Silver-containing polarizing glass and optical isolator

Abstract

To provide polarizing glass having a glass substrate that has excellent chemical durability, is suppressed from an increase of raw material cost, and is reduced in 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, comprises SiO2: 50.0 to 65.0%, B2O3: 10.0 to 22.0%, Al2O3: 5.0 to 10.0%, Li2O: 3.0% or less, Na2O: 9.0% or less, K2O: 16.0% or less, a total content of Li2O, Na2O, and K2O [Li2O+Na2O+K2O]: 6.0 to 18.0%, ZrO2: 2.0 to 8.0%, TiO2: 1.10 to 1.80%, Ag: 0.10 to 0.35%, and Cl and Br in a total chemical equivalent amount equal to or greater than 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] Polarizing glass is known to contain shape-anisotropic metallic silver particles. Ag is introduced into the glass using raw materials such as AgCl, but these raw materials are expensive. Therefore, reducing the amount of Ag introduced while maintaining the desired polarizing glass properties is a challenge.

[0004] 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 reduction in the amount of light transmitted through the polarizing glass. Such glass is called photochromic glass.

[0005] That is, there is a demand for polarizing glass that has excellent durability in various environments, that suppresses increases in raw material costs, and that has a glass substrate with reduced photochromic properties.

[0006] Patent Document 1 discloses polarizing glass containing shape-anisotropic metallic silver particles, but the Al2O3 content is low, so it is not intended for use in a variety of environments, and there is no mention of durability. Patent Document 2 discloses polarizing glass containing shape-anisotropic metallic silver particles in at least the surface layer, and Patent Document 3 discloses a polarizing material containing silver as flattened metal particles in a glass substrate, but both contain a high silver content and make no mention of reducing the amount of silver incorporated. Patent Document 4 discloses polarizing glass containing dispersed shape-anisotropic metallic silver particles, but there is no expectation that the glass substrate will discolor due to light exposure, and there is no disclosure of reducing the photochromic properties of the glass by adding a predetermined amount of TiO2 or the like. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-98349 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-150122 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-170312 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-126921 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above circumstances, and has as its object to provide polarizing glass having a glass substrate with excellent chemical durability, suppressing increases in raw material costs, and reduced photochromic properties. [Means for solving the problem]

[0009] The gist of the present invention is as follows. (1) A polarizing glass comprising shape-anisotropic metal particles oriented and dispersed in at least the surface layer of a glass substrate, The glass substrate is expressed in mass %, SiO2 50.0~65.0%, B2O3 10.0~22.0%, Al2O3 5.0~10.0%, Li2O 3.0% or less, Na2O 9.0% or less, K2O 16.0% or less, The total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is 6.0 to 18.0%; ZrO2 2.0~8.0%, TiO2 1.10~1.80%, Ag 0.10~0.35%, Total chemical equivalents of Cl and Br are equal to or greater than the chemical equivalent of Ag Including, Polarizing glass, wherein the shape-anisotropic metal particles are metallic Ag particles.

[0010] (2) The polarizing glass according to (1), wherein the glass substrate contains 1.50 to 1.80% of TiO2.

[0011] (3) An optical isolator comprising the polarizing glass described in (1) or (2) above. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide polarizing glass having a glass substrate with excellent chemical durability, suppressing increases in raw material costs, and reduced photochromic properties. [Brief explanation of the drawings]

[0013] [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 drawn glass prepared in the example. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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 %."

[0015] 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.

[0016] 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.

[0017] An embodiment of the present invention will be described below.

[0018] 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").

[0019] (glass substrate) In the glass substrate, the SiO2 content is 50.0 to 65.0%. The lower limit of the SiO2 content is preferably 51.0%, more preferably 52.0%. The upper limit of the SiO2 content is preferably 63.0%, more preferably 61.0%. By setting the SiO2 content within the above range, the chemical durability of the glass substrate can be improved. On the other hand, if the SiO2 content is too low, the chemical durability and thermal stability of the glass substrate may decrease. Furthermore, if the SiO2 content is too high, the melting temperature of the glass may increase, making melting difficult.

[0020] The glass substrate contains 10.0 to 22.0% B2O3. The lower limit of the B2O3 content is preferably 12.0%, more preferably 14.0%. The upper limit of the B2O3 content is preferably 21.0%, more preferably 20.0%. 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 satisfactorily in the 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.

[0021] In the glass base, the Al2O3 content is 5.0 to 10.0%. The lower limit of the Al2O3 content is preferably 5.5%, more preferably 6.0%. 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, and the glass may be more susceptible to crystallization.

[0022] In the glass substrate, the Li2O content is 3.0% or less. The lower limit of the Li2O content is preferably 0.0%, with 0.5% and 0.8% being more preferred. The upper limit of the Li2O content is preferably 2.8%, and more preferably 2.5%. By setting the Li2O content within the above range, silver halide particles can be favorably precipitated in the glass substrate during the heat treatment described below. On the other hand, if the Li2O content is too low, the melting property of the glass may decrease, and the glass transition temperature Tg may decrease. If the Li2O content is too high, silver halide particles may not be favorably precipitated in the glass substrate, and the glass may become thermally unstable and prone to crystallization.

[0023] In the glass substrate, the Na2O content is 9.0% or less. The lower limit of the Na2O content is preferably 0.0%, with 1.0% and 2.0% being more preferred. The upper limit of the Na2O content is preferably 8.0%, and more preferably 7.0%. By setting the Na2O content within the above range, silver halide particles can be favorably precipitated in the glass substrate during the heat treatment described below. On the other hand, if the Na2O content is too low, the melting property of the glass may decrease, and the glass transition temperature Tg may decrease. If the Na2O content is too high, silver halide particles may not be favorably precipitated in the glass substrate.

[0024] In the glass substrate, the K2O content is 16.0% or less. The lower limit of the K2O content is preferably 0.0%, with 1.0% and 3.0% being more preferred. The upper limit of the K2O content is preferably 13.0%, and more preferably 10.0%. By setting the K2O content within the above range, silver halide particles can be favorably precipitated in the glass substrate during the heat treatment described below. On the other hand, if the K2O content is too low, the melting property of the glass may decrease, and the glass transition temperature Tg may decrease. If the K2O content is too high, silver halide particles may not be favorably precipitated in the glass substrate.

[0025] In the glass substrate, the total content of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is 6.0 to 18.0%. The lower limit of this total content is preferably 7.0%, more preferably 9.0%. The upper limit of this total content is preferably 17.0%, more preferably 15.0%. 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 in the glass substrate during the heat treatment described below.

[0026] 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 glass may be more susceptible to crystallization.

[0027] The TiO2 content in the glass substrate is 1.10 to 1.80%. The lower limit of the TiO2 content is preferably 1.15%, with 1.20% and 1.25% being more preferred. The upper limit of the TiO2 content is preferably 1.75%, and more preferably 1.70%. 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. Furthermore, if the TiO2 content is too high, silver halide particles may not be precipitated well in the glass substrate during the heat treatment described below.

[0028] The glass substrate contains Ag, Cl, and Br. The Ag content in the glass substrate is 0.10 to 0.35% by mass. The lower limit of the Ag content is preferably 0.11%, more preferably 0.13%. The upper limit of the Ag content is preferably 0.30%, more preferably 0.25%. By setting the Ag content within the above range, a polarizing glass having a glass substrate with reduced increases in raw material costs can be obtained. On the other hand, if the Ag content is too low, silver halide particles may not be precipitated well in the glass substrate during the heat treatment described below. If the Ag content is too high, raw material costs may increase and insertion loss may increase. Furthermore, 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.

[0029] It is preferable that the glass substrate does not substantially contain Cu. That is, the Cu content is preferably 0%. Cu is dissolved in the glass during the heat treatment for precipitating silver halide particles. 2+ From Cu + At this time, electrons are released and Ag +There is a risk that Cu may reduce the ions to Ag metal, thereby promoting photochromism. Except for inclusion as an unavoidable impurity, the Cu content is preferably 0% in order to reduce photochromic properties.

[0030] To precipitate silver halide particles in a glass substrate by heat treatment, 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 alkali metal chlorides and bromides for replenishment. Therefore, the total chemical equivalent of Cl and Br contained in the glass substrate is equal to or 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.

[0031] As described above, the total chemical equivalent of Cl and Br contained in the glass substrate is equal to or greater than the chemical equivalent of Ag.

[0032] 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."

[0033] 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. The phrase "the total chemical equivalent of Cl and Br is equal to or greater than the chemical equivalent of Ag" means that the sum of the number of Cl atoms and the number of Br atoms contained in the glass is equal to or greater than the number of Ag atoms contained in the glass.

[0034] In the glass substrate, the total content of Cl and Br is preferably 0.05 to 2.0% by mass. Similarly, the content of Cl is preferably 0.05 to 1.0%. Similarly, the content of Br is preferably 0.0 to 1.0%, more preferably 0.05 to 1.0%.

[0035] Non-limiting examples of the content of glass components other than those described above in the glass base are shown below.

[0036] It is preferable that the glass substrate is substantially free of alkaline earth metal oxides RO (R=Mg, Ca, Sr, Ba). The alkaline earth metal oxides MgO, CaO, SrO, and BaO have the effect of increasing the basicity of the glass and preventing the reduction of silver. From the viewpoint of favorable precipitation of silver halide particles in the glass substrate in the heat treatment described below, it is preferable that the glass substrate is substantially free of alkaline earth metal oxides, except for inclusion as unavoidable impurities. Furthermore, it is preferable that BaO is substantially free of BaO, as this may reduce the chemical durability of the glass substrate.

[0037] It is preferable that the glass substrate does not substantially contain CeO2. CeO2 is a component that functions as a fining agent for glass. If the glass substrate contains CeO2, Ce 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 grains, Ag + This may cause ion reduction, resulting in the promotion of photochromism. Therefore, from the viewpoint of reducing photochromic properties, it is preferable that the glass substrate does not substantially contain CeO2, except for inclusion as an unavoidable impurity. In other words, the CeO2 content is preferably 0%.

[0038] 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.

[0039] In the glass base, the lower limit of the Nb2O5 content is preferably 0.0%, and more preferably 0.1%, 0.3%, and 0.6% in that order. The upper limit of the Nb2O5 content is preferably 5.0%, and more preferably 4.5% and 4.0% in that order. From the viewpoints of improving the meltability of the glass and suppressing coloration during glass molding, it is preferable that the Nb2O5 content be within the above range.

[0040] The glass substrate is preferably composed mainly of the above-mentioned glass components, i.e., SiO2, B2O3, Al2O3, ZrO2, TiO2, Ag, Cl, Br, Li2O, Na2O, and K2O, 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.

[0041] 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%.

[0042] 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.

[0043] (Other ingredients) 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] (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.

[0048] Water resistance Dw can be evaluated using the method specified in JOGIS 06 2019. That is, 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]

[0049] <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.

[0050] Acid resistance Da can be evaluated using the method shown in JOGIS 06 2019. That is, to evaluate acid resistance Da, powdered glass (particle size 425-600 μm) with a mass equivalent to the specific gravity is placed in a platinum cage, immersed in a quartz glass round-bottom flask containing 80 mL of 0.01 mol / L nitric acid solution, and treated 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]

[0051] (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 ratio to the dimension perpendicular to that direction (aspect ratio) is, for example, in the range of 0.5 to 20.

[0052] (Optical properties of polarizing glass) <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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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)

[0058] 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)

[0059] (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.

[0060] [(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, 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.

[0061] (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.

[0062] 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。

[0063] [(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.

[0064] [(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.

[0065] 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.

[0066] 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 the direction perpendicular to the major axis of the silver halide particles to a small size. To obtain excellent optical properties, the average size of the metallic Ag particles in the 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.

[0067] (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 free-space optical isolators and pigtail optical isolators in the wavelength band used in optical communications.

[0068] (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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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]

[0073] 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.

[0074] 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.

[0075] [(A) Preparation and melting of glass raw materials] The glass raw materials used were SiO2, H3BO3, Al(OH)3, Li2CO3, Na2CO3, K2CO3, KNO3, ZrO2, TiO2, NaCl, NaBr, and AgCl. These raw materials were placed in a 5-liter platinum crucible and melted at approximately 1450°C. The melt was then poured into a metal mold and slowly cooled to room temperature. A glass substrate was obtained.

[0076] The composition of the obtained glass substrate (after melting) is as shown in Example 1 in Table 1(1). Table 1(2) shows the chemical equivalent of Ag in the glass substrate and the total chemical equivalent of Cl and Br. In Table 1(2), the atomic weight of Ag is 107.87, the atomic weight of Cl is 35.45, and the atomic weight of Br is 79.9, and the chemical equivalents of Ag, Cl, and Br were calculated accordingly.

[0077] (B) Precipitation of Silver Halide Grains The glass substrate obtained in (A) above was heat-treated at 700°C for approximately 8 hours to precipitate AgClBr particles in the glass, and then cut into a size of 120 mm wide, 250 mm long, and 6 mm thick to prepare a preform. In Example 1, which had a TiO2 content of 1.60%, the preform exhibited a homogeneous white opacity, and silver halide particles were uniformly precipitated.

[0078] [(C) Stretching of glass substrate] The preform obtained in (B) above was heated in a drawing furnace and stretched under a tension of 33.7 MPa, which changed the shape of the silver halide particles (AgClBr) contained in the glass from spherical to elongated (approximately ellipsoidal) shapes extending in the stretching direction.

[0079] [(D) Reduction] The glass film obtained in the stretching step (C) above, approximately 0.6 mm thick, was cut into a rectangular shape, polished to a thickness of 0.2 mm, and heat-treated in a hydrogen atmosphere at 440°C for approximately 7 hours to reduce the unidirectionally stretched silver halide particles to silver particles. Polarizing glass containing metallic Ag particles as shape-anisotropic metal particles oriented and dispersed in the surface layer of the glass substrate was obtained.

[0080] <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 shape-anisotropic metal particles dispersed in orientation on the surface of the polarizing glass.

[0081] (Example 2) The preparation and melting of the (A) glass raw materials were carried out in the same manner as in Example 1 so that the composition of the glass substrate after melting would be the composition of Example 2 in Table 1(1). Table 1(2) shows the chemical equivalent of Ag in the glass substrate and the total chemical equivalent of Cl and Br.

[0082] Regarding this glass substrate, a heat treatment for the precipitation of silver halide particles in (B) was carried out in the same manner as in Example 1 to produce a preform. In Example 2 where the TiO2 content was 1.30%, the preform exhibited uniform turbidity and silver halide particles were precipitated homogeneously.

[0083] Polarizing glass was produced through the steps of (C) and (D) in the same manner as in Example 1. Observation of the TEM photograph confirmed the existence of metal Ag particles as shape-anisotropic metal particles dispersed in orientation on the surface of the polarizing glass.

[0084] (Example 3) The preparation and melting of the (A) glass raw materials were carried out in the same manner as in Example 1 so that the composition of the glass substrate after melting would be the composition of Example 3 in Table 1(1). Table 1(2) shows the chemical equivalent of Ag in the glass substrate and the total chemical equivalent of Cl and Br. <XXXXXX>[[ID=XX]]<XXXXXX> Regarding this glass substrate, a heat treatment for the precipitation of silver halide particles in (B) was carried out in the same manner as in Example 1 to produce a preform. In Example 3 where the TiO2 content was 1.80%, the preform exhibited uniform turbidity and silver halide particles were precipitated homogeneously.

[0086] Polarizing glass was produced through steps (C) and (D) in the same manner as in Example 1. TEM photographs confirmed the presence of metallic Ag particles as oriented and dispersed shape-anisotropic metal particles on the surface of the polarizing glass.

[0087] (Comparative Example 1) (A) Glass raw materials were prepared and melted in the same manner as in Example 1 so that the composition of the glass substrate after melting would be the composition of Comparative Example 1 in Table 1(1). Table 1(2) shows the chemical equivalent of Ag and the total chemical equivalent of Cl and Br in the glass substrate.

[0088] This glass substrate was subjected to heat treatment for the precipitation of silver halide particles (B) in the same manner as in Example 1 to produce a preform. This preform had some dark and light areas of opacity, and did not become homogeneously opaque. This is presumably because the TiO2 content of 1.90% was too high, preventing the silver halide particles from being uniformly precipitated during the heat treatment, and the particle size and density of the silver halide particles generated by the heat treatment became non-uniform within the preform.

[0089] Polarizing glass was produced through steps (C) and (D) in the same manner as in Example 1. TEM photographs confirmed the presence of metallic Ag particles as oriented and dispersed, shape-anisotropic particles on the surface of the polarizing glass.

[0090] (Comparative Example 2) (A) Glass raw materials were prepared and melted in the same manner as in Example 1 so that the composition of the glass substrate after melting would be the composition of Comparative Example 2 in Table 1(1). Table 1(2) shows the chemical equivalent of Ag and the total chemical equivalent of Cl and Br in the glass substrate.

[0091] This glass substrate was subjected to heat treatment (B) for the precipitation of silver halide particles in the same manner as in Example 1, to produce a preform. The preform exhibited a homogeneous opacity, with silver halide particles uniformly precipitated. Polarizing glass was produced through steps (C) and (D) in the same manner as in Example 1. TEM photographs confirmed the presence of metallic Ag particles as oriented and dispersed, shape-anisotropic particles on the surface of the polarizing glass.

[0092] [Table 1(1)]

[0093] [Table 1(2)]

[0094] <Chemical durability Water resistance Dw> In Examples 1, 2, and 3, the water resistance Dw of the glass substrates obtained in (A) above was evaluated. That is, powdered glass (particle size 425 to 600 μm) with a mass 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 to 7.5), and treated in a boiling water bath for 60 minutes. The weight loss rate (%) was then classified and evaluated into the grades shown in Table A. As a result, the water resistance Dw of the glass substrates obtained in Examples 1, 2, and 3 was all Grade 1.

[0095] <Chemical durability Acid resistance Da> In Examples 1, 2, and 3, the acid resistance Da of the glass substrates obtained in (A) above was evaluated. That is, powdered glass (particle size 425 to 600 μm) with a mass 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 0.01 mol / L nitric acid aqueous solution, and treated in a boiling water bath for 60 minutes. The weight loss rate (%) was then classified and evaluated into the grades shown in Table B. As a result, the acid resistance Da of the glass substrates obtained in Examples 1, 2, and 3 was all Grade 1.

[0096] <Extinction ratio, insertion loss> An anti-reflection coating (AR coating) was applied to one side of the polarizing glass obtained in Examples 1 to 3 and Comparative Examples 1 and 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.

[0097] 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 2.

[0098] [Table 2]

[0099] As shown in Table 2, in Comparative Example 1, which contained 1.90% TiO2, the extinction ratio at a wavelength of 1270 nm and a measurement distance of 5 mm was low, at 35 dB or less. The extinction ratio at a wavelength of 1650 nm and a measurement distance of 300 mm was also low, at 45 dB or less. The reason for the lower extinction ratio in Comparative Example 1 compared to the values ​​in Examples 1, 2, and 3 is presumably due to the TiO2 content being too high, resulting in low density of silver halide particles or small particle size in some areas, preventing uniform generation of silver halide particles and insufficient production of anisotropically shaped metallic silver particles as a result of reduction. On the other hand, the insertion loss in Comparative Example 1 was low, at 0.200 dB or less, both at a wavelength of 1270 nm and a measurement distance of 5 mm, and at a wavelength of 1650 nm and a measurement distance of 300 mm.

[0100] Next, in Example 1 with a TiO2 content of 1.60%, Example 2 with a TiO2 content of 1.30%, and Example 3 with a TiO2 content of 1.80%, the extinction ratio at a wavelength of 1270 nm and a measurement distance of 5 mm was high at 38.0 dB or more.The extinction ratio at a wavelength of 1650 nm and a distance of 300 mm was also high at 55.0 dB or more.

[0101] The insertion loss of Examples 1 and 3 was low, at 0.190 dB or less, at a measurement distance of 5 mm at a wavelength of 1270 nm. The insertion loss at a wavelength of 1650 nm and a measurement distance of 300 mm was low, at 0.198 dB.

[0102] The insertion loss of Example 2 was low at 0.198 dB at a measurement distance of 5 mm at a wavelength of 1270 nm, and low at 0.203 dB at a measurement distance of 300 mm at a wavelength of 1650 nm.

[0103] The insertion loss was lower in Examples 1 and 3 than in Example 2, presumably because the TiO2 content in Example 2 was 1.30%, which was lower than in Example 1 (1.60%) and Example 3 (1.80%).

[0104] Next, in Comparative Example 2 where the TiO2 content was 1.00%, the extinction ratio at a measurement distance of 5 mm at a wavelength of 1270 nm was 37 dB or less, which was lower than that of Example 1, Example 2, and Example 3. Also, the extinction ratio at a distance of 300 mm at a wavelength of 1650 nm was also 55 dB or less, which was lower than that of Example 1, Example 2, and Example 3.

[0105] The insertion loss of Comparative Example 2 was 0.241 dB at a measurement distance of 5 mm at a wavelength of 1270 nm, which was higher than that of Example 1, Example 2, and Example 3. The insertion loss at a distance of 300 mm at a wavelength of 1650 nm was 0.232 dB, which was higher than that of Example 1, Example 2, and Example 3. In Comparative Example 2 where the TiO2 content was 1.00%, it is presumed that the insertion loss increased because the amount of TiO2 was small and the effect of suppressing photochromism was small.

[0106] From the above, in Example 3 where the TiO2 content was 1.80%, the preform made from the glass substrate exhibited uniform cloudiness, and the silver halide particles were deposited uniformly. The extinction ratio of the polarizing glass produced in Example 3 was high and within a preferable range. Similarly, in Example 1 where the TiO2 content was 1.60% and Example 2 where the TiO2 content was 1.30%, preforms with uniform cloudiness were obtained, and their extinction ratios were high and within a preferable range. From the above findings, it was confirmed that in a glass substrate for polarizing glass for producing a preform with uniformly deposited silver halide particles and obtaining a preferable extinction ratio, the TiO2 content is preferably 1.80% or less.

[0107] <Effect of reducing photochromic properties by TiO2 content> The glass film obtained by stretching the glass substrate of (C) in Comparative Example 2 and the glass film obtained by stretching the glass substrate of (C) in Example 1 were placed side by side and left under a fluorescent lamp at the same time. A photograph about 9 days after the start of leaving under the fluorescent lamp is shown in Fig. 3.

[0108] As shown in FIG. 3, the composition with a low TiO2 content (Comparative Example 2) turned black when irradiated with fluorescent light, while the composition of Example 1 was inhibited from discoloring when irradiated with fluorescent light.

[0109] Next, the glass film obtained by stretching the glass substrate (C) of Comparative Example 2 and the glass film obtained by stretching the glass substrate (C) of Example 1 were cut into lengths of approximately 20 mm. These glass films were irradiated with ultraviolet light mainly having a wavelength of 365 nm at 50 mW / cm using an ultraviolet irradiator. 2 The glass film was irradiated with UV light for 10 minutes at an illuminance of 1000 nm. The spectral transmittance of the glass film at wavelengths of 400 nm, 1310 nm, and 1550 nm was measured using a spectrophotometer before and after UV irradiation. The ratio of the transmittance after irradiation to the transmittance before irradiation is shown in Table 3.

[0110] [Table 3]

[0111] As shown in Table 3, in the composition with 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 transmittance was maintained at 97% in the composition with a high TiO2 content (Example 1). 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 99% 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. By increasing the TiO2 content, photochromism was significantly suppressed.

[0112] 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.

[0113] 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 50.00~65.00%, B 2 O 3 10.0~22.0%、 <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"> 5.0~10.0%、 Li 2 0 3.0% or less, Na 2 O 9.0% or less, K 2 O Below 16.0%, Li 2 O, Na 2 O, and K 2 The total content of O [Li 2 O + Na 2 O+K 2 O] 6.0 to 18.0%, ZrO 2 2.0~8.0%、 TO 2 1.10 to 1.80%, Ag 0.10-0.35%, Total chemical equivalent of Cl and Br Not less than the chemical equivalent of Ag Including, The shape-anisotropic metal particles are silver particles.

2. The glass substrate is TiO 2 2. The polarizing glass according to claim 1, wherein the content is 1.50 to 1.80%.

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

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