Optical isolator

Abstract

To provide an optical isolator capable of effectively reducing the influence of heat generation and having high light resistance.SOLUTION: An optical isolator comprises one or more metal particle-dispersed glass polarizers and one or more Faraday rotators in a propagation direction of light. An optical transmission plate having higher thermal conductivity than the metal particle-dispersed glass polarizers and a refractive index of 2.5 or less at a use wavelength is joined to at least one of the light transmission surfaces of the metal particle-dispersed glass polarizers without use of an organic adhesive.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical isolator used in, for example, optical communications and optical measurements. [Background technology]

[0002] In optical communications and optical measurement, if light emitted from a semiconductor laser is reflected by the surface of a component installed along the transmission path and the reflected light returns to the semiconductor laser, the laser oscillation becomes unstable. To block this reflected light, an optical isolator is used that uses a Faraday rotator, which rotates the polarization plane non-reciprocally.

[0003] An optical isolator typically consists of one or more polarizers arranged in the direction of light transmission, one or more Faraday rotators, and magnets arranged around these to apply a magnetic field parallel to the direction of propagation of the transmitted light.

[0004] For example, in an optical isolator consisting of a Faraday rotator, two polarizers positioned on either side of the Faraday rotator in the direction of light transmission, and a magnet positioned around the Faraday rotator to apply a magnetic field parallel to the direction of light transmission, incident light is linearly polarized by the first polarizer and passes through the Faraday rotator. The incident linearly polarized light has its polarization plane rotated by 45° by the Faraday rotator and exits through the second polarizer, whose transmitted polarization plane is tilted 45° from the vertical. The returning light contains various polarization components, but only the polarization component tilted 45° from the vertical passes through the second polarizer. This polarization component is rotated by 45° by the Faraday rotator and becomes polarized light tilted perpendicular to the transmitted polarization plane of the first polarizer. Therefore, it cannot pass through the first polarizer, and no light returns to the light source. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-281129 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-43853 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-108344 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, optical isolators have been required to support the increasing power of laser light sources. One of the challenges in supporting high-power laser light sources is the temperature rise caused by light absorption in the Faraday rotator. When the temperature of the Faraday rotator rises, the Faraday rotation angle changes, degrading the extinction ratio and other characteristics of the optical isolator.

[0007] Various proposals have been made to solve these problems. For example, Patent Document 1 proposes a configuration in which a magneto-optical crystal is sandwiched between garnet substrates. However, the thermal conductivity of the garnet substrate is insufficient, and it is difficult to suppress the temperature rise of the Faraday rotator at an output exceeding 100 mW.

[0008] In addition, in Patent Document 2, a sapphire single crystal, which exhibits high thermal conductivity, is brought into contact with the Faraday rotator to enhance the heat dissipation effect. However, since the sapphire single crystal is a birefringent crystal, there is a problem that the extinction ratio deteriorates depending on the angle of incidence of light.

[0009] In Patent Document 3, the deterioration of the extinction ratio is prevented by aligning the crystal axis directions of the wedge-shaped birefringent crystal plate and the sapphire single crystal plate. However, the manufacturing process, which requires consideration of the crystal axis of the transparent crystal plate, becomes very complicated.

[0010] In optical communications, efforts are being made to increase the optical output of individual LD ​​(Laser Diode) chips used in order to achieve high speeds, high optical density, and long distances, and to reduce the number of repeaters. To reduce the number of optical components such as optical isolators, the signal light from the LD chip is further multiplexed with four or eight waves before passing through the optical isolator. As a result, the signal light passing through the optical isolator has increased from the previous level of around several to 20 mW to around 150 to 500 mW.

[0011] Because the incident light is polarized LD light, polarization with an extinction ratio of about 20 dB (100:1) is transmitted, and by aligning the incident polarization of the optical isolator, it is transmitted with a loss of about 0.07 to 0.1 dB (transmittance of 97.7 to 98.4%, which corresponds to a maximum optical absorption of about 12 mW when calculated from the signal light). On the other hand, if we assume that 4% reflection occurs at the glass end of the fiber, etc., the amount of light will be equivalent to 20 mW, and that light will be absorbed by the optical isolator and converted to heat. Furthermore, if we assume that there is a high optical reflection of about 30% due to the presence of other reflective media such as prisms or amplifiers, the amount of light will be about 150 mW, and that light will be absorbed by the optical isolator and converted to heat.

[0012] In experiments with laser light reflection and folding at the near end, polarized light returns unchanged to the optical isolator, allowing it to pass through the second polarizer without modification, while the first polarizer blocks the light. The backscattered light from the polarizer surface (approximately 5-8% of the returned light) and the polarizer completely blocks the light (the remaining 92-95% of the returned light) are absorbed and converted into heat. As a result of this concentrated heat transfer, the adhesive layer at the interface between the first polarizer and the Faraday rotator breaks. Alternatively, when the polarization state of the returned light is close to circular polarization, the second polarizer absorbs 3 dB (equivalent to 50%) of the returned light and converts it into heat, causing heat concentration that breaks the adhesive layer between the second polarizer and the Faraday rotator.

[0013] The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical isolator that can effectively reduce the influence of heat generation and has high light resistance. [Means for solving the problem]

[0014] The present invention has been made to achieve the above-mentioned object, and provides an optical isolator equipped with one or more metal particle dispersed glass polarizers and one or more Faraday rotators in the direction of light propagation, in which a light-transmitting plate having a higher thermal conductivity than the metal particle dispersed glass polarizer and a refractive index of 2.5 or less at the wavelength used is bonded to at least one of the light-transmitting surfaces of the metal particle dispersed glass polarizer without using an organic adhesive.

[0015] Such an optical isolator can effectively reduce the influence of heat generation and has high light resistance.

[0016] In this case, the optical isolator can be one in which the light-transmitting plate is provided on the light-transmitting surface of the metal particle-dispersed glass polarizer on the Faraday rotator side, and the light-transmitting plate and the Faraday rotator are joined together via an organic adhesive.

[0017] This makes it possible to more effectively prevent distortion caused by differences in the thermal expansion coefficients between the materials from affecting the optical characteristics, and also makes it easier to set up the polarizer.

[0018] In this case, the optical isolator can be one that is attached to the end of an optical fiber, and has the light-transmitting plate on the light-transmitting surface of the metal particle-dispersed glass polarizer opposite the Faraday rotator, and the end of the optical fiber can be attached to the light-transmitting plate.

[0019] This allows the light from the optical fiber to spread more widely, increasing the beam diameter that reaches the optical isolator material, and further reducing the influence of heat. [Effects of the Invention]

[0020] As described above, the optical isolator of the present invention can effectively reduce the influence of heat generation and has high light resistance. [Brief explanation of the drawings]

[0021] [Figure 1] 1 shows an example (cross-sectional view) of an optical isolator using a polarizer and a Faraday rotator bonded to a light-transmitting plate. [Figure 2] 1 shows an example of an optical isolator attached to the end of an optical fiber. [Figure 3] 1 shows an example (cross-sectional view) of a metal particle dispersed glass polarizer. [Figure 4] 1 shows an example (cross-sectional view) in which a light-transmitting plate according to the present invention is bonded to the metal particle reduction layer surface of a metal particle dispersed glass polarizer. [Figure 5] 1 shows an example (cross-sectional view) of an optical isolator according to a conventional example (Comparative Example 1). [Figure 6] 1 shows an example (cross-sectional view) of an optical isolator according to a conventional example (Comparative Example 2) attached to the end of an optical fiber. [Figure 7] Assuming that the light-transmitting plate is 0.2 mm thick and the NA of the optical fiber (SM fiber) is 0.14, the refractive index dependence of the ratio between the spreading area of ​​light passing through the light-transmitting plate and the area at the core end of the optical fiber is shown. [Figure 8] The figure shows the optical fiber end area comparison when the thickness of the light-transmitting plate is changed. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in detail below, but the present invention is not limited thereto.

[0023] As described above, there has been a demand for an optical isolator that can effectively reduce the effects of heat generation and has high light resistance.

[0024] As a result of extensive research into the above-mentioned problems, the inventors have discovered that an optical isolator comprising one or more metal particle-dispersed glass polarizers and one or more Faraday rotators in the direction of light propagation, in which a light-transmitting plate having a higher thermal conductivity than the metal particle-dispersed glass polarizers and a refractive index of 2.5 or less at the wavelength used is bonded to at least one of the light-transmitting surfaces of the metal particle-dispersed glass polarizers without an organic adhesive, can effectively reduce the effects of heat generation and provide an optical isolator with high light resistance. This invention is described below with reference to the drawings.

[0025] [Optical isolator] First, an optical isolator according to the present invention will be described. FIG. 1 shows an example of an optical isolator 100 using a metal particle dispersed glass polarizer bonded with a light-transmitting plate and a Faraday rotator. As shown in FIG. 1, the optical isolator 100 according to the present invention comprises one or more metal particle dispersed glass polarizers 2 (first glass polarizer 8, second glass polarizer 9) and one or more Faraday rotators 1 in the direction of light propagation. A light-transmitting plate 4 is bonded to at least one of the light-transmitting surfaces of the metal particle dispersed glass polarizer 2 without using an organic adhesive. The light-transmitting plate 4 has a higher thermal conductivity than the metal particle dispersed glass polarizer 2 and a refractive index at the wavelength used of 0.01 mm. 2.5 The following is used. In this type of optical isolator, backscattered light is diffused by the light-transmitting plate 4, and heat generated by light absorption in the metal particle dispersed glass polarizer is also transferred by the light-transmitting plate 4, reducing thermal damage to the adhesive layer between the light-transmitting plate 4 and the Faraday rotator. This effectively reduces the effects of heat generation, resulting in a highly light-resistant isolator.

[0026] The light-transmitting plate 4 and the Faraday rotator 1 can be joined without using an organic adhesive (even by direct joining). However, it has been found that distortion due to differences in the thermal expansion coefficients between the materials affects the optical characteristics (deterioration of isolation and increase in insertion loss), and it becomes difficult to precisely align the polarizer's relative angle of 45°. To achieve high isolation, the relative angles of the two materials must be aligned while the laser light is transmitted through them. However, adhesive-free joining requires that the bonding strength be ensured by plasma activation treatment of the material surfaces in a vacuum, which are contradictory processes.

[0027] Therefore, it is preferable to install a light-transmitting plate 4 on the light-transmitting surface of the metal particle-dispersed glass polarizer 2 on the Faraday rotator 1 side, and bond the light-transmitting plate 4 to the Faraday rotator 1 via an adhesive layer 5 made of an organic adhesive. Such an optical isolator can more effectively prevent distortion caused by differences in thermal expansion coefficients between materials from affecting the optical characteristics, and also makes it easy to set the polarizer. Furthermore, the alignment of the relative angles of the polarizers is easy in that the bonding process using an organic adhesive allows high-precision alignment while transmitting laser light, and the adhesive layer can absorb bonding distortion between the materials.

[0028] Furthermore, as shown in FIG. 2, the optical isolator according to the present invention is preferably attached to the end of an optical fiber and includes a light-transmitting plate 4 on the light-transmitting surface of the metal particle-dispersed glass polarizer 2 opposite the Faraday rotator 1, with the end of the optical fiber 7 attached to this light-transmitting plate 4. This type of optical isolator increases the divergence of light from the optical fiber, thereby increasing the beam diameter reaching the optical isolator material and further reducing thermal effects. FIG. 7 shows the refractive index dependence of the ratio of the divergence area of ​​light passing through the light-transmitting plate to the area at the core end of the optical fiber, assuming a light-transmitting plate thickness of 0.2 mm and an optical fiber (SM fiber) with an NA of 0.14. It can be seen that a refractive index of 2.5 or less is desirable to achieve a 5-fold increase or more in the area at the optical fiber end to reduce thermal effects. FIG. 8 also shows the comparison of the optical fiber end area with different thicknesses of the light-transmitting plate. A thicker plate increases the diffusion area, but this also increases the length of the isolator's light-transmitting section, resulting in a larger isolator.

[0029] The wavelength used in the optical isolator according to the present invention is not particularly limited, but may be, for example, 1100 nm or more and 2500 nm or less. Each element of the optical isolator according to the present invention will be described in more detail below.

[0030] (Metal particle dispersed glass polarizer) First, we will explain the metal particle dispersion glass polarizer. The metal particle dispersion glass polarizer 2 used in the present invention is not particularly limited as long as it is a glass polarizer in which metal particles are dispersed. Its polarization mechanism is due to the resonance absorption of conduction electrons in the metal particles. Examples of such metal particle dispersion glass polarizer 2 that can be used include Polarcor manufactured by Corning, CUPO manufactured by HOYA, and colorPol manufactured by CODIXX.

[0031] The metal particle dispersion glass polarizer 2 can have a total thickness of, for example, 0.2 mm to 0.5 mm, and the surface layer, approximately 0.05 to 0.10 mm thick, is a reduction layer 3, in which metal particles are formed by reducing metal halide through a glass material reduction process (Figures 3 and 4(a)). The orientation of this reduction layer 3 is the mechanism for controlling transmitted polarization. The light that is blocked can be broadly divided into light that hits the metal particles and is scattered backward by about 5 to 8%, and light that hits the metal particles and is absorbed and converted to heat. Note that if the thickness of the metal particle dispersion glass polarizer 2 is thin (e.g., 0.15 mm or less), it is possible for the entire metal particle dispersion glass polarizer 2 to have a structure in which the reduction layer 3 is the entire layer (Figure 4(b)).

[0032] It is preferable that one side of the metal particle dispersed glass polarizer 2 is coated with an air AR coating, and the other side is coated with an anti-reflection coating that matches the refractive index of the light-transmitting plate described below.

[0033] (light transmitting plate) Next, the light-transmitting plate will be described. As described above, the light-transmitting plate according to the present invention has higher thermal conductivity (thermal conductivity) than a metal particle-dispersed glass polarizer and a refractive index of 2.5 or less at the wavelength used. Furthermore, it is preferable that the light-transmitting plate has high transmittance in the light wavelength range used and high extinction performance of 35 dB or more (small strain within the material).

[0034] Table 1 shows examples of materials that can be used as light-transmitting plates, along with examples of metal particle-dispersed glass polarizers and Faraday rotators. Note that these are examples of characteristics for wavelengths between 1100 nm and 2500 nm.

[0035] [Table 1]

[0036] Specific materials that can be used for the light-transmitting plate of the optical isolator according to the present invention include quartz (SiO2), YAG, GGG, Y2O3, CaF2, Al2O3, and MgO, among the materials listed in Table 1. Materials with a thermal expansion coefficient within ±30% of the thermal expansion coefficient of the metal particle dispersed glass polarizer are more preferable. In actual usage environments, temperature fluctuations of -40 to +100°C are expected, and considering ease of processing, YAG, GGG, and the like, which have thermal expansion coefficients closer to those of the metal particle dispersed glass polarizer, are particularly preferable for the light-transmitting plate.

[0037] The method for bonding the light-transmitting plate 4 to the light-transmitting surface of the metal particle-dispersed glass polarizer 2 is not particularly limited as long as it is bonded via an organic adhesive. For example, possible methods include a method of plasma-activating the material surface in a vacuum and then bonding, a method of atomic diffusion on the material surface, a method of hydrophilizing the material surface and then bonding, and a method of bonding by anodic bonding.

[0038] Figure 3 shows an example (cross-section) of a metal particle dispersion glass polarizer. One side of the flat metal particle dispersion glass polarizer 2 can be coated with an air-resistant AR coating, and the other side can be coated with an anti-reflection coating that matches the refractive index of the light-transmitting heat diffusion plate. The flat metal particle dispersion glass polarizer 2 coated with the anti-reflection coating is then bonded to a 0.2 mm-thick light-transmitting plate 4 without the use of an organic adhesive.

[0039] Figure 4(a) shows an example of joining a 0.5 mm thick metal particle dispersed glass polarizer 2 (part of which is a reduced layer 3) to a light-transmitting plate 4, and Figure 4(b) shows an example of joining a 0.12 mm thick metal particle dispersed glass polarizer 2 (the entirety of which is a reduced layer 3) to a light-transmitting plate 4.

[0040] (Faraday rotator) Next, the Faraday rotator will be described. A Faraday rotator has the property of rotating the polarization direction of light when a magnetic field is applied (magneto-optical effect = Faraday effect). The Faraday rotator used in the optical isolator according to the present invention is not particularly limited, but for example, bismuth-substituted rare earth iron garnet, Y3Fe5O 12 (YIG), Tb3Ga5O 12(TGG), etc. An anti-reflection coating (anti-adhesive AR coating) such as an anti-epoxy AR coating may be applied to the interface between the adhesive (adhesive layer 5) and the Faraday rotator 1.

[0041] (others) As shown in Figures 1 and 2, a permanent magnet 6 or the like can be provided as a means for applying a magnetic field to the Faraday rotator 1. The permanent magnet 6 is not particularly limited, but examples thereof include SmCo magnets and NdFeB magnets. The permanent magnet 6 is preferably hollow and cylindrical. A single magnet of the desired shape may be used, or multiple magnets may be combined to form the desired shape. The metal particle dispersed glass polarizer 2, the light-transmitting plate 4, and the Faraday rotator 1 are preferably in contact with the permanent magnet 6. This configuration allows heat generated by the metal particle dispersed glass polarizer 2 to be more effectively dissipated through the light-transmitting plate 4 and the permanent magnet 6.

[0042] Furthermore, it is also preferable to provide heat dissipation members with higher thermal conductivity than the permanent magnets 6 between the metal particle dispersed glass polarizer 2, light transmitting plate 4, Faraday rotator 1, and permanent magnets 6, so that the metal particle dispersed glass polarizer 2, light transmitting plate 4, and Faraday rotator 1 come into contact with the heat dissipation members. This allows for more effective dissipation of heat generated by the metal particle dispersed glass polarizer 2. Examples of heat dissipation members that can be used include stainless steel (SUS304, SUS430), carbon steel, aluminum, brass, copper, and alumina, and it is preferable to use a material with a thermal conductivity of 20 W / (m·K) or higher. [Example]

[0043] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0044] (Comparative Example 1) Fig. 5 shows an example of the configuration of an optical isolator 300 using glass polarizers. The first glass polarizer 8 and the second glass polarizer 9 are flat-plate metal particle-dispersed glass polarizers 2 (Corning Polarcor) in which metal particles (Ag particles) are oriented. The first glass polarizer 8 and the second glass polarizer 9 are fixed to the Faraday rotator 1 via adhesive layer 5, which is a thermosetting epoxy adhesive. A permanent magnet 6 for applying a magnetic field is placed outside the polarizer. The Faraday rotator 1 is made of (GdBi)3(FeGa)5O 12 was used.

[0045] The fabrication method was as follows. The surfaces of the first and second glass polarizers 8 and 9 (11 mm square, 0.2 mm thick, 52 dB extinction) were coated with an air-resistant AR coating at 1550 nm. A 45.0° Faraday rotator 1 (11 mm square, 0.54 mm thick) at 1550 nm was coated with an epoxy coating on both sides and bonded to the uncoated surfaces of the first and second glass polarizers 8 and 9 using epoxy adhesive. The first and second glass polarizers 8 and 9 were then bonded and fixed so that the relative angle was 45.0°. The polarizers were then cut to 2 mm square and inserted into a permanent magnet (outer diameter φ5.0 mm x inner diameter φ2.9 mm x length 1.2 mm) for bonding and fixing.

[0046] When polarized CW light with a beam diameter of 0.2 mm and an output of 150 mW was incident from the output side of the second glass polarizer 9, aligned with the transmission polarization axis of the second glass polarizer, damage occurred after approximately 30 minutes, with holes appearing in the beam transmission section of the adhesive layer 5 at the interface between the first glass polarizer 8 and the Faraday rotator 1. Similarly, when polarized CW light with a beam diameter of 0.2 mm and an output of 150 mW was incident in a direction offset by approximately 45 degrees from the transmission polarization axis of the second glass polarizer 9, damage occurred after approximately 40 minutes, with holes appearing in the adhesive layer 5 at the interface between the second glass polarizer 9 and the Faraday rotator 1. In both cases, no damage was observed within the Faraday rotator or glass polarizer, suggesting that the adhesive layer was damaged by the heat generated when light absorbed in the metal particle reduction layer of the metal particle-dispersed glass polarizer was converted to heat.

[0047] (Comparative Example 2) FIG. 6 shows an example of an optical isolator 400 according to a conventional example (Comparative Example 2) attached to the end of an optical fiber, as another example of an optical isolator configuration. The differences from FIG. 5 are that the output surface of the second glass polarizer 9 is not AR-coated, and that the optical fiber fixing member 10, such as a ferrule, is fixed to the fixing surface of the optical fiber 7 with an epoxy adhesive (adhesive layer 5). When 150 mW polarized CW light was incident on the optical fiber 7 side and its polarization direction was rotated, it was confirmed that when the polarization axis was perpendicular to the transmission polarization axis of the second glass polarizer 9, the adhesive layer 5 at the output end of the optical fiber was first damaged, followed by damage to the Faraday rotator 1 and the adhesive layer 5 between the second glass polarizer 9. When the transmission polarization axis was aligned with that of the second glass polarizer 9, it was confirmed that the bonding interface between the first glass polarizer 8 and the Faraday rotator 1 was broken. This result was similar to that of the configuration example of Comparative Example 1 in FIG. 5, which did not have a fiber fixing member.

[0048] Example 1

[0049] The structure of a metal particle dispersed glass polarizer is shown in Figure 3. One side of the flat metal particle dispersed glass polarizer 2 is coated with an air AR coating, and the other side is coated with an anti-reflection coating that matches the refractive index of the light-transmitting heat diffusion plate.

[0050] A flat metal particle-dispersed glass polarizer 2 with an anti-reflection coating was bonded to a 0.2 mm-thick light-transmitting plate 4 without using an organic adhesive. In this example, the bonding was performed after plasma activation of the material surfaces in a vacuum.

[0051] Figure 4(a) shows an example of an actual fabricated metal particle dispersed glass polarizer 2 with a thickness of 0.5 mm bonded to a light-transmitting plate 4 made of Y2O3, and Figure 4(b) shows an example of an actual fabricated metal particle dispersed glass polarizer 2 with a thickness of 0.12 mm bonded to a light-transmitting plate 4 made of YAG.

[0052] In Example 1, the fabricated structure shown in Fig. 4(b) and a Faraday rotator were used, and they were bonded and fixed with epoxy adhesive while adjusting the relative angle of the polarizer to 45°. The light-transmitting plate 4 bonded to the polarizer was fixed in a configuration facing the Faraday rotator (Fig. 1).

[0053] Polarized CW light with a beam diameter of 0.2 mm and an output of 150 mW was incident on the output side of the second glass polarizer 9, aligned with the transmission polarization axis of the second glass polarizer 9. After approximately 60 minutes, no changes were observed in the light-transmitting plate 4, whether made of quartz, YAG, GGG, Al2O3, or MgO. After 10 hours, discoloration began to appear around the adhesive on the quartz material, but no abnormalities were observed with other materials. Similarly, when polarized CW light with a beam diameter of 0.2 mm and an output of 150 mW was incident in a direction offset by approximately 45 degrees from the transmission polarization axis of the second glass polarizer, no abnormalities were observed in the adhesive layer of any material after approximately 60 minutes.

[0054] Next, we conducted heat and light resistance tests. When the temperature of the optical isolator was changed over a range of -40 to +100, the isolation at the four corners of the chip was 3 to 5 dB lower than at the center for quartz, Al2O3, and MgO. We believe this is because the joint between the heat sink and the borosilicate glass polarizer had distortion due to differences in thermal expansion coefficients, which ultimately deteriorated the extinction performance of the glass polarizer and led to a deterioration in isolation.

[0055] (Comparative Example 3) As Comparative Example 3, a heat and light resistance test was conducted using an optical isolator made of the same materials and structure as in Example 1, except that a Si light-transmitting plate 4 was used. When the temperature of the optical isolator was changed from -40 to +100°C, the isolation at the four corners of the chip was 5 to 7 dB lower than at the center. This is believed to be due to distortion caused by differences in thermal expansion coefficients at the junction between the light-transmitting plate and the borosilicate glass polarizer, which ultimately degraded the extinction performance of the glass polarizer and led to a deterioration in isolation. Furthermore, a light resistance test was conducted by attaching the same chip structure to the end of an optical fiber and returning light from the fiber side. While no abnormalities were observed at the bonded interface within the chip in the Example 1 chip, abnormalities (such as peeling) were observed at the bonded (adhesive) interface in the Si chip. This is believed to be due to the high refractive index of the light-transmitting plate, which resulted in insufficient heat diffusion due to the concentrated light, resulting in damage to the adhesive interface. (This is believed to be due to the light-transmitting plate's refractive index exceeding 2.5, which prevented the beam diameter reaching the optical isolator from increasing, thereby reducing the thermal impact reduction effect.)

[0056] Example 2 Tests were conducted using the same materials as in Example 1 and the exemplary configuration of the optical isolator 200 shown in Figure 2. This example differs from the optical isolator in Figure 1 in that the output surface of the second glass polarizer 9 was not AR-coated and was fixed to the fixing surface of the optical fiber 7 with epoxy adhesive. Polarized CW light of 150 mW was incident on the optical isolator 200 from the optical fiber 7 side, and its polarization direction was rotated. When the direction of polarization was perpendicular to the transmission polarization axis of the second glass polarizer 9, no abnormalities were observed in the adhesive layer at the output end of the optical fiber 7. Next, it was confirmed that the adhesive layer 5 between the Faraday rotator 1 and the second glass polarizer 9 was not damaged, and no abnormalities were observed at the junction interface between the first glass polarizer and the Faraday rotator, even when the transmission polarization axis of the second glass polarizer was aligned.

[0057] As described above, according to the embodiment of the present invention, an optical isolator that can effectively reduce the influence of heat generation and has high light resistance can be obtained.

[0058] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0059] 1...Faraday rotator, 2...metal particle dispersed glass polarizer, 3...reduction layer, 4...light-transmitting plate, 5...adhesive layer, 6...permanent magnet, 7...optical fiber, 8...First glass polarizer (flat-type metal particle-dispersed glass polarizer), 9...Second glass polarizer (flat-type metal particle dispersed glass polarizer), 10...Optical fiber fixing component, 100...optical isolator, 200...optical isolator attached to the end of an optical fiber; 300...optical isolator, 400...Optical isolator attached to the end of an optical fiber.

Claims

1. An optical isolator comprising one or more metal particle dispersed glass polarizers and one or more Faraday rotators in the direction of light propagation, a light-transmitting plate having a higher thermal conductivity than the metal particle-dispersed glass polarizer and a refractive index of 2.5 or less at the wavelength used, bonded to at least one of the light-transmitting surfaces of the metal particle-dispersed glass polarizer without using an organic adhesive; An optical isolator characterized in that the light-transmitting plate is provided on the light-transmitting surface of the metal particle dispersed glass polarizer on the Faraday rotator side, and the light-transmitting plate and the Faraday rotator are bonded together via an organic adhesive.

2. the optical isolator is attached to an end of an optical fiber; 2. The optical isolator according to claim 1, wherein the metal particle dispersed glass polarizer is provided with a light transmitting plate on the light transmitting surface opposite to the Faraday rotator, and an end of the optical fiber is attached to the light transmitting plate.

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