WO2003001276A1 - Optical isolator - Google Patents

Abstract

An optical isolator surface-mountable, having a high heat resistance temperature and an improved reliability, and not requiring any adjustment of the optical axis of the polarizer when assembling the optical isolator. In the optical isolator, a first polarizer (18a), a Faraday element (12), and a second polarizer (18b) are arrayed in this order along the optical axis, and a permanent magnet (10) for applying a magnetic field the direction of which is along the optical axis to the Faraday element is disposed outside the Faraday element (12). The permanent magnet is U-shaped. In the inside space, the Faraday element is secured, thus fabricating a Faraday rotator assembly (16). The first and second polarizers are secured to a holder plate (20) at intervals, thus fabricating a polarizer assembly (24). The Faraday assembly and the polarizer assembly are so assembled into one unit that the edge faces of both legs of the permanent magnet face to the upper side of the holder plate.

Description

 Technical Paper Optical Isolation Evening Technology

 The present invention relates to an optical isolator used in an optical communication system or an optical measurement system, and more specifically, a combination of a permanent magnet containing a Faraday element and a holder plate equipped with a polarizer and the like. It relates to an optical isolator that can be mounted in a plane with an integrated structure. Background technology

 An optical isolator is a non-reciprocal optical device that allows light to pass in one direction but blocks light in the opposite direction.For example, in an optical communication system using a semiconductor laser as a light source, laser light is reflected. It is used to prevent returning to the light source side. In this type of optical isolator, a first polarizer, a Faraday element, and a second polarizer (analyzer) are arranged in the optical axis direction in that order, and the optical axis of the Faraday element is arranged outside the Faraday element. In general, a permanent magnet for applying a magnetic field in a direction is provided. The Faraday element rotates the polarization plane of incident light by 45 degrees by the magnetic field of a permanent magnet, and the first polarizer and the second polarizer have polarization optic axes different by 45 degrees with respect to the optical axis. The orientation is set.

 As a permanent magnet for applying a magnetic field in the optical axis direction to the Faraday element, a cylindrical permanent magnet magnetized in the axial direction has conventionally been used. For example, a configuration in which both polarizers are mounted in a cylindrical polarizer holder, the polarizer holders are arranged before and after the permanent magnet in the axial direction, and the optical axis of one polarizer is adjusted and then fixed. Has been adopted. However, such a configuration requires a lot of man-hours for adjusting the optical axis, has a problem in that it is difficult to reduce the size, and is not suitable for mounting on a flat surface (plane mounting).

Therefore, in recent years, polarizers have been placed before and after the Faraday element, and block-shaped permanent magnets have been placed on both sides of the Faraday element. A configuration that incorporates a Raday element and a second polarizer has been proposed.

 These optical isolators having a configuration using block-shaped or U-shaped permanent magnets can be mounted on a plane. In particular, a configuration using a U-shaped permanent magnet is excellent in terms of miniaturization. However, it is not always easy to accurately integrate the first polarizer, the Faraday element, and the second polarizer into the narrow and small inner space of the U-shaped permanent magnet. However, since the polarizer and the Faraday element usually have significantly different coefficients of thermal expansion, the polarizer and the Faraday element are liable to be damaged by thermal expansion and have a problem of reduced heat resistance. Therefore, it is difficult to manufacture optical isolators that require high heat resistance. Disclosure of the invention

 An object of the present invention is to provide a highly reliable optical isolator that can be mounted on a plane, has a high heat resistance temperature, and has a high reliability. It is another object of the present invention to provide an optical isolator having a structure that does not require adjustment of the optical axis of a polarizer during assembly and is easy to manufacture. Still another object of the present invention is to provide an optical isolator having a structure in which the positions of the centers of the Faraday rotator assembly and the polarizer assembly can be easily set and twisting can be prevented. The present invention relates to an optical isolator in which a Faraday element and a polarizer are arranged in the optical axis direction and a permanent magnet for applying a magnetic field in the optical axis direction to the Faraday element is provided. A Faraday rotator assembly is fixed to the inner space to form a Faraday rotator assembly, a polarizer is fixed to a holder plate to form a polarizer assembly, and the Faraday rotator assembly and the polarizer assembly are formed of a permanent magnet. An optical isolator characterized in that both leg end faces are combined and integrated so as to face the upper surface of the holder plate. In the case where incident light is polarized in one direction, such as light emitted from a semiconductor laser, it is possible to omit one (incident side) polarizer.

Further, the present invention provides a method in which a first polarizer, a Faraday element, and a second polarizer are arranged in the optical axis direction in that order, and a permanent magnetic field is applied outside the Faraday element to the Faraday element in the optical axis direction. In an optical isolator provided with magnets, the permanent magnet has a U shape, and a Faraday element is fixed in the space inside the permanent magnet to form a Faraday rotator assembly, and the first and second polarizers are placed on a holder plate. Fix the polarizer at an interval An optical isolator, wherein the Faraday rotator assembly and the polarizer assembly are combined and combined so that the end faces of both legs of the permanent magnet face the upper surface of the holder plate.

 When assembling, the fixing temperature of the adhesive between the Faraday rotator assembly and the polarizer assembly is determined by the fixing temperature of the adhesive between the permanent magnet and the Faraday element and the fixing temperature of the adhesive between the polarizer and the holder plate. Set lower than. For example, solder is used to bond the Faraday-rotor assembly to the polarizer assembly, and glass bonding material is used to bond the permanent magnet to the Faraday element and to bond the polarizer to the holder plate. As the permanent magnet, for example, a samarium-cobalt based sintered magnet is used.

Grooves are formed at both corners of the square space inside the U-shaped permanent magnet, and the Faraday element in the shape of a square plate is fused at both corners with the glass adhesive material arranged in the groove, thereby setting the Faraday element to a predetermined value. Can be easily and accurately stored in the position. On the other hand, a non-magnetic ceramic such as alumina is usually used as the holder plate. By forming a concave portion on the upper surface of the holder plate and fusing the polarizer at both corners with the glass adhesive material arranged in the concave portion, the polarizer can be easily and accurately installed at a predetermined position.

 Preferably, at least the opposing surfaces of the permanent magnet and the holder plate are gold-plated so that the permanent magnet and the holder plate can be easily soldered. Normally, optical isolators are mounted on a flat surface by soldering the back surface of the holder plate to a flat surface. For this purpose, it is preferable to apply gold plating to the entire back surface of the holder plate. In addition, in consideration of normal mounting by soldering, it is desirable to use high-temperature solder for soldering the permanent magnet and the holder plate.

 The first and second polarizers have a rectangular plate shape, the optical axis of one polarizer is oriented in a direction parallel to the mounting reference side, and the optical axis of the other polarizer is 45 to the mounting reference side. If it is oriented in the right direction, the optical axis is automatically adjusted just by bringing the reference side into close contact with the holder plate, so that assembly can be performed with virtually no adjustment and man-hours can be reduced.

Furthermore, the holder plate has a chevron structure in which the upper surface facing the permanent magnet has an inclined surface that becomes lower toward the outside, and the end surfaces of both legs of the permanent magnet correspond to this. If the slope is inclined, the center of the Faraday rotator assembly and the polarizer assembly is automatically positioned, and at the same time, mutual twisting can be prevented, so that the assembly is further facilitated. Brief explanation of drawings

FIG. 1 is an explanatory view showing one embodiment of an optical isolator according to the present invention.

Figure 2 is an illustration of the Faraday rotator assembly.

FIG. 3 is an explanatory view of a polarizer assembly.

FIG. 4 is an explanatory view showing another embodiment of the optical isolator according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

 FIG. 1 is an explanatory view showing one embodiment of an optical isolator according to the present invention, and shows a manufacturing process thereof. As shown in A (the upper side represents the upper side and the lower side represents the front), the Faraday element 12 is housed in the center of the inner space of the inverted U-shaped permanent magnet 10, and the glass adhesive 14 The Faraday rotator assembly 16 is formed by welding using the Faraday rotator. Also, as shown in B (the upper side represents the top side and the lower side represents the front side), the first and second polarizers 18a and 18b are placed on the holder plate 20 at intervals. The polarizer assembly 24 is obtained by arranging them in parallel and welding them using a glass adhesive 22. Then, as shown in C, the Faraday rotator assembly 16 and the polarizer assembly 4 are combined such that the end faces of both legs of the permanent magnet 10 face the upper surface of the holder plate 20, and the solder 2 6 is interposed and fused to combine and integrate. In this way, as shown in D (the upper side represents the upper surface and the lower side represents the front), the first polarizer 18a, the Faraday element 12 and the second polarizer 18b are combined. An optical isolator is arranged in the optical axis direction in that order, and provided with a permanent magnet 10 that applies a magnetic field in the optical axis direction to the Faraday element 12 outside the Faraday element 12.

The detailed structure of the Faraday single rotor assembly 16 is shown in FIG. Here, the permanent magnet 10 is made of an Sm-Co based sintered magnet, and has a square U-shaped structure as shown in A and B. Here, it is manufactured by grinding a rectangular block from one side and making a rectangular cut. Both ends to prevent dull corners The protruding grinding tool is used, so that grooves 30 are finally left at both corners. This groove 30 will be used for an adhesive pool in a later step. After that, the entire outer surface is gold-plated. Functionally, it is sufficient to gold-plate only the surface facing the holder plate (the end surfaces of both legs, that is, the upper surface in the state of A), but the entire outer surface is gold-plated in consideration of workability. This permanent magnet is magnetized so that a magnetic field is applied in the direction of the optical axis (in the state of C, in the front-back direction of the paper).

 The Faraday element 12 has a rectangular plate shape that fits in the space inside the permanent magnet 10. It is composed of a magneto-optical crystal such as a Bi-substituted rare earth iron garnet LPE (liquid phase epitaxy) single crystal film, etc., and changes the polarization plane of light at the operating wavelength (eg, 1.31 ^ m) by 45 degrees. Rotating thickness. As shown in C and D, the Faraday element 10 is arranged at the center of the inner space of the permanent magnet 12 and fused at both corners by the glass adhesive 14 arranged in the groove 30. At this time, the Faraday element 10 is slightly inclined with respect to the optical axis.

 FIG. 3 shows the detailed structure of the polarizer assembly 24. Here, the holder plate 20 is a flat member made of non-magnetic ceramics such as aluminum. Concave recesses 32 are formed in four places at the center of the top surface, and gold plating 34 is applied to both sides of the top surface (see A and B). Further, although not shown, the entire back surface is also plated with gold. The first and second polarizers 18a and 18b may be made of polarizing glass or the like, and have a rectangular plate shape that fits in the space inside the permanent magnet with a margin. These are arranged in parallel on the holder plate 20 with an attachment reference side downward at an interval, and are fused at both lower corners by a glass adhesive 22 arranged in each recess 32. Also in this case, both polarizers 18a and 18b are slightly inclined with respect to the optical axis (see E). First polarizer (eg, incident side polarizer) 18 The optical axis of a is oriented parallel to the mounting reference side (see C), and second polarizer (eg, exit side polarizer) 1 If both polarizers are manufactured so that the optical axis of 8b is attached and oriented at 45 degrees to the reference side (see D), adjustment of the optical axis during assembly is unnecessary.

The Faraday rotator assembly and the polarizer assembly are combined so that the end faces of both legs of the permanent magnet 10 face the upper surface of the holder plate 20 as shown in FIG. And are fused and integrated. With permanent magnet 10 Since the mutually facing surfaces of the holder plate 20 are plated with gold, they can be easily soldered. By using a material whose welding temperature is higher than the soldering temperature of the solder 26 as the glass adhesives 14 and 22, the Faraday element 12 and the polarizer 18 a, This prevents the 18b from becoming loose or misaligned.

 In this way, an optical isolator as shown in FIG. 1D can be constructed. Match the thermal expansion coefficients of the permanent magnet and the Faraday element constituting the Faraday single-rotor assembly and their adhesives, and the thermal expansion of the polarizer and the holder plate constituting the polarizer assembly and their adhesives It is easy to match the coefficients, and even if the permanent magnet and the holder plate are combined, the Faraday element is free with respect to the holder plate, and the polarizer is free with respect to the permanent magnet. In addition, it is possible to prevent the Faraday element and the polarizer from cracking due to the difference in thermal expansion, and to raise the heat resistance temperature.

 As a final product, a marker is attached so that a polarizer with an optical axis in the horizontal direction (here, the first polarizer) can be distinguished. Since the first polarizer, the Faraday element, and the second polarizer are all slightly inclined with respect to the optical axis, it is possible to prevent the reflected light from returning on the surface of each optical element. Since the lower surface of the holder plate is also plated with gold, it can be easily mounted on a flat surface such as equipment or a board by soldering. By using high-temperature solder for joining the Faraday rotator assembly and the polarizer assembly, loosening or deformation of the optical isolator during soldering during mounting can be prevented. FIG. 4 is an explanatory view showing another embodiment of the optical isolator according to the present invention. Except for the permanent magnet and the outer shape of the holder plate, the configuration may be the same as that of the above-described embodiment. As shown in B, the holder plate 40 has a shape having an inclined surface in which a portion of the upper surface facing the permanent magnet becomes lower toward the outside. On the other hand, as shown in A, the end faces of both legs of the permanent magnet 42 have slopes corresponding to them. When such a Faraday rotator assembly 44 and a polarizer assembly 46 are combined, the center of the Faraday rotator assembly and the polarizer assembly are automatically positioned, and at the same time, The torsion can be prevented, so that the assembly can be performed more easily and accurately.

As described above, the present invention holds a permanent magnet holding a Faraday element and a polarizer. Since it is configured to combine holder plates, it is possible to select an appropriate material to match the coefficient of thermal expansion, to increase the heat resistance temperature, and to enable flat mounting with the holder plate.

 According to the present invention, it is not necessary to adjust the optical axis of the polarizer at the time of assembling only by manufacturing the optical axis of the polarizer to be used so that it is oriented in a predetermined direction with respect to the reference side. Production becomes easier.

 Further, in the present invention, if the outer shapes of the permanent magnet and the holder plate are devised and the inclined facing surfaces are used, the center positions of the Faraday rotator assembly and the polarizer assembly can be easily set, twisting can be prevented, and axial displacement can be prevented. Can be controlled.

Claims

The scope of the claims 1. An optical isolator in which a Faraday element and a polarizer are arranged in the optical axis direction and a permanent magnet for applying a magnetic field in the optical axis direction to the Faraday element is provided.  The permanent magnet has a U-shape, a Faraday element is fixed in the space inside the permanent magnet to form a Faraday rotator assembly, and a polarizer is fixed on a holder plate to form a polarizer assembly. An optical isolator, wherein an assembly and a polarizer assembly are combined and integrated so that both leg end faces of the permanent magnet face the upper surface of the holder plate. 2. The first polarizer, the Faraday element, and the second polarizer are arranged in the optical axis direction in that order, and a permanent magnet that applies a magnetic field in the optical axis direction to the Faraday element outside the Faraday element. In the optical isolator set up,  The permanent magnet has a U shape, and a Faraday element is fixed in the space inside the permanent magnet to form a Faraday rotator assembly, and the first and second polarizers are fixed on a holder plate at an interval and polarized. An optical isolator, wherein the Faraday rotator assembly and the polarizer assembly are combined and integrated so that both leg end faces of the permanent magnet face the upper surface of the holder plate. . 3. The fixing temperature of the Faraday rotator assembly and the polarizer assembly with the adhesive is lower than the fixing temperature of the permanent magnet with the Faraday element and the fixing temperature of the polarizer with the holder plate. The optical isolator according to claim 1 or 2, ^ 4. The optical isolator according to claim 3, wherein solder is used for bonding between the Faraday rotator assembly and the polarizer assembly, and glass bonding material is used for bonding between the permanent magnet and the Faraday element and between the polarizer and the holder plate. evening. 5. The first and second polarizers are in the form of a rectangular plate, and the optical axis of one polarizer is oriented in a direction parallel to the mounting reference side, and the optical axis of the other polarizer is relative to the mounting reference side. 3. The optical isolator of claim 2, wherein the optical isolator is oriented at 45 degrees. 6. The optical isolator according to claim 1, wherein grooves are formed at both corners of the inner space of the U-shaped permanent magnet, and the Faraday element is fused at the corners by a glass adhesive material arranged in the grooves. 7. The optical isolator according to claim 1, wherein a concave portion is formed on the upper surface of the holder plate, and the polarizer is fused at both corners by a glass adhesive material disposed in the concave portion. 8. The optical isolator according to claim 1, wherein the holder plate is made of a non-magnetic ceramic. 9. The optical isolator according to any one of claims 1 to 8, wherein at least opposing surfaces of the permanent magnet and the holder plate are provided with gold plating. 10. The optical isolator according to claim 1, wherein the entire back surface of the holder plate is plated with gold. 11. The optical isolator according to claim 1, wherein a portion of the upper surface of the holder plate facing the permanent magnet forms a slope that becomes lower outward, and the end surfaces of both legs of the permanent magnet also have corresponding slopes. .