587.56 nm).

[0013] Furthermore, the Abbe number νd is used as a value that represents the properties related to dispersion, and is expressed by the following formula. Here, nF is the refractive index of blue hydrogen at the F line (wavelength 486.13 nm), and nC is the refractive index of red hydrogen at the C line (656.27 nm). νd=(nd-1) / nF-nC

[0014] The optical glass according to an embodiment of the present invention is described below. The optical glass according to this embodiment has a refractive index nd of 1.950 or higher. The P2O5 content is 10.0 to 40.0% by mass. The TiO2 content is 5.0 to 40.0% by mass. The Nb2O5 content is 20.0 to 60.0% by mass. The content of Bi2O3 is 20.0 mass% or less, the total content of Al2O3 and SiO2 [Al2O3 + SiO2] is 2.0 mass% or less, the total content of Li2O, Na2O and K2O [Li2O + Na2O + K2O] is 5.0 mass% or less, the total content of ZnO, SrO and BaO [ZnO + SrO + BaO] is 0.01 - 12.0 mass%, which is characterized. Hereinafter, each requirement will be described.

[0015] In the optical glass according to this embodiment, the refractive index nd is 1.950 or more. The lower limit of the refractive index nd is preferably 1.955, and may be 1.960, 1.965, 1.970, 1.975 or 1.980. Also, the upper limit of the refractive index nd is preferably 2.300, and may be 2.250, 2.200, 2.150, 2.100 or 2.050.

[0016] In the optical glass according to this embodiment, the content of P2O5 is 10.0 - 40.0%. The upper limit of the content of P2O5 is preferably 38.0%, and may further be 35.0%, 33.0%, 30.0% or 28.0%. Also, the lower limit of the content of P2O5 is preferably 13.0%, and may further be 15.0%, 18.0% or 20.0%.

[0017] P2O5 is a network - forming component and is an essential component for containing a large amount of highly dispersed components in the glass. By setting the content of P2O5 within the above range, it becomes easy to obtain a desired refractive index and the melting temperature can be controlled within an appropriate range.

[0018] In the optical glass according to this embodiment, the content of TiO2 is 5.

[0019] TiO2 significantly contributes to high refractive index and high dispersion. It also contributes to low specific gravity among high refractive index components. By keeping the TiO2 content within the above range, both high refractive index and low specific gravity can be achieved, and chemical durability can also be improved. On the other hand, if the TiO2 content is too high, the melting temperature rises, and during the process of shaping and slowly cooling the molten glass to obtain optical glass, crystal formation within the glass is promoted, leading to a decrease in transparency (cloudiness) of the glass. Coloration also increases.

[0020] In the optical glass according to this embodiment, the Nb2O5 content is 20.0 to 60.0%. The upper limit of the Nb2O5 content is preferably 58.0%, and may further be 55.0%, 53.0%, 50.0%, or 48.0%. The lower limit of the Nb2O5 content is preferably 23.0%, and may further be 25.0%, 28.0%, 30.0%, 33.0%, 35.0%, 38.0%, or 40.0%.

[0021] Nb2O5 is a component that contributes to higher refractive index and higher dispersion. Furthermore, by keeping the Nb2O5 content within the above range, the thermal stability and chemical durability of the glass can be improved. On the other hand, if the Nb2O5 content becomes too high, the melting temperature increases, the thermal stability of the glass decreases, and the glass tends to become more discolored. Additionally, the specific gravity of the glass may increase.

[0022] In the optical glass according to this embodiment, the Bi2O3 content is 20.0% or less. The upper limit of the Bi2O3 content is preferably 15.0%, and may further be 10.0%, 5.0%, 3.0%, 1.0%, or 0.1%. The lower limit of the Bi2O3 content may be 0%.

[0023] Bi2O3 is a glass component that increases the refractive index of glass. On the other hand, increasing the Bi2O3 content increases the coloration of the glass and also causes a higher specific gravity. Therefore, it is preferable that the Bi2O3 content be within the above range.

[0024] In the optical glass according to this embodiment, the total content of Al2O3 and SiO2 [Al2O3+SiO2] is 2.0% or less. The upper limit of this total content is preferably 1.8%, and may further be 1.5%, 1.3%, 1.0%, 0.8%, or 0.5%. The lower limit of this total content may be 0%.

[0025] Al2O3 and SiO2 are network-forming components of glass, improving its thermal stability, chemical durability, and weather resistance, as well as increasing the viscosity of molten glass and making it easier to mold. However, if the total content is too high, the desired refractive index may not be achieved.

[0026] In the optical glass according to this embodiment, the total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is 5.0% or less. The upper limit of the total content is preferably 4.8%, and may further be 4.5%, 4.3%, or 4.0%. The lower limit of the total content is preferably 0.1%, and may further be 0.5%, 1.0%, 1.5%, or 2.0%.

[0027] By keeping the total content [Li2O + Na2O + K2O] within the above range, thermal stability can be improved and the melting temperature can be lowered. On the other hand, if the total content is too high, chemical durability and weather resistance may decrease. Also, the refractive index may decrease.

[0028] In the optical glass according to this embodiment, the total content of ZnO, SrO, and BaO [ZnO+SrO+BaO] is 0.01 to 12.0%. The upper limit of the total content is preferably 11.5%, and may further be 11.0%, 10.5%, 10.0%, 9.5%, 9.0%, 8.5%, or 8.0%. The lower limit of the total content is preferably 0.1%, and may further be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%.

[0029] ZnO, SrO, and BaO are all glass components that lower the melting temperature of glass and improve its thermal stability and resistance to devitrification. However, if the total content [ZnO + SrO + BaO] is too high, the desired refractive index may not be achieved, and the specific gravity may also increase. On the other hand, if the total content is too low, the stability of the glass may decrease.

[0030] The following are non-limiting examples of the content, ratio, and properties of glass components other than those mentioned above in the optical glass according to this embodiment.

[0031] The optical glass according to this embodiment is substantially free of F (fluorine). That is, in the optical glass according to this embodiment, the anionic component is mainly O (oxygen). When expressed as a mass % relative to the total amount of glass based on oxides, the F content is preferably less than 1.0% on an external basis, and more preferably 0.5% or less, 0.2% or less, and 0.1% or less, in that order.

[0032] Here, "external division" refers to the amount of F component expressed in mass percentage, assuming that all the cationic components constituting the glass are oxides bonded with oxygen in sufficient quantities to balance the charge, and that the total amount of material in the glass made of these oxides is 100%.

[0033] In the optical glass according to this embodiment, the upper limit of the SiO2 content is preferably 2.0%, and may further be 1.8%, 1.5%, 1.3%, 1.0%, 0.8%, or 0.5%. The SiO2 content may also be 0%.

[0034] SiO2 is a network-forming component in glass, improving its thermal stability, chemical durability, and weather resistance, as well as increasing the viscosity of molten glass and making it easier to mold. On the other hand, a high SiO2 content makes it difficult to obtain the desired refractive index.

[0035] In the optical glass according to this embodiment, the upper limit of the B2O3 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, or 1.0%. The B2O3 content may also be 0%.

[0036] B2O3 is a network-forming component in glass. Furthermore, among the network-forming components of glass, it contributes to increasing the refractive index. By keeping the B2O3 content within the above range, the melting temperature can be controlled within an appropriate range, improving the thermal stability of the glass. On the other hand, if the B2O3 content is too high, it tends to hinder the increase in refractive index and reduce resistance to devitrification.

[0037] In the optical glass according to this embodiment, the upper limit of the Al2O3 content is preferably 2.0%, and may further be 1.8%, 1.5%, 1.3%, 1.0%, 0.8%, or 0.5%. The Al2O3 content may also be 0%.

[0038] Al2O3 is a glass component that improves the chemical durability and weather resistance of glass, and can be considered a network-forming component. On the other hand, if the Al2O3 content is high, it becomes difficult to obtain the desired refractive index, the melting temperature rises, and the devitrification resistance of the glass decreases. Furthermore, problems such as an increase in the glass transition temperature (Tg) and a decrease in thermal stability tend to occur.

[0039] In the optical glass according to this embodiment, the upper limit of the Li2O content is preferably 5.0%, and may further be 4.5%, 4.0%, 3.5%, 3.0%, or 2.5%. The lower limit of the Li2O content is preferably 0.01%, and may further be 0.02%, 0.03%, 0.04%, or 0.05%. The Li2O content may also be 0%.

[0040] By keeping the Li2O content within the above range, the melting temperature can be lowered, the specific gravity can be reduced, and the thermal stability of the glass can be improved. In addition, Li2O contributes to a higher refractive index among alkaline components. On the other hand, if the Li2O content is too high, it becomes difficult to obtain the desired refractive index, and thermal stability, chemical durability, and weather resistance may decrease.

[0041] In the optical glass according to this embodiment, the upper limit of the Na2O content is preferably 5.0%, and may further be 4.5%, 4.0%, 3.5%, 3.0%, 2.5%, or 2.0%. The lower limit of the Na2O content is preferably 0%, and the Na2O content may be 0%.

[0042] Na2O lowers the melting temperature and improves the thermal stability of the glass, contributing to a lower specific gravity. However, if the content is too high, it becomes difficult to obtain the desired refractive index.

[0043] In the optical glass according to this embodiment, the upper limit of the K2O content is preferably 5.0%, and may further be 4.8%, 4.5%, 4.3%, 4.0%, 3.8%, or 3.5%. The lower limit of the K2O content is preferably 0.1%, and may further be 0.3%, 0.5%, 0.8%, 1.0%, or 1.5%.

[0044] K2O lowers the melting temperature and improves the thermal stability of glass, contributing to a lower specific gravity. However, if the content is too high, it becomes difficult to obtain the desired refractive index.

[0045] In the optical glass according to this embodiment, the upper limit of the Cs2O content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the Cs2O content is preferably 0%.

[0046] Cs2O lowers the melting temperature and improves the thermal stability of the glass, contributing to a lower specific gravity. However, if its content is too high, it becomes difficult to obtain the desired refractive index.

[0047] In the optical glass according to this embodiment, the upper limit of the MgO content is preferably 15.0%, and may further be 10.0%, 8.0%, 5.0%, or 3.0%. Alternatively, the MgO content may be 0%. MgO is a glass component that lowers the melting temperature of the glass and improves its thermal stability and devitrification resistance. However, if the MgO content is high, it becomes difficult to obtain the desired refractive index, and the thermal stability and devitrification resistance of the glass decrease.

[0048] In the optical glass according to this embodiment, the upper limit of the CaO content is preferably 15.0%, and may further be 10.0%, 8.0%, 5.0%, or 3.0%. Alternatively, the CaO content may be 0%. CaO is a glass component that lowers the melting temperature of the glass and improves its thermal stability and devitrification resistance. However, if the CaO content is high, it becomes difficult to obtain the desired refractive index, and the thermal stability and devitrification resistance of the glass decrease.

[0049] In the optical glass according to this embodiment, the upper limit of the SrO content is preferably 12.0%, and may further be 10.0%, 8.0%, 5.0%, or 3.0%. The lower limit of the SrO content is preferably 0%. SrO is a glass component that lowers the melting temperature of the glass and improves its thermal stability and resistance to devitrification. However, if the SrO content is high, the specific gravity increases, making it difficult to obtain the desired refractive index, and the thermal stability and resistance to devitrification of the glass decrease.

[0050] In the optical glass according to this embodiment, the upper limit of the BaO content is preferably 12.0%, and may further be 11.5%, 11.0%, 10.5%, 10.0%, 9.5%, 9.0%, 8.5%, or 8.0%. The lower limit of the BaO content is preferably 0.1%, and may further be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%. BaO is a glass component that lowers the melting temperature of the glass and improves its thermal stability and resistance to devitrification. However, if the BaO content is high, the specific gravity increases, making it difficult to obtain the desired refractive index, and the thermal stability and resistance to devitrification of the glass decrease.

[0051] In the optical glass according to this embodiment, the upper limit of the ZnO content is preferably 12.0%, and may further be 10.0%, 8.0%, 5.0%, or 3.0%. The lower limit of the ZnO content is preferably 0%. ZnO is a glass component that lowers the melting temperature of the glass and improves its thermal stability and devitrification resistance. However, if the ZnO content increases, the specific gravity increases, making it difficult to obtain the desired refractive index, and the thermal stability and devitrification resistance of the glass decrease.

[0052] In the optical glass according to this embodiment, the upper limit of the ZrO2 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the ZrO2 content is preferably 0%. ZrO2 is a glass component that increases the refractive index of the glass and improves thermal stability and devitrification resistance. However, if the ZrO2 content is too high, the specific gravity increases, the melting temperature rises, and thermal stability tends to decrease.

[0053] In the optical glass according to this embodiment, the upper limit of the WO3 content is preferably 15.0%, and may further be 13.0%, 10.0%, 8.0%, 5.0%, 3.0%, or 1.0%. The WO3 content may also be 0%. WO3 is a glass component that increases the refractive index of the glass. However, if the WO3 content is too high, the specific gravity increases and the thermal stability tends to decrease.

[0054] In the optical glass according to this embodiment, the upper limit of the Ta2O5 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the Ta2O5 content is preferably 0%. Ta2O5 is a glass component that increases the refractive index of the glass. However, if the Ta2O5 content increases, the specific gravity of the glass increases, the thermal stability of the glass decreases, and the melting temperature of the glass rises.

[0055] In the optical glass according to this embodiment, the upper limit of the La2O3 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the La2O3 content is preferably 0%. La2O3 is a glass component that increases the refractive index of the glass. However, if the La2O3 content increases, the specific gravity of the glass increases, the thermal stability of the glass decreases, and the melting temperature of the glass rises.

[0056] In the optical glass according to this embodiment, the upper limit of the Y2O3 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the Y2O3 content is preferably 0%. Y2O3 is a glass component that increases the refractive index of the glass. However, if the Y2O3 content increases, the specific gravity of the glass increases, the thermal stability of the glass decreases, and the melting temperature of the glass rises.

[0057] In the optical glass according to this embodiment, the upper limit of the Gd2O3 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the Gd2O3 content is preferably 0%. Gd2O3 is a glass component that increases the refractive index of the glass. However, if the Gd2O3 content increases, the specific gravity of the glass increases, the thermal stability of the glass decreases, and the melting temperature of the glass rises.

[0058] In the optical glass according to this embodiment, the upper limit of the Lu2O3 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the Lu2O3 content is preferably 0%. Lu2O3 is a glass component that increases the refractive index of the glass. However, as the Lu2O3 content increases, the specific gravity of the glass increases.

[0059] In the optical glass according to this embodiment, the upper limit of the Yb2O3 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the Yb2O3 content is preferably 0%. Yb2O3 is a glass component that increases the refractive index of the glass. However, as the Yb2O3 content increases, the specific gravity of the glass increases.

[0060] In the optical glass according to this embodiment, the upper limit of the GeO2 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the GeO2 content is preferably 0%. GeO2 has the function of increasing the refractive index nd, and is also a particularly expensive component among the commonly used glass components. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, it is preferable that the GeO2 content be within the above range.

[0061] In the optical glass according to this embodiment, the upper limit of the HfO2 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the HfO2 content is preferably 0%. HfO2 has the function of increasing the refractive index nd, increasing the specific gravity, and is an expensive component. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, it is preferable that the HfO2 content be within the above range.

[0062] In the optical glass according to this embodiment, the upper limit of the In2O3 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the In2O3 content is preferably 0%. In2O3 has the function of increasing the refractive index nd, increasing the specific gravity, and is an expensive component. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, it is preferable that the In2O3 content be within the above range.

[0063] In the optical glass according to this embodiment, the upper limit of the Ga2O3 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the Ga2O3 content is preferably 0%. Ga2O3 has the function of increasing the refractive index nd, increasing the specific gravity, and is an expensive component. Therefore, from the viewpoint of reducing the manufacturing cost of the glass, it is preferable that the Ga2O3 content be within the above range.

[0064] In the optical glass according to this embodiment, the upper limit of the Sc2O3 content is preferably 10.0%, and may further be 8.0%, 5.0%, 3.0%, 1.0%, 0.5%, or 0.1%. The lower limit of the Sc2O3 content is preferably 0%. Sc2O3 has the effect of increasing the refractive index nd and increasing the specific gravity. Therefore, from the viewpoint of reducing the specific gravity of the glass, it is preferable that the Sc2O3 content be within the above range.

[0065] In the optical glass according to this embodiment, the upper limit of the total content of P2O5, TiO2, and Nb2O5 [P2O5+TiO2+Nb2O5] is preferably 98.0%, and may further be 97.0%, 96.0%, or 95.0%. The lower limit of the total content is preferably 70.0%, and may further be 73.0%, 75.0%, 78.0%, or 80.0%. When the total content [P2O5+TiO2+Nb2O5] is within the above range, the melting temperature is reduced and the stability of the glass is improved.

[0066] In the optical glass according to this embodiment, the upper limit of the total content of SrO and BaO [SrO+BaO] is preferably 12.0%, and may further be 11.5%, 11.0%, 10.5%, 10.0%, 9.5%, 9.0%, 8.5%, or 8.0%. The lower limit of the total content is preferably 0.1%, and may further be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%. All of these components have the function of improving the thermal stability of the glass. However, if the total content [SrO+BaO] is high, the specific gravity increases, and the desired refractive index may not be obtained.

[0067] In the optical glass according to this embodiment, the upper limit of the total content of MgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO] is preferably 12.0%, and may further be 11.5%, 11.0%, 10.5%, 10.0%, 9.5%, 9.0%, 8.5%, or 8.0%. The lower limit of the total content is preferably 0.1%, and may further be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%. All of these components have the function of lowering the melting temperature of the glass and improving its thermal stability. However, if the total content [MgO+CaO+ZnO+SrO+BaO] is too high, the desired refractive index may not be obtained.

[0068] In the optical glass according to this embodiment, the upper limit of the total content of Li2O, Na2O, K2O, MgO, CaO, ZnO, SrO, and BaO [Li2O+Na2O+K2O+MgO+CaO+ZnO+SrO+BaO] is preferably 17.0%, and may further be 16.0%, 15.0%, 14.0%, 13.0%, 12.0%, 11.0%, or 10.0%. The lower limit of the total content is preferably 0.5%, and may further be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, or 4.5%. All of these components have the function of lowering the melting temperature of the glass and improving its thermal stability. However, if the total content [Li2O+Na2O+K2O+MgO+CaO+ZnO+SrO+BaO] is too high, the desired refractive index may not be obtained.

[0069] In the optical glass according to this embodiment, the upper limit of the total content of TiO2 and Nb2O5 [TiO2+Nb2O5] is preferably 80.0%, and may further be 78.0%, 75.0%, 73.0%, or 70.0%. The lower limit of the total content is preferably 40.0%, and may further be 43.0%, 45.0%, 48.0%, 50.0%, 53.0%, or 55.0%. By having the total content [TiO2+Nb2O5] within the above range, a high refractive index is obtained and the stability of the glass is improved.

[0070] In the optical glass according to this embodiment, the upper limit of the total content of TiO2, Nb2O5, WO3, and Bi2O3 [TiO2+Nb2O5+WO3+Bi2O3] is preferably 80.0%, and may further be 78.0%, 75.0%, 73.0%, or 70.0%. The lower limit of the total content is preferably 40.0%, and may further be 43.0%, 45.0%, 48.0%, 50.0%, 53.0%, or 55.0%. By setting the total content [TiO2+Nb2O5+WO3+Bi2O3] within the above range, a high refractive index can be obtained and the stability of the glass can be improved.

[0071] In the optical glass according to this embodiment, the upper limit of the mass ratio [P2O5 / (P2O5+TiO2+Nb2O5)] between the P2O5 content and the total content of P2O5, TiO2, and Nb2O5 [P2O5+TiO2+Nb2O5] is preferably 0.40, and may further be 0.38, 0.35, 0.33, or 0.30. The lower limit of the mass ratio is 0.15, and may further be 0.18, 0.20, or 0.23. By having the mass ratio within the above range, it becomes easier to obtain the desired refractive index and the stability of the glass is improved.

[0072] In the optical glass according to this embodiment, the lower limit of the mass ratio [K2O / (Li2O+Na2O+K2O)] between the K2O content and the total content of Li2O, Na2O, and K2O [Li2O+Na2O+K2O] is preferably greater than 0, and may be 0.10, 0.20, 0.30, 0.40, or 0.50. When the mass ratio is within the above range, the stability of the glass is improved.

[0073] In the optical glass according to this embodiment, the upper limit of the mass ratio [TiO2 / (Li2O+Na2O+K2O)] between the TiO2 content and the total content of Li2O, Na2O, and K2O [Li2O+Na2O+K2O] is preferably 500, and may further be 450, 400, or 300. The lower limit of the mass ratio is preferably 1.0, and may further be 1.5, 2.0, 2.5, or 3.0. Furthermore, when the mass ratio is within the above range, it becomes easier to obtain the desired refractive index and the stability of the glass is improved.

[0074] In the optical glass according to this embodiment, the upper limit of the mass ratio [(MgO+CaO+ZnO+SrO+BaO) / (Li2O+Na2O+K2O)] between the total content of MgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO] and the total content of Li2O, Na2O, and K2O [Li2O+Na2O+K2O] is preferably 300, and may further be 250, 200, or 150. The lower limit of the mass ratio is preferably 0.10, and may further be 0.20, 0.30, 0.40, or 0.50. When the mass ratio is within the above range, the stability of the glass is improved.

[0075] In the optical glass according to this embodiment, the lower limit of the mass ratio [BaO / (MgO+CaO+ZnO+SrO+BaO)] between the BaO content and the total content of MgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO] is preferably greater than 0, and may be 0.1, 0.2, 0.3, 0.4, or 0.5. When the mass ratio is within the above range, the stability of the glass is improved.

[0076] In the optical glass according to this embodiment, the upper limit of the mass ratio [TiO2 / (MgO+CaO+ZnO+SrO+BaO)] between the TiO2 content and the total content of MgO, CaO, ZnO, SrO, and BaO [MgO+CaO+ZnO+SrO+BaO] is preferably 50.0, and may further be 45.0, 40.0, 35.0, or 30.0. The lower limit of the mass ratio is preferably 0.1, and may further be 0.3, 0.5, 0.8, or 1.0. Furthermore, when the mass ratio is within the above range, it becomes easier to obtain the desired refractive index at a low specific gravity, and the stability of the glass is improved.

[0077] In the optical glass according to this embodiment, the upper limit of the mass ratio [TiO2 / (TiO2+Nb2O5)] between the TiO2 content and the total content of TiO2 and Nb2O5 [TiO2+Nb2O5] is preferably 0.60, and may further be 0.58, 0.55, 0.53, 0.50, 0.48, or 0.45. The lower limit of this mass ratio is preferably 0.10, and may further be 0.13, 0.15, 0.18, or 0.20. Both TiO2 and Nb2O5 are glass components that contribute to high refractive index and high dispersion, but they also cause a higher specific gravity. Compared to Nb2O5, TiO2 contributes to a higher refractive index, but does not easily increase the specific gravity of the glass. Therefore, in the embodiment of the present invention, by setting the mass ratio [TiO2 / (TiO2+Nb2O5)] within the above range, an optical glass with a high refractive index, high stability, and low specific gravity can be obtained.

[0078] In the optical glass according to this embodiment, the upper limit of the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+Bi2O3)] between the TiO2 content and the total content of TiO2, Nb2O5, WO3, and Bi2O3 is preferably 0.60, and may further be 0.58, 0.55, 0.53, 0.50, 0.48, or 0.45. The lower limit of this mass ratio is preferably 0.10, and may further be 0.13, 0.15, 0.18, or 0.20. TiO2, Nb2O5, WO3, and Bi2O3 are all glass components that contribute to high refractive index and high dispersion, but they also cause an increase in specific gravity. Compared to Nb2O5, WO3, and Bi2O3, TiO2 contributes to high refractive index, but does not easily increase the specific gravity of the glass. Therefore, in embodiments of the present invention, by setting the mass ratio [TiO2 / (TiO2+Nb2O5+WO3+Bi2O3)] within the above range, an optical glass with a high refractive index and low specific gravity can be obtained.

[0079] In the optical glass according to this embodiment, the upper limit of the mass ratio [TiO2 / Nb2O5] between the TiO2 content and the Nb2O5 content is preferably 2.0, and may further be 1.8, 1.5, 1.3, 1.0, or 0.8. The lower limit of the mass ratio is preferably 0.10, and may further be 0.13, 0.15, 0.18, or 0.20. Both TiO2 and Nb2O5 are glass components that contribute to high refractive index and high dispersion, but they also cause a high specific gravity. Compared to Nb2O5, TiO2 contributes to a high refractive index, but does not easily increase the specific gravity of the glass. Therefore, in the embodiment of the present invention, by setting the mass ratio [TiO2 / Nb2O5] within the above range, an optical glass with a high refractive index, high stability, and low specific gravity can be obtained.

[0080] In the optical glass according to this embodiment, the upper limit of the mass ratio [TiO2 / (Nb2O5+WO3+Bi2O3)] between the TiO2 content and the total content of Nb2O5, WO3, and Bi2O3 is preferably 2.0, and may further be 1.8, 1.5, 1.3, 1.0, or 0.8. The lower limit of this mass ratio is preferably 0.10, and may further be 0.13, 0.15, 0.18, or 0.20. TiO2, Nb2O5, WO3, and Bi2O3 are all glass components that contribute to high refractive index and high dispersion, but they also cause an increase in specific gravity. Compared to Nb2O5, WO3, and Bi2O3, TiO2 contributes to high refractive index, but does not easily increase the specific gravity of the glass. Therefore, in embodiments of the present invention, by setting the mass ratio [TiO2 / (Nb2O5+WO3+Bi2O3)] within the above range, an optical glass with a high refractive index, high stability, and low specific gravity can be obtained.

[0081] In the optical glass according to this embodiment, the upper limit of the mass ratio [(Li2O+Na2O+MgO+CaO+ZnO+SrO) / (K2O+BaO)] between the total content of Li2O, Na2O, MgO, CaO, ZnO, and SrO [Li2O+Na2O+MgO+CaO+ZnO+SrO] and the total content of K2O and BaO [K2O+BaO] is preferably 10.0, and may further be 8.0, 5.0, 3.0, 1.0, or 0.8. By setting the mass ratio [(Li2O+Na2O+MgO+CaO+ZnO+SrO) / (K2O+BaO)] within the above range, a highly stable optical glass can be obtained.

[0082] In the optical glass according to this embodiment, the upper limit of the mass ratio [(TiO2+Nb2O5) / (SiO2+B2O3+Li2O+Na2O+K2O+MgO+CaO+ZnO+SrO+BaO)] between the total content of TiO2 and Nb2O5 [TiO2+Nb2O5] and the total content of SiO2, B2O3, Li2O, Na2O, K2O, MgO, CaO, ZnO, SrO, and BaO [SiO2+B2O3+Li2O+Na2O+K2O+MgO+CaO+ZnO+SrO+BaO] is preferably 20.0, and may further be 18.0, 15.0, 13.0, or 10.0. The lower limit of the mass ratio is preferably 0.5, and may further be 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, or 4.0. By setting the mass ratio [(TiO2+Nb2O5) / (SiO2+B2O3+Li2O+Na2O+K2O+MgO+CaO+ZnO+SrO+BaO)] within the above range, optical glass with a high refractive index and high stability can be obtained.

[0083] <Other component composition> Pb, As, Cd, Tl, Be, Se, and Te are all toxic. Therefore, it is preferable that the optical glass according to this embodiment does not contain these elements as glass components.

[0084] U, Th, and Ra are all radioactive elements. Therefore, it is preferable that the optical glass according to this embodiment does not contain these elements as glass components.

[0085] V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, and Tm can increase the coloration of glass and become sources of fluorescence. Therefore, it is preferable that the optical glass according to this embodiment does not contain these elements as glass components.

[0086] Sb(Sb2O3), Ce(CeO2), and Sn(SnO2) are elements that can be optionally added and function as clarifying agents. Of these, Sb(Sb2O3) is a clarifying agent with a large clarifying effect. Ce(CeO2) has a smaller clarifying effect compared to Sb(Sb2O3). Adding large amounts of Ce(CeO2) tends to increase the coloration of the glass.

[0087] In this specification, the content of Sb(Sb2O3), Ce(CeO2), and Sn(SnO2) is expressed as an external percentage and is not included in the total content of all glass components expressed on an oxide basis. That is, in this specification, the total content of all glass components excluding Sb(Sb2O3), Ce(CeO2), and Sn(SnO2) is considered to be 100% by mass.

[0088] The Sb2O3 content is expressed as an external percentage. That is, when the total content of all glass components other than Sb2O3, CeO2, and SnO2 is taken as 100% by mass, the Sb2O3 content is preferably 1.0% or less, and more preferably 0.5% or less, 0.1% or less, 0.08% or less, 0.06% or less, 0.04% or less, and 0.02% or less, in that order. The Sb2O3 content may be 0%.

[0089] The CeO2 content is also expressed as an external percentage. That is, when the total content of all glass components other than Sb2O3, CeO2, and SnO2 is taken as 100% by mass, the CeO2 content is preferably 2.0% or less, and more preferably 1.0% or less, 0.5% or less, and 0.1% or less, in that order. The CeO2 content may be 0%. The clarity of the glass can be improved by setting the CeO2 content within the above range.

[0090] The SnO2 content is also expressed as an external percentage. That is, when the total content of all glass components other than Sb2O3, CeO2, and SnO2 is taken as 100% by mass, the SnO2 content is preferably 2.0% or less, and more preferably 1.0% or less, 0.5% or less, and 0.1% or less, in that order. The SnO2 content may be 0%. The clarity of the glass can be improved by setting the SnO2 content within the above range.

[0091] <Properties of Glass> The refractive index nd of the optical glass according to this embodiment is 1.950 or higher. In addition to having such a high refractive index, the optical glass according to this embodiment preferably has the following characteristics.

[0092] (Abbe number) In the optical glass according to this embodiment, the lower limit of the Abbe number νd is preferably 15.0, and may further be 15.5, 16.0, or 16.5 in order to obtain the desired dispersion characteristics. The upper limit of the Abbe number νd is preferably 20.0, and may further be 19.5, 19.0, 18.5, or 18.0.

[0093] (specific gravity) The optical glass according to this embodiment is a high refractive index glass, yet its specific gravity is not high. 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 low, it leads to a decrease in thermal stability.

[0094] Therefore, in the optical glass according to this embodiment, the upper limit of the specific gravity is preferably 4.20, and may further be 4.15, 4.10, 4.05, 4.00, 3.95, 3.90, 3.85, or 3.80.

[0095] (Ratio of refractive index nd to specific gravity d) In the optical glass according to this embodiment, the lower limit of the ratio of refractive index nd to specific gravity d (nd / d) is preferably 0.48, and may further be 0.49, 0.50, 0.51, or 0.52. The upper limit of the ratio (nd / d) is preferably 0.60, and may further be 0.59, 0.58, or 0.57. By satisfying the above ranges for refractive index nd and specific gravity d, an optical glass with a high refractive index and relatively reduced specific gravity can be obtained.

[0096] (Glass transition temperature Tg) In the optical glass according to this embodiment, the upper limit of the glass transition temperature Tg is preferably 800°C, and may further be 780°C, 750°C, 730°C, or 700°C, from the viewpoint of lowering the temperature at which the glass is slowly cooled, the temperature at which it is heated and softened, or the press temperature. The lower limit of the glass transition temperature Tg is not particularly limited, but is usually 380°C. Furthermore, from the viewpoint of making the network structure of the glass stronger and suppressing glass cracking, or from the viewpoint of reducing the thermal expansion of the glass and improving the heat resistance of the glass, the lower limit of the glass transition temperature Tg is preferably 390°C, and may further be 400°C, 410°C, 420°C, 430°C, or 440°C. In particular, for glass with a high refractive index, in order to improve heat resistance, the lower limit of the glass transition temperature Tg can preferably be 460°C, and may further be 480°C, 500°C, 510°C, 520°C, 530°C, or 535°C. The glass transition temperature (Tg) can be controlled primarily by adjusting the content of Li, Na, and K, their total content, and the Zn content.

[0097] (Color intensity λ70 and λ5) The light transmittance of the optical glass according to this embodiment can be evaluated by the degree of coloration λ70 and λ5. For a glass sample with a thickness of 10.0 mm ± 0.1 mm, the spectral transmittance is measured in the wavelength range of 200 to 700 nm. The wavelength at which the external transmittance is 70% is defined as λ70, and the wavelength at which the external transmittance is 5% is defined as λ5.

[0098] The upper limit of λ70 of the optical glass according to this embodiment is preferably 650 nm, and may further be 640 nm, 630 nm, 620 nm, 610 nm, or 600 nm. The upper limit of λ5 is preferably 450 nm, and may further be 440 nm, 430 nm, 420 nm, 410 nm, or 400 nm.

[0099] <Manufacturing of optical glass> An optical glass according to an embodiment of the present invention may be produced by blending glass raw materials to achieve the predetermined refractive index and composition, and then manufacturing the blended glass raw materials according to a known glass manufacturing method. For example, several types of compounds may be blended and thoroughly mixed to form a batch raw material, and the batch raw material may be roughly melted in a quartz crucible or a platinum crucible. The molten material obtained by rough melting may be rapidly cooled and pulverized to produce cullet. The cullet may then be heated in a platinum crucible and remelted to produce molten glass, which may then be clarified and homogenized before being molded and slowly cooled to obtain optical glass. Known methods may be applied to mold and slowly cool the molten glass.

[0100] Furthermore, the compounds used when preparing the batch raw materials are not particularly limited, as long as the desired glass components can be introduced into the glass in the desired amounts. Examples of such compounds include oxides, carbonates, nitrates, hydroxides, and fluorides.

[0101] <Manufacturing of optical elements, etc.> To manufacture an optical element using the optical glass according to the embodiment of the present invention, known methods can be applied. For example, glass raw materials can be melted to form molten glass, and this molten glass can be poured into a mold and formed into a plate to produce a glass material made of the optical glass according to the present invention. The obtained glass material can be cut, ground, and polished as appropriate to produce cut pieces of a size and shape suitable for press molding. The cut pieces can be heated and softened, and then press-molded (reheat-pressed) using known methods to produce an optical element blank that approximates the shape of the optical element. The optical element blank can be annealed, and then ground and polished using known methods to produce an optical element.

[0102] Depending on the intended use, the optical functional surface of the fabricated optical element may be coated with an anti-reflective coating, a total reflection coating, or the like.

[0103] According to one aspect of the present invention, an optical element made of the above-mentioned optical glass can be provided. Examples of types of optical elements include lenses such as planar lenses, spherical lenses, and aspherical lenses, prisms, diffraction gratings, and light guide plates. Examples of lens shapes include biconvex lenses, plano-convex lenses, biconcave lenses, plano-concave lenses, convex meniscus lenses, and concave meniscus lenses. Examples of applications for the light guide plate include display devices such as augmented reality (AR) display type glasses-type devices and mixed reality (MR) display type glasses-type devices. Such a light guide plate is a plate-shaped glass attached to the frame of the glasses-type device and is made of the above-mentioned optical glass. A diffraction grating may be formed on the surface of the light guide plate as needed to change the direction of propagation of light that propagates through the inside of the light guide plate by performing total internal reflection. The diffraction grating can be formed by known methods. When a glasses-type device having the above-mentioned light guide plate is worn, the light that has propagated through the inside of the light guide plate enters the pupil, thereby exhibiting the functions of augmented reality (AR) display and mixed reality (MR) display. Such spectacle-type devices are disclosed, for example, in Japanese Patent Publication No. 2017-534352. The light guide plate can be manufactured by known methods. The optical element can be manufactured by a method that includes a process of processing a glass molded body made of the optical glass described above. Examples of processing include cutting, machining, rough grinding, fine grinding, and polishing. By using the glass described above when performing such processing, breakage can be reduced, and high-quality optical elements can be supplied stably.

[0104] <Image display device> A light guide plate and an image display device using the same, which are embodiments of the present invention, will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0105] Figure 1 shows the configuration of a head-mounted display 1 (hereinafter abbreviated as "HMD1") using a light guide plate 10, which is one embodiment of the present invention. Figure 1(a) is a front side perspective view of the HMD1, and Figure 1(b) is a rear side perspective view of the HMD1. As shown in Figures 1(a) and 1(b), eyeglass lenses 3 are attached to the front part of an eyeglass-type frame 2 that is worn on the user's head. A backlight 4 for illuminating the image is attached to the mounting part 2a of the eyeglass-type frame 2. A signal processing device 5 for displaying the image and a speaker 6 for reproducing sound are provided on the temple portion of the eyeglass-type frame 2. Flexible Printed Circuits (FPCs) 7, which constitute the wiring drawn from the circuit of the signal processing device 5, are wired along the eyeglass-type frame 2. A display element unit (e.g., a liquid crystal display element) 20 is wired by the FPC 7 to the center position of both eyes of the user, and is held so that the approximate center of the display element unit 20 is positioned on the optical axis of the backlight 4. The display element unit 20 is fixed relative to the light guide plate 10 so as to be located approximately in the center of the light guide plate 10. In addition, HOE (Holographic Optical Element) 32R and 32L (first optical elements) are tightly fixed to the first surface 10a of the light guide plate 10 by adhesive or the like at the location in front of the user's eyes. HOE 52R and 52L are stacked on the second surface 10b of the light guide plate 10 at positions opposite the display element unit 20 across the light guide plate 10.

[0106] Figure 2 is a schematic side view showing the configuration of an HMD1, which is one embodiment of the present invention. In Figure 2, only the main parts of the image display device are shown for clarity, and the spectacle-type frame 2, etc., are omitted from the illustration. As shown in Figure 2, the HMD1 has a symmetrical structure with respect to the center line X connecting the center of the image display element 24 and the center of the light guide plate 10. Furthermore, the light of each wavelength incident from the image display element 24 to the light guide plate 10 is divided into two, as will be described later, and guided to the user's right eye and left eye, respectively. The optical paths of each wavelength of light guided to each eye are also substantially symmetrical with respect to the center line X.

[0107] As shown in Figure 2, the backlight 4 includes 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, and is driven, for example, by a field sequential method. The laser light source 21 has laser light sources corresponding to wavelengths R (wavelength 436 nm), G (wavelength 546 nm), and B (wavelength 633 nm), and sequentially emits light of each wavelength at high speed. Light of each wavelength is incident on the diffusion optical system 22 and the microlens array 23, converted into a uniform, highly directional parallel light beam without light intensity unevenness, and incident perpendicularly on the display panel surface of the image display element 24.

[0108] The image display element 24 is, for example, a transmissive liquid crystal (LCDT-LCOS) panel driven by a field sequential method. The image display element 24 modulates light of each wavelength according to the image signal generated by the image engine (not shown) of the signal processing device 5. The light of each wavelength modulated by the pixels in the effective region of the image display element 24 is incident on the light guide plate 10 with a predetermined light beam cross-section (approximately the same shape as the effective region). The image display element 24 can also be replaced with other types of display elements, such as a DMD (Digital Mirror Device), a reflective liquid crystal (LCOS) panel, MEMS (Micro Electro Mechanical Systems), organic EL (Electro-Luminescence), or inorganic EL.

[0109] The display element unit 20 is not limited to a field sequential display element, but may also be an image generation unit for a simultaneous display element (a display element having a predetermined arrangement of RGB color filters on the front surface of the output surface). In this case, for example, a white light source is used as the light source.

[0110] As shown in Figure 2, light of each wavelength modulated by the image display element 24 is sequentially incident into the interior of the light guide plate 10 from the first surface 10a. HOE52R and 52L (second optical elements) are stacked on the second surface 10b of the light guide plate 10. HOE52R and 52L are, for example, rectangular reflective volume-phase HOEs, and have a structure consisting of three stacked photopolymers, each with interference fringes corresponding to R, G, and B wavelengths of light recorded on it. That is, HOE52R and 52L are configured to have a wavelength-selective function that diffracts light of R, G, and B wavelengths and transmits light of other wavelengths.

[0111] Furthermore, HOE32R and 32L are also reflective volume-phase HOEs and have the same layer structure as HOE52R and 52L. HOE32R and 32L and 52R and 52L may, for example, have substantially the same interference fringe pattern pitch.

[0112] HOE52R and 52L are stacked with their centers aligned and their interference fringe patterns inverted by 180 degrees. They are then tightly fixed to the second surface 10b of the light guide plate 10 by adhesive or the like, so that their centers coincide with the center line X in their stacked state. Light of each wavelength modulated by the image display element 24 is sequentially incident on HOE52R and 52L through the light guide plate 10.

[0113] HOE52R and 52L each diffract light of each wavelength that is incident sequentially, assigning a predetermined angle to guide it to the right eye and the left eye, respectively. The light of each wavelength diffracted by HOE52R and 52L undergoes total internal reflection at the interface between the light guide plate 10 and the air, propagates inside the light guide plate 10, and is incident on HOE32R and 32L. Here, HOE52R and 52L assign the same diffraction angle to light of each wavelength. Therefore, light of all wavelengths that are incident at approximately the same position on the light guide plate 10 (or, to put it another way, emitted from approximately the same coordinates within the effective area of ​​the image display element 24) propagates along approximately the same optical path inside the light guide plate 10 and is incident at approximately the same position on HOE32R and 32L. From another perspective, HOE52R and 52L diffract light of each wavelength of RGB so that the pixel positional relationship within the effective area of ​​the image displayed in the effective area of ​​the image display element 24 is faithfully reproduced on HOE32R and 32L.

[0114] Thus, in one embodiment of the present invention, HOE52R and 52L are diffracted so that light of all wavelengths emitted from substantially the same coordinates within the effective region of the image display element 24 is incident on substantially the same position on HOE32R and 32L. Alternatively, HOE52R and 52L may be configured to diffract so that light of all wavelengths that would otherwise constitute the same pixel but are relatively shifted within the effective region of the image display element 24 is incident on substantially the same position on HOE32R and 32L.

[0115] Light of each wavelength incident on HOE32R and 32L is diffracted by HOE32R and 32L and sequentially emitted outward from the second surface 10b of the light guide plate 10, approximately perpendicular to the surrounding area. The light of each wavelength emitted in this manner as approximately parallel light is then imaged onto the user's right and left eye retinas, respectively, of the image generated by the image display element 24. Furthermore, HOE32R and 32L may be given a condenser effect so that the user can observe the enlarged virtual image I. That is, light incident on the peripheral areas of HOE32R and 32L may be emitted at an angle so that it is closer to the center of the pupil and imaged onto the user's retina. Alternatively, in order to allow the user to observe the enlarged virtual image I, HOE52R and 52L may be configured to diffract light of each wavelength of RGB such that the pixel positional relationship on HOE32R and 32L forms an enlarged, similar shape to the pixel positional relationship within the effective area of ​​the image displayed in the effective area of ​​the image display element 24.

[0116] Since the air-equivalent optical path length of light traveling through the light guide plate 10 becomes shorter as the refractive index increases, using the optical glass according to this embodiment, which has a high refractive index, makes it possible to increase the apparent viewing angle with respect to the width of the image display element 24. Furthermore, since the specific gravity is kept low despite the high refractive index, it is possible to provide a light guide plate that is lightweight while achieving the above effect.

[0117] Furthermore, a light guide plate according to one aspect of the present invention can be used in see-through, transmissive, or opaque head-mounted displays.

[0118] These head-mounted displays, because their light guide plates are made of optical glass with a high refractive index and low specific gravity as in this embodiment, offer excellent immersion due to their wide field of view. They are suitable as image display devices for use in combination with information terminals, for providing AR (Augmented Reality), and for providing movie viewing, games, VR (Virtual Reality), etc.

[0119] The above explanation uses a head-mounted display as an example, but the light guide plate may also be attached to other image display devices. [Examples]

[0120] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the embodiments shown in the examples.

[0121] (Example 1) Table below Glass samples having the glass composition shown were prepared using the following procedure and evaluated in various ways. The evaluation results were then obtained. Table below This will be shown.

[0122] [Fabrication of optical glass] Compound raw materials corresponding to the constituent components of glass, namely phosphates, carbonates, oxides, etc., were weighed and thoroughly mixed to form a blended raw material. This blended raw material was placed in a platinum crucible and heated to 1000-1350°C under an atmospheric environment to melt it. It was then homogenized and clarified by stirring to obtain molten glass. The molten glass was cast into a mold and shaped, then slowly cooled to obtain block-shaped glass samples.

[0123] [Confirmation of glass component composition] The obtained glass samples were then analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) to determine the content of each glass component. Table below We confirmed that the compositions were as shown. Furthermore, we confirmed that none of the glass samples contained F (fluorine).

[0124] [Measurement of optical properties] The specific gravity, refractive index nd, Abbe number νd, glass transition temperature Tg, and color intensity λ70 and λ5 of the obtained glass samples were measured using the method described below.

[0125] [1] Specific gravity The specific gravity was measured using the Archimedes method.

[0126] [2] Refractive index nd and Abbe number νd The refractive indices nd, ng, nF, and nC were measured according to the refractive index measurement method of JIS B 7071-1, and the Abbe number νd was calculated based on the following formula. νd=(nd-1) / (nF-nC)

[0127] [3] Glass transition temperature Tg The glass transition temperature (Tg) was measured using a differential scanning calorimetry analyzer (DSC3300SA) manufactured by NETZSCH JAPAN. The sample was crushed to a weight of approximately 0.02 cc, placed in a φ5 mm Pt pan, and measured under conditions of a heating rate of 10°C / min and a maximum temperature of 1000°C. Alumina (Al2O3) was used as the standard sample.

[0128] [4] λ70, λ5 The above sample was processed to have two parallel, optically polished planes with a thickness of 10 mm, and its spectral transmittance was measured in the wavelength range from 280 nm to 700 nm. The intensity of light rays incident perpendicularly to one of the optically polished planes was defined as intensity A, and the intensity of light rays emitted from the other plane was defined as intensity B, and the spectral transmittance B / A was calculated. The wavelength at which the spectral transmittance was 70% was defined as λ70, and the wavelength at which the spectral transmittance was 5% was defined as λ5. Note that the spectral transmittance includes the reflection loss of light rays at the sample surface.

[0129] The results are shown in the table below. [Table 1-1] [Table 1-2] [Table 2-1] [Table 2-2] [Table 3-1] [Table 3-2] [Table 4-1] [Table 4-2] [Table 5-1] [Table 5-2]

[0130] (Example 2) Using the optical glass prepared in Example 1, lens blanks were fabricated by known methods, and various lenses were manufactured by processing the lens blanks by known methods such as polishing. The optical lenses fabricated include various types such as planar lenses, biconvex lenses, biconcave lenses, plano-convex lenses, plano-concave lenses, concave meniscus lenses, and convex meniscus lenses. By combining various lenses with lenses made of other types of optical glass, secondary chromatic aberration could be effectively corrected.

[0131] Furthermore, because the glass has a low specific gravity, each lens is lighter than lenses with equivalent optical properties and size, making them suitable for use in goggle-type or eyeglass-type AR or MR display devices. Similarly, prisms were fabricated using the various optical glasses prepared in Example 1.

[0132] (Example 3) Each optical glass prepared in Example 1 was processed into a rectangular thin plate measuring 50 mm in length, 20 mm in width, and 1.0 mm in thickness to obtain a light guide plate. This light guide plate was incorporated into the head-mounted display 1 shown in Figure 1.

[0133] When the images from the resulting head-mounted display were evaluated at the eye point, it was possible to observe images with a wide field of view, high brightness, and high contrast.

[0134] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended.

[0135] For example, by performing the compositional adjustments described in the specification on the glass composition exemplified above, an optical glass according to one aspect of the present invention can be produced. Furthermore, it is certainly possible to arbitrarily combine two or more items described as examples or preferred scopes in the specification.

Claims

1. The refractive index nd is 1.950 or higher. P 2 O 5 The content is 10.0 to 40.0% by mass, TiO 2 The content is 5.0 to 40.0% by mass, Nb 2 O 5 The content is 20.0 to 60.0% by mass, Bi 2 O 3 The content is 20.0% by mass or less. WO 3 The content is 10.0% by mass or less. Al 2 O 3 and SiO 2 The total content of [Al 2 O 3 + SiO 2 is 2.0% by mass or less, Li 2 O, Na 2 O and K 2 Total O content [Li 2 O + Na 2 O+K 2 O] is 0.1 to 5.0 mass%, The total content of ZnO, SrO, and BaO [ZnO + SrO + BaO] is 0.01 to 12.0% by mass. Li 2 O, Na 2 O, K 2 Total content of O, MgO, CaO, ZnO, SrO and BaO [Li 2 O + Na 2 O+K 2 The concentration of [O + MgO + CaO + ZnO + SrO + BaO] is 12.0% by mass or less. TiO 2 The content and TiO 2 and Nb 2 O 5 Total content [TiO 2 +Nb 2 O 5 The mass ratio of [TiO 2 / (TiO 2 +Nb 2 O 5 ) ] is 0.20 to 0.50, The total content of TiO₂ and Nb₂O₅ [TiO₂ + Nb₂O₅] is 70% by mass or less. The mass ratio [(MgO + CaO + ZnO + SrO + BaO)] between the total content of MgO, CaO, ZnO, SrO, and BaO [MgO + CaO + ZnO + SrO + BaO] and the total content of Li₂O, Na₂O, and K₂O [Li₂O + Na₂O + K₂O] is 0.10 or higher, Optical glass having a mass ratio [TiO₂ / Nb₂O₅] of 0.80 or less for the TiO₂ content to the Nb₂O₅ content.

2. An optical element blank made of optical glass as described in claim 1.

3. An optical element made of optical glass as described in claim 1.

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