Polarizing glass and optical isolators

Abstract

To provide a polarizing glass with higher heat resistance than before, and an optical isolator including the same.SOLUTION: In a polarizing glass, metal layers in which a number of metal microparticles with an approximately needle-like shape are oriented and diffused in parallel are formed from both surfaces to the inside, and a metal halide layer including metal halide microparticles is formed between the metal layers. The polarizing glass has a total thickness of less than 0.12 mm, the metal layer has a thickness of 0.030 to 0.045 mm, and the metal halide layer has a thickness of 0.001 to 0.040 mm. Alternatively, the polarizing glass has a total thickness of less than 0.12 mm, the metal layer has a thickness of 0.010 to 0.030 mm, and the metal halide layer has a thickness of 0.001 to 0.060 mm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to polarizing glass used for optical components such as optical isolators, and particularly to polarizing glass with high heat resistance and an optical isolator provided with the same.

Background Art

[0002] Conventionally, as a polarizing element for an optical isolator, polarizing glass in which needle-shaped metal fine particles made of silver or copper are dispersed in a glass substrate so that their longitudinal directions are oriented in a specific direction has been used. It is well known that such polarizing glass can be produced by reducing an elongated glass containing copper halide particles or a glass containing silver halide particles. For example, Patent Document 1 discloses a method for producing polarizing glass from a glass containing copper halide particles by the following procedure.

[0003] (1) A glass material containing cuprous chloride is prepared to have a desired composition, melted at about 1450 ° C, and then cooled to room temperature. (2) Thereafter, heat treatment is performed to precipitate fine particles of cuprous chloride in the glass. (3) After precipitating fine particles of cuprous chloride, a preform having an appropriate shape is produced by machining. (4) The preform is stretched under predetermined conditions to obtain needle-shaped fine particles of cuprous chloride. (5) The stretched glass is reduced in a hydrogen atmosphere to obtain needle-shaped metallic copper fine particles.

[0004] In such polarizing glass, conventionally, those with a thickness of 0.20 mm have been mainstream, and those with a thickness of 0.15 mm or 0.12 mm have been put into practical use for thinner ones. However, due to the demand for miniaturization of optical isolators, thinner polarizing glass is required. Furthermore, in recent years, with the increasing speed of communication in the field of optical communications, higher energy laser light is being used at higher frequencies, which has led to problems such as heat buildup in optical isolators. As a result, there is a demand for polarizing glass used in optical isolators that has high heat resistance. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-208844 [Overview of the project] [Problems that the invention aims to solve]

[0006] Figure 4 shows the results of testing the heat resistance of polarizing glass manufactured by the method described in Patent Document 1. Conventional polarizing glass commonly used with thicknesses of 0.20, 0.15, and 0.12 mm, and with a metal layer (reduction layer) thickness of 0.038 mm formed from both surfaces of the glass toward the interior, were heat-treated at temperatures of 420°C, 440°C, and 460°C for 2 hours, respectively, and the extinction ratio at a measurement wavelength of 1650 nm before and after heat treatment was compared. As shown in Figure 4, the extinction ratio of conventional polarizing glass with a thickness of 0.20 mm decreased by 1.57 dB at 420 °C, 2.36 dB at 440 °C, and 6.32 dB at 460 °C. Similarly, the extinction ratio of conventional polarizing glass with a thickness of 0.15 mm decreased by 0.36 dB at 420 °C, 0.14 dB at 440 °C, and 4.22 dB at 460 °C. Furthermore, the extinction ratio of conventional polarizing glass with a thickness of 0.12 mm decreased by 0.32 dB at 420 °C, 0.19 dB at 440 °C, and 3.21 dB at 460 °C.

[0007] This invention has been made in view of these circumstances, and its objective is to provide a polarizing glass that is thinner than conventional ones while having excellent heat resistance, and an optical isolator equipped with the same. [Means for solving the problem]

[0008] In order to achieve the above objective, the inventors conducted diligent research and discovered that by reducing the thickness of the polarizing glass itself, and by thinning the unreduced layer (metal halide layer) between the metal layers formed on both sides by the reduction process, it is possible to obtain polarizing glass with excellent heat resistance while suppressing a decrease in extinction ratio. The present invention is based on this finding.

[0009] In other words, the polarizing glass of the present invention is a polarizing glass in which a metal layer is formed from both surfaces toward the interior, in which a large number of substantially needle-shaped metal nanoparticles are oriented and dispersed in parallel, and a metal halide layer containing metal halide nanoparticles is formed between the metal layers, wherein the total thickness of the polarizing glass is less than 0.12 mm, the thickness of the metal layer is 0.030 to 0.045 mm, and the thickness of the metal halide layer is 0.001 to 0.0 30 It is characterized by being in mm.

[0010] From another perspective, the polarizing glass of the present invention is a polarizing glass in which a metal layer is formed from both surfaces toward the interior, in which a large number of substantially needle-shaped metal nanoparticles are oriented and dispersed in parallel, and a metal halide layer containing metal halide nanoparticles is formed between the metal layers, wherein the total thickness of the polarizing glass is less than 0.12 mm, the thickness of the metal layer is 0.010 to 0.030 mm, and the thickness of the metal halide layer is 0.001 to 0.060 mm. The metal particles are silver particles. It is characterized by the following:

[0011] Furthermore, it is desirable that the metal nanoparticles be copper or silver nanoparticles.

[0012] From another perspective, the optical isolator of the present invention is characterized by comprising any of the above-mentioned polarizing glasses. [Effects of the Invention]

[0013] As described above, the present invention provides a polarizing glass that is thinner than conventional glass while having excellent heat resistance, and an optical isolator equipped with the same. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic diagram illustrating the structure of a polarizing glass according to an embodiment of the present invention. [Figure 2] Figure 2 is a schematic side cross-sectional view illustrating the configuration of an optical isolator using polarizing glass according to an embodiment of the present invention, and the optical system surrounding it. [Figure 3] Figure 3 is a digital microscope photograph showing a cross-section of a polarizing glass (Example 1) according to an embodiment of the present invention. [Figure 4] Figure 4 shows the results of testing the heat resistance of polarizing glass manufactured using conventional methods. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0016] Figure 1 is a schematic diagram illustrating the structure of the polarizing glass 10 according to an embodiment of the present invention, where Figure 1(a) is a plan view and Figure 1(b) is a side cross-sectional view. Figure 2 is a schematic side cross-sectional view showing the configuration of an optical isolator 100 using the polarizing glass 10 of this embodiment and the optical system around it. As shown in Figures 1 and 2, the polarizing glass 10 of this embodiment (shown as polarizing elements "10A" and "10B" in Figure 2) is a polarizing element attached to both sides of the Faraday rotor 110 of the optical isolator 100, and is an optical element in which needle-shaped metal nanoparticles made of silver or copper are dispersed in a glass substrate so that their longitudinal direction is oriented in a specific direction.

[0017] As shown in FIG. 2, the optical system around the optical isolator 100 of the present embodiment is composed of a lens 115, 115', an optical fiber 116, a light source 117 such as a semiconductor laser, etc. centered on the optical isolator 100. In FIG. 2, 118, 118' schematically show the light fluxes of the feedback light returning to the light source 117. The light flux 118 shows the reflected light reflected by the end face of the optical fiber 116, etc., and the light flux 118' shows the light flux after passing through the polarization element 10B. In the optical isolator 100 shown in FIG. 2, the polarization transmission axes of the polarization elements 10A and 10B are arranged to form an angle of 45 degrees with each other, and the polarization plane rotation angle in the Faraday rotator 110 is set so as to be 45 degrees by setting its optical path length. The light flux (not shown) emitted from the light source 117 is converted into a parallel light flux by the lens 115', and only the light having polarization parallel to the polarization transmission axis of the polarization element 10B enters the Faraday rotator 110. The polarization direction of the light incident on the Faraday rotator 110 is rotated by 45 degrees due to the Faraday effect by a permanent magnet (not shown). As described above, since the polarization transmission axes of the polarization elements 10A and 10B form an angle of 45 degrees with each other, the polarization direction of the light passing through the Faraday rotator 110 coincides with the polarization transmission axis of the polarization element 10A. Therefore, the light passing through the Faraday rotator 110 passes through the polarization element 10A almost without loss, is condensed by the lens 115, and is incident on the optical fiber 116.

[0018] The feedback light flux 118 reflected by the end face of the optical fiber 116 or an optical element (not shown) disposed in the subsequent stage and returning to the light source passes through the reverse optical path of the light flux emitted from the light source 117 described above and returns to the light source 117. In this case, due to the non-reciprocity of the Faraday rotator 110, the polarization direction of the feedback light flux 118 after passing through the Faraday rotator 110 forms an angle of 90 degrees with the polarization transmission axis of the polarization element 10B. Therefore, when passing through the polarization element 10B, its light energy is greatly damaged (that is, the feedback light 118 can be blocked).

[0019] Thus, by using the optical isolator 100 provided with the polarizing glasses 10 on both surfaces of the Faraday rotator 110, the feedback light 118' returning to the light source 117 can be blocked.

[0020] As shown in FIG. 1, the polarizing glass 10 of the present embodiment has an appearance of a rectangular plate (for example, 11 mm (lateral direction) × 11 mm (vertical direction), thickness 0.02 to 0.11 mm), and metal layers 12 and 14 in which a large number of substantially needle-shaped metal fine particles are arranged and dispersed in parallel are formed on the front and back surfaces, and a metal halide layer (unreduced layer) 16 containing metal halide fine particles is formed between the metal layers 12 and 14 (FIG. 1(b)). The metal layers 12 and 14 are layers having a predetermined thickness (for example, 0.010 to 0.045 mm) formed by depositing needle-shaped metal fine particles made of silver or copper by a reduction process described later. The metal halide layer 16 is a layer having a predetermined thickness (for example, 0.001 to 0.060 mm) formed inside by forming the metal layers 12 and 14 by a reduction process described later.

[0021] [Manufacturing method of polarizing glass 10] The polarizing glass 10 of the present embodiment is manufactured by the following procedure. (1) A glass material containing copper or silver is formulated to have a desired composition, melted at about 1450° C., and then cooled to room temperature (manufacturing process of glass substrate). (2) By performing heat treatment, fine particles of cuprous chloride or silver chloride are precipitated in the glass (precipitation process of metal halide fine particles). (3) A preform having an appropriate shape is produced by machining (preform production process). (4) The preform is heated and stretched under predetermined conditions to obtain a glass sheet (stretching process of glass). (5) The glass sheet is cut and polished on both sides to produce a double-sided polished product (production process of polished product). (6) By reducing the polished product in a hydrogen atmosphere, needle-shaped metal (copper or silver) fine particles are precipitated, and the metal layers 12 and 14 and the metal halide layer 16 are formed (reduction process).

[0022] [Glass substrate] The glass substrate of the polarizing glass 10 in this embodiment is a glass selected from the group consisting of silicate glass, borate glass, and borosilicate glass, and the specific raw material composition when copper fine particles are deposited is, when calculated in wt%, SiO2: 48~65 B2O3: 13~33, Al2O3: 6-13 AlF3 0~5, Alkali metal oxides: 7-17 Alkali metal chlorides: 0-5 Alkaline earth metal oxides: 0-5, Copper oxide and copper halide: 0.3-2.5 SnO: 0~0.6 As2O3: 0~5 A composition that includes at least one additive component selected from the group consisting of Y2O3, La2O3, V2O5, Ta2O5, WO3, and Nb2O5 is preferred. In this case, the content of each selected additive is preferably in the range of 0.05 to 4% in molar percentage, the total content when multiple additives are selected is preferably 6% or less in molar percentage, and furthermore, when calculated in wt% relative to the entire glass substrate, the amount of Cl contained in the glass substrate is preferably 0.47 to 0.58 wt%.

[0023] Furthermore, the specific raw material composition for precipitating silver nanoparticles is as follows: SiO2: 50-65%, B2O3: 15-22% Al2O3: 0-4% ZrO2: 2-8%, 6% <Al2O3+ ZrO2< 12%、 R2O: 6-16% (where R is at least one of Li, Na, and K) Li2O: 0-3%, Na2O: 0-9% K2O: 4-16% Li2O + Na2O <K2O、 BaO and / or SrO: 0-7%, TiO2: 0-3% Based on the above, for a substantially 100 wt% composition, Ag: 0.15~1.0%, Cl and / or Br: greater than or equal to the stoichiometric equivalent of Ag. Preferably, it contains at least [the specified ingredient].

[0024] In polarized glass 10 manufactured by such a manufacturing process, needle-shaped metal nanoparticles are basically present only near the surface of the polarized glass 10 (i.e., in the metal layers 12 and 14), and the range of that region from the glass surface (i.e., the thickness of each of the metal layers 12 and 14) depends on the conditions of the reduction process, such as the ambient temperature and the time exposed to the reducing atmosphere. In other words, by controlling the conditions of the reduction process, the thickness of the metal layers 12 and 14 can be controlled, and the thickness of the metal halide layer 16 formed between the metal layers 12 and 14 can also be controlled.

[0025] The inventors then diligently investigated the heat resistance of the polarizing glass 10 and found that the glass transition temperature Tg of the polarizing glass 10 is approximately 500°C. However, as mentioned above, in the case of thicknesses of 0.20, 0.15, and 0.12 mm (i.e., in the case of conventional polarizing glass), the extinction ratio decreases below 500°C (i.e., the polarization characteristics deteriorate), and the amount of this decrease becomes more pronounced as the thickness of the polarizing glass increases (Figure 4). Regarding this, since the melting points of the halide metals CuCl, AgCl, and AgBr inside the polarizing glass are 430°C, 455°C, and 434°C, respectively, when the polarizing glass 10 is exposed to high temperatures of 430-455°C, the needle-shaped halide metals in the metal halide layer 16 liquefy, and the internal strain of the nearby metal layers 12 and 14 is relieved. As a result, the elongated needle-shaped form becomes blunt, the shape of the needle-shaped metal nanoparticles becomes blunt, and their aspect ratio (length-to-width ratio) decreases, which can be considered to result in a decrease in the extinction ratio. Furthermore, it can be considered that the heat of solidification released when the liquefied halide metal solidifies after the heat treatment similarly relieves the internal strain of the nearby metal layers 12 and 14, dulling the elongated needle-like shape and the shape of the needle-like metal nanoparticles, resulting in a decrease in their aspect ratio (length-to-width ratio) and consequently a decrease in the extinction ratio. Therefore, in this embodiment, the overall thickness of the polarizing glass 10 is reduced to control (i.e., thin) the thickness of the metal halide layer 16, thereby reducing the effects of liquefaction and solidification of the halide metal and improving the heat resistance of the polarizing glass 10. Generally, the extinction characteristics of the polarizing glass 10 vary depending on the aspect ratio (length-to-width ratio) of the needle-shaped metal nanoparticles, as well as their density, size, and the thickness of the metal layers 12 and 14. On the other hand, the insertion loss characteristics deteriorate if the needle-shaped metal nanoparticles become too large or if the thickness of the metal layers 12 and 14 becomes too thick. These parameters have an appropriate range depending on the composition of the polarizing glass 10, and are designed to be within this appropriate range as needed (details will be described later).

[0026] Another way to thin the metal halide layer 16 is to increase the thickness of the metal layers 12 and 14 without changing the overall thickness of the polarizing glass 10. However, this method has the problem that it takes time to thicken the metal layers 12 and 14 (i.e., the reduction process takes time), which increases costs.

[0027] Generally, the distance L over which hydrogen diffuses from the surface of the polarizing glass 10 is expressed by the following equation (1). L=2(Dt) 1 / 2 ...(1) Here, D is the diffusion coefficient and t is time. Since the diffusion distance L is proportional to the square root of time t, doubling the thickness of metal layers 12 and 14 will require four times the reduction time. Furthermore, when the metal layers 12 and 14 created in this manner are relatively thick, the boundary between the metal layers 12 and 14 and the metal halide layer 16 becomes difficult to observe. The inventors conducted thorough research and found that the boundaries between the metal layers 12 and 14 and the metal halide layer 16 can be clearly observed with an optical microscope or digital microscope (for example, a Keyence VHX series digital microscope) if the thickness of each metal layer 12 and 14 is 0.045 mm or less, and the measurement accuracy of each thickness can be measured within ±0.002 mm. However, when the thickness of each metal layer 12 and 14 exceeds 0.045 mm, the boundaries between the metal layers 12 and 14 and the metal halide layer 16 become unclear, resulting in measurement errors of ±0.005 mm or more. Furthermore, if the reduction time is extended and the thickness of the metal layers 12 and 14 exceeds 0.045 mm, there is a concern that a large amount of incompletely reduced portions, i.e., metal halides, will remain in the reduced metal layers 12 and 14. When a heat resistance test is performed on such polarizing glass 10 (i.e., when heated), the metal halides remaining in the metal layers 12 and 14, as described above, release solidification heat due to liquefaction and solidification during cooling, which relieves internal strain and dulls the shape of the needle-shaped metal nanoparticles. As a result, the aspect ratio of the metal nanoparticles decreases, and the extinction ratio decreases. Furthermore, if such metal halides are present inside the metal layers 12 and 14, the needle-shaped metal particles that affect them will be closer together, which is thought to lead to a greater decrease in the extinction ratio. In such a case, the heat resistance is not expected to improve significantly despite the increased thickness of the metal layers 12 and 14 and the thinning of the metal halide layer 16. Furthermore, if the thickness of the metal layers 12 and 14 is 0.010 mm or less, the thickness of the metal layers 12 and 14 that provide the polarization properties is too thin, and a sufficient extinction ratio cannot be obtained. Furthermore, the inventors have conducted thorough studies and found that in polarizing glass 10 with metal layers 12 and 14 with a thickness of 0.009 mm or less, the extinction ratio is approximately 25 dB, which is too low to be suitable for use as an optical isolator.

[0028] Thus, in this embodiment, the thickness of each metal layer 12, 14 is set to 0.010 to 0.045 mm, and the overall thickness of the polarizing glass 10 is reduced, thereby thinning the metal halide layer 16, reducing the effects of liquefaction and solidification of the halide metal, and improving the heat resistance of the polarizing glass 10. More specifically, the thickness of the polarizing glass 10 is set to less than 0.12 mm, and the thickness of the metal layers 12 and 14 is controlled by controlling the conditions of the reduction process. When the thickness of each metal layer 12 and 14 is 0.030 to 0.045 mm, the thickness of the metal halide layer 16 is set to be in the range of 0.001 to 0.040 mm, and when the thickness of each metal layer 12 and 14 is 0.010 to 0.030 mm, the thickness of the metal halide layer 16 is set to be in the range of 0.001 to 0.060 mm.

[0029] The polarizing glass 10 of this embodiment will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following embodiments.

[0030] (Example 1) [1. Manufacturing process of glass substrate] The polarizing glass 10 in Example 1 used a glass substrate with the following wt% composition: SiO2: 58.4, B2O3: 20.1, Al2O3: 6.7, AlF3: 2.0, Na2O: 8.8, NaCl: 1.7, Y2O3: 1.7, CuCl: 0.5, and SnO: 0.1. The raw materials were SiO2, H3BO3, Al(OH)3, AlF3, Na2CO3, NaCl, Y2O3, CuCl, and SnO, which were melted in a 5-liter platinum crucible at approximately 1450°C. The mixture was then poured into a graphite mold for shaping and slowly cooled to room temperature.

[0031] [2. Deposition process of metal halide fine particles] This glass substrate was placed in a heat-resistant mold and heat-treated at 700°C for 6 hours to precipitate CuCl fine particles.

[0032] [3. Preform Manufacturing Process] Afterward, it was processed into a preform with dimensions of 120 x 250 x 4 mm.

[0033] [4. Glass stretching process] By heating and stretching the preform in a wire drawing furnace at a temperature of approximately 620°C, a glass sheet with a width of approximately 18 mm and a thickness of approximately 0.5 mm was obtained.

[0034] [5. Polishing process] This glass sheet was cut and both sides were polished to produce two types of double-sided polished products with a main surface of 11 mm square and thicknesses of 0.1 mm and 0.08 mm.

[0035] [6. Reduction Process] These two types of double-sided polished products were subjected to heat treatment at 440°C for 7 hours in a hydrogen atmosphere. This reduced the stretched CuCl nanoparticles, precipitated needle-shaped Cu metal nanoparticles, and produced polarizing glass 10 with polarizing properties. Figure 3 is a digital microscope photograph showing a cross-section of the polarizing glass 10 of Example 1 after the reduction process. Figure 3(a) shows an example of a cross-section of the polarizing glass 10 with a thickness of 0.1 mm, and Figure 3(b) shows an example of a cross-section of the polarizing glass 10 with a thickness of 0.08 mm. As shown in Figure 3, the metal layers 12 and 14 formed on the front and back surfaces of the polarizing glass 10, and the metal halide layer (unreduced layer) 16 formed between the metal layers 12 and 14, are observed as differences in color. Note that the outer (left and right) parts of the polarizing glass 10 in Figure 3 are backgrounds prepared to clearly show the boundaries of the polarizing glass 10.

[0036] (Comparative Example 1) As Comparative Example 1, four types of polarizing glass with a main plane of 11 mm square and thicknesses of 0.06 mm, 0.12 mm, 0.15 mm, and 0.20 mm were fabricated using the same method as in Example 1.

[0037] Table 1 shows the cross-sectional structures of polarizing glass 10 from Example 1 and polarizing glass from Comparative Example 1. The metal layer thickness (one side), metal layer thickness (total of both sides), and unreduced layer thickness in Table 1 were obtained by splitting each sample in two and measuring the thickness of the metal layer (metal layers 12, 14: Cu layer (brown colored portion)) and the unreduced layer (metal halide layer 16: (uncolored portion)) in the thickness direction of the fracture surface using a digital microscope. The unit of each value in Table 1 is "mm". Also, "*" in Table 1 indicates Comparative Example 1.

[0038] [Table 1]

[0039] [Heat Resistance Test 1] For each sample of polarizing glass 10 from Example 1 and the polarizing glass from Comparative Example 1, the extinction ratio was measured at room temperature. Then, each sample was placed upright in a SUS holder and placed in an electric furnace, where it was heat-treated at temperatures of 420°C, 440°C, and 460°C for 2 hours. After heat treatment, the extinction ratio of each sample was measured, and the extinction ratios before and after heat treatment were compared.

[0040] Table 2 shows a comparison of the extinction ratio at a measurement wavelength of 1650 nm before and after heat treatment for polarizing glass 10 of Example 1 and polarizing glass of Comparative Example 1. The unit of each value in Table 2 is "dB". Also, "*" in Table 2 indicates Comparative Example 1.

[0041] [Table 2]

[0042] Table 2 clearly shows that the decrease in extinction ratio due to heat treatment at 460°C for 2 hours decreases as the thickness of the polarizing glass decreases. Furthermore, with a thickness of 0.12 mm (Comparative Example 1), the decrease in extinction ratio was -3.21 dB, which was about half the decrease compared to a thickness of 0.20 mm (Comparative Example 1). Also, with a thickness of 0.10 mm (Example 1) and a thickness of 0.08 mm (Example 1), the decrease in extinction ratio was -2.57 dB and -2.50 dB, respectively, which was about 40% of the decrease compared to a thickness of 0.20 mm. Furthermore, for thicknesses of 0.10 mm and 0.08 mm (Example 1), the decrease in extinction ratio was -3.00 dB or less in all heat treatments at 420°C, 440°C, and 460°C, clearly demonstrating extremely high heat resistance. Furthermore, in the sample with a thickness of 0.06 mm (Comparative Example 1) that lacked the metal halide layer 16 (unreduced layer), the thickness of the metal layers 12 and 14 was thinner compared to samples of other thicknesses. As a result, the extinction ratio before heat treatment was approximately 10 dB lower than that of samples of other thicknesses. Therefore, although the decrease in the extinction ratio after heat treatment was kept to a minimum, the extinction ratio after heat treatment was also lower than that of other samples due to the lower initial extinction ratio.

[0043] From the above, it was found that by setting the thickness of the polarizing glass 10 to less than 0.12 mm, the thickness of each metal layer 12 and 14 to 0.030 mm or more, and the thickness of the metal halide layer 16 to less than 0.044 mm, it is possible to make the material thinner than conventional materials while maintaining extremely high heat resistance. As mentioned above, if the thickness of the metal layers 12 and 14 becomes too thick, the reduction time will be required, and the boundary between the metal layers 12 and 14 and the metal halide layer 16 will become unclear. Furthermore, if the thickness exceeds 0.045 mm, there is a concern that halide metal may remain within the metal layers 12 and 14 near the boundary with the metal halide layer 16. Therefore, it was found that it is preferable to set the thickness of each metal layer 12 and 14 to 0.030 to 0.045 mm. Furthermore, it was found that if the total thickness of the polarizing glass becomes too thin, the metal halide layer 16 disappears, and the thickness of the metal layers 12 and 14 that produce the extinction properties also becomes thin, a sufficient extinction ratio cannot be obtained. Therefore, it was found that it is preferable to set the thickness of the metal halide layer 16 to 0.001 to 0.040 mm. Moreover, setting the thickness of the metal halide layer 16 to 0.001 to 0.030 mm is even preferable in terms of heat resistance.

[0044] (Example 2) [1. Manufacturing process of glass substrate] The polarizing glass 10 in Example 2 used a glass substrate with the following wt% composition: SiO2: 58.7, B2O3: 18.0, Al2O3: 2.0, Li2O: 1.8, K2O: 7.9, BaO: 3.4, TiO2: 1.5, ZrO2: 5.9, Ag: 0.3, and Cl: 0.5. The raw materials used were SiO2, H3BO3, Al(OH)3, Li2CO3, K2CO3, KNO3, BaCO3, TiO2, ZrO2, KCl, and AgCl. These were melted in a 5-liter platinum crucible at approximately 1450°C, then poured into a graphite mold for shaping, and slowly cooled to room temperature.

[0045] [2. Deposition process of metal halide fine particles] This glass substrate was placed in a heat-resistant mold and heat-treated at 720°C for 6 hours to precipitate AgCl fine particles.

[0046] [3. Preform Manufacturing Process] Afterward, it was processed into a preform with dimensions of 110 x 280 x 4 mm.

[0047] [4. Glass stretching process] By heating and stretching the preform in a wire drawing furnace at a temperature of approximately 640°C, a glass sheet with a width of approximately 17 mm and a thickness of approximately 0.6 mm was obtained.

[0048] [5. Polishing process] This glass sheet was cut and both sides were polished to produce three types of double-sided polished products with a main surface of 11 mm square and thicknesses of 0.1 mm, 0.08 mm, and 0.06 mm.

[0049] [6. Reduction Process] These three types of double-sided polished products were subjected to heat treatment at 440°C for 4 hours in a hydrogen atmosphere. This reduced the stretched AgCl nanoparticles, precipitated needle-shaped Ag metal nanoparticles, and produced polarizing glass 10 with polarizing properties.

[0050] (Comparative Example 2) As Comparative Example 2, four types of polarizing glass with a main plane of 11 mm square and thicknesses of 0.046 mm, 0.12 mm, 0.15 mm, and 0.20 mm were fabricated using the same method as in Example 2.

[0051] Table 3 shows the cross-sectional structures of polarizing glass 10 from Example 2 and polarizing glass from Comparative Example 2. The metal layer thickness (one side), metal layer thickness (total of both sides), and unreduced layer thickness in Table 3 were obtained by splitting each sample in two and measuring the thickness of the metal layer (metal layers 12, 14: Ag layer (yellowish-brown colored portion)) and the unreduced layer (metal halide layer 16: (uncolored portion)) in the thickness direction of the fracture surface using an optical microscope. The unit of each value in Table 3 is "mm". Also, in Table 3, "*" indicates Comparative Example 2.

[0052] [Table 3]

[0053] [Heat resistance test 2] For each sample of polarizing glass 10 from Example 2 and the polarizing glass from Comparative Example 2, the extinction ratio was measured at room temperature. Then, each sample was placed upright in a SUS holder and placed in an electric furnace, where it was heat-treated at temperatures of 420°C, 440°C, and 460°C for 2 hours. After heat treatment, the extinction ratio of each sample was measured, and the extinction ratios before and after heat treatment were compared.

[0054] Table 4 shows a comparison of the extinction ratio at a measurement wavelength of 1650 nm before and after heat treatment for polarizing glass 10 of Example 2 and polarizing glass of Comparative Example 2. The unit of each value in Table 4 is "dB". Also, "*" in Table 4 indicates Comparative Example 2.

[0055] [Table 4]

[0056] Table 4 shows that the decrease in extinction ratio due to heat treatment at 460°C for 2 hours decreases as the thickness of the polarizing glass decreases. Furthermore, for thicknesses of 0.10 mm, 0.08 mm, and 0.06 mm (Example 2), the decrease in extinction ratio was -2.62 dB or less in all heat treatments at 420°C, 440°C, and 460°C, clearly demonstrating extremely high heat resistance. Furthermore, in the sample with a thickness of 0.046 mm (Comparative Example 2) that lacked the metal halide layer 16 (unreduced layer), the thickness of the metal layers 12 and 14 was thinner compared to samples of other thicknesses. As a result, the extinction ratio before heat treatment was approximately 10 dB lower than that of samples of other thicknesses. Therefore, although the decrease in the extinction ratio after heat treatment was kept to a minimum, the extinction ratio after heat treatment was also lower than that of other samples due to the lower initial extinction ratio.

[0057] From the above, it was found that in Example 2, by setting the thickness of the polarizing glass 10 to less than 0.12 mm, the thickness of each metal layer 12 and 14 to 0.028 mm (≒0.030 mm) or less, and the thickness of the metal halide layer 16 to less than 0.064 mm, it is possible to make the material thinner than conventional materials while maintaining extremely high heat resistance. As mentioned above, when the thickness of the metal layers 12 and 14 is 0.010 mm or less, the thickness of the metal layers 12 and 14 that provide the polarization characteristics is too thin, and a sufficient extinction ratio cannot be obtained. Therefore, it was found that it is preferable to set the thickness of the metal layers 12 and 14 to 0.010 to 0.030 mm. Furthermore, it was found that if the total thickness of the polarizing glass becomes too thin, the metal halide layer 16 disappears, and the thickness of the metal layers 12 and 14 that produce the extinction properties also becomes thin, a sufficient extinction ratio cannot be obtained. Therefore, it was found that it is preferable to set the thickness of the metal halide layer 16 in the range of 0.001 to 0.060 mm. Moreover, setting the thickness of the metal halide layer 16 in the range of 0.001 to 0.050 mm is even more preferable from the standpoint of heat resistance.

[0058] (Comparison between Example 1 (Comparative Example 1) and Example 2 (Comparative Example 2)) Comparing the polarizing glass with a thickness of 0.06 mm in Comparative Example 1 (Tables 1 and 2) with the polarizing glass with a thickness of 0.046 mm in Comparative Example 2 (Tables 3 and 4), both had an unreduced layer thickness of 0.000 mm. However, the decrease in extinction ratio after heat treatment at 460°C for 2 hours in the 0.06 mm thick polarizing glass of Comparative Example 1 was -2.31 dB (Table 2), while in the 0.046 mm thick polarizing glass of Comparative Example 2 it was -1.69 dB. In other words, the decrease in extinction ratio was suppressed more in the 0.046 mm thick polarizing glass of Comparative Example 2 compared to the 0.06 mm thick polarizing glass of Comparative Example 1. This is because the thickness of each metal layer 12 and 14 was 0.030 mm in the polarizing glass with a thickness of 0.06 mm in Comparative Example 1, and 0.023 mm in the polarizing glass with a thickness of 0.046 mm in Comparative Example 2. The polarizing glass with a thickness of 0.06 mm in Comparative Example 1 had thicker metal layers 12 and 14, and as mentioned above, it contained more insufficiently reduced metal halides within the metal layers 12 and 14. Therefore, after heat treatment at 460°C for 2 hours, the liquefaction and solidification of the remaining metal halides caused a greater blunting of the needle-shaped metal nanoparticles, and a greater decrease in the extinction ratio.

[0059] Furthermore, comparing the polarizing glass 10 with a thickness of 0.08 mm in Example 1 (Tables 1 and 2) and the polarizing glass 10 with a thickness of 0.06 mm in Example 2 (Tables 3 and 4), both have an unreduced layer thickness of 0.004 mm. However, the decrease in extinction ratio after heat treatment at 460°C for 2 hours in the 0.08 mm thick polarizing glass 10 of Example 1 was -2.50 dB (Table 2), while in the 0.06 mm thick polarizing glass 10 of Example 2 it was -1.82 dB. In other words, the decrease in extinction ratio is suppressed more in the 0.06 mm thick polarizing glass 10 of Example 2 compared to the 0.08 mm thick polarizing glass 10 of Example 1. The reason for this is the same as that stated in the comparison between the 0.06 mm thick polarizing glass of Comparative Example 1 and the 0.046 mm thick polarizing glass of Comparative Example 2. The 0.08 mm thick polarizing glass 10 of Example 1 has thicker metal layers 12 and 14, and therefore contains more insufficiently reduced metal halides. After heat treatment at 460°C for 2 hours, the liquefaction and solidification of the remaining metal halides caused a greater blunting of the needle-shaped metal nanoparticles, resulting in a greater decrease in the extinction ratio.

[0060] Furthermore, comparing the polarizing glass 10 with a thickness of 0.10 mm in Example 1 (Tables 1 and 2) with the polarizing glass 10 with a thickness of 0.10 mm in Example 2 (Tables 3 and 4), the decrease in extinction ratio after heat treatment at 460°C for 2 hours in the polarizing glass 10 with a thickness of 0.10 mm in Example 1, which had an unreduced layer thickness of 0.024 mm, was -2.57 dB (Table 2), while the decrease in extinction ratio in the polarizing glass 10 with a thickness of 0.10 mm in Example 2, which had an unreduced layer thickness of 0.044 mm, was -2.62 dB. In other words, the decrease in extinction ratio was about the same for the polarizing glass 10 with a thickness of 0.10 mm in Example 1 and the polarizing glass 10 with a thickness of 0.10 mm in Example 2. The reason for this is the same as the reason mentioned above; the polarizing glass 10 with a thickness of 0.10 mm in Example 2 has thinner metal layers 12 and 14, and therefore fewer insufficiently reduced metal halides in the metal layers 12 and 14, resulting in a lower extinction ratio after heat treatment at 460°C for 2 hours. relatively It is kept low, and the thickness of the unreduced layer is From the polarizing glass 10 with a thickness of 0.10 mm in Example 1 Even with a thickness increase of 0.020 mm, the overall decrease in extinction ratio after heat treatment is considered to be about the same as that of the 0.10 mm thick polarizing glass 10 in Example 1.

[0061] The above describes embodiments of the present invention, but the present invention is not limited to the configuration of the above embodiments, and various modifications are possible within the scope of its technical concept.

[0062] It should be noted that the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0063] 10: Polarized glass 10A: Polarizing element 10B: Polarizing element 12: Metal layer 14: Metal layer 16: Metal halide layer 100: Optical Isolator 110: Faraday rotor 115: Lens 115': Lens 116: Optical fiber 117 :Light source 118: Return beam 118': Returning beam

Claims

1. A polarizing glass having a metal layer formed from both surfaces toward the interior, in which numerous roughly needle-shaped metal nanoparticles are oriented and dispersed in parallel, and a metal halide layer containing metal halide nanoparticles is formed between the metal layers, The total thickness of the polarizing glass is less than 0.12 mm. The thickness of the aforementioned metal layer is 0.030 to 0.045 mm. The thickness of the metal halide layer is 0.001 to 0.030 mm. The metal nanoparticles are copper nanoparticles. Polarizing glass characterized by the following features.

2. A polarizing glass having a metal layer formed from both surfaces toward the interior, in which numerous roughly needle-shaped metal nanoparticles are oriented and dispersed in parallel, and a metal halide layer containing metal halide nanoparticles is formed between the metal layers, The total thickness of the polarizing glass is 0.08 mm or less. The thickness of the aforementioned metal layer is 0.010 to 0.030 mm. The thickness of the metal halide layer is 0.001 to 0.060 mm. The metal nanoparticles are silver nanoparticles. Polarizing glass characterized by the following features.

3. A polarizing glass having a metal layer formed from both surfaces toward the interior, in which numerous roughly needle-shaped metal nanoparticles are oriented and dispersed in parallel, and a metal halide layer containing metal halide nanoparticles is formed between the metal layers, The raw material composition includes 7 wt% or less of BaO or SrO as an essential component. The total thickness of the polarizing glass is less than 0.12 mm. The thickness of the aforementioned metal layer is 0.010 to 0.030 mm. The thickness of the metal halide layer is 0.001 to 0.060 mm. The metal nanoparticles are silver nanoparticles. Polarizing glass characterized by the following features.

4. A polarizing glass having a metal layer formed from both surfaces toward the interior, in which a large number of substantially needle-shaped metal nanoparticles are oriented and dispersed in parallel, and a metal halide layer containing metal halide nanoparticles is formed between the metal layers, The total thickness of the polarizing glass is 0.06 to 0.08 mm. The thickness of the aforementioned metal layer is 0.010 to 0.030 mm. The thickness of the metal halide layer is 0.004 to 0.024 mm. The metal nanoparticles are silver nanoparticles. Polarizing glass characterized by the following features.

5. An optical isolator characterized by comprising a polarizing glass according to any one of claims 1 to 4.

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