Silver-including polarizing glass and optical isolator

Abstract

To provide polarizing glass having a glass substrate having excellent chemical durability and reduced photochromic characteristics.SOLUTION: A polarizing glass containing shape-anisotropic metal particles that are oriented and dispersed at least in a surface layer of a glass substrate, wherein the glass substrate, expressed in mass percent, contains SiO2: 50.0 to 60.0%, B2O3: 10.0 to 25.0%, Al2O3: 3.0 to 10.0%, total content of Li2O, Na2O, and K2O [Li2O+Na2O+K2O]: 5.0 to 20.0%, ZrO2: 2.0 to 8.0%, TiO2: 0.1 to 5.0%, Nb2O5: 0.1 to 5.0%, total content of TiO2 and Nb2O5 [TiO2+Nb2O5]: 0.2 to 10.0%, Ag, and Cl and / or Br in an amount at least equivalent to that of Ag, and wherein the shape-anisotropic metal particles are metal Ag particles.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Optical isolators have the function of transmitting only light traveling in the forward direction and blocking light traveling in the reverse direction. Polarizing glass is an optical glass that transmits only light vibrating in a specific direction (polarized light), and is an optical component used in optical isolators, etc. Optical isolators are currently used in a variety of environments, and polarizing glass is required to have excellent durability.

[0003] Furthermore, when the glass substrate of polarizing glass discolors due to exposure to light, its functionality as polarizing glass may be impaired. Specifically, a phenomenon known as photochromism occurs, in which the glass substrate darkens when exposed to ultraviolet light or short-wavelength visible light, resulting in a problem of reduced light transmission through the polarizing glass.

[0004] That is, there is a need for polarizing glass that has excellent durability under various environments and has a glass substrate with reduced photochromic properties.

[0005] Patent Document 1 discloses polarizing glass containing shape-anisotropic metallic silver particles, but the Al2O3 and ZrO2 contents are low, so it is not intended for use in a variety of environments, and there is no mention of durability. Patent Document 2 also discloses polarizing glass containing dispersed shape-anisotropic metallic silver particles, but it is not intended for the glass substrate to discolor due to light exposure, and there is no disclosure of reducing the photochromic properties of the glass by adding a predetermined amount of Nb2O5 or the like. Patent Document 3 discloses polarizing materials containing silver as flattened metal particles in a glass substrate, but both have a high silver content, and there is no mention of reducing the amount of silver introduced. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 56-169140 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-126921 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-150132 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide polarizing glass having a glass substrate with excellent chemical durability and reduced photochromic properties. [Means for solving the problem]

[0008] The gist of the present invention is as follows. A polarizing glass comprising shape-anisotropic metal particles oriented and dispersed in at least a surface layer of a glass substrate, The glass substrate is expressed in mass %, SiO2 50.0~60.0%, B2O3 10.0~25.0%, Al2O3 3.0-10.0%, Total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] 5.0 to 20.0%; ZrO2 2.0~8.0%, TiO2 0.1-5.0%, Nb2O50.1~5.0% Total content of TiO2 and Nb2O5 [TiO2+Nb2O5] 0.2~10.0% Ag, and Cl and / or Br Ag equivalent or more Including, Polarizing glass, wherein the shape-anisotropic metal particles are metallic Ag particles.

[0009] (2) An optical isolator comprising the polarizing glass described in (1) above. [Effects of the Invention]

[0010] According to the present invention, a polarizing glass can be provided which has a glass substrate with excellent chemical durability and reduced photochromic properties. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional side view showing the optical system of a free-space type optical isolator. [Figure 2] FIG. 2 is a schematic cross-sectional side view showing the optical system of the pigtail-type optical isolator. [Figure 3] FIG. 3 is a photograph showing the degree of discoloration of the stretched glasses prepared in the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0012] In this invention and this specification, glass compositions are expressed on an oxide basis unless otherwise specified. Here, "oxide-based glass composition" refers to a glass composition obtained by converting the glass raw materials into oxides that exist in the glass after they are all decomposed during melting. Each glass component is conventionally expressed as SiO2, TiO2, etc. Furthermore, elements related to polarization properties, such as Ag, Cl, and Br, are expressed as elements rather than oxides. The contents and total contents of glass components are expressed on a mass basis unless otherwise specified, and "%" means "mass %."

[0013] The content of glass components can be quantified by known methods, such as inductively coupled plasma atomic emission spectroscopy (ICP-AES), inductively coupled plasma mass spectroscopy (ICP-MS), etc. In this specification and the present invention, a content of 0% of a component means that the component is substantially not contained, and it is acceptable for the component to be present at an unavoidable impurity level.

[0014] In this specification, the chemical durability of glass refers to excellent water resistance and acid resistance, and the thermal stability of glass refers to the resistance to the precipitation of crystals other than silver halide particles when molten glass solidifies.

[0015] An embodiment of the present invention will be described below.

[0016] The polarizing glass according to this embodiment has a glass substrate and contains shape-anisotropic metal particles oriented and dispersed in at least the surface layer of the glass substrate. The polarizing glass transmits polarized light in a specific vibration direction (referred to as the "polarization transmission axis") and absorbs polarized light in the direction perpendicular to the specific vibration direction (referred to as the "polarization extinction axis").

[0017] (glass substrate) In the glass base, the SiO2 content is 50.0 to 60.0%. The lower limit of the SiO2 content is preferably 51.0%, more preferably 52.0%. 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 base can be improved. On the other hand, if the SiO2 content is too low, the chemical durability and thermal stability of the glass base may decrease. Furthermore, if the SiO2 content is too high, the meltability of the glass may decrease.

[0018] The glass substrate contains 10.0 to 25.0% B2O3. The lower limit of the B2O3 content is preferably 12.0%, with 13.0% and 14.0% being more preferred. The upper limit of the B2O3 content is preferably 23.0%, with 21.0% and 20.0% being more preferred. By keeping the B2O3 content within the above range, the chemical durability of the glass substrate can be improved. On the other hand, if the B2O3 content is too low, the meltability of the glass may be reduced, and silver halide particles may not be precipitated well over the entire glass substrate during the heat treatment described below. On the other hand, if the B2O3 content is too high, the chemical durability of the glass substrate may be reduced.

[0019] In the glass base, the Al2O3 content is 3.0 to 10.0%. The lower limit of the Al2O3 content is preferably 4.0%, more preferably 4.5%. The upper limit of the Al2O3 content is preferably 9.0%, more preferably 8.0%. By setting the Al2O3 content within the above range, the chemical durability of the glass base can be improved. On the other hand, if the Al2O3 content is too low, the chemical durability of the glass base may be significantly reduced. Furthermore, if the Al2O3 content is too high, the meltability of the glass may be reduced, making it more susceptible to devitrification.

[0020] In the glass substrate, the total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is 5.0 to 20.0%. The lower limit of this total content is preferably 7.0%, more preferably 9.0%. The upper limit of this total content is preferably 18.0%, more preferably 16.0%. By setting this total content within the above range, the chemical durability of the glass substrate can be improved. In particular, by containing two or more alkali metals, the chemical durability of the glass substrate can be improved. On the other hand, if the total content is too low, the meltability of the glass may be reduced. Furthermore, if the total content is too high, silver halide particles may not be precipitated well over the entire glass substrate during the heat treatment described below.

[0021] In the glass base, the ZrO2 content is 2.0 to 8.0%. The lower limit of the ZrO2 content is preferably 2.5%, more preferably 3.0%. 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 base can be improved. On the other hand, if the ZrO2 content is too low, the chemical durability of the glass base may be significantly reduced. Furthermore, if the ZrO2 content is too high, the meltability of the glass may be reduced and the liquidus temperature may be increased.

[0022] The TiO2 content in the glass substrate is 0.1 to 5.0%. The lower limit of the TiO2 content is preferably 0.3%, more preferably 0.6%. The upper limit of the TiO2 content is preferably 4.5%, more preferably 4.0%. TiO2 is a glass component that contributes to improving the chemical durability of glass and effectively absorbs light in the near-ultraviolet to visible short wavelength range. Therefore, by setting the TiO2 content within the above range, a polarizing glass having a glass substrate 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 substrate may decrease and the photochromic properties of the glass substrate may increase. If the TiO2 content is too high, the meltability of the glass may decrease, the liquidus temperature may increase, and coloring may become stronger during glass molding.

[0023] The Nb2O5 content in the glass base is 0.1 to 5.0%. The lower limit of the Nb2O5 content is preferably 0.3%, more preferably 0.6%. The upper limit of the Nb2O5 content is preferably 4.5%, more preferably 4.0%. Nb2O5 is a glass component that effectively absorbs light in the near-ultraviolet to visible short wavelength range. Therefore, by setting the Nb2O5 content within the above range, a polarizing glass having a glass base with reduced photochromic properties can be obtained. On the other hand, if the Nb2O5 content is too low, the photochromic properties of the glass base may be increased. Furthermore, if the Nb2O5 content is too high, the meltability of the glass may decrease, the liquidus temperature may increase, and further coloring may be intensified during glass molding.

[0024] In the glass substrate, the total content of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 0.2 to 10.0%. The lower limit of this total content is preferably 0.5%, more preferably 1.0%. The upper limit of this total content is preferably 9.0%, more preferably 8.0%. By keeping this total content within the above range, a polarizing glass having a glass substrate with improved chemical durability and reduced photochromic properties can be obtained. On the other hand, if the total content is too low, the chemical durability of the glass substrate may decrease and the photochromic properties of the glass substrate may increase. If the total content is too high, the meltability of the glass may decrease and the liquidus temperature may increase.

[0025] The glass substrate contains Ag, Cl, and Br. In the glass substrate, the lower limit of the Ag content is preferably 0.10%, with 0.11% and 0.13% being more preferred. The upper limit of the Ag content is preferably 1.0%, with 0.8% and 0.6% being more preferred. By including Ag in the glass substrate, a polarizing glass having a glass substrate with excellent chemical durability can be obtained. On the other hand, if the Ag content is too low, silver halide particles may not be precipitated well over the entire glass substrate during the heat treatment described below. If the Ag content is too high, insertion loss may increase, and silver halide particles may precipitate in the glass when the glass is melted and cooled, making it difficult to control the particle size of the silver halide particles.

[0026] It is preferable that the glass substrate does not substantially contain Cu, that is, the Cu content is preferably 0%.

[0027] To precipitate silver halide particles throughout the glass substrate, Ag is added to the glass substrate raw materials, for example, as AgCl and AgBr. However, AgBr is a toxic substance and must be handled with care, and its use is not recommended from an environmental perspective. Furthermore, Cl and Br are prone to volatilization during glass melting, so they are added in excess as chlorides or bromides of alkali metals or alkaline earth metals to replenish them. Therefore, the glass substrate contains Cl and / or Br in amounts greater than the chemical equivalent of Ag. The amount of excess Cl and Br added can be adjusted depending on the glass melting method and scale.

[0028] As described above, the glass substrate contains Cl and / or Br in an amount equal to or greater than the chemical equivalent of Ag. That is, in the glass substrate, the chemical equivalent of at least one of Cl and Br is equal to or greater than the chemical equivalent of Ag. The chemical equivalent of both Cl and Br may be equal to or greater than the chemical equivalent of Ag.

[0029] The Iwanami Dictionary of Physics and Chemistry (5th edition) defines chemical equivalent as "a fixed amount of an element (simple substance) or compound determined based on chemical reactivity. It is also simply called equivalent." The chemical equivalent of an element is also defined as "When the mass of an element that combines with 7.999 g of oxygen (equivalent to 1 / 2 mol of oxygen atoms) is Wg, W is called the chemical equivalent of that element. The chemical equivalent of an element that does not combine directly with oxygen can be determined using an appropriate element other than oxygen as an intermediary."

[0030] In this embodiment, referring to the above description in the Iwanami Dictionary of Physics and Chemistry, the chemical equivalents of Ag, Cl, and Br correspond to the chemical equivalents of the elements. That is, the chemical equivalent of Cl is the Cl content expressed in mass % divided by the atomic weight of Cl, the chemical equivalent of Br is the Br content expressed in mass % divided by the atomic weight of Br, and the chemical equivalent of Ag is the Ag content expressed in mass % divided by the atomic weight of Ag. And, "the chemical equivalent of Cl and / or Br is equal to or greater than the chemical equivalent of Ag" means that the number of Cl atoms and / or Br atoms contained in the glass is equal to or greater than the number of Ag atoms.

[0031] In the glass substrate, the total content of Cl and Br is preferably 0.05 to 2.0%. The content of Cl is preferably 0.05 to 1.0%. Similarly, the content of Br is preferably 0.05 to 1.0%.

[0032] Non-limiting examples of the content of glass components other than those described above in the glass base are shown below.

[0033] In the glass base, the lower limit of the Li2O content is preferably 0.0%, more preferably 0.5%, and more preferably 0.8%. The upper limit of the Li2O content is preferably 5.0%, more preferably 4.0%, and more preferably 3.5%. From the viewpoint of improving the meltability of the glass and lowering the glass transition temperature Tg, it is preferable to set the lower limit of the Li2O content as described above. From the viewpoint of favorable precipitation of silver halide particles over the entire glass base in the heat treatment described below, it is preferable to set the upper limit of the Li2O content as described above.

[0034] In the glass base, the lower limit of the Na2O content is preferably 0.0%, with 1.0% and 3.0% being more preferred in that order. The upper limit of the Na2O content is preferably 10.0%, with 8.0% and 7.0% being more preferred in that order. From the viewpoint of improving the meltability of the glass and lowering the glass transition temperature Tg, it is preferable to set the lower limit of the Na2O content as described above. Furthermore, from the viewpoint of favorable precipitation of silver halide particles over the entire glass base in the heat treatment described below, it is preferable to set the upper limit of the Na2O content as described above.

[0035] In the glass base, the lower limit of the K2O content is preferably 0.0%, more preferably 1.0%, and more preferably 3.0%. The upper limit of the K2O content is preferably 10.0%, more preferably 8.0%, and more preferably 7.0%. From the viewpoint of improving the meltability of the glass and lowering the glass transition temperature Tg, it is preferable to set the lower limit of the K2O content as described above. From the viewpoint of favorable precipitation of silver halide particles over the entire glass base in the heat treatment described below, it is preferable to set the upper limit of the K2O content as described above.

[0036] In the glass base, the lower limit of the MgO content is preferably 0.0%. The MgO content may be 0.0%. The upper limit of the MgO content is preferably 5.0%, more preferably 3.0%. From the viewpoint of improving the thermal stability and meltability of the glass, it is preferable that the MgO content be within the above range.

[0037] In the glass base, the lower limit of the CaO content is preferably 0.0%. The CaO content may be 0.0%. The upper limit of the CaO content is preferably 5.0%, more preferably 3.0%. From the viewpoint of improving the thermal stability and meltability of the glass, it is preferable that the CaO content be within the above range.

[0038] In the glass base, the lower limit of the SrO content is preferably 0.0%. The SrO content may be 0.0%. The upper limit of the SrO content is preferably 5.0%, more preferably 3.0%. From the viewpoint of improving the thermal stability and meltability of the glass, it is preferable that the SrO content be within the above range.

[0039] In the glass base, the lower limit of the BaO content is preferably 0.0%. The BaO content may be 0.0%. The upper limit of the BaO content is preferably 5.0%, more preferably 3.0%. From the viewpoint of suppressing an increase in specific gravity, it is preferable that the BaO content be within the above range.

[0040] In the glass base, the lower limit of the total content of MgO, CaO, SrO, and BaO [MgO + CaO + SrO + BaO] is preferably 0.0%. The total content may be 0.0%. The upper limit of the total content is preferably 5.0%, more preferably 3.0%. Although these elements improve the thermal stability and meltability of the glass and increase the basicity of the glass, thereby preventing silver reduction, they may also reduce the chemical durability of the glass base, so it is preferable to keep the total content within the above range.

[0041] In the glass base, the lower limit of the ZnO content is preferably 0.0%. The ZnO content may be 0.0%. The upper limit of the ZnO content is preferably 5.0%, more preferably 3.0%. From the viewpoint of improving the thermal stability of the glass, it is preferable that the ZnO content be within the above range.

[0042] The glass substrate is preferably composed mainly of the above-mentioned glass components, i.e., SiO2, B2O3, Al2O3, ZrO2, TiO2, Nb2O5, Ag, Cl, Br, Li2O, Na2O, KO, MgO, CaO, SrO, BaO, and ZnO, and the total content of the above-mentioned glass components is preferably 95% or more, more preferably 98% or more, even more preferably 99% or more, and even more preferably 99.5% or more.

[0043] The glass substrate is preferably basically composed of the above glass components, but may contain other components as long as they do not impair the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

[0044] The glass substrate is mainly formed of oxides. That is, the main anion component in the glass substrate is O, and the glass substrate may also contain trace amounts of Cl and Br. The glass substrate may also contain F as an anion component other than O, Cl, and Br. In the glass substrate, the F content is preferably 0.5% or less, and more preferably 0.0%.

[0045] (Other ingredients) In the glass substrate, the lower limit of the CeO2 content is preferably 0.0%. The CeO2 content may be 0.0%. The upper limit of the CeO2 content is preferably 3.0%, more preferably 1.0%. CeO2 is a component that functions as a glass fining agent. In addition, when CeO2 is present in the glass, 4+ Ions and Ce 3+ Ionic states coexist, usually Ag +However, the equilibrium of this valence state easily changes depending on the temperature, so during the heat treatment to precipitate silver halide fine particles, Ag + There is a risk that ion reduction will occur, resulting in promotion of photochromism. Therefore, it is preferable that the CeO2 content be within the above range.

[0046] Pb is a toxic component that poses a concern for its environmental impact. Therefore, it is preferable that the glass substrate does not substantially contain Pb. In other words, the Pb content is preferably 0% in terms of oxide.

[0047] Cd, As, Th, etc. are components that pose a concern for their environmental impact. Therefore, the content of each of CdO, ThO2, and As2O3 is preferably 0 to 0.1%, more preferably 0 to 0.05%, and even more preferably 0 to 0.01%, and it is particularly preferable that CdO, ThO2, and As2O3 are substantially not contained.

[0048] The glass substrate preferably does not contain any coloring elements. Examples of coloring elements include Co, Ni, Fe, Cr, Eu, Nd, Er, etc. The content of each element is preferably less than 100 ppm by mass, more preferably 0 to 80 ppm by mass, even more preferably 0 to 50 ppm by mass or less, and particularly preferably substantially none.

[0049] Furthermore, Ga, Te, Tb, etc. are components that do not need to be incorporated and are expensive components, so 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%, even more preferably 0 to 0.01%, even more preferably 0 to 0.005%, and even more preferably 0 to 0.001%, and it is particularly preferable that they are not substantially contained.

[0050] (Glass substrate characteristics) <Chemical durability Water resistance Dw> In the glass substrate, the water resistance Dw is preferably grade 3 or higher, more preferably grade 2 or higher, and even more preferably grade 1.

[0051] Water resistance Dw can be evaluated using the method specified in JOGIS 06:2019. Specifically, water resistance Dw is evaluated by placing a mass of powdered glass (particle size 425-600 μm) equivalent to the specific gravity in a platinum cage, immersing it in a quartz glass round-bottom flask containing 80 mL of pure water (pH = 6.5-7.5), and treating it in a boiling water bath for 60 minutes. The weight loss rate (%) is then classified and evaluated according to the grade in Table A. [Table A]

[0052] <Chemical durability Acid resistance Da> The acid resistance Da of the glass substrate is preferably grade 3 or higher, more preferably grade 2 or higher, and even more preferably grade 1.

[0053] Acid resistance Da can be evaluated using the method specified in JOGIS 06:2019. Specifically, acid resistance Da is evaluated by placing a mass of powdered glass (particle size 425-600 μm) equivalent to the specific gravity in a platinum cage, immersing it in a quartz glass round-bottom flask containing 80 mL of 0.01 mol / L nitric acid solution, and treating it in a boiling water bath for 60 minutes. The weight loss rate (%) is then classified and evaluated according to the grade in Table B. [Table B]

[0054] (shape-anisotropic metal particles) The polarizing glass according to this embodiment contains shape-anisotropic metal particles oriented and dispersed in at least the surface layer of the glass substrate, and the shape-anisotropic metal particles are metallic Ag particles. In the polarizing glass according to this embodiment, the surface layer containing shape-anisotropic silver particles occupies part or all of the surface of the glass substrate, and the thickness of this surface layer is, for example, 20 to 100 μm. The dimension of the shape-anisotropic metal silver particles in the direction along the major axis of the silver halide particles is, for example, in the range of 10 to 1000 nm, and the aspect ratio with respect to the dimension perpendicular to that direction is, for example, in the range of 0.5 to 20.

[0055] <Extinction ratio and insertion loss> Generally, the optical properties required for polarizing glass are a high extinction ratio and low insertion loss. "Extinction ratio" is the ratio of the transmittance of light parallel to the polarized light extinction axis to light parallel to the polarized light transmission axis, and the higher the extinction ratio, the better the optical properties. It is measured in dB. "Insertion loss" refers to the loss that light parallel to the polarized light transmission axis incurs when passing through a polarizing element, and the lower the insertion loss, the better the optical properties. It is measured in dB.

[0056] As shown in Figure 13 of Patent No. 4642921, for which the present inventor is the inventor, when the distance (measurement distance) between the polarizing glass and the detector power meter is short, such as 5 mm, the detector receives re-emitted light from the polarizing glass, and the extinction ratio decreases by the amount of re-emitted light. When the measurement distance is long, such as 300 mm, the detector receives less re-emitted light from the polarizing glass, and the extinction ratio increases. Therefore, when the distance between the polarizing glass and the power meter is short, the extinction ratio is low, and as the distance increases, the extinction ratio increases. The insertion loss is an approximately constant value, independent of the measurement distance.

[0057] In the polarizing glass according to this embodiment, the extinction ratio at a measurement distance of 5 mm for light having a wavelength of 1270 nm is preferably 38.0 dB or more, more preferably 38.2 dB or more. Also, the extinction ratio at a measurement distance of 300 mm for light having a wavelength of 1650 nm is preferably 55.0 dB or more, more preferably 56.0 dB or more.

[0058] In the polarizing glass according to this embodiment, when an anti-reflection film is applied to one side of the polarizing glass, the insertion loss at a measurement distance of 5 mm for light with a wavelength of 1270 nm is preferably 0.204 dB or less, and the insertion loss at a measurement distance of 300 mm for light with a wavelength of 1650 nm is preferably 0.204 dB or less.

[0059] 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 of the polarizing glass. The Glan-Thompson prism is inserted to obtain linearly polarized light in a specific direction.

[0060] The polarizing glass is rotated and the minimum transmitted light amount P1 is measured, then the polarizing glass is rotated 90 degrees and the maximum transmitted light amount P2 is measured, and the extinction ratio is calculated using the following formula. Extinction ratio (dB)=-10Log(P1 / P2)

[0061] The insertion loss is calculated by measuring the amount of light P0 when no polarizing glass is present and using the following formula: Insertion loss (dB) = -10Log(P2 / P0)

[0062] (Polarizing Glass Manufacturing Method) The method for producing polarizing glass according to this embodiment can be broadly divided into the following steps: (A) blending and melting glass raw materials, (B) precipitating silver halide particles, (C) stretching the glass substrate, and (D) reduction.

[0063] [(A) Preparation and melting of glass raw materials] Glass raw materials are prepared. 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 glass is then molded and slowly cooled to room temperature to obtain a glass substrate.

[0064] (B) Precipitation of Silver Halide Grains The glass substrate obtained in (A) above is heat-treated for several hours to about 20 hours (preferably about 4 hours to 10 hours) at a temperature of 650° C. to 800° C. In order to generate silver halide particles of an appropriate size, generally, when the heat treatment time is short, the heat treatment is performed at a high temperature, and when the heat treatment time is long, the heat treatment is performed at a relatively low temperature.

[0065] When the glass contains AgCl as silver halide, the above heat treatment causes Cl ions, Br ions, and Ag ions to aggregate, resulting in the precipitation of liquid AgClBr particles. In the subsequent cooling process, the temperature of the glass drops to around the glass transition temperature (Tg), for example, around 500°C, and the glass state is maintained. Even in this state, AgClBr exists as a liquid, but when the temperature of the glass drops further and falls below the melting point of AgClBr, 420 to 460°C, AgClBr undergoes a phase change from liquid to solid. While not limited to this, the precipitated silver halide particles (AgClBr) are formed in approximately spherical shapes. To be precise, AgClBr is AgCl (x) Br (1-x) (0 <x<1)である。

[0066] [(C) Stretching of glass substrate] The glass substrate on which silver halide particles have precipitated is heated and stretched in one direction. For example, the heating temperature in this stretching process can be 550°C to 650°C, and the tension in this stretching process can be approximately 25 MPa to 50 MPa. AgClBr changes from a solid to a liquid by heating and stretching, and then changes back to a solid when the temperature drops below the melting point of AgClBr. This stretching process causes all of the silver halide particles to change into a shape elongated in approximately the same direction.

[0067] [(D) Reduction] A glass substrate with silver halide particles extending in one direction is reduced to obtain polarizing glass. The reduction process is carried out at a temperature below the glass transition temperature (Tg), for example, in a hydrogen atmosphere. As a result, the silver halide particles are reduced to metallic Ag particles while the glass structure remains in a glassy state.

[0068] In this reduction process, the regions of the silver halide grains that are elongated in one direction are maintained as they are and become hollow, and one or more shape-anisotropic metal Ag particles are generated within these hollows.

[0069] Here, if the precipitation temperature is increased in the above step (B), the volume of the precipitated silver halide particles increases, making it difficult to control the size of the metallic Ag particles obtained by reducing the silver halide particles in a direction perpendicular to the major axis of the silver halide particles. To obtain excellent optical properties, the average size of the metallic Ag particles in a direction perpendicular to the major 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 the precipitation step (B) can be set, for example, within a temperature range of 690°C to 710°C when the heat treatment time is 8 hours.

[0070] (Application) The polarizing glass according to this embodiment can be applied to any optical device that uses polarizing glass, and its use is not particularly limited. For example, it can be used as polarizing glass for pigtail-type optical isolators in the wavelength band used in optical communications.

[0071] (optical isolator) An optical isolator has the function of transmitting only light traveling in the forward direction and blocking light traveling in the reverse direction. The optical isolator according to this embodiment includes the polarizing glass described above. The optical isolator is not particularly limited, but examples include a free-space optical isolator and a pigtail optical isolator.

[0072] FIG. 1 is a schematic side cross-sectional view showing the optical system of a free-space optical isolator. In the figure, 111 and 112 are polarizing elements, 113 is a Faraday rotator, 114 is an optical isolator composed of polarizing elements 111 and 112 and 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 lines showing the feedback light beam returning to light source 117, with 118' being the light beam after passing through polarizing element 112. Polarizing elements 111 and 112 can be made of polarizing glass according to this embodiment. In optical isolator 114 shown in FIG. 1, the polarization transmission axes of polarizing elements 111 and 112 are arranged at a 45-degree angle, and the optical path length is set so that the polarization plane rotation angle of Faraday rotator 113 is 45 degrees. In this configuration, a light beam (not shown) emitted from the light source 117 is converted into a parallel light beam by the lens 115′, and only the light polarized parallel to the polarization transmission axis of the polarizing element 112 enters the Faraday rotator 113. The polarization direction of the light entering the Faraday rotator 113 is rotated by 45 degrees due to the Faraday effect caused by a permanent magnet (not shown). As described above, the polarization transmission axes of the polarizing elements 111 and 112 form a 45-degree angle with each other, so the polarization direction of the light transmitted through the Faraday rotator 113 coincides with the polarization transmission axis of the polarizing element 111. Therefore, the light transmitted through the Faraday rotator 113 passes through the polarizing element 111 with almost no loss, is converged by the lens 115, and enters the optical fiber 116.

[0073] On the other hand, the return light beam 118 that is reflected by the optical fiber 116 or an optical element or the like (not shown) arranged downstream and returns to the light source will return to the light source 117 via an optical path that is reverse to that of the light beam emitted from the light source 117 described above. 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 with the polarization transmission axis of the polarizing glass 112 (hereinafter, this axis will be referred to as the "polarization extinction axis"), and therefore the light energy of the return light beam 118 is significantly lost when passing through the polarizing element 112.

[0074] Recently, due to demands for miniaturization of optical components, so-called pigtail-type optical isolators are becoming mainstream. Fig. 2 is a schematic side cross-sectional view showing the optical system of a pigtail-type optical isolator. In the figure, 141 denotes anisotropic metal particles contained in the polarizing element 111, 142 denotes an arrow showing the propagation direction of scattered light, and 143 denotes the optical path of the feedback light beam. In the pigtail-type optical isolator, the polarizing glass according to this embodiment can be used as the polarizing elements 111 and 112.

[0075] The optical system of the pigtail-type optical isolator differs from the optical system of the free-space-type optical isolator shown in Fig. 1 in that (1) the optical fiber 116 is directly coupled to the polarizing element 111, and (2) there is only one lens. As a result, the optical path of the feedback beam 143 differs between the two, but the configuration of the optical isolator 114 is almost the same. [Example]

[0076] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the embodiments shown in the examples.

[0077] Example 1 A polarizing glass was obtained through the following steps (A) to (D): Metallic Ag particles precipitated on the surface of the obtained polarizing glass were observed by TEM.

[0078] [(A) Preparation and melting of glass raw materials] 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, melted at about 1450°C, then poured into a metal mold for shaping, and slowly cooled to room temperature. A glass substrate having the composition shown in Example 1 of 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), with the atomic weight of Ag being 107.87, the atomic weight of Cl being 35.45, and the atomic weight of Br being 79.9, the chemical equivalents of Ag, Cl, and Br were calculated respectively.

[0079] [(B) Precipitation of silver halide particles] The glass substrate obtained in (A) above was heat-treated at 704°C for about 8 hours to precipitate AgClBr particles in the glass, and then cut into a size of 120 mm in width, 250 mm in length, and 6 mm in thickness to prepare a preform.

[0080] [(C) Drawing of the glass substrate] The preform obtained in (B) above was heated in a drawing furnace and drawn with a tension of 32.0 MPa. As a result, a plurality of silver halide particles (AgClBr) contained in the glass changed from a spherical shape to an elongated shape (substantially ellipsoidal shape) extending along the drawing direction.

[0081] [(D) Reduction] The glass film with a thickness of about 0.6 mm obtained in the drawing step of (C) above was cut into a rectangle, polished to a thickness of 0.2 mm, and heat-treated in a hydrogen atmosphere at 440°C for about 7 hours to reduce the silver halide particles extended in one direction to silver particles. A polarizing glass containing metal Ag particles as orientation-dispersed shape-anisotropic metal particles was obtained on the surface layer of the glass substrate.

[0082] <Observation in TEM photograph> The surface of the obtained polarizing glass was observed with a transmission electron microscope (TEM) photograph. It was confirmed that metal Ag particles exist as orientation-dispersed shape-anisotropic metal particles on the surface of the polarizing glass.

[0083] (Comparative Example 1) A glass substrate having the composition shown in Comparative Example 1 in Table 1(1) was obtained in the same manner as in the procedure described in (A) above. 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 the glass shown in Example No. 10 of WO2007 / 119794.

[0084] The obtained 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. A polarizing glass was obtained in the same manner as in (D) above. Observation of TEM photographs similar to those in Example 1 confirmed the presence of metallic Cu particles as oriented and dispersed shape-anisotropic particles on the surface of the polarizing glass.

[0085] (Comparative Example 2) A glass substrate having the composition shown in Comparative Example 2 in Table 1(1) was obtained using the same procedure as in (A) above. Table 1(2) shows the chemical equivalents of Ag, Cl, and Br in the glass substrate. The obtained glass substrate was heat-treated using the same procedure as in (B) above and then heat-stretched using the same procedure as in (C) above. A polarizing glass was obtained using the same procedure as in (D) above. Observation of TEM photographs similar to those in Example 1 confirmed the presence of metallic Ag particles as oriented and dispersed, shape-anisotropic particles on the surface of the polarizing glass.

[0086] [Table 1(1)]

[0087] [Table 1(2)]

[0088] <Chemical durability Water resistance Dw> The water resistance Dw of the glass substrates obtained in the above (A) in Example 1 and Comparative Example 1 was evaluated. That is, powdered glass (particle size 425 - 600 μm) with a mass corresponding to the specific gravity of the glass substrate was placed in a platinum basket, which was immersed in a round-bottom quartz glass flask containing 80 mL of pure water (pH = 6.5 - 7.5), and treated in a boiling water bath for 60 minutes, and the weight loss rate (%) was calculated. The weight loss rate was 0.03% for the glass substrate of Example 1 and 0.04% or more for the glass substrate of Comparative Example 1.

[0089] <Chemical durability Acid resistance Da> The acid resistance Da of the glass substrates obtained in the above (A) in Example 1 and Comparative Example 1 was evaluated. That is, powdered glass (particle size 425 - 600 μm) with a mass corresponding to the specific gravity of the glass substrate was placed in a platinum basket, which was immersed in a round-bottom quartz glass flask containing 80 mL of 0.01 mol / L nitric acid aqueous solution and treated in a boiling water bath for 60 minutes, and the weight loss rate (%) was calculated. The weight loss rate was 0.07% for the glass substrate of Example 1 and 0.21% or more for the glass substrate of Comparative Example 1.

[0090] <Effect of reduction of photochromic properties by Nb2O5> In Example 1 and Comparative Example 2, glass substrates were produced by the procedure shown in the above (A).

[0091] The obtained glass substrates were heat-treated by the same procedure as in the above (B) and heat-stretched by the same procedure as in the above (C) to obtain glass films. The glass films were cut to a length of about 20 mm. The glass film of Comparative Example 2 and the glass film of Example 1 were arranged side by side, and mainly ultraviolet light with a wavelength of 365 nm was irradiated using an ultraviolet irradiator at an illuminance of 50 mW / cm 2 for 10 minutes. The glass films after ultraviolet irradiation are shown in Figure 3. Also, for the glass films before and after ultraviolet irradiation, the spectral transmittances at wavelengths of 400 nm, 1310 nm, and 1550 nm were measured with a spectrophotometer. The ratio of the transmittance after irradiation to the transmittance before ultraviolet irradiation is shown in Table 2.

[0092] As shown in FIG. 3, the sample of Comparative Example 2, which did not contain Nb2O5, turned black when irradiated with light, whereas the sample of Example 1 was inhibited from discoloring when irradiated with light.

[0093] [Table 2]

[0094] As shown in Table 2, in the composition containing no Nb2O5 and a low TiO2 content (Comparative Example 2), the ratio of the transmittance after UV irradiation to the transmittance before UV irradiation dropped significantly to 83% at 400 nm, a short wavelength in the visible range, whereas the composition containing Nb2O5 (Example 1) maintained a transmittance of 99%. At 1310 nm, the wavelength band used in optical communications, the ratio of the transmittance after UV irradiation to the transmittance before UV irradiation dropped to 92% in Comparative Example 2, whereas the transmittance was maintained at 100% in Example 1. At a wavelength of 1550 nm, the ratio of the transmittance after UV irradiation to the transmittance before UV irradiation dropped to 94% in Comparative Example 2, whereas the transmittance was maintained at 100% in Example 1. The inclusion of Nb2O5 significantly suppressed photochromism.

[0095] <Extinction ratio Insertion loss> An anti-reflection coating (AR coating) was applied to one side of the polarizing glass obtained in Example 1 and Comparative Example 2 to reduce the reflectance due to the refractive index of the polarizing glass. The anti-reflection coating was formed as a multilayer film consisting of a metal oxide layer, such as TiO2 or Ta2O5, and a SiO2 layer. Polarizing glass used in optical isolators is often used by bonding a 0-degree polarizing glass (a polarizing glass product cut so that the polarization transmission axis of the light component passing through the polarizing glass is parallel to the outer edge of the Faraday rotator) to one side of a Faraday element (garnet) and a 45-degree polarizing glass (a polarizing glass product cut so that the polarization transmission axis is at a 45-degree angle with the 0-degree polarizing glass) to the other side with adhesive, so only one side is often exposed to the atmosphere. For these reasons, the AR coating of the polarizing glass was applied to only one side.

[0096] A rectangular piece of polarizing glass, 0.2 mm thick and AR-coated on one side, was attached to adhesive tape that peels off when exposed to ultraviolet (UV) light, and then cut to the product size of 11 mm square. The polarizing glass was then peeled off from the adhesive tape by exposure to UV light. The extinction ratio and insertion loss of the polarizing glass were measured when the laser light source wavelength was set to 1270 nm and the distance between the polarizing glass and the detector power meter (measurement distance) was set to 5 mm, and when the laser light source wavelength was set to 1650 nm and the measurement distance was set to 300 mm. The results are shown in Table 3.

[0097] [Table 3]

[0098] In Comparative Example 2, which did not contain Nb2O5 and had a TiO2 content of 1.0%, the extinction ratio at a wavelength of 1270 nm and a measurement distance of 5 mm was 36.91 dB, which was lower than that of Example 1. Furthermore, the extinction ratio at a wavelength of 1650 nm and a distance of 300 mm in Comparative Example 2 was 53.65 dB, which was also lower than that of Example 1.

[0099] 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, which was higher than that of Example 1. It is presumed that the high insertion loss of Comparative Example 2, which did not contain Nb2O5 and had a TiO2 content of 1.0%, was due to the effects of photochromism.

[0100] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0101] For example, by adjusting the composition of the glass compositions exemplified above as described in the specification, a polarizing glass according to one aspect of the present invention can be produced. Furthermore, it is of course possible to arbitrarily combine two or more of the items described in the specification as examples or preferred ranges.

Claims

1. A polarizing glass comprising shape-anisotropic metal particles oriented and dispersed in at least a surface layer of a glass substrate, The glass substrate is, in mass %, Yes 2 50.00~60.00%, B 2 O 3 10.0~25.0%、 <h2 style=";text-align:left;direction:ltr">Al<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> O<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> 3.0~10.0%、 Li 2 O, Na 2 O, and K 2 The total content of O [Li 2 O + Na 2 O+K 2 O] 5.0 to 20.0%, ZrO 2 2.0~8.0%、 TO 2 0.1 to 5.0%, Nb 2 O 5 0.1~5.0%、 TiO 2 and Nb 2 O 5 The total content [TiO 2 +Nb 2 O 5 ] 0.2 to 10.0%, Ag, and Cl and / or Br Ag chemical equivalent or more Including, The shape-anisotropic metal particles are silver particles.

2. An optical isolator comprising the polarizing glass of claim 1.

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