SILVER-CONTAINING POLARIZING GLASS AND OPTICAL INSULATOR

Abstract

A polarizing glass contains shape-anisotropic metal particles that are aligned and dispersed in at least one surface layer of a glass substrate. The glass substrate contains, in mass %, 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, total amount 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 a total chemical equivalent of Cl and Br: equal to or greater than a chemical equivalent of Ag. The shape-anisotropic metal particles are metallic Ag particles.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a polarizing glass used in an optical component such as an optical isolator or the like, particularly to a polarizing glass containing shape-anisotropic metallic silver particles.

[0002] An optical isolator has the function of transmitting only light in a forward direction and blocking light in a reverse direction. Polarizing glass is an optical glass that transmits only light oscillating in a specific direction (polarized light) and is an optical component used in optical isolators and the like. Currently, optical isolators are used in a wide variety of environments, and excellent durability is required for polarizing glass.

[0003] A polarizing glass containing shape-anisotropic metallic silver particles is known. To incorporate Ag into the glass, a raw material such as AgCl is used, but this is expensive. Therefore, the challenge is to reduce the amount of Ag incorporated while maintaining the desired properties of the polarizing glass.

[0004] Furthermore, the function of the polarizing glass may be impaired if the glass serving as the substrate becomes discolored due to light irradiation or similar factors. In particular, a phenomenon known as photochromism occurs, in which the glass substrate darkens upon exposure to ultraviolet light or short-wavelength visible light, and the amount of light passing through the polarizing glass decreases, which poses a problem. Such glass is called glass with photochromic properties.

[0005] Thus, a polarizing glass containing a glass substrate that has excellent durability in a variety of environments, suppresses an increase in raw material costs, and has reduced photochromic properties is needed.

[0006] Patent Document 1 discloses a polarizing glass containing shape-anisotropic metallic silver particles; however, the amount of Al2O3 is small, the polarizing glass is not expected to be used in a variety of environments, and durability is not addressed. Furthermore, Patent Document 2 discloses a polarizing glass containing shape-anisotropic metallic silver particles in at least one surface layer of the polarizing glass, and Patent Document 3 discloses a polarizing material containing silver in the form of flattened metallic particles in a glass substrate. However, in both cases, the amount of silver is high, and there is no mention of reducing the amount of silver incorporated.Furthermore, Patent Document 4 discloses a polarizing glass containing dispersed shape-anisotropic metallic silver particles; however, it is not assumed that a glass substrate is discolored due to light irradiation or the like, and there is no disclosure about reducing the photochromic properties of a glass by containing a predetermined amount of TiO2 or the like. CITATION LISTPATENT SPECIFICATION Patent Document 1: JP 2003-98349 A Patent Document 2: JP 2010-150122 A Patent Document 3: JP 2011-170312 A Patent Document 4: JP 2013-126921 A SUMMARY OF THE INVENTION

[0007] The present invention has been made in view of these circumstances, and an object of the present invention is to provide a polarizing glass including a glass substrate having excellent chemical resistance, suppressing an increase in raw material costs, and having reduced photochromic properties.

[0008] The concept of the present invention is as follows.

[0009] (1) A polarizing glass contains shape-anisotropic metal particles aligned and dispersed in at least one surface layer of a glass substrate. The glass substrate contains, in mass%, 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, total amount 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 a total chemical equivalent of Cl and Br: equal to or greater than a chemical equivalent of Ag. The shape-anisotropic metal particles are metallic Ag particles.

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

[0011] (3) An optical isolator contains the polarizing glass according to (1) or (2).

[0012] According to the present invention, a polarizing glass can be provided which has a glass substrate with excellent chemical resistance, suppresses an increase in raw material costs, and has reduced photochromic properties. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic side cross-sectional view showing an optical system of a free-space optical isolator; Fig. 2 is a schematic side cross-sectional view showing an optical system of a pigtail optical isolator; and Fig. Figure 3 is a photograph showing the degree of discoloration of a drawn glass produced in the example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In the present invention and this specification, an oxide-based glass composition is expressed unless otherwise specified. Here, the "oxide-based glass composition" refers to a glass composition obtained by converting all glass raw materials into oxides present in the glass after they are completely decomposed during melting, and each glass component is expressed as SiO2, TiO2, or the like in accordance with the notation convention. Furthermore, the elements Ag, Cl, and Br, which relate to polarization properties, are expressed as elements rather than oxides. The amount and total amount of the glass components are based on mass unless otherwise specified, and "%" means "mass%."

[0014] The amount of each glass component can be quantified by a known method, such as inductively coupled plasma atomic emission spectroscopy (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), or the like. Furthermore, in this specification and the present invention, the amount of a component that is 0% means that the component is substantially absent, and the component may be present in an unavoidable impurity level.

[0015] In this description, the chemical resistance of glass refers to its excellent resistance to water and acids. Furthermore, the thermal stability of glass refers to the difficulty of depositing crystals other than silver halide particles when molten glass solidifies.

[0016] An embodiment of the present invention will be described below.

[0017] A polarizing glass according to the present embodiment comprises a glass substrate and contains shape-anisotropic metal particles aligned and dispersed in at least one surface layer of the glass substrate. The polarizing glass has the function of transmitting polarized light in a specific vibration direction (referred to as the "polarization transmission axis") and absorbing polarized light in a direction orthogonal to the specific vibration direction (referred to as the "polarization extinction axis"). (glass substrate)

[0018] In the glass substrate, the amount of SiO2 is 50.0 to 65.0%. The lower limit of the amount of SiO2 is preferably 51.0%, and more preferably 52.0%. The upper limit of the amount of SiO2 is preferably 63.0%, and more preferably 61.0%. The chemical resistance of the glass substrate can be improved by adjusting the amount of SiO2 within the above-described range. Conversely, if the amount of SiO2 is too small, the chemical resistance and thermal stability of the glass substrate may decrease. In addition, if the amount of SiO2 is too high, the melting temperature of the glass may rise, and the glass may become difficult to melt.

[0019] In the glass substrate, the amount of B2O3 is 10.0 to 22.0%. The lower limit of the amount of B2O3 is preferably 12.0%, and more preferably 14.0%. The upper limit of the amount of B2O3 is preferably 21.0%, particularly preferably 20.0%. The chemical resistance of the glass substrate can be improved by adjusting the amount of B2O3 within the above-described range. If the amount of B2O3 is too low, the fusibility of the glass may decrease, and silver halide particles may not favorably settle in the glass substrate during the heat treatment described later. Furthermore, if the amount of B2O3 is too high, the chemical resistance of the glass substrate may decrease.

[0020] In the glass substrate, the proportion of Al2O3 is 5.0 to 10.0%. The lower limit of the amount of Al2O3 is preferably 5.5%, and more preferably 6.0%. The upper limit of the Al2O3 content is preferably 9.0%, and more preferably 8.0%. The chemical resistance of the glass substrate can be improved by adjusting the amount of Al2O3 within the above-described range. Conversely, if the amount of Al2O3 is too low, the chemical resistance of the glass substrate may significantly decrease. If the amount of Al2O3 is too high, the fusibility of the glass may decrease, and the glass may be prone to crystallization.

[0021] In the glass substrate, the amount of Li2O is 3.0% or less. The lower limit of the amount of Li2O is preferably 0.0%, and more preferably 0.5% and 0.8% in that order. Furthermore, the upper limit of the amount of Li2O is preferably 2.8%, and more preferably 2.5%. Silver halide particles can be favorably deposited in the glass substrate during the heat treatment to be described later if the amount of Li2O is adjusted within the range described above. If the amount of Li2O is too small, the fusibility of the glass may decrease and the glass transition temperature Tg may lower. If the amount of Li2O is too large, the silver halide particles cannot favorably deposit in the glass substrate, and the glass substrate may become thermally unstable and prone to crystallization.

[0022] In the glass substrate, the amount of Na2O is 9.0% or less. The lower limit of the amount of Na2O is preferably 0.0%, and more preferably 1.0% and 2.0% in that order. Furthermore, the upper limit of the amount of Na2O is preferably 8.0%, and more preferably 7.0%. Silver halide particles can be favorably deposited in the glass substrate during the heat treatment to be described later if the amount of Na2O is set within the range described above. If the amount of Na2O is too low, the fusibility of the glass may decrease and the glass transition temperature Tg may lower. In addition, if the amount of Na2O is too high, the silver halide particles may not deposit well in the glass substrate.

[0023] In the glass substrate, the amount of K2O is 16.0% or less. The lower limit of the amount of K2O is preferably 0.0%, and more preferably 1.0% and 3.0% in that order. Further, the upper limit of the amount of K2O is preferably 13.0%, and more preferably 10.0%. Silver halide particles can be advantageously deposited in the glass substrate during the heat treatment to be described later if the amount of K2O is set within the range described above. If the amount of K2O is too low, the fusibility of the glass may decrease and the glass transition temperature Tg may lower. In addition, if the amount of K2O is too high, the silver halide particles may not advantageously deposit in the glass substrate.

[0024] In the glass substrate, the total amount of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is 6.0 to 18.0%. The lower limit of the total amount is preferably 7.0%, and more preferably 9.0%. Furthermore, the upper limit of the total amount is preferably 17.0%, and more preferably 15.0%. The chemical resistance of the glass substrate can be improved by adjusting the total amount within the above-described range. In particular, the chemical resistance of the glass substrate can be improved by containing two or more alkali metals. However, if the total amount is too small, the fusibility of the glass may decrease. Furthermore, if the total amount is too large, the silver halide particles may not advantageously settle in the glass substrate during the heat treatment to be described later.

[0025] In the glass substrate, the ZrO2 content is 2.0 to 8.0%. The lower limit of the ZrO2 amount is preferably 2.5%, and more preferably 3.0%. The upper limit of the ZrO2 amount is preferably 7.7%, and more preferably 7.0%. The chemical resistance of the glass substrate can be improved by adjusting the ZrO2 amount within the above-described range. Conversely, if the ZrO2 amount is too small, the chemical resistance of the glass substrate may significantly decrease. If the ZrO2 amount is too high, the fusibility of the glass may decrease, and the glass may become more susceptible to crystallization.

[0026] In the glass substrate, the amount of TiO2 is 1.10 to 1.80%. The lower limit of the amount of TiO2 is preferably 1.15%, and more preferably 1.20% and 1.25% in that order. The upper limit of the amount of TiO2 is preferably 1.75%, and more preferably 1.70%. TiO2 is a glass component that contributes to improving the chemical resistance of the glass and absorbs light well from the near ultraviolet to the visible short wavelengths. Therefore, the polarizing glass containing the glass substrate with improved chemical resistance and reduced photochromic properties can be obtained by adjusting the amount of TiO2 within the above-described range. If the amount of TiO2 is too low, the chemical resistance of the glass substrate may decrease and the photochromic properties of the glass substrate may increase.In addition, if the amount of TiO2 is too high, the silver halide particles cannot advantageously settle in the glass substrate during the heat treatment described later.

[0027] The glass substrate contains Ag, Cl, and Br. The amount of Ag in the glass substrate is 0.10 to 0.35 mass%. The lower limit of the amount of Ag is preferably 0.11%, and more preferably 0.13%. Further, the upper limit of the amount of Ag is preferably 0.30%, and more preferably 0.25%. The polarizing glass including the glass substrate, in which an increase in raw material cost is suppressed, can be obtained by adjusting the amount of Ag within the range described above. However, if the amount of Ag is too small, the silver halide particles cannot advantageously deposit in the glass substrate during the heat treatment to be described later.In addition, if the Ag content is too high, the raw material cost may increase and the insertion loss may increase, and when the glass is melted and cooled, silver halide particles may be deposited in the glass, and the particle size of the silver halide particles may be difficult to control.

[0028] Furthermore, it is advantageous that the glass substrate contains essentially no Cu. It is preferable that the amount of Cu be 0%. The valence of Cu changes from Cu in the glass. 2+ to Cu + during the heat treatment to deposit silver halide particles, and at this time electrons are released and Ag + Ions are reduced to Ag metal, which can promote photochromism. Besides being an unavoidable impurity, it is desirable that the amount of Cu be 0% to reduce the photochromic properties.

[0029] To deposit silver halide particles in the glass substrate by heat treatment, Ag is added to the raw materials for the glass substrate, for example, in the form of AgCl and AgBr. However, since AgBr is a hazardous substance, AgBr must be handled with care, and from an environmental perspective, it is preferable not to use AgBr. Since Cl and Br are likely to volatilize during glass melting, they are added in excess as alkali metal chlorides or bromides for make-up. 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. Preferably, the amount of Cl and Br added in excess is adjusted depending on the glass melting process or scale.

[0030] As described above, the total chemical equivalent contained in the glass substrate is equal to or greater than the chemical equivalent of Ag.

[0031] The Iwanami Dictionary of Physics and Chemistry (5th edition) defines chemical equivalent as "a given amount of an element (simple substance) or compound determined based on its chemical reactivity. It is also simply referred to as equivalent." The chemical equivalent of an element is also defined as follows: "If the mass of an element that combines with 7.999 g of oxygen (equivalent to 1 / 2 mol of oxygen atoms) is W g, 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 by using a suitable element other than oxygen as an intermediary."

[0032] In the present embodiment, the chemical equivalent of Ag, Cl, or Br corresponds to the chemical equivalent of the element according to the above description in "Iwanami Dictionary of Physics and Chemistry." Thus, the chemical equivalent of Cl is the amount of Cl, expressed in mass%, divided by the atomic weight of Cl, the chemical equivalent of Br is the amount of Br, expressed in mass%, divided by the atomic weight of Br, and the chemical equivalent of Ag is the amount of Ag, expressed in mass%, divided by the atomic weight of Ag. Therefore, if the chemical equivalent of Cl and / or Br is equal to or greater than the chemical equivalent of Ag, it 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 contained in the glass.

[0033] In the glass substrate, the total amount of Cl and Br is preferably 0.05 to 2.0 mass%. Likewise, the amount of Cl is preferably 0.05 to 1.0%. Similarly, the amount of Br is preferably 0.0 to 1.0%, and more preferably 0.05 to 1.0%.

[0034] The following are non-limiting examples of the amounts of glass components other than those described above in the glass substrate.

[0035] It is preferable that the glass substrate substantially contains no alkaline earth metal oxides RO (R = Mg, Ca, Sr, and Ba). MgO, CaO, SrO, and BaO, which are alkaline earth metal oxides, have the effect of increasing the basicity of the glass and preventing the reduction of silver. From the viewpoint of favorable deposition of silver halide particles in the glass substrate during the heat treatment to be described later, it is preferable that the glass substrate substantially contains no alkaline earth metal oxides unless they are contained as unavoidable impurities. Furthermore, since BaO can reduce the chemical resistance of the glass substrate, it is preferable that BaO is substantially absent.

[0036] It is preferable that the glass substrate contains essentially no CeO2. CeO2 is a component that acts as a refining agent for glass. When the glass substrate contains CeO2, the states of Ce 4+-ions and Ce 3+ -ions in the glass and normally serve to maintain the oxidation state of Ag + -ions; however, since the equilibrium of the valence state changes slightly depending on the temperature, Ag + -ions are conversely reduced during the heat treatment for deposition of silver halide particles, which can promote photochromism. Therefore, from the perspective of reducing photochromic properties, it is preferable that the glass substrate contain essentially no CeO2 unless it is present as an unavoidable impurity. Preferably, the CeO2 content is 0%.

[0037] In the glass substrate, the lower limit of the amount of ZnO is preferably 0.0%. The amount of ZnO may be 0.0%. Further, the upper limit of the amount of ZnO is preferably 5.0%, and more preferably 3.0%. From the viewpoint of improving the thermal stability of the glass, it is preferable that the amount of ZnO be within the above-described range.

[0038] In the glass substrate, the lower limit of the amount of Nb2O5 is preferably 0.0%, and more preferably 0.1%, 0.3%, and 0.6% in this order. Furthermore, the upper limit of the amount of Nb2O5 is preferably 5.0%, and more preferably 4.5% and 4.0% in this order. From the viewpoint of improving the meltability of the glass and suppressing coloration during glass forming, it is preferable that the amount of Nb2O5 be within the above-described range.

[0039] Preferably, the glass substrate consists mainly of the above-described glass components, namely SiO2, B2O3, Al2O3, ZrO2, TiO2, Ag, Cl, Br, Li2O, Na2O and K2O, and the total amount of the above-described glass components is preferably 95% or more, more preferably 98% or more, more preferably 99% or more, and even more preferably 99.5% or more.

[0040] The glass substrate consists mainly of an oxide. The main anion component in the glass substrate is O, and the glass substrate may also contain traces of Cl and Br. The glass substrate may contain F as an anion component other than O, Cl, and Br. The amount of F in the glass substrate is preferably 0.5% or less, and more preferably 0.0%.

[0041] Preferably, the glass substrate consists essentially of the glass components described above, but may also contain other components as long as the other components do not impair the influences and effects of the present invention. Furthermore, the present invention does not preclude the inclusion of unavoidable impurities. (Other components)

[0042] Pb is a toxic component and a concern due to its environmental impact. Therefore, it is preferable that the glass substrate contains essentially no Pb. In particular, it is desirable that the amount of Pb be 0% when converted to an oxide.

[0043] Cd, As, Th and the like are components that are of concern due to their environmental impact.

[0044] Therefore, the amount of CdO, ThO2 and As2O3 is preferably 0 to 0.1%, more preferably 0 to 0.05%, more preferably 0 to 0.01%, and even more preferably CdO, ThO2 and As2O3 are substantially not contained.

[0045] It is preferable that the glass substrate does not contain any coloring elements. Examples of the coloring elements include Co, Ni, Fe, Cr, Eu, Nd, Er, and the like. Each of these elements is preferably contained in an amount of less than 100 ppm by mass, more preferably in an amount of 0 to 80 ppm by mass, more preferably in an amount of 0 to 50 ppm by mass or less, and even more preferably substantially not contained.

[0046] Furthermore, Ga, Te, Tb, and the like are expensive components that do not need to be incorporated. Therefore, the range of the amount of Ga2O3, TeO2, and TbO2, expressed in mass %, is preferably 0 to 0.1%, more preferably 0 to 0.05%, better 0 to 0.01%, even better 0 to 0.005%, even better 0 to 0.001%, and most preferably Ga2O3, TeO2, and TbO2 are substantially not included. (Properties of glass substrate)<Chemische Beständigkeit: Wasserresistenz Dw>

[0047] The glass substrate preferably has a water resistance Dw of class 3 or higher, more preferably class 2 or higher, and even more preferably class 1.

[0048] The water resistance Dw can be assessed according to the method described in JOGIS 06:2019. The water resistance Dw is determined by placing powdered glass (particle size 425 to 600 µm) with a mass corresponding to the specific gravity into a platinum basket, immersing the platinum basket in a round-bottomed glass quartz flask containing 80 ml of pure water (pH = 6.5 to 7.5), treating the powdered glass in a boiling water bath for 60 minutes, and classifying the powdered glass into the classes in Table A according to the mass loss rate (%). [Table A] Class Mass loss (%) 1 less than 0.05% 2 0.05% or more but less than 0.10% 3 0.10% or more, but less than 0.25% 4 0.25% or more but less than 0.60% 5 0.60% or more but less than 1.10% 6 1.10% or more <Chemische Beständigkeit: Säureresistenz Da>

[0049] The glass substrate has an acid resistance Da which preferably corresponds to class 3 or higher, more preferably class 2 or higher, and even more preferably class 1.

[0050] Acid resistance Da can be assessed according to the method described in JOGIS 06:2019. Acid resistance Da is assessed by placing powdered glass (particle size 425 to 600 µm) with a mass corresponding to the specific gravity into a platinum basket, immersing the platinum basket in a round-bottomed glass quartz flask containing 80 ml of a 0.01 mol / L nitric acid solution, treating the powdered glass in a boiling water bath for 60 minutes, and classifying the powdered glass into the classes in Table B according to the mass loss rate (%). [Table B] Class Mass loss (%) 1 less than 0.20% 2 0.20% or more, but less than 0.35% 3 0.35% or more, but less than 0.65% 4 0.65% or more but less than 1.20% 5 1.20% or more but less than 2.20% 6 2.20% or more (shape anisotropic metal particles)

[0051] The polarizing glass according to the present embodiment contains shape-anisotropic metal particles aligned and dispersed at least in the surface layer of the glass substrate, and the shape-anisotropic metal particles are metallic Ag particles. In the polarizing glass according to the present embodiment, the surface layer containing the shape-anisotropic silver particles forms a part including the surface of the glass substrate or the entirety of the glass substrate, and the thickness of the surface layer is, for example, 20 to 100 μm. Furthermore, the dimension of the shape-anisotropic metallic silver particles in a direction along the major axis of the silver halide particles is, for example, in a range of 10 to 1000 nm, and the ratio of the dimension to a dimension in a direction perpendicular to this direction (aspect ratio) is, for example, in a range of 0.5 to 20. (Optical properties of polarizing glass)<Extinktionsverhältnis und Einfügedämpfung>

[0052] The optical properties required for polarizing glass are generally a high extinction ratio and low insertion loss. The "extinction ratio" is the ratio of the transmittance of light in a direction parallel to the polarization extinction axis to light in a direction parallel to the polarization transmission axis. The higher the extinction ratio, the better the optical properties. The unit is dB. Furthermore, "insertion loss" refers to the loss suffered by light parallel to the polarization transmission axis during transmission through a polarizing element. The lower the insertion loss, the better the optical properties. The unit is dB.

[0053] As shown in Japanese Patent No. 4642921, in which the present inventor is named as the inventor, Fig. As shown in Figure 13, when the distance (measurement distance) between a polarizing glass and a detector's power meter is only 5 mm, a detector receives light re-emitted from the polarizing glass, so the extinction ratio decreases by the amount of re-emitted light. When the measurement distance is 300 mm, the detector is less likely to receive light re-emitted from the polarizing glass, so the extinction ratio becomes high. Therefore, when the distance between the polarizing glass and the power meter is short, the extinction ratio becomes low, and when the distance is long, the extinction ratio becomes high. The insertion loss is independent of the measurement distance; it is an essentially constant value.

[0054] In the polarizing glass according to the present embodiment, the extinction ratio for light with a wavelength of 1270 nm at a measurement distance of 5 mm is preferably 38.0 dB or more, and more preferably 38.2 dB or more. Furthermore, the extinction ratio for light with a wavelength of 1650 nm at a measurement distance of 300 mm is preferably 55.0 dB or more, and more preferably 56.0 dB or more.

[0055] In the polarizing glass according to the present embodiment, when an anti-reflection film is applied to a surface of the polarizing glass, the insertion loss for light having a wavelength of 1270 nm at a measuring distance of 5 mm is preferably 0.204 dB or less, and the insertion loss for light having a wavelength of 1650 nm at a measuring distance of 300 mm is preferably 0.204 dB or less.

[0056] The extinction ratio and insertion loss of the polarizing glass can be measured as follows. A semiconductor laser light source and a Glan-Thompson prism are arranged on one side of the polarizing glass, and a detector (power meter) is arranged on the other side of the polarizing glass. The Glan-Thompson prism is used to obtain a linearly polarized wave in a specific direction.

[0057] The extinction ratio is determined using the following equation by rotating the polarizing glass to measure a minimum amount of transmitted light P1 and rotating the polarizing glass 90 degrees to measure a maximum amount of transmitted light P2. Extinction ratio(dB)=−10Log(P1 / P2)

[0058] The insertion loss is determined using the following equation by measuring a quantity of light P0 in a state without polarizing glass. Insertion loss(dB)=−10Log(P2 / P0) (Method for producing a polarizing glass)

[0059] A method for producing a polarizing glass according to the present embodiment is roughly divided into the steps of (A) mixing and melting glass raw materials, (B) depositing silver halide particles, (C) drawing a glass substrate material, and (D) reduction. [(A) Mixing and melting of glass raw materials]

[0060] The glass raw materials are mixed. Examples of glass raw materials include SiO2, H3BO3, Al(OH)3, Li2CO3, Na2CO3, K2CO3, KNO3, ZrO2, TiO2, NaCl, NaBr, and AgCl. The glass raw materials are placed in a platinum crucible and melted at approximately 1300°C to 1500°C. The glass raw materials are then molded and slowly cooled to room temperature to obtain a glass substrate material. [(B) Deposition of silver halide particles]

[0061] The glass substrate material obtained above (A) is heat-treated at a temperature of 650°C to 800°C for about several to 20 hours (preferably about 4 to 10 hours). To form silver halide particles of a suitable size, it is generally preferable that the heat treatment be carried out at a high temperature for a short heat treatment time, and the heat treatment be carried out at a relatively low temperature for a long heat treatment time.

[0062] If the glass contains AgCl as the silver halide, the heat treatment described above causes Cl, Br, and Ag ions to aggregate, and AgClBr particles are deposited in a liquid state. In the subsequent cooling step, when the temperature of the glass drops close to the glass transition temperature (Tg), for example, to about 500°C, the glass is maintained in a glassy state. Even in this state, AgClBr exists in a liquid state; however, if the temperature of the glass drops further and falls below the melting point of AgClBr, which is between 420 and 460°C, AgClBr transforms into a solid state. The deposited silver halide particles (AgClBr) are not confined, but they form essentially spherical bodies. Incidentally, AgClBr is strictly speaking AgCl. (x) Br (1-x) (0 < x <1). (C) Drawing of glass substrate material]

[0063] The glass substrate material in which the silver halide particles are deposited is heated and drawn unidirectionally. The heating temperature in the drawing step can be set, for example, to 550°C to 650°C, and the drawing force in the drawing step can be set to approximately 25 MPa to 50 MPa. AgClBr changes from a solid state to a liquid state through heating and drawing, and undergoes a phase transition back to the solid state when the temperature drops below the melting point of AgClBr. The drawing step forces all the silver halide particles into a shape that is essentially elongated in the same direction. [(D) Reduction]

[0064] The glass substrate material, in which the silver halide particles are unidirectionally elongated, is reduced to obtain a polarizing glass. The reduction step is carried out at a temperature equal to or lower than the glass transition temperature (Tg), for example, in a hydrogen atmosphere. Therefore, the silver halide particles are reduced to metallic Ag particles, while the glass structure retains a glassy state.

[0065] In the reduction step, the region of the silver halide particles that elongates unidirectionally is maintained and becomes a cavity, and one or more divided, shape-anisotropic metallic Ag particles are formed in the cavity.

[0066] If the deposition temperature is increased in the above-described step (B), the volume of the silver halide particles to be deposited increases, and it becomes difficult to control the dimension of the metallic Ag particles obtained by reducing the silver halide particles in a direction perpendicular to a direction along the major axis of the silver halide particles to be small. To obtain excellent optical properties, the average value of the dimension of the metallic Ag particles in the direction perpendicular to the direction along the major axis of the silver halide particles is preferably 20 nm or less. To suppress an increase in the volume of the silver halide particles to be deposited, the temperature can be set in a range of 690°C to 710°C during the heat treatment during the deposition step (B), for example, when the heat treatment time is 8 hours. (Application)

[0067] The polarizing glass according to the present embodiment can be used for any optical device that uses a polarizing glass, and there are no particular restrictions on its application. For example, the polarizing glass according to the present embodiment can be used as a polarizing glass for free-space optical isolators and pigtail optical isolators in wavelength bands used in optical communications. (Optical isolator)

[0068] An optical isolator has the function of transmitting only forward-traveling light and blocking backward-traveling light. An optical isolator according to the present embodiment includes the polarizing glass described above. The optical isolator is not particularly limited, but a free-space optical isolator and a pigtail optical isolator can be cited as examples.

[0069] Fig. Figure 1 is a schematic side cross-sectional view schematically showing an optical system of the free-space optical isolator. Fig.1, reference numerals 111 and 112 denote polarizing elements, reference numeral 113 denotes a Faraday rotator, reference numeral 114 denotes an optical isolator consisting of the polarizing elements 111 and 112 and the Faraday rotator 113, reference numerals 115 and 115' denote lenses, reference numeral 116 denotes an optical fiber, reference numeral 117 denotes a light source such as a semiconductor laser, reference numerals 118 and 118' denote groups of lines schematically showing the luminous flux of the light returning to the light source 117, and in particular, reference numeral 118' denotes the luminous flux after the returning light has passed through the polarizing element 112. The polarizing glass according to the present embodiment can be used in the form of the polarizing elements 111 and 112. In the Fig.In the optical isolator 114 shown in Figure 1, the polarization transmission axes of the polarizing elements 111 and 112 are arranged to form an angle of 45 degrees with each other, and the optical path length of the optical isolator 114 is set so that the rotation angle of the polarization plane of the Faraday rotator 113 is 45 degrees. In such a configuration, a luminous flux emitted by the light source 117 (not shown) is converted into a parallel luminous flux by the lens 115', and only light with a polarization in a direction parallel to the polarization transmission axis of the polarizing element 112 is incident on the Faraday rotator 113. The polarization direction of the light incident on the Faraday rotator 113 is rotated by 45 degrees due to the Faraday effect caused by a permanent magnet (not shown).Since, as described above, the polarization transmission axes of the polarizing elements 111 and 112 form an angle of 45 degrees with each other, the polarization direction of the light that has passed through the Faraday rotator 113 coincides with the polarization transmission axis of the polarizing element 111. Therefore, the light that has passed through the Faraday rotator 113 is transmitted through the polarizing element 111 with essentially no loss, collimated by the lens 115, and incident on the optical fiber 116.

[0070] The returning luminous flux 118 reflected by the optical fiber 116 or an optical element or the like (not shown) arranged behind the optical fiber 116 returns to the light source 117 via an optical path opposite to the above-described optical path of the luminous flux emitted from the light source 117; however, in this case, due to the non-reciprocity of the Faraday rotator 113, the polarization direction of the returning luminous flux 118, after the returning luminous flux passes through the Faraday rotator 113, forms an angle of 90 degrees with the polarization transmission axis of the polarizing element 112 (hereinafter, the axis in this direction is referred to as the "polarization extinction axis"), so that the optical energy of the returning luminous flux 118 is largely lost when passing through the polarizing element 112.

[0071] In addition, in recent years, due to the demand for miniaturization of optical components, a so-called optical pigtail isolator has become established. Fig. Figure 2 is a schematic side cross-sectional view schematically showing an optical system of the optical pigtail isolator. In Fig. In Figure 2, reference numeral 141 denotes a shape-anisotropic metal particle contained in the polarizing element 111, reference numeral 142 denotes an arrow schematically showing the propagation direction of the scattered light, and reference numeral 143 denotes the optical path of the returning light flux. The polarizing glass according to the present embodiment can also be used in the pigtail optical isolator in the form of the polarizing elements 111 and 112.

[0072] The optical system of the optical pigtail isolator is different from that in Fig.1 in that (1) the optical fiber 116 is directly coupled to the polarizing element 111 and (2) only one lens is present. As a result, the optical path of the returning light flux 143 is different for both isolators; however, the configuration of the optical isolator 114 is essentially the same. EXAMPLES

[0073] The present invention will be described in more detail below using examples. However, the present invention is not limited to the embodiments illustrated in the examples. (Example 1)

[0074] A polarizing glass was obtained by the following steps (A) to (D). Metallic Ag particles deposited on the surface of the obtained polarizing glass were examined by TEM. [(A) Mixing and melting of glass raw materials]

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

[0076] The composition of the resulting glass substrate (after melting) corresponds to 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. In Table 1(2), the chemical equivalents of Ag, Cl, and Br were calculated based on 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. (B) Deposition of silver halide particles]

[0077] The glass substrate obtained in step (A) above was heat-treated at 700°C for about 8 hours to deposit AgClBr particles in the glass, and then cut to a size of 120 mm wide, 250 mm long, and 6 mm thick to produce a preform. In Example 1, where the amount of TiO2 was 1.60%, the preform exhibited a homogeneous white haze, and the silver halide particles were homogeneously deposited. (C) Drawing of glass substrate material]

[0078] The preform obtained in step (B) above was heated in a drawing furnace and drawn with a tensile force of 33.7 MPa. Accordingly, a plurality of silver halide particles (AgClBr) contained in the glass changed from a spherical shape to an elongated shape (substantially ellipsoidal shape) elongated along a drawing direction. [(D) Reduction]

[0079] A glass film with a thickness of approximately 0.6 mm obtained in the above-described drawing step (C) 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 drawn silver halide particles to silver particles. A polarizing glass containing metallic Ag particles as aligned and dispersed shape-anisotropic metal particles in the surface layer of the glass substrate was obtained. <Beobachtung in TEM-Aufnahme>

[0080] The surface of the obtained polarizing glass was observed using transmission electron microscopy (TEM). It was confirmed that the metallic Ag particles were present on the surface of the polarizing glass as aligned and dispersed, shape-anisotropic metal particles. (Example 2)

[0081] (A) The mixing and melting of the glass raw materials were carried out in the same manner as in Example 1, so that the composition of a glass substrate material after melting corresponds to the composition of Example 2 shown 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.

[0082] (B) A heat treatment for depositing silver halide particles was performed on the glass substrate material in the same manner as in Example 1 to prepare a preform. In Example 2, where the amount of TiO2 was 1.30%, the preform had a homogeneous white turbidity, and the silver halide particles were deposited homogeneously.

[0083] A polarizing glass was prepared through steps (C) and (D) in the same manner as in Example 1. Observation of TEM images confirmed that metallic Ag particles were present on the surface of the polarizing glass as aligned and dispersed, shape-anisotropic metal particles. (Example 3)

[0084] (A) The mixing and melting of the glass raw materials were carried out in the same manner as in Example 1, so that the composition of a glass substrate material after melting corresponds to the composition of Example 3 shown 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.

[0085] (B) The heat treatment for depositing silver halide particles was performed on the glass substrate material in the same manner as in Example 1 to prepare a preform. In Example 3, where the amount of TiO2 was 1.80%, the preform had a homogeneous white turbidity, and the silver halide particles were deposited homogeneously.

[0086] A polarizing glass was prepared through steps (C) and (D) in the same manner as in Example 1. Observation of TEM images confirmed that metallic Ag particles were present on the surface of the polarizing glass as aligned and dispersed, shape-anisotropic metal particles. (Comparison example 1)

[0087] (A) The mixing and melting of the glass raw materials were carried out in the same manner as in Example 1, so that the composition of a glass substrate material after melting was the same as that of Comparative Example 1 shown 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] (B) Heat treatment to deposit silver halide particles was performed on the glass substrate material in the same manner as in Example 1 to prepare a preform. In the preform, partial areas of dense white haze and areas of weak white haze were present, and homogeneous white haze was not achieved. This is presumably because the amount of TiO2 was too high at 1.90%, the silver halide particles could not be deposited homogeneously during the heat treatment, and the particle size and density of the silver halide particles formed by the heat treatment became inhomogeneous in the preform.

[0089] A polarizing glass was prepared by steps (C) and (D) in the same manner as in Example 1. Observation of TEM images confirmed that metallic Ag particles were present on the surface of the polarizing glass as aligned and dispersed, shape-anisotropic particles. (Comparison example 2)

[0090] (A) The mixing and melting of the glass raw materials were carried out in the same manner as in Example 1, so that the composition of a glass substrate material after melting corresponds to the composition of Comparative Example 2 shown 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] (B) A heat treatment for depositing silver halide particles was performed on the glass substrate material in the same manner as in Example 1 to prepare a preform. The preform had a homogeneous white turbidity, and the silver halide particles were homogeneously deposited. A polarizing glass was prepared through steps (C) and (D) in the same manner as in Example 1. Observation of TEM images confirmed that metallic Ag particles were present on the surface of the polarizing glass as aligned and dispersed, shape-anisotropic particles. Table 1(1) Glass composition (mass%) Comparison example 1 Example 1 Example 2 Comparison example 2 Example 3 SiO2 56,7 56,9 57,0 57,2 56,8 B2O3 16,2 16,2 16,3 16,3 16,2 Li2O 1,8 1,8 1,8 1,8 1,8 Na2O 4,6 4,6 4,6 4,7 4,6 K2O 5,8 5,9 5,9 5,9 5,8 Al2O3 7,0 7,0 7,1 7,1 7,0 ZrO2 5,2 5,2 5,2 5,2 5,2 TiO2 1,90 1,60 1,30 1,00 1,80 Ag 0,23 0,23 0,23 0,23 0,23 Cl 0,40 0,40 0,40 0,40 0,40 Br 0,17 0,17 0,17 0,17 0,17 Total 100 100 100 100 100 Table 1(2) Comparison example 1 Example 1 Example 2 Comparison example 2 Example 3 Mass% Ag 0,23 0,23 0,23 0,23 0,23 Cl 0,40 0,40 0,40 0,40 0,40 Br 0,17 0,17 0,17 0,17 0,17 chemical equivalent Ag 0,0021 0,0021 0,0021 0,0021 0,0021 Cl+Br 0,0134 0,0134 0,0134 0,0134 0,0134 <Chemische Beständigkeit: Wasserresistenz Dw>

[0092] In Example 1, Example 2, and Example 3, the glass substrate materials obtained in step (A) above were evaluated for their water resistance Dw. The water resistance Dw was evaluated by placing powdered glass (particle size 425 to 600 μm) with a mass corresponding to the specific gravity of the glass substrate material in a platinum basket, immersing the platinum basket in a glass-quartz round-bottom flask containing 80 ml of pure water (pH = 6.5 to 7.5), treating the powdered glass in a boiling water bath for 60 minutes, and classifying the powdered glass into the classes shown in Table A according to the mass loss rate (%). As a result, the water resistance Dw of the glass substrate materials obtained in Example 1, Example 2, and Example 3 was classified into Class 1. <Chemische Beständigkeit: Säureresistenz Da>

[0093] In Example 1, Example 2, and Example 3, the glass substrate materials obtained in step (A) above were evaluated for their acid resistance Da. Namely, the acid resistance Da was evaluated by placing powdered glass (particle size 425 to 600 μm) with a mass corresponding to the specific gravity of the glass substrate material in a platinum basket, immersing the platinum basket in a glass-quartz round-bottom flask containing 80 ml of a 0.01 mol / L nitric acid water solution, treating the powdered glass in a boiling water bath for 60 minutes, and classifying the powdered glass into the classes shown in Table B according to the mass loss rate (%). As a result, the acid resistance Da was Class 1 for all the glass substrate materials obtained in Example 1, Example 2, and Example 3. <Extinktionsverhältnis und Einfügedämpfung>

[0094] An anti-reflective (AR) layer was applied to one surface of each of the polarizing glasses obtained in Examples 1 to 3 and Comparative Examples 1 and 2 to reduce reflection due to the refractive index of the polarizing glass. The anti-reflective layer was formed as a multilayer film consisting of a metal oxide layer such as TiO2 or Ta2O5 and a SiO2 layer.Since the polarizing glass used in optical isolators is often used in such a way that a 0-degree product (a polarizing glass product cut so that the polarization transmission axis of a light component passing through the polarizing glass is parallel to the outer edge of the Faraday rotator) is bonded to one surface of a Faraday element (garnet) and a 45-degree product (a polarizing glass product cut so that the 0-degree product and the polarization transmission axis form a 45-degree angle) is bonded to the other surface with an adhesive, in most cases only one surface comes into contact with the atmosphere. For the reasons mentioned above, the AR film of the polarizing glass was bonded to only one surface.

[0095] A rectangular polarizing glass with a thickness of 0.2 mm and an AR coating applied to one surface was bonded to an adhesive tape that peels off upon irradiation with ultraviolet (UV) light and cut to a product size of 11 mm square. The polarizing glass was peeled off the adhesive tape by irradiating the adhesive tape with UV light. The extinction ratio and insertion loss of the polarizing glass were measured when the wavelength of the laser light source was set to 1270 nm and the distance (measurement distance) between the polarizing glass and the detector's power meter was set to 5 mm, and when the wavelength of the laser light source was set to 1650 nm and the measurement distance was set to 300 mm. The results are shown in Table 2. Table 2 wavelength Measuring distance Example 1 Example 2 Example 3 Comparison example 1 Comparison example 2 Extinction ratio (dB) 1270 nm 5 mm 38,70 38,40 38,20 32,28 36,91 1650 nm 300 mm 57,20 56,23 56,48 44,51 53,65 Insertion loss (dB) 1270 nm 5 mm 0,190 0,198 0,189 0,187 0,241 1650 nm 300 mm 0,198 0,203 0,198 0,197 0,232

[0096] As shown in Table 2, in Comparative Example 1, in which the amount of TiO2 was 1.90%, the extinction ratio at a wavelength of 1270 nm and a measuring distance of 5 mm was low, at 35 dB or less. Furthermore, the extinction ratio at a wavelength of 1650 nm and a distance of 300 mm decreased to 45 dB or less. The reason why the extinction ratio of Comparative Example 1 was lower than those of Examples 1, 2, and 3 is presumably that the amount of TiO2 was too high, that there were areas where the density of the silver halide particles was low or the particle size was small, that the silver halide particles could not be formed homogeneously, and that the metallic silver particles with an anisotropic shape obtained as a result of the reduction could not be sufficiently obtained.The insertion loss of Comparative Example 1 was low at 0.200 dB or less at both a wavelength of 1270 nm and a measurement distance of 5 mm and a wavelength of 1650 nm and a distance of 300 mm.

[0097] In Example 1, where the amount of TiO2 was 1.60%, in Example 2, where the amount of TiO2 was 1.30%, and in Example 3, where the amount of TiO2 was 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. Furthermore, the extinction ratio at a wavelength of 1650 nm and a measurement distance of 300 mm was also high, at 55.0 dB or more.

[0098] The insertion loss of Examples 1 and 3 was low at 0.190 dB or less at a wavelength of 1270 nm and a measurement distance of 5 mm. The insertion loss was low at 0.198 dB at a wavelength of 1650 nm and a measurement distance of 300 mm.

[0099] The insertion loss of Example 2 was low at 0.198 dB at a wavelength of 1270 nm and a measurement distance of 5 mm. The insertion loss was low at 0.203 dB at a wavelength of 1650 nm and a measurement distance of 300 mm.

[0100] Incidentally, the reason why the insertion loss in Example 1 and Example 3 was lower than in Example 2 is probably because the amount of TiO2 in Example 2 was 1.30% lower than in Example 1 (1.60%) and Example 3 (1.80%).

[0101] In Comparative Example 2, in which the amount of TiO2 was 1.00%, the extinction ratio at the wavelength of 1270 nm and the measuring distance of 5 mm was 37 dB or less lower than in Example 1, Example 2, and Example 3. Furthermore, the extinction ratio at the wavelength of 1650 nm and the measuring distance of 300 mm was also 55 dB or less lower than in Example 1, Example 2, and Example 3.

[0102] The insertion loss of Comparative Example 2 was 0.241 dB at the wavelength of 1270 nm and the measuring distance of 5 mm, which was higher than Example 1, Example 2, and Example 3. The insertion loss at the wavelength of 1650 nm and the measuring distance of 300 mm was 0.232 dB higher than Example 1, Example 2, and Example 3. In Comparative Example 2, in which the amount of TiO2 was 1.00%, it is assumed that the insertion loss was high because the amount of TiO2 was small and the photochromism suppression effect was small.

[0103] From the above results, it is clear that in Example 3, in which the amount of TiO2 was 1.80%, the preform prepared from the glass substrate material had a homogeneous white turbidity, and the silver halide particles were deposited homogeneously. The extinction ratio of the polarizing glass prepared in Example 3 was high and within a preferable range. Similarly, in Example 1, in which the amount of TiO2 was 1.60%, and Example 2, in which the amount of TiO2 was 1.30%, preforms were obtained that had a homogeneous white turbidity, and the extinction ratios were high and within a preferable range. From the above results, it was confirmed that in the glass substrate material for polarizing glass for preparing the preform in which homogeneous silver halide particles were deposited and a preferable extinction ratio was obtained, the amount of TiO2 was preferably 1.80% or less. <Einfluss der Menge an TiO2 auf die Verringerung der photochromen Eigenschaften>

[0104] The glass film obtained by drawing the glass substrate material as described in the above step (C) in Comparative Example 2 and the glass film obtained by drawing the glass substrate material as described in the above step (C) in Example 1 were simultaneously left side by side under a fluorescent lamp. Fig. Figure 3 shows a photograph taken approximately 9 days after the start of exposure of the glass films to the fluorescent lamp.

[0105] As in Fig. 3, in the composition containing a small amount of TiO2 (Comparative Example 2), the glass film was blackened by the irradiation with light from the fluorescent lamp, while in the composition of Example 1, the discoloration was suppressed by the irradiation with light from the fluorescent lamp.

[0106] Next, the glass film obtained by drawing the glass substrate material according to the above step (C) in Comparative Example 2 and the glass film obtained by drawing the glass substrate material according to the above step (C) in Example 1 were cut to a length of about 20 mm. These glass films were irradiated with ultraviolet light having a wavelength of mainly 365 nm at an illuminance of 50 mW / cm 2 for 10 minutes using an ultraviolet irradiator. The spectral transmittance of the glass films before and after irradiation with ultraviolet light was measured with a spectrophotometer at wavelengths of 400 nm, 1310 nm, and 1550 nm. Table 3 shows the relationship between the transmittance after irradiation and the transmittance before irradiation. Table 3 Wavelength (nm) Comparison example 2 Example 1 400 83% 97% 1310 92% 99% 1550 94% 100%

[0107] As shown in Table 3, in the composition containing a small amount of TiO2 (Comparative Example 2), the ratio of the transmittance after ultraviolet light irradiation to the transmittance before irradiation decreased significantly to 83% at a visible short wavelength of 400 nm, while in the composition containing a high amount of TiO2 (Example 1), where the ratio was 97%, the transmittance remained unchanged. At 1310 nm, the wavelength band used in optical communications, the ratio of the transmittance after ultraviolet light irradiation to the transmittance before irradiation decreased to 92% in Comparative Example 2, while the transmittance remained unchanged at 99% in Example 1.At a wavelength of 1550 nm, the ratio of the transmittance after ultraviolet light irradiation to the transmittance before irradiation decreased to 94% in Comparative Example 2, while the transmittance in Example 1, where the ratio was 100%, remained unchanged. Photochromism was significantly suppressed by increasing the amount of TiO2.

[0108] It should be noted that the embodiment disclosed herein is exemplary in every respect and does not limit the present invention. The scope of the present invention is defined not by the above description, but by the claims, and is intended to encompass all modifications within the concept and scope of the claims and equivalents.

[0109] For example, by adapting the composition to the glass composition exemplified above as described in the specification, the polarizing glass according to one aspect of the present invention can be produced.

[0110] Furthermore, two or more of the items described in the description as examples or preferred areas can, of course, be combined as desired. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2003-98349 A

[0006] JP 2010-150122 A

[0006] JP 2011-170312 A

[0006] JP 2013-126921 A

[0006] Cited non-patent literature

[0000] JOGIS 06:2019 [0048, 0050]

Claims

[1] Polarizing glass comprising: shape-anisotropic metal particles aligned and dispersed in at least one surface layer of a glass substrate, wherein the glass substrate contains in mass%, 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 amount 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 a total chemical equivalent of Cl and Br: equal to or greater than a chemical equivalent of Ag, and where the shape-anisotropic metal particles are metallic Ag particles. [2] The polarizing glass according to claim 1, wherein the glass substrate contains 1.50 to 1.80% TiO2. [3] Optical isolator comprising: the polarizing glass according to claim 1. [4] Optical isolator comprising: the polarizing glass according to claim 2.

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