SILVER-CONTAINING POLARIZING GLASS AND OPTICAL INSULATOR

Abstract

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 60.0%, B2O3: 10.0 to 25.0%, Al2O3: 3.0 to 10.0%, a total amount of Li2O, Na2O, and K2O [Li2O + Na2O + K2O]: 5.0 to 20.0%, ZrO2: 2.0 to 8.0%, TiO2: 0.1 to 5.0%, Nb2O5: 0.1 to 5.0%, a total amount of TiO2 and Nb2O5 [TiO2 + Nb2O5]: 0.2 to 10.0%, Ag, and Cl and / or 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] In addition, if the glass serving as the substrate becomes discolored due to light irradiation or similar, the function of the polarizing glass may be impaired. 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 transmitted through the polarizing glass decreases, which poses a problem.

[0004] What is needed is a polarizing glass with a glass substrate that has excellent durability in a variety of environments and reduced photochromic properties.

[0005] Patent Document 1 discloses a polarizing glass containing shape-anisotropic metallic silver particles; however, the amount of Al2O3 or ZrO2 is small, it is not expected that the polarizing glass will be used in a variety of environments, and durability is not addressed. Furthermore, Patent Document 2 discloses a polarizing glass containing dispersed shape-anisotropic metallic silver particles; however, it is not expected that a glass substrate will be discolored due to light irradiation or the like, and there is no disclosure of reducing the photochromic properties of the glass by containing a predetermined amount of Nb2O5 or the like.Patent Document 3 discloses polarizing materials containing silver in the form of flattened metal particles in a glass substrate material; however, the content of silver is high in each case, and there is no mention of reducing the amount of incorporated silver. CITATION LISTPATENT SPECIFICATION Patent Document 1: JP S56-169140 A Patent Document 2: JP 2013-126921 A Patent Document 3: JP 2010-150132 A SUMMARY OF THE INVENTION

[0006] 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 and reduced photochromic properties.

[0007] The concept of the present invention is as follows.

[0008] (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 60.0%, B2O3: 10.0 to 25.0%, Al2O3: 3.0 to 10.0%, a total amount of Li2O, Na2O, and K2O [Li2O + Na2O + K2O]: 5.0 to 20.0%, ZrO2: 2.0 to 8.0%, TiO2: 0.1 to 5.0%, Nb2O5: 0.1 to 5.0%, a total amount of TiO2 and Nb2O5 [TiO2 + Nb2O5]: 0.2 to 10.0%, Ag, and Cl and / or Br: equal to or greater than a chemical equivalent of Ag. The shape-anisotropic metal particles are metallic Ag particles.

[0009] (2) An optical isolator containing the polarizing glass according to the above disclosure (1).

[0010] According to the present invention, a polarizing glass can be provided which has a glass substrate with excellent chemical resistance and 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 the drawn glasses produced in the example and the comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 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 %."

[0012] 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 that the component may be present in an unavoidable impurity level.

[0013] 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.

[0014] An embodiment of the present invention will be described below.

[0015] 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 functions to transmit polarized light in a specific vibration direction (referred to as the "polarization transmission axis") and absorb polarized light in a direction perpendicular to the specific vibration direction (referred to as the "polarization extinction axis"). (glass substrate)

[0016] In the glass substrate, the amount of SiO2 is 50.0 to 60.0%. The lower limit of the amount of SiO2 is preferably 51.0%, and more preferably 52.0%. Furthermore, the upper limit of the amount of SiO2 is preferably 59.0%, and more preferably 58.0%. 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. If the amount of SiO2 is too high, the fusibility of the glass may also decrease.

[0017] In the glass substrate, the amount of B2O3 is 10.0 to 25.0%. The lower limit of the amount of B2O3 is preferably 12.0%, and more preferably 13.0% and 14.0% in that order. The upper limit of the amount of B2O3 is preferably 23.0%, and more preferably 21.0% and 20.0% in that order. The chemical resistance of the glass substrate can be improved by adjusting the amount of B2O3 within the range described above. If the amount of B2O3 is too low, the fusibility of the glass may decrease, and the silver halide particles may not be favorably deposited throughout the glass substrate during the heat treatment to be described later. Furthermore, if the amount of B2O3 is too high, the chemical resistance of the glass substrate may decrease.

[0018] In the glass substrate, the amount of Al2O3 is 3.0 to 10.0%. The lower limit of the amount of Al2O3 is preferably 4.0%, and more preferably 4.5%. The upper limit of the amount of Al2O3 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 small, the chemical resistance of the glass substrate may be significantly reduced. Furthermore, if the amount of Al2O3 is too high, the fusibility of the glass may decrease, and the glass may become prone to devitrification.

[0019] In the glass substrate, the total amount of Li2O, Na2O, and K2O [Li2O + Na2O + K2O] is 5.0 to 20.0%. 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 18.0%, and more preferably 16.0%. 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. Conversely, 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 be favorably deposited throughout the glass substrate during the heat treatment to be described later.

[0020] The amount of ZrO2 in the glass substrate is 2.0 to 8.0%. The lower limit of the amount of ZrO2 is preferably 2.5%, and more preferably 3.0%. The upper limit of ZrO2 is preferably 7.7%, and more preferably 7.0%. The chemical resistance of the glass substrate can be improved by adjusting the amount of ZrO2 within the above-described range. However, if the amount of ZrO2 is too small, the chemical resistance of the glass substrate may be significantly reduced. Furthermore, if the amount of ZrO2 is too high, the meltability of the glass may decrease and the liquidus temperature may rise.

[0021] In the glass substrate, the amount of TiO2 is 0.1 to 5.0%. The lower limit of the amount of TiO2 is preferably 0.3%, and more preferably 0.6%. The upper limit of the amount of TiO2 is preferably 4.5%, and more preferably 4.0%. TiO2 is a glass component that contributes to improving the chemical resistance of the glass and absorbs light well from the near ultraviolet to 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.If the amount of TiO2 is too high, the fusibility of the glass may decrease, the liquidus temperature may increase, and the coloration may be increased during glass forming.

[0022] In the glass substrate, the amount of Nb2O5 is 0.1 to 5.0%. The lower limit of the amount of Nb2O5 is preferably 0.3%, and more preferably 0.6%. Furthermore, the upper limit of the amount of Nb2O5 is preferably 4.5%, and more preferably 4.0%. Nb2O5 is a glass component that absorbs light well from the near ultraviolet to the visible short wavelengths. Therefore, the polarizing glass containing the glass substrate with reduced photochromic properties can be obtained by adjusting the amount of Nb2O5 within the above-described range. If the amount of Nb2O5 is too low, the photochromic properties of the glass substrate may increase. If the amount of Nb2O5 is too high, the meltability of the glass may decrease, the liquidus temperature may rise, and coloration may increase during glass forming.

[0023] In the glass substrate, the total amount of TiO2 and Nb2O5 [TiO2 + Nb2O5] is 0.2 to 10.0%. The lower limit of the total amount is preferably 0.5%, and more preferably 1.0%. Further, the upper limit of the total amount is preferably 9.0%, and more preferably 8.0%. The polarizing glass containing the glass substrate with improved chemical resistance and reduced photochromic properties can be obtained by adjusting the total amount within the above-described range. If the total amount is too low, the chemical resistance of the glass substrate may decrease and the photochromic properties of the glass substrate may increase. Furthermore, if the total amount is too high, the meltability of the glass may decrease and the liquidus temperature may increase.

[0024] The glass substrate contains Ag, Cl, and Br. In the glass substrate, the lower limit of the Ag amount is preferably 0.10%, and more preferably 0.11% and 0.13% in that order. Furthermore, the upper limit of the Ag amount is preferably 1.0%, and more preferably 0.8% and 0.6% in that order. The polarizing glass containing the glass substrate with excellent chemical resistance can be obtained by ensuring that the glass substrate contains Ag. On the other hand, if the amount of Ag is too small, the silver halide particles may not be favorably deposited throughout the glass substrate during the heat treatment to be described later. In addition, if the amount of Ag is too large, the insertion loss may increase, and when the glass is melted and cooled, silver halide particles may be deposited in the glass, and it may become difficult to control the particle size of the silver halide particles.

[0025] Furthermore, it is advantageous that the glass substrate contains essentially no Cu. Thus, the amount of Cu is preferably 0%.

[0026] To deposit silver halide particles throughout the glass substrate, Ag is added to the glass substrate raw materials, for example, in the form of AgCl and AgBr. However, since AgBr is a hazardous substance, AgBr must be handled with care, and it is preferable from an environmental perspective that AgBr is not used. Furthermore, since Cl and Br may volatilize during glass melting, Cl and Br are added in excess as alkali metal or alkaline earth metal chlorides or bromides for make-up. Therefore, the glass substrate contains Cl and / or Br in an amount 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.

[0027] As described above, the glass substrate contains Cl and / or Br in an amount equal to or greater than the chemical equivalent of Ag. This means that in the glass substrate, the chemical equivalent of at least one of Cl and Br is equal to or greater than the chemical equivalent of Ag. The chemical equivalents of both Cl and Br can be equal to or greater than the chemical equivalent of Ag.

[0028] 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."

[0029] 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.

[0030] In the glass substrate, the total amount of Cl and Br is preferably 0.05 to 2.0%. The amount of Cl is preferably 0.05 to 1.0%. Similarly, the amount of Br is preferably 0.05 to 1.0%.

[0031] The following are non-limiting examples of the amounts of glass components other than those described above in the glass substrate.

[0032] In the glass substrate, the lower limit of the amount of Li2O is preferably 0.0%, and more preferably 0.5% and 0.8% in that order. Further, the upper limit of the amount of Li2O is preferably 5.0%, and more preferably 4.0% and 3.5% in that order. From the viewpoint of improving the meltability of the glass and lowering the glass transition temperature Tg, it is advantageous to set the lower limit of the amount of Li2O as described above. Furthermore, from the viewpoint of favorable deposition of silver halide particles throughout the glass substrate during the heat treatment to be described later, it is advantageous to set the upper limit of the amount of Li2O as described above.

[0033] In the glass substrate, the lower limit of the amount of Na2O is preferably 0.0%, and more preferably 1.0% and 3.0% in that order. Furthermore, the upper limit of the amount of Na2O is preferably 10.0%, and more preferably 8.0% and 7.0% in that order. In order to improve the fusibility of the glass and lower the glass transition temperature Tg, the lower limit of the amount of Na2O is preferably set as described above. Furthermore, in view of the favorable deposition of silver halide particles throughout the glass substrate during the heat treatment to be described later, it is advantageous to set the upper limit of the amount of Na2O as described above.

[0034] In the glass substrate, the lower limit of K2O is preferably 0.0%, and more preferably 1.0% and 3.0% in that order. Further, the upper limit of K2O is preferably 10.0%, and more preferably 8.0% and 7.0% in that order. In order to improve the fusibility of the glass and lower the glass transition temperature Tg, the lower limit of the amount of K2O should preferably be set as described above. Furthermore, in view of the favorable deposition of silver halide particles throughout the glass substrate during the heat treatment to be described later, it is advantageous to set the upper limit of the amount of K2O as described above.

[0035] In the glass substrate, the lower limit of the amount of MgO is preferably 0.0%. The amount of MgO may be 0.0%. Furthermore, the upper limit of the amount of MgO is preferably 5.0%, and more preferably 3.0%. In view of improving the thermal stability and meltability of the glass, the amount of MgO is preferably within the above-described range.

[0036] In the glass substrate, the lower limit of the amount of CaO is preferably 0.0%. The amount of CaO may be 0.0%. Furthermore, the upper limit of the amount of CaO is preferably 5.0%, and more preferably 3.0%. In order to improve the thermal stability and meltability of the glass, the amount of CaO should preferably be set within the range described above.

[0037] In the glass substrate, the lower limit of the SrO content is preferably 0.0%. The SrO content may be 0.0%. Furthermore, the upper limit of the SrO content is preferably 5.0%, and more preferably 3.0%. In view of improving the thermal stability and meltability of the glass, it is advantageous for the SrO content to be within the above-described range.

[0038] In the glass substrate, the lower limit of the amount of BaO is preferably 0.0%. The amount of BaO may be 0.0%. Furthermore, the upper limit of the amount of BaO is preferably 5.0%, and more preferably 3.0%. In order to suppress an increase in specific gravity, the amount of BaO is within the range described above.

[0039] In the glass substrate, the lower limit of the total amount of MgO, CaO, SrO, and BaO [MgO + CaO + SrO + BaO] is preferably 0.0%. The total amount may be 0.0%. Further, the upper limit of the total amount is preferably 5.0%, and more preferably 3.0%. MgO, CaO, SrO, and BaO have the effect of improving the thermal stability and fusibility of the glass and increasing the basicity of the glass to prevent silver reduction, but may reduce the chemical resistance of the glass substrate, so the total amount is set within the above-described range.

[0040] In the glass substrate, the lower limit of the amount of ZnO is preferably 0.0%. The amount of ZnO may be 0.0%. Furthermore, the upper limit of the amount of ZnO is preferably 5.0%, and more preferably 3.0%. In view of improving the thermal stability of the glass, the amount of ZnO is preferably set within the above-described range.

[0041] Preferably, the glass substrate consists mainly of the above-described glass components, namely SiO2, B2O3, Al2O3, ZrO2, TiO2, Nb2O5, Ag, Cl, Br, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO and ZnO, 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.

[0042] 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 effects of the present invention. Furthermore, the present invention does not preclude the inclusion of unavoidable impurities.

[0043] The glass substrate is primarily composed of an oxide. 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 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%. (Other components)

[0044] In the glass substrate, the lower limit of the amount of CeO2 is preferably 0.0%. The amount of CeO2 may be 0.0%. Furthermore, the upper limit of the amount of CeO2 is preferably 3.0%, and more preferably 1.0%. CeO2 is a component that functions as a refining agent for glass. Furthermore, the states of Ce 4+ -ions and Ce 3+ ions and normally act to change 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, the amount of CeO2 is preferably adjusted within the range described above.

[0045] Pb is a toxic component and a concern due to environmental impact. Therefore, the glass substrate preferably contains essentially no Pb. In particular, the amount of Pb is preferably 0% when converted to an oxide.

[0046] Cd, As, Th and the like are components that are of concern due to their environmental impact.

[0047] Therefore, the amount of CdO, ThO2 and As2O3 is preferably 0 to 0.1%, better 0 to 0.05%, even better 0 to 0.01%, and most preferably CdO, ThO2 and As2O3 are substantially absent.

[0048] Preferably, the glass substrate contains no coloring elements. Examples of 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, even more preferably in an amount of 0 to 50 ppm by mass or less, and most preferably substantially not contained.

[0049] 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%, even more preferably 0 to 0.01%, even more preferably 0 to 0.005%, even more preferably 0 to 0.001%, and most preferably, Ga2O3, TeO2, and TbO2 are substantially absent. (Properties of the glass substrate)<Chemische Beständigkeit: Wasserresistenz Dw>

[0050] In the glass substrate, a water resistance Dw preferably corresponds to class 3 or higher, better class 2 or higher, and most preferably class 1.

[0051] The water resistance Dw can be assessed according to the method shown 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 in 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>

[0052] In the glass substrate, acid resistance Da preferably corresponds to class 3 or higher, better class 2 or higher, and even better class 1.

[0053] The acid resistance Da can be assessed according to the method shown in JOGIS 06:2019. The acid resistance Da is assessed by placing powdered glass (particle size 425 to 600 µm) with a mass corresponding to the specific gravity in a platinum basket, immersing the platinum basket in a round-bottomed glass quartz flask containing 80 ml of 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 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)

[0054] 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. <Extinktionsverhältnis und Einfügedämpfung>

[0055] 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 when passing through a polarizing element; the lower the insertion loss, the better the optical properties. The unit is dB.

[0056] As 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 by 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 by 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.

[0057] 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.

[0058] 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.

[0059] 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 inserted to obtain a linearly polarized wave in a specific direction.

[0060] 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)

[0061] 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)

[0062] 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]

[0063] The glass raw materials are mixed. Examples of glass raw materials include SiO2, H3BO3, Al(OH)3, Li2CO3, Na2CO3, K2CO3, KNO3, ZrO2, TiO2, Nb2O5, 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]

[0064] The glass substrate material obtained in step (A) above is heat-treated at a temperature of 650°C to 800°C for approximately several to 20 hours (preferably about 4 to 10 hours). To form silver halide particles of a suitable size, it is generally preferable to heat-treat at a high temperature for a short heat-treatment time, and to heat-treat at a relatively low temperature for a long heat-treatment time.

[0065] 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. When the temperature of the glass drops close to the glass transition temperature (Tg), for example, to about 500°C, in the subsequent cooling step, 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 420 to 460°C, AgClBr undergoes a phase transition from liquid to solid. Without being limited to this, the deposited silver halide particles (AgClBr) form essentially spherical bodies. Incidentally, AgClBr is strictly speaking AgCl. (x) Br (1-x) (0 < x <1). (C) Drawing of glass substrate material]

[0066] 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, between 550°C and 650°C, and the drawing force in the drawing step can be set between approximately 25 MPa and 50 MPa. AgClBr changes from the solid state to the liquid state through heating and drawing, and undergoes a phase transition back to the liquid 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]

[0067] 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.

[0068] In the reduction step, the region of the silver halide particles which is unidirectionally elongated is maintained and becomes a cavity, and in the cavity one or more divided, shape-anisotropic metallic Ag particles are formed.

[0069] 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)

[0070] The polarizing glass according to the present embodiment can be used for any optical device that utilizes 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 optical pigtail isolators in wavelength bands used in optical communications. (Optical isolator)

[0071] 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; however, a free-space optical isolator and a pigtail optical isolator can be cited as examples.

[0072] 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 composed 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 adjusted so that the rotation angle of the Faraday rotator 113 relative to the polarization plane 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 passes through the polarizing element 111 with essentially no loss, is collimated by the lens 115, and is incident on the optical fiber 116.

[0073] The returning luminous flux 118, which is 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 a large part of the optical energy of the returning luminous flux 118 is lost when passing through the polarizing element 112.

[0074] In addition, a so-called optical pigtail isolator has become established in recent years due to the demand for miniaturization of optical components. 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 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.

[0075] 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 differs between the two isolators; however, the configuration of the optical isolator 114 is essentially the same. EXAMPLES

[0076] 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)

[0077] 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]

[0078] SiO2, H3BO3, Al(OH)3, Li2CO3, Na2CO3, K2CO3, KNO3, ZrO2, TiO2, Nb2O5, NaCl, NaBr, and AgCl were used as glass raw materials. These raw materials were placed in a 5-liter platinum crucible, melted at about 1450°C, then poured into a metal mold for molding and slowly cooled to room temperature. A glass substrate material with the composition shown in Example 1 of Table 1(1) was obtained. Table 1(2) shows the chemical equivalents of Ag, Cl, and Br in the glass substrate. In Table 1(2), 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]

[0079] The glass substrate obtained in the above step (A) was heat-treated at 704°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 prepare a preform. [(C) Drawing of glass substrate material]

[0080] The preform obtained in step (B) above was heated in a drawing furnace and drawn with a tensile force of 32.0 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]

[0081] 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>

[0082] 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. (Comparison example 1)

[0083] A glass substrate material having the composition shown in Comparative Example 1 of Table 1(1) was prepared by the same method as in step (A) above. Table 1(2) shows the chemical equivalents of Ag, Cl, and Br in the glass substrate. Incidentally, the composition of Comparative Example 1 is the same as the glass composition in Example 10 of WO 2007 / 119794.

[0084] The obtained glass substrate was heat-treated according to the same method as in step (B) above, and then heated and drawn according to the same method as in step (C) above. A polarizing glass was prepared according to the same method as in step (D) above. Observation of TEM images similar to those in Example 1 confirmed that metallic Cu particles were present on the surface of the polarizing glass in the form of aligned and dispersed, shape-anisotropic particles. (Comparison example 2)

[0085] A glass substrate material having the composition shown in Comparative Example 2 of Table 1(1) was obtained by the same method as in step (A) above. Table 1(2) shows the chemical equivalents of Ag, Cl, and Br in the glass substrate. The obtained glass substrate material was heat-treated by the same method as in step (B) above and then heated and drawn by the same method as in step (C) above. A polarizing glass was prepared by the same method as in step (D) above. Observation of TEM photographs similar to those in Example 1 confirmed that metallic Ag particles were present on the surface of the polarizing glass in the form of aligned and dispersed, shape-anisotropic particles. Table 1(1) Glass composition (mass%) Example 1 Comparison example 1 Comparison example 2 SiO2 55,1 58,6 57,2 B2O3 16,3 20,4 16,3 AlF3 2,2 Al2O3 5,4 7,0 7,1 Li2O 1,8 1,8 Na2O 4,5 10,1 4,7 K2O 5,8 5,9 Y2O3 0,2 ZrO2 6,1 5,2 TiO2 1,6 1,0 Nb2O5 2,6 SnO 0,1 Ag 0,23 0,23 Cu 0,5 Cl 0,40 0,9 0,40 Br 0,17 0,17 Total 100 100 100 Li2O + Na2O + K2O 12,1 10,1 12,4 TiO2 + Nb2O5 4,2 0,0 1,0 Table 1(2) Example 1 Comparison example 1 Comparison example 2 Mass% Ag 0,23 0,23 Cl 0,40 0,90 0,40 Br 0,17 0,17 chemical equivalent Ag 0,0021 0,0000 0,0021 Cl 0,0113 0,0254 0,0113 Br 0,0021 0,0000 0,0021 <Chemische Beständigkeit: Wasserresistenz Dw>

[0086] In Example 1 and Comparative Example 1, the glass substrate materials obtained in step (A) above were evaluated for their water resistance Dw. For this purpose, powdered glass (particle size 425 to 600 μm) with a mass corresponding to the specific gravity of the glass substrate material was placed in a platinum basket. The platinum basket was immersed in a round-bottomed glass quartz flask containing 80 ml of pure water (pH = 6.5 to 7.5). The powdered glass was treated in a boiling water bath for 60 minutes, and the mass loss rate (%) was calculated. The mass loss rate of the glass substrate material of Example 1 was 0.03%, and the mass loss rate of the glass substrate material of Comparative Example 1 was 0.04% or more. <Chemische Beständigkeit: Säureresistenz Da>

[0087] In Example 1 and Comparative Example 1, the glass substrate material obtained in step (A) above was evaluated for its acid resistance Da. For this purpose, powdered glass (particle size 425 to 600 μm) with a mass corresponding to the specific gravity of the glass substrate material was placed in a platinum basket. The platinum basket was immersed in a round-bottomed glass quartz flask containing 80 ml of a 0.01 mol / L nitric acid water solution. The powdered glass was treated in a boiling water bath for 60 minutes, and the mass loss rate (%) was calculated. The mass loss rate of the glass substrate material of Example 1 was 0.07%, and the mass loss rate of the glass substrate material of Comparative Example 1 was 0.21% or more. <Wirkung von Nb2O5 auf die Verringerung photochromer Eigenschaften>

[0088] In Example 1 and Comparative Example 2, the glass substrates were prepared according to the method described in step (A) above.

[0089] The obtained glass substrates were heat-treated according to the same method as in step (B) above, and then heated and drawn according to the same method as in step (C) above to obtain glass films. The glass films were cut to a length of approximately 20 mm. The glass films of Comparative Example 2 and the glass films of Example 1 were placed side by side and 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 lamp. The glass films after irradiation with ultraviolet light are in Fig.3. Furthermore, the spectral transmittance of the glass films before and after ultraviolet light irradiation was measured with a spectrophotometer at wavelengths of 400 nm, 1310 nm, and 1550 nm. Table 2 shows the ratio of the transmittance after ultraviolet light irradiation to the transmittance before irradiation.

[0090] As in Fig. As shown in Figure 3, the sample of Comparative Example 2, which did not contain Nb2O5, was blackened by light irradiation, while the discoloration of the sample of Example 1 was suppressed by light irradiation. Table 2 wavelength Example 1 Comparison example 2 400 nm 99% 83% 1310 nm 100% 92% 1550 nm 100% 94%

[0091] As shown in Table 2, in the composition containing no Nb2O5 and 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 Nb2O5 (Example 1), where the ratio was 99%, the transmittance remained unchanged. At 1310 nm, the wavelength range 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 in Example 1, where the ratio was 100%.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 remained at 100% in Example 1. Photochromism was significantly suppressed by the inclusion of Nb2O5. <Extinktionsverhältnis und Einfügedämpfung>

[0092] An anti-reflective (AR) layer was applied to one surface of each of the polarizing glasses obtained in Example 1 and Comparative Example 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 stated above, the AR film of the polarizing glass was bonded to only one surface.

[0093] 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 3. Table 3 wavelength Measuring distance Example 1 Comparison example 2 Extinction ratio (dB) 1270 nm 5 mm 38,60 36,91 1650 nm 300 mm 56,80 53,65 Insertion loss (dB) 1270 nm 5 mm 0,187 0,241 1650 nm 300 mm 0,196 0,232

[0094] In Comparative Example 2, which did not contain Nb2O5 and had a TiO2 content of 1.0%, the extinction ratio at a wavelength of 1270 nm and a measurement distance of 5 mm was 36.91 dB lower than that in Example 1. Furthermore, the extinction ratio at a wavelength of 1650 nm and a measurement distance of 300 mm in Comparative Example 2 was 53.65 dB, which was also lower than that in Example 1.

[0095] The insertion loss of Comparative Example 2 was 0.241 dB at a wavelength of 1270 nm and a measurement distance of 5 mm, which was higher than that of Example 1. The insertion loss at a wavelength of 1650 nm and a measurement distance of 300 mm was 0.232 dB higher than that of Example 1. In Comparative Example 2, which did not contain Nb2O5 and contained 1.0% TiO2, it is suspected that the insertion loss was increased due to the influence of photochromism.

[0096] It should be noted that the embodiments disclosed herein are exemplary in every respect and do 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.

[0097] 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.

[0098] 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 S56-169140 A

[0005] JP 2013-126921 A

[0005] JP 2010-150132 A

[0005] Cited non-patent literature

[0000] JOGIS 06:2019

[0053]

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 60.0%, B2O3: 10.0 to 25.0%, Al2O3: 3.0 to 10.0%, a total amount of Li2O, Na2O and K2O [Li2O + Na2O + K2O]: 5.0 to 20.0%, ZrO2: 2.0 to 8.0%, TiO2: 0.1 to 5.0%, Nb2O5: 0.1 to 5.0%, a total amount of TiO2 and Nb2O5 [TiO2+ Nb2O5]: 0.2 to 10.0%, Ag, and Cl and / or Br: equal to or greater than one chemical equivalent of Ag, and where the shape-anisotropic metal particles are metallic Ag particles. [2] Optical isolator comprising: the polarizing glass according to claim 1.

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