Silver-containing polarizing glass and optical isolator

Abstract

Provided is a polarizing glass having a glass substrate which has excellent chemical durability and which has reduced photochromic properties. A polarizing glass which contains shape-anisotropic metal particles dispersed in orientation in at least the surface layer of a glass substrate, and wherein the glass substrate contains, in mass%, 50.0-60.0% of SiO2, 0.5-1.0% of SiO2, 0.5-1.0% of SiO2, 0.5-1.0% of SiO2, 0.5-1.0% of SiO2, 0.5-1.0% of SiO2, and 0.5-1.0% of SiO2. 10.0% to 25.0% of B2O3 (boron trioxide); 3.0 to 10.0 percent of Al2O3 (aluminum oxide); the total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is 5.0 to 20.0%; 2.0%-8.0% of ZrO2 (zirconium dioxide); 0.1 to 5.0 percent of TiO2 (titanium dioxide); 0.1 to 5.0 percent of Nb2O5; the total content [TiO2 + Nb2O5] of the TiO2 and the Nb2O5 is 0.2 to 10.0 percent; ag; and Cl and / or Br greater than the stoichiometric amount of Ag, and the shape anisotropic metal particles are metal Ag particles.

Description

Technical Field

[0001] The present invention relates to polarizing glass for use in optical components such as optical isolators, and more particularly to polarizing glass containing shape-anisotropic metallic silver particles. Background Art

[0002] Optical isolators transmit only forward-traveling light and block reverse-traveling light. Polarizing glass, an optical glass that transmits only light vibrating in a specific direction (polarized light), is an optical component used in optical isolators and other applications. Optical isolators are used in a variety of environments, requiring polarizing glass to possess excellent durability.

[0003] Furthermore, in polarizing glass, if the base glass discolors due to exposure to light, etc., the function of the polarizing glass may be reduced. Specifically, exposure to ultraviolet light or short-wavelength visible light causes a photochromic phenomenon in which the base glass darkens, reducing the amount of light passing through the polarizing glass.

[0004] That is, there is a demand for polarizing glass having a glass base having excellent durability under various environments and reducing photochromic properties.

[0005] Patent Document 1 discloses a polarizing glass containing anisotropically shaped metallic silver particles. However, the Al2O3 and ZrO2 contents are low, the various environmental conditions under which the polarizing glass will be used are not considered, and durability is not mentioned. Furthermore, Patent Document 2 discloses a polarizing glass containing dispersed anisotropically shaped metallic silver particles. However, this does not consider the discoloration of the base glass due to light exposure, nor does it disclose reducing the photochromic properties of the glass by including a specified amount of Nb2O5. Patent Document 3 discloses a polarizing material containing silver as flattened metal particles in a glass substrate. However, the silver content is high, and there is no mention of reducing the amount of silver incorporated.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 56-169140;

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-126921;

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 2010-150132. Summary of the Invention

[0011] Problems to be solved by the invention

[0012] The present invention has been made in view of such actual circumstances, and an object of the present invention is to provide a polarizing glass having a glass substrate having excellent chemical durability and reduced photochromic properties.

[0013] Solutions for solving problems

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

[0015] (1) A polarizing glass comprising anisotropic metal particles dispersed in an orientation at least on a surface layer of a glass substrate, wherein:

[0016] Expressed in mass %, the glass matrix comprises:

[0017] SiO2: 50.0~60.0%;

[0018] B2O3: 10.0~25.0%;

[0019] Al2O3: 3.0~10.0%;

[0020] The total content of Li2O, Na2O, and K2O [Li2O+Na2O+K2O]: 5.0-20.0%;

[0021] ZrO2: 2.0~8.0%;

[0022] TiO2: 0.1~5.0%;

[0023] Nb2O5: 0.1~5.0%;

[0024] The total content of TiO2 and Nb2O5 [TiO2+Nb2O5]: 0.2-10.0%;

[0025] Ag; and

[0026] Cl and / or Br above the chemical equivalent of Ag,

[0027] The above-mentioned shape-anisotropic metal particles are metal Ag particles.

[0028] (2) An optical isolator comprising the polarizing glass described in (1) above.

[0029] Effects of the Invention

[0030] According to the present invention, it is possible to provide a polarizing glass having a glass base having excellent chemical durability and reduced photochromic properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 FIG. 1 is a schematic side sectional view schematically showing an optical system of a free-space optical isolator.

[0032] Figure 2 This is a schematic side sectional view schematically showing the optical system of the pigtail type optical isolator.

[0033] Figure 3 These are photographs showing the degree of discoloration of stretched glasses produced in Examples and Comparative Examples. DETAILED DESCRIPTION

[0034] In the present invention and this specification, unless otherwise specified, glass composition is expressed on an oxide basis. Here, "oxide-based glass composition" refers to the glass composition calculated by converting the glass raw materials into oxides present in the glass after complete decomposition during melting. The individual glass components are expressed as SiO2, TiO2, etc., following common practice. Furthermore, Ag, Cl, and Br, elements involved in polarization properties, are expressed as elements rather than oxides. Unless otherwise specified, the content and total content of glass components are expressed by mass, and "%" means "mass %."

[0035] The content of the 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). In this specification and the present invention, a content of a component of 0% means that the component is substantially not contained, but the presence of the component at the level of unavoidable impurities is permitted.

[0036] In this specification, the chemical durability of glass refers to excellent water resistance and acid resistance. In addition, the thermal stability of glass refers to the difficulty of crystallization other than silver halide grains when the molten glass is hardened.

[0037] Hereinafter, one embodiment of the present invention will be described.

[0038] The polarizing glass of this embodiment comprises a glass substrate containing anisotropically oriented metal particles at least on its surface. The polarizing glass transmits polarized light in a specific vibration direction (called the "polarization transmission axis") and absorbs polarized light in an orthogonal direction (called the "polarization extinction axis").

[0039] (Glass substrate)

[0040] The SiO2 content in the glass matrix is ​​50.0-60.0%. The lower limit of the SiO2 content is preferably 51.0%, more preferably 52.0%. Furthermore, the upper limit of the SiO2 content is preferably 59.0%, more preferably 58.0%. By setting the SiO2 content within the above range, the chemical durability of the glass matrix can be improved. On the other hand, if the SiO2 content is too low, the chemical durability and thermal stability of the glass matrix may be reduced. Furthermore, if the SiO2 content is too high, the solubility of the glass may be reduced.

[0041] The B2O3 content in the glass matrix is ​​10.0 to 25.0%. The lower limit of the B2O3 content is preferably 12.0%, and more preferably 13.0% and 14.0%. The upper limit of the B2O3 content is preferably 23.0%, and more preferably 21.0% and 20.0%. By setting the B2O3 content within the above range, the chemical durability of the glass matrix can be improved. On the other hand, if the B2O3 content is too low, the solubility of the glass may be reduced, and it may not be possible to properly precipitate silver halide particles in the entire glass matrix during the heat treatment described later. In addition, if the B2O3 content is too high, the chemical durability of the glass matrix may be reduced.

[0042] The content of Al2O3 in the glass matrix is ​​3.0 to 10.0%. The lower limit of the Al2O3 content is preferably 4.0%, more preferably 4.5%. In addition, the upper limit of the Al2O3 content is preferably 9.0%, more preferably 8.0%. By setting the Al2O3 content to the above range, the chemical durability of the glass matrix can be improved. On the other hand, when the Al2O3 content is too low, the chemical durability of the glass matrix may be significantly reduced. In addition, when the Al2O3 content is too high, the solubility of the glass may be reduced and devitrification may be easy.

[0043] In the glass matrix, the total content of Li2O, Na2O, and K2O [Li2O+Na2O+K2O] is 5.0 to 20.0%. The lower limit of the total content is preferably 7.0%, more preferably 9.0%. In addition, the upper limit of the total content is preferably 18.0%, more preferably 16.0%. By setting the total content to the above range, the chemical durability of the glass matrix can be improved. In particular, by containing two or more alkali metals, the chemical durability of the glass matrix can be improved. On the other hand, when the total content is too low, the solubility of the glass may be reduced. In addition, when the total content is too high, it may be impossible to well precipitate silver halide particles in the entire glass matrix during the heat treatment described later.

[0044] The ZrO2 content in the glass matrix is ​​2.0 to 8.0%. The lower limit of the ZrO2 content is preferably 2.5%, more preferably 3.0%. In addition, the upper limit of the ZrO2 content is preferably 7.7%, more preferably 7.0%. By setting the ZrO2 content within the above range, the chemical durability of the glass matrix can be improved. On the other hand, when the ZrO2 content is too low, the chemical durability of the glass matrix may be significantly reduced. In addition, when the ZrO2 content is too high, the solubility of the glass may be reduced, causing the liquidus temperature to rise.

[0045] The TiO2 content in the glass matrix is ​​0.1-5.0%. The lower limit of the TiO2 content is preferably 0.3%, more preferably 0.6%. Furthermore, the upper limit of the TiO2 content is preferably 4.5%, more preferably 4.0%. TiO2 is a glass component that helps improve the chemical durability of glass and effectively absorbs light from the near-ultraviolet to visible short wavelengths. Therefore, by setting the TiO2 content within the above range, a polarizing glass having a glass matrix with improved chemical durability and reduced photochromic properties can be obtained. On the other hand, if the TiO2 content is too low, the chemical durability of the glass matrix may be reduced, increasing the photochromic properties of the glass matrix. Furthermore, if the TiO2 content is too high, the glass's solubility may be reduced, causing the liquidus temperature to rise, thereby increasing the coloration of the glass during molding.

[0046] The Nb2O5 content in the glass matrix is ​​0.1-5.0%. The lower limit of the Nb2O5 content is preferably 0.3%, more preferably 0.6%. Furthermore, the upper limit of the Nb2O5 content is preferably 4.5%, more preferably 4.0%. Nb2O5 is a glass component that effectively absorbs light from the near-ultraviolet to short-wavelength visible wavelengths. Therefore, by setting the Nb2O5 content within the above range, a polarizing glass having a glass matrix with reduced photochromic properties can be obtained. On the other hand, if the Nb2O5 content is too low, the photochromic properties of the glass matrix may be increased. Furthermore, if the Nb2O5 content is too high, the glass's solubility may be reduced, causing the liquidus temperature to rise, thereby increasing the coloration of the glass during molding.

[0047] The combined content of TiO2 and Nb2O5 [TiO2 + Nb2O5] in the glass matrix is ​​0.2 to 10.0%. The lower limit of this combined content is preferably 0.5%, more preferably 1.0%. Furthermore, the upper limit of this combined content is preferably 9.0%, more preferably 8.0%. By setting this combined content within the above range, a polarizing glass having a glass matrix with improved chemical durability and reduced photochromic properties can be obtained. On the other hand, if this combined content is too low, the chemical durability of the glass matrix may be reduced, thereby increasing the photochromic properties of the glass matrix. Furthermore, if this combined content is too high, the solubility of the glass may be reduced, causing the liquidus temperature to rise.

[0048] The glass matrix contains Ag, Cl, and Br. The lower limit of the Ag content in the glass matrix is ​​preferably 0.10%, and more preferably 0.11% and 0.13% in that order. Furthermore, the upper limit of the Ag content is preferably 1.0%, and more preferably 0.8% and 0.6% in that order. By incorporating Ag into the glass matrix, a polarizing glass having a glass matrix with excellent chemical durability can be obtained. On the other hand, if the Ag content is too low, silver halide particles may not be properly precipitated throughout the entire glass matrix during the heat treatment described later. Furthermore, if the Ag content is too high, insertion loss may increase, and silver halide particles may precipitate in the glass during melting and cooling, making it difficult to control the particle size of the silver halide particles.

[0049] Furthermore, it is preferred that the glass base material contains substantially no Cu. In other words, the Cu content is preferably 0%.

[0050] In order to precipitate silver halide particles in the entire glass matrix, Ag is added to the glass matrix raw material in the form of, for example, AgCl and AgBr. However, since AgBr is a highly toxic substance, care must be taken during handling, and it is preferably not used for environmental reasons. In addition, since Cl and Br easily volatilize during glass melting, they are added in excess in the form of chlorides or bromides of alkali metals or alkaline earth metals to replenish them. Therefore, the glass matrix contains Cl and / or Br in an amount greater than the chemical equivalent of Ag. The amount of Cl and Br added in excess can be adjusted according to the glass melting method and scale.

[0051] As described above, the glass matrix contains Cl and / or Br in an amount equal to or greater than the chemical equivalent of Ag. That is, in the glass matrix, the chemical equivalent of at least one of Cl and Br is equal to or greater than the chemical equivalent of Ag. Alternatively, the chemical equivalents of both Cl and Br may be equal to or greater than the chemical equivalent of Ag.

[0052] The Iwanami Chemical Dictionary (5th edition) defines chemical equivalent as "a fixed amount of an element (single element) or compound determined by chemical reactivity. It is also referred to as equivalent." Furthermore, the chemical equivalent of an element is defined as "When the mass of an element combined with 7.999 g of oxygen (equivalent to 1 / 2 mol of oxygen atoms) is Wg, W is called the chemical equivalent of the element. For elements that cannot directly combine with oxygen, the chemical equivalent can be determined using an appropriate element other than oxygen as an intermediary."

[0053] In this embodiment, referring to the above description in the Iwanami Chemical Dictionary, the chemical equivalents of Ag, Cl, and Br correspond to the chemical equivalents of the elements. Specifically, the chemical equivalent of Cl is obtained by dividing the Cl content (expressed in mass%) by the atomic weight of Cl, the chemical equivalent of Br is obtained by dividing the Br content (expressed in mass%) by the atomic weight of Br, and the chemical equivalent of Ag is obtained by dividing the Ag content (expressed in mass%) by the atomic weight of Ag. Furthermore, the chemical equivalent of Cl and / or Br being greater than or equal to the chemical equivalent of Ag means that the number of Cl atoms and / or Br atoms contained in the glass is greater than or equal to the number of Ag atoms contained in the glass.

[0054] In the glass matrix, the total content of Cl and Br is preferably 0.05 to 2.0%. The Cl content is preferably 0.05 to 1.0%. Similarly, the Br content is preferably 0.05 to 1.0%.

[0055] Non-limiting examples of the contents of glass components other than those described above in the glass matrix are shown below.

[0056] The lower limit of the Li₂O content in the glass matrix is ​​preferably 0.0%, with 0.5% and 0.8% being more preferred in that order. Furthermore, the upper limit of the Li₂O content is preferably 5.0%, with 4.0% and 3.5% being more preferred in that order. The lower limit of the Li₂O content is preferably set as described above from the perspective of improving the meltability of the glass and lowering the glass transition temperature (Tg). Furthermore, the upper limit of the Li₂O content is preferably set as described above from the perspective of ensuring that silver halide particles are well precipitated throughout the entire glass matrix during the heat treatment described below.

[0057] The lower limit of the Na2O content in the glass matrix is ​​preferably 0.0%, with 1.0% and 3.0% being more preferred in that order. Furthermore, the upper limit of the Na2O content is preferably 10.0%, with 8.0% and 7.0% being more preferred in that order. The lower limit of the Na2O content is preferably set as described above from the perspective of improving the meltability of the glass and lowering the glass transition temperature (Tg). Furthermore, the upper limit of the Na2O content is preferably set as described above from the perspective of ensuring that the silver halide particles are well precipitated throughout the entire glass matrix during the heat treatment described below.

[0058] The lower limit of the K₂O content in the glass matrix is ​​preferably 0.0%, with 1.0% and 3.0% being more preferred in that order. Furthermore, the upper limit of the K₂O content is preferably 10.0%, with 8.0% and 7.0% being more preferred in that order. The lower limit of the K₂O content is preferably set as described above from the perspective of improving the meltability of the glass and lowering the glass transition temperature (Tg). Furthermore, the upper limit of the K₂O content is preferably set as described above from the perspective of ensuring that silver halide particles are well precipitated throughout the entire glass matrix during the heat treatment described below.

[0059] The lower limit of the MgO content in the glass matrix is ​​preferably 0.0%. The MgO content may also be 0.0%. Furthermore, the upper limit of the MgO content is preferably 5.0%, and more preferably 3.0%. From the perspective of improving the thermal stability and solubility of the glass, it is preferred that the MgO content be within the above range.

[0060] The lower limit of the CaO content in the glass matrix is ​​preferably 0.0%. The CaO content may also be 0.0%. Furthermore, the upper limit of the CaO content is preferably 5.0%, and more preferably 3.0%. From the perspective of improving the thermal stability and solubility of the glass, it is preferred that the CaO content be within the above range.

[0061] The lower limit of the SrO content in the glass matrix is ​​preferably 0.0%. The SrO content may also be 0.0%. Furthermore, the upper limit of the SrO content is preferably 5.0%, and more preferably 3.0%. From the perspective of improving the thermal stability and solubility of the glass, it is preferred that the SrO content be within the above range.

[0062] In the glass matrix, the lower limit of the BaO content is preferably 0.0%. The BaO content may also be 0.0%. In addition, the upper limit of the BaO content is preferably 5.0%, and more preferably 3.0%. From the perspective of suppressing an increase in specific gravity, it is preferable to set the BaO content within the above range.

[0063] The lower limit of the combined content of MgO, CaO, SrO, and BaO (MgO + CaO + SrO + BaO) in the glass matrix is ​​preferably 0.0%. This combined content may also be 0.0%. Furthermore, the upper limit of this combined content is preferably 5.0%, and more preferably 3.0%. While this improves the thermal stability and solubility of the glass, increases the alkalinity of the glass, and prevents silver reduction, it may reduce the chemical durability of the glass matrix. Therefore, it is preferable to keep this combined content within the above range.

[0064] The lower limit of the ZnO content in the glass matrix is ​​preferably 0.0%. The ZnO content may also be 0.0%. In addition, the upper limit of the ZnO content is preferably 5.0%, and more preferably 3.0%. From the perspective of improving the thermal stability of the glass, it is preferred that the ZnO content be within the above range.

[0065] It is preferred that the glass matrix is ​​mainly composed of the above-mentioned glass components, namely, SiO2, B2O3, Al2O3, ZrO2, TiO2, Nb2O5, Ag, Cl, Br, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, and ZnO, and the total content of the above-mentioned glass components is preferably above 95%, more preferably above 98%, further preferably above 99%, and further preferably above 99.5%.

[0066] Although it is preferable that the glass matrix is ​​basically composed of the above-mentioned glass components, it can also contain other components within the range that does not impair the effects of the present invention. In addition, the present invention does not exclude the inclusion of inevitable impurities.

[0067] The glass matrix is ​​primarily composed of oxides. Specifically, the primary anion component in the glass matrix is ​​O. Furthermore, the glass matrix may also contain trace amounts of Cl and Br. The glass matrix may also contain F as an anion component other than O, Cl, and Br. The F content in the glass matrix is ​​preferably 0.5% or less, more preferably 0.0%.

[0068] (Other ingredients)

[0069] In the glass matrix, the lower limit of the CeO2 content is preferably 0.0%. The CeO2 content can also be 0.0%. In addition, the upper limit of the CeO2 content is preferably 3.0%, more preferably 1.0%. CeO2 is a component that functions as a clarifier for glass. In addition, although CeO2 is present in the glass, 4+ ions and Ce 3+ ions coexist and usually tend to maintain Ag + The direction of the oxidation state of the ions plays a role, but since the balance of the valence state is easily changed by temperature, it is possible that when heat treatment is performed to precipitate silver halide particles, Ag is reversely oxidized. + Therefore, it is preferable to set the content of CeO2 within the above range.

[0070] Pb is toxic and is a component that may pose a threat to the environment. Therefore, it is preferred that the glass matrix contains substantially no Pb. In other words, the Pb content is preferably 0% in terms of oxide.

[0071] Cd, As, Th and the like are components that are of concern for their environmental burden.

[0072] Therefore, the content of each of CdO, ThO2, and As2O3 is preferably 0 to 0.1%, more preferably 0 to 0.05%, further preferably 0 to 0.01%, and particularly preferably substantially no CdO, ThO2, or As2O3 is contained.

[0073] The glass matrix preferably contains no coloring elements. Examples of coloring elements include Co, Ni, Fe, Cr, Eu, Nd, and Er. The concentration of any of these elements is preferably less than 100 mass ppm, more preferably 0 to 80 mass ppm, and even more preferably 0 to 50 mass ppm. It is particularly preferred that the glass matrix contains substantially no such elements.

[0074] In addition, Ga, Te, Tb, etc. are unnecessary components and are also expensive components. Therefore, the range of the content of Ga2O3, TeO2, and TbO2 expressed in mass % is preferably 0 to 0.1%, more preferably 0 to 0.05%, further preferably 0 to 0.01%, further preferably 0 to 0.005%, and even more preferably 0 to 0.001%, and it is particularly preferred that these substances are substantially not contained.

[0075] (Characteristics of glass matrix)

[0076] <Chemical durability, water resistance Dw>

[0077] In the glass substrate, the water resistance Dw is preferably level 3 or higher, more preferably level 2 or higher, and even more preferably level 1.

[0078] Water resistance Dw can be evaluated using the method described in JOGIS 06:2019. Specifically, water resistance Dw can be evaluated by placing a mass of powdered glass (particle size 425-600 μm) equivalent to its specific gravity in a platinum cage, immersing the cage in a quartz glass round-bottom flask containing 80 mL of pure water (pH 6.5-7.5), and treating the cage in a boiling water bath for 60 minutes. The water resistance Dw is then classified according to the reduction rate (%) as shown in Table A.

[0079] [Table A]

[0080] grade Mass reduction (%) 1 Less than 0.05% 2 0.05% or more and less than 0.10% 3 0.10% or more and less than 0.25% 4 0.25% or more and less than 0.60% 5 0.60% or more and less than 1.10% 6 1.10% or more

[0081] <Chemical durability, acid resistance Da>

[0082] In the glass substrate, the acid resistance Da is preferably level 3 or higher, more preferably level 2 or higher, and further preferably level 1.

[0083] Acid resistance Da can be evaluated using the method described in JOGIS 06:2019. Specifically, acid resistance Da can be evaluated by placing a mass of powdered glass (particle size 425-600 μm) equivalent to its specific gravity in a platinum cage, immersing the cage in a quartz glass round-bottom flask containing 80 mL of a 0.01 mol / L nitric acid aqueous solution, and treating the flask in a boiling water bath for 60 minutes. The reduction rate (%) is then classified into the grades shown in Table B.

[0084] [Table B]

[0085] grade Mass reduction (%) 1 Less than 0.20% 2 0.20% or more and less than 0.35% 3 0.35% or more and less than 0.65% 4 0.65% or more and less than 1.20% 5 1.20% or more and less than 2.20% 6 2.20% or more

[0086] (Shape anisotropic metal particles)

[0087] In the polarizing glass of this embodiment, at least the surface layer of the glass substrate contains shape-anisotropic metal particles dispersed in an orientation. The shape-anisotropic metal particles are metallic Ag particles. In the polarizing glass of this embodiment, the surface layer containing the shape-anisotropic silver particles comprises a portion or the entire surface of the glass substrate, and the thickness of this surface layer is, for example, 20 to 100 μm. Furthermore, the dimension of the shape-anisotropic metallic silver particles in a direction parallel to the long axis of the silver halide particles is, for example, in the range of 10 to 1000 nm, and the ratio of the dimension perpendicular to this direction (aspect ratio) is, for example, in the range of 0.5 to 20.

[0088] <Extinction ratio and insertion loss>”

[0089] Generally, the optical properties required of polarizing glass are a high extinction ratio and low insertion loss. The "extinction ratio" refers to the ratio of the transmittance of light parallel to the polarization extinction axis to the transmittance of light parallel to the polarization transmission axis. A higher extinction ratio indicates superior optical properties. The unit is dB. Furthermore, "insertion loss" refers to the loss experienced by light parallel to the polarization transmission axis when passing through the polarizing element. Lower insertion loss indicates superior optical properties. The unit is dB.

[0090] As shown in Figure 13 of Japanese Patent No. 4642921, for which the present inventors are the inventors, when the distance between the polarizing glass and the detector power meter (measurement distance) is as close as 5 mm, the detector receives re-emitted light from the polarizing glass, resulting in a lower extinction ratio. At a measurement distance of 300 mm, the detector receives less re-emitted light from the polarizing glass, resulting in a higher extinction ratio. Therefore, when the distance between the polarizing glass and the power meter is close, the extinction ratio is low, while when the distance is far, the extinction ratio increases. Insertion loss is independent of the measurement distance and remains a nearly constant value.

[0091] In the polarizing glass of this embodiment, the extinction ratio for light with a wavelength of 1270 nm at a measurement distance of 5 mm is preferably 38.0 dB or greater, more preferably 38.2 dB or greater. Furthermore, the extinction ratio for light with a wavelength of 1650 nm at a measurement distance of 300 mm is preferably 55.0 dB or greater, more preferably 56.0 dB or greater.

[0092] In the polarizing glass of this embodiment, when an anti-reflection film is provided on a single surface of the polarizing glass, the insertion loss for light having a wavelength of 1270 nm is preferably less than 0.204 dB when measured at a distance of 5 mm. Furthermore, the insertion loss for light having a wavelength of 1650 nm is preferably less than 0.204 dB when measured at a distance of 300 mm.

[0093] The extinction ratio and insertion loss of polarizing glass can be measured as follows: A semiconductor laser light source and a Glan-Thompson prism are placed on one side of the polarizing glass, and a detector (power meter) is placed on the other side. The Glan-Thompson prism is inserted to obtain linearly polarized waves in a specific direction.

[0094] The polarizing glass is rotated and the minimum transmitted light amount P1 is measured. The polarizing glass is rotated 90 degrees and the maximum transmitted light amount P2 is measured. The extinction ratio is calculated using the following formula.

[0095] Extinction ratio (dB) = -10Log(P1 / P2)

[0096] The amount of light P0 without polarizing glass was measured, and the insertion loss was calculated using the following formula.

[0097] Insertion loss (dB) = -10Log(P2 / P0)

[0098] (Method for Manufacturing Polarizing Glass)

[0099] The method for producing the polarizing glass of the present embodiment is roughly divided into the following steps: (A) preparation and melting of glass raw materials, (B) precipitation of silver halide particles, (C) stretching of the glass substrate, and (D) reduction.

[0100] [(A) Preparation and Melting of Glass Raw Materials]

[0101] Prepare glass raw materials. Examples of glass raw materials include SiO2, H3BO3, Al(OH)3, Li2CO3, Na2CO3, K2CO3, KNO3, ZrO2, TiO2, Nb2O5, NaCl, NaBr, and AgCl. These glass raw materials are placed in a platinum crucible and melted at approximately 1300°C to 1500°C. The resulting material is then shaped and slowly cooled to room temperature to obtain a glass substrate.

[0102] [(B) Precipitation of Silver Halide Grains]

[0103] The glass substrate obtained in (A) is heat-treated at a temperature of 650°C to 800°C for several hours to about 20 hours (preferably about 4 hours to 10 hours). In order to produce silver halide grains of appropriate size, the heat treatment is usually performed at a high temperature when the heat treatment time is short, and at a relatively low temperature when the heat treatment time is long.

[0104] In the case where the glass contains AgCl as a silver halide, the Cl ions, Br ions, and Ag ions condense through the above-mentioned heat treatment, and AgClBr particles in a liquid state are precipitated. In the subsequent cooling process, when the temperature of the glass is reduced to near the glass transition temperature (Tg), for example, when it is reduced to near 500°C, it remains in a glass state. Although AgClBr also exists in the form of liquid in this state, when the temperature of the glass is further reduced and is lower than the melting point of AgClBr, 420-460°C, AgClBr changes from a liquid phase to a solid. Although not limited to this, the precipitated silver halide particles (AgClBr) are formed into roughly spheres. In addition, to be precise, AgClBr is AgCl (x) Br (1-x) (0<x<1).

[0105] [(C) Stretching of Glass Substrate]

[0106] The glass substrate on which the silver halide particles are deposited is heated and stretched in one direction. For example, the heating temperature during this stretching process can be 550°C to 650°C, and the tension during this stretching process can be approximately 25 MPa to 50 MPa. AgClBr undergoes heating and stretching, transforming from a solid to a liquid. Once the temperature drops below the melting point of AgClBr, the phase transitions to a solid. This stretching process transforms all the silver halide particles into a shape elongated in approximately the same direction.

[0107] [(D)Restore]

[0108] Polarizing glass is obtained by reducing a glass substrate containing elongated silver halide particles in one direction. The reduction process is performed at a temperature below the glass transition temperature (Tg), for example, in a hydrogen atmosphere. Thus, the silver halide particles are reduced to metallic Ag particles while the glass structure remains in a glassy state.

[0109] In this reduction step, the regions of the silver halide grains elongated in one direction remain as they are, forming cavities, and in these cavities, metal Ag grains anisotropically divided into one or more parts are generated.

[0110] In step (B), increasing the precipitation temperature increases the volume of the precipitated silver halide particles, making it difficult to control the size of the metal Ag particles obtained by reducing the silver halide particles to be small in a direction perpendicular to the long axis of the silver halide particles. To achieve excellent optical properties, the average size of the metal Ag particles in a direction perpendicular to the long axis of the silver halide particles is preferably 20 nm or less. To suppress the increase in the volume of the precipitated silver halide particles, the heat treatment in step (B) can be set within a temperature range of 690°C to 710°C, for example, for an 8-hour heat treatment.

[0111] (use)

[0112] The polarizing glass of this embodiment can be applied to all optical devices using polarizing glass, and is not particularly limited in its use. For example, it can be used as polarizing glass for pigtail-type optical isolators in the wavelength band used in optical communications.

[0113] (Optical Isolator)

[0114] The optical isolator has the function of transmitting only forward-traveling light and blocking reverse-traveling light. The optical isolator of this embodiment includes the aforementioned polarizing glass. The optical isolator is not particularly limited, and examples thereof include free-space optical isolators and pigtail optical isolators.

[0115] Figure 1 FIG. 1 is a schematic side sectional view schematically showing an optical system of a free-space optical isolator.

[0116] In the figure, 111 and 112 are polarization elements, 113 is a Faraday rotator, 114 is an optical isolator composed of the polarization elements 111 and 112 and the Faraday rotator 113, 115 and 115' are lenses, 116 is an optical fiber, 117 is a light source such as a semiconductor laser, and 118 and 118' are line groups schematically showing the light beam of the return light returning to the light source 117. In particular, 118' is the light beam after passing through the polarization element 112. As the polarization elements 111 and 112, the polarization glass of this embodiment can be used. Figure 1In the illustrated optical isolator 114, the polarization transmission axes of polarization elements 111 and 112 are arranged at a 45-degree angle relative to each other, and the optical path length is set so that the plane of polarization of Faraday rotator 113 is rotated by 45 degrees. In this configuration, a light beam (not shown) emitted from light source 117 is converted into a parallel beam by lens 115'. Only light with a polarization direction parallel to the polarization transmission axis of polarization element 112 enters Faraday rotator 113. The polarization direction of the light entering Faraday rotator 113 is rotated by 45 degrees due to the Faraday effect generated by a permanent magnet (not shown). As described above, since the polarization transmission axes of polarization elements 111 and 112 form a 45-degree angle relative to each other, the polarization direction of light passing through Faraday rotator 113 coincides with the polarization transmission axis of polarization element 111. Therefore, the light passing through Faraday rotator 113 passes through polarization element 111 with minimal loss, is focused by lens 115, and enters optical fiber 116.

[0117] On the other hand, the return light beam 118, which is reflected by the optical fiber 116 or an optical element disposed downstream thereof (not shown) and returns to the light source, travels along an optical path opposite to that of the light beam emitted from the light source 117 and returns to the light source 117. However, in this case, due to the non-reciprocity of the Faraday rotator 113, the polarization direction of the return light beam 118 after passing through the Faraday rotator 113 forms an angle of 90 degrees (hereinafter referred to as the "polarization extinction axis") with the polarization transmission axis of the polarizing glass 112. Therefore, when passing through the polarizing element 112, its light energy is significantly lost.

[0118] However, in recent years, due to demands for miniaturization of optical components, so-called pigtail-type optical isolators have become mainstream. Figure 2 This is a schematic side cross-sectional view schematically illustrating the optical system of a pigtail-type optical isolator. In this figure, 141 denotes the anisotropically shaped metal particles contained in polarizing element 111, 142 denotes arrows schematically indicating the propagation direction of scattered light, and 143 denotes the optical path of the return beam. In pigtail-type optical isolators, the polarizing glass of this embodiment can also be used as polarizing elements 111 and 112.

[0119] Optical system of pigtail type optical isolator and Figure 1 The optical system of the free-space optical isolator shown differs in two points: (1) direct coupling of optical fiber 116 to polarization element 111, and (2) the use of only a single lens. As a result, while the optical path of return beam 143 differs in these two points, the structure of optical isolator 114 is essentially the same.

[0120] [Example]

[0121] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the embodiments shown in the Examples.

[0122] (Example 1)

[0123] Polarizing glass was obtained by the following steps (A) to (D). Metal Ag particles deposited on the surface of the obtained polarizing glass were observed by TEM.

[0124] [(A) Preparation and Melting of Glass Raw Materials]

[0125] As glass raw materials, SiO2, H3BO3, Al(OH)3, Li2CO3, Na2CO3, K2CO3, KNO3, ZrO2, TiO2, Nb2O5, NaCl, NaBr, and AgCl were used. These raw materials were placed in a 5-liter platinum crucible, dissolved at approximately 1450°C, poured into a metal mold, and slowly cooled to room temperature. A glass substrate having the composition shown in Example 1 in Table 1(1) was obtained. Table 1(2) shows the chemical equivalents of Ag, Cl, and Br in the glass substrate. In Table 1(2), the atomic weight of Ag was set to 107.87, the atomic weight of Cl was set to 35.45, and the atomic weight of Br was set to 79.9, and the chemical equivalents of Ag, Cl, and Br were calculated.

[0126] [(B) Precipitation of Silver Halide Grains]

[0127] The glass substrate obtained in the above (A) was heat-treated at 704° C. for about 8 hours to precipitate AgClBr particles in the glass. The preform was then cut into pieces with a width of 120 mm, a length of 250 mm, and a thickness of 6 mm to produce a preform.

[0128] [(C) Stretching of Glass Substrate]

[0129] The preform obtained in step (B) was heated in a drawing furnace and stretched at a tension of 32.0 MPa. This caused the plurality of silver halide particles (AgClBr) contained in the glass to change from a spherical shape to an elongated shape (approximately an ellipsoidal shape) elongated in the stretching direction.

[0130] [(D)Restore]

[0131] The glass film, approximately 0.6 mm thick, obtained in the stretching step (C) above, was cut into rectangular shapes, polished to a thickness of 0.2 mm, and then heat-treated at 440°C for approximately 7 hours in a hydrogen atmosphere to reduce the silver halide particles stretched in one direction to silver particles. This resulted in a polarizing glass containing metallic Ag particles, which were shape-anisotropic metal particles, dispersed in an orientationally dispersed manner on the surface of the glass substrate.

[0132] TEM Photographs

[0133] The surface of the obtained polarizing glass was observed by a transmission electron microscope (TEM) photograph. It was confirmed that metal Ag particles, which were shape-anisotropic metal particles with orientation and dispersion, were present on the surface of the polarizing glass.

[0134] (Comparative Example 1)

[0135] In the same manner as in step (A) above, a glass substrate having the composition shown in Comparative Example 1 in Table 1(1) was obtained. Table 1(2) shows the chemical equivalents of Ag, Cl, and Br in the glass substrate. The composition of Comparative Example 1 is the same as that of the glass shown in Example No. 10 of WO2007 / 119794.

[0136] The resulting glass substrate was heat treated in the same manner as in (B) above, and then heat-stretched in the same manner as in (C) above. Polarizing glass was obtained in the same manner as in (D) above. Observation of the TEM image, similar to that in Example 1, confirmed the presence of oriented and dispersed anisotropically shaped metallic Cu particles on the surface of the polarizing glass.

[0137] (Comparative Example 2)

[0138] In the same manner as in the above-mentioned step (A), a glass substrate having the composition shown in Comparative Example 2 of Table 1 (1) was obtained. Table 1 (2) shows the chemical equivalents of Ag, Cl, and Br in the glass substrate. The obtained glass substrate was heat-treated in the same manner as in the above-mentioned step (B), and heat-stretched in the same manner as in the above-mentioned step (C). Polarizing glass was obtained in the same manner as in the above-mentioned step (D). By observing the same TEM photograph as in Example 1, it was confirmed that metal Ag particles as anisotropic particles with an orientation dispersion were present on the surface of the polarizing glass.

[0139] [Table 1(1)]

[0140] Table 1(1)

[0141]

[0142] [Table 1(2)]

[0143] Table 1(2)

[0144]

[0145] <Chemical durability, water resistance Dw>

[0146] The glass substrates obtained by the above-described (A) in Example 1 and Comparative Example 1 were evaluated for their water resistance Dw. Specifically, a mass of powdered glass (particle size 425-600 μm) equivalent to the specific gravity of the glass substrate was placed in a platinum cage, immersed in a quartz glass round-bottom flask containing 80 mL of pure water (pH = 6.5-7.5), and treated in a boiling water bath for 60 minutes. The water resistance (%) was calculated. The reduction rate for the glass substrate in Example 1 was 0.03%, while the reduction rate for the glass substrate in Comparative Example 1 was 0.04% or greater.

[0147] <Chemical durability, acid resistance Da>

[0148] The glass substrates obtained by the above-described (A) in Example 1 and Comparative Example 1 were evaluated for their acid resistance Da. Specifically, a mass of powdered glass (particle size 425-600 μm) equivalent to the specific gravity of the glass substrate was placed in a platinum cage, immersed in a quartz glass round-bottom flask containing 80 mL of a 0.01 mol / L nitric acid aqueous solution, and treated in a boiling water bath for 60 minutes. The reduction rate (%) was calculated. The reduction rate for the glass substrate in Example 1 was 0.07%, while the reduction rate for the glass substrate in Comparative Example 1 was 0.21% or greater.

[0149] <Nb2O5’s effect in reducing photochromic properties>

[0150] In Example 1 and Comparative Example 2, glass substrates were produced according to the procedure shown in (A) above.

[0151] The obtained glass substrate was heat treated in the same manner as in (B) above and heated and stretched in the same manner as in (C) above to obtain a glass film. The glass film was cut into pieces of approximately 20 mm in length. The glass film of Comparative Example 2 was placed side by side with the glass film of Example 1 and irradiated with an ultraviolet irradiator at 50 mW / cm 2 The glass film after ultraviolet irradiation is as follows: Figure 3 The transmittance of the glass film before and after UV irradiation at wavelengths of 400 nm, 1310 nm, and 1550 nm was measured using a spectrophotometer. The ratio of the transmittance after UV irradiation to the transmittance before UV irradiation is shown in Table 2.

[0152] like Figure 3 As shown, in the sample of Comparative Example 2 which does not contain Nb2O5, the color changes due to light irradiation, while in the sample of Example 1, the color change due to light irradiation is suppressed.

[0153] [Table 2]

[0154] Table 2

[0155] wavelength Example 1 Comparative Example 2 400nm 99％ 83％ 1310nm 100％ 92％ 1550nm 100％ 94％

[0156] As shown in Table 2, in the composition containing no Nb2O5 and a low TiO2 content (Comparative Example 2), the ratio of transmittance after UV irradiation to transmittance before UV irradiation dropped significantly to 83% at 400nm, a short wavelength in the visible light region. In contrast, the composition containing Nb2O5 (Example 1) maintained a transmittance ratio of 99%. At 1310nm, a wavelength band used for optical communications, the ratio of transmittance after UV irradiation to transmittance before UV irradiation dropped to 92% in Comparative Example 2, while Example 1 maintained a transmittance ratio of 100%. At a wavelength of 1550nm, the ratio of transmittance after UV irradiation to transmittance before UV irradiation dropped to 94% in Comparative Example 2, while Example 1 maintained a transmittance ratio of 100%. The inclusion of Nb2O5 significantly suppresses photochromism.

[0157] <Extinction ratio, insertion loss>

[0158] An anti-reflection film (AR coating) is provided on one side of the polarizing glass obtained in Example 1 and Comparative Example 2 to reduce the reflectivity caused by the refractive index of the polarizing glass. The anti-reflection film is formed by a multilayer film consisting of a metal oxide layer such as TiO2, Ta2O5 and a SiO2 layer. For the polarizing glass used in the optical isolator, most of the time, a 0-degree product (a polarizing glass product cut in such a way that the polarization transmission axis of the light component passing through the polarizing glass is parallel to the outer edge of the Faraday rotator) is bonded to one side of the Faraday element (garnet) using an adhesive, and a 45-degree product (a polarizing glass product cut in such a way that the 0-degree product maintains an angle of 45 degrees with the polarization transmission axis) is bonded to the other side for use. Therefore, in most cases, the polarizing glass is only exposed to the atmosphere on one side. Due to the above reasons, the AR film of the polarizing glass is only provided on one side.

[0159] A 0.2mm thick rectangular polarizing glass with AR coating on one side was attached to an adhesive tape that can be peeled off by irradiation with ultraviolet light (UV light). The product was cut into 11mm squares and irradiated with UV light to peel the polarizing glass from the adhesive tape. The extinction ratio and insertion loss of the polarizing glass were measured when the laser light source wavelength was set to 1270nm and the distance between the polarizing glass and the power meter detector (measurement distance) was set to 5mm. The extinction ratio and insertion loss of the polarizing glass were also measured when the laser light source wavelength was set to 1650nm and the measurement distance was set to 300mm. The results are shown in Table 3.

[0160] [Table 3]

[0161]

Table 3

[0162]

[0163] In Comparative Example 2, which contains no Nb2O5 and has a TiO2 content of 1.0%, the extinction ratio at a wavelength of 1270nm and a measurement distance of 5mm is 36.91dB, which is lower than that of Example 1. Furthermore, the extinction ratio at a wavelength of 1650nm and a distance of 300mm in Comparative Example 2 is 53.65dB, also lower than that of Example 1.

[0164] The insertion loss of Comparative Example 2 was 0.241 dB at a wavelength of 1270 nm and a measurement distance of 5 mm, which was higher than that of Example 1. The insertion loss at a wavelength of 1650 nm and a distance of 300 mm was 0.232 dB, also higher than that of Example 1. It is speculated that the higher insertion loss in Comparative Example 2, which contains no Nb2O5 and has a TiO2 content of 1.0%, was caused by the influence of photochromism.

[0165] The embodiments disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is indicated not by the above description but by the scope of the claims, and all modifications within the meaning and scope equivalent to the scope of the claims are intended to be encompassed.

[0166] For example, the polarizing glass of one embodiment of the present invention can be produced by adjusting the composition of the glass composition exemplified above as described in the specification.

[0167] Furthermore, it is of course possible to arbitrarily combine two or more items described as examples or preferred ranges in the specification.

Claims

1. A polarizing glass comprising oriented and dispersed shape anisotropic metal particles at least on the surface layer of a glass substrate, wherein: Expressed in mass %, the glass matrix comprises: SiO2: 50.0~60.0%; B2O3: 10.0~25.0%; Al2O3: 3.0~10.0%; The total content of Li2O, Na2O, and K2O [Li2O+Na2O+K2O]: 5.0-20.0%; ZrO2: 2.0~8.0%; TiO2: 0.1~5.0%; Nb2O5: 0.1~5.0%; The total content of TiO2 and Nb2O5 [TiO2+Nb2O5]: 0.2-10.0%; Ag; and Cl and / or Br above the chemical equivalent of Ag, The shape-anisotropic metal particles are metal Ag particles.

2. An optical isolator comprising the polarizing glass according to claim 1.

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