JPH064735U - Optical isolator - Google Patents

Abstract

(57) [Summary] [Purpose] To provide an optical isolator that does not cause internal damage by improving the shape and material that do not cause damage inside the fragile glass polarizer. [EN] An optical isolator that constitutes a housing made up of a holder A and a holder B containing a glass polarizer 3, a Faraday rotator 9, and a permanent magnet 10. The holder A includes a doughnut-shaped A holder 1 and a plurality of holders. It is divided into a cylindrical A holder 2 having a slit portion 5, and a holder B also has a donut plate-shaped B holder 4 and a cylindrical B holder having a plurality of slit portions 5.
A housing divided into a holder 11 is used, and the donut plate-shaped A holder 1 and the donut plate-shaped B holder are made of a metal or ceramic material having a small difference in thermal expansion coefficient between the glass polarizer and the Faraday rotator. An optical isolator characterized by using a metal or ceramic material for a cylindrical A holder 2 and a cylindrical B holder 4 each having a plurality of slits.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an optical isolator used in fields such as optical communication and optical measurement.

[0002]

[Prior art]

 Conventionally, an optical isolator has been used for the purpose of preventing reflected return light of laser light, and in the optical communication field, it is often installed immediately after a semiconductor laser which is a source of optical signals. In this case, generally, a semiconductor laser, an optical isolator, an optical coupling lens and the like are collectively incorporated in a casing and used in the form of a semiconductor laser module. As a method of assembling an optical isolator, in order to ensure long-term reliability of a semiconductor laser module, which is generally a sealed structure, no low-melting point glass, solder material, etc. are used without using any organic adhesive that may cause degassing. It is often done only with inorganic materials. A general example of an optical isolator by the soldering joining method is shown in FIGS. 2 (a) and 2 (b). FIG. 2A is a perspective view of an optical isolator according to the bonded attachment method. FIG. 2B is a front sectional view. In FIG. 2, the permanent magnet 10 and the glass polarizer A31 are soldered and joined to the holder A12, and the Faraday rotator 9 is soldered and joined to the holder B13 by the glass polarizer B32 and the holder C14. Is fitted and joined to the holder A12 via the permanent magnet 10.

By the way, when an optical isolator is assembled by joining with an inorganic material, a difference in thermal expansion coefficient between the components to be joined becomes a problem. As an example, the case where a stainless material (SUS304 material) is used as the material of the holder that is the housing of the optical isolator and a glass polarizer is used as the optical element will be described. Coefficient of thermal expansion around room temperature of both about 17 × 10 ^-6 / ℃ in stainless steel, significantly different is 6 × 10 ^-6 / ℃ in glass polarizer. Therefore, if the two are directly joined, stress distortion occurs in the joined portion due to the temperature difference between the temperature rise and the room temperature during joining, and the relatively weak glass polarizer side is damaged.

However, as a holder that is a housing of an optical isolator, stainless steel is generally indispensable because of its ease of YAG laser welding. This is because (1) YAG laser welding is excellent for permanently fixing the relative angle of the two polarizers necessary for the construction of the optical isolator after optically adjusting the relative angle. As (2), YAG laser welding is often used as a method of permanently fixing the optical isolator in the optical system used by the user, for two reasons. On the other hand, if a glass polarizer is used as the polarizer as described above, it is necessary to somehow eliminate the strain stress generated in the joint due to the difference in the thermal expansion coefficient between the two.

Conventionally, as a solution to this problem, a tin-lead solder having a low melting point and a softness is used as an inorganic bonding material, and the tin-lead solder absorbs the stress strain due to the difference in the thermal expansion coefficient. Was there. However, in recent years, more reliable products have been required for optical isolators, and the fact that tin-lead solder is soft and has a low melting point poses problems in terms of heat resistance and long-term stability. There is a demand for optical isolators assembled with bonding materials.

[0006]

[Problems to be solved by the device]

 From the viewpoint of heat resistance and long-term reliability, gold-tin solder and low melting point glass are known as bonding materials suitable for use in assembling an optical isolator. Hereinafter, these will be referred to as highly reliable bonding materials. Each of these materials has a melting point higher than that of tin-lead solder (gold-tin solder 280 ° C., low-melting glass 400 ° C. or higher) and is an extremely hard material. Therefore, if only the bonding material is replaced without changing the structure of the conventional optical isolator using tin-lead solder, it will result from the difference in the thermal expansion coefficient between the optical isolator constituent materials caused by the temperature rise during bonding. Since the joint material does not absorb the strain, the structurally weakest member in the joint will be damaged. For example, in the case of joining the holder and the glass polarizer with the above-mentioned stainless steel material (SUS304), breakage usually occurs inside the glass polarizer which is relatively weakest. There is a demand for an optical isolator structure that does not cause internal damage by devising the shape so that such a phenomenon does not occur.

[0007]

[Means for Solving the Problems]

 That is, the present invention is as follows. In an optical isolator that forms a housing consisting of a holder A, a holder B, and a holder C that include a plurality of glass polarizers, a Faraday rotator, and a permanent magnet, the holder A is provided with a donut plate-shaped A holder and a plurality of slits. An optical isolator having a structure in which the housing is divided into a cylindrical A holder having the same, and the holder B is also divided into a donut plate-shaped B holder and a cylindrical B holder having a plurality of slit portions. . 2. The optical isolator according to claim 1, wherein the donut plate-shaped A holder, the cylindrical A holder, the donut plate-shaped B holder, and the cylindrical B holder are made of metal having a small difference in thermal expansion coefficient between the glass polarizer and the Faraday rotator. An optical isolator characterized by using a ceramic material.

[0008]

[Action]

 If gold-tin solder or low melting point glass is used as an adhesive material for assembling the optical isolator, it is impossible to directly bond the optical element to the optical isolator housing made of stainless steel, as described above. Therefore, we will make a disc-shaped buffer plate with a material whose coefficient of thermal expansion is close to that of the optical element, such as ceramics and kovar, and attach the optical element to it. Next, the buffer plate is adhesively fixed to a stainless steel case. By this method, each optical element can be fixed to the stainless steel case. An example of an optical isolator according to this method is shown in FIG. In this case, if a buffer plate (a donut plate-shaped A holder 1 of the same ceramic) is adhered and fixed to a stainless steel casing (a stainless steel cylindrical A holder 2 in the figure) without any measures, it is shown in FIG. 1 (b). As described above, the ceramic donut plate-shaped A holder 1 serving as the buffer plate is bent due to the difference in thermal expansion coefficient between the two materials to be bonded, and as a result, a crack 8 is generated at the bonded portion of the optical element (the same glass polarizer A31). Then, peeling occurs. This is because the ceramic donut plate-shaped A holder 1 buffer plate having a strain stress direction 7 originating from the difference in thermal expansion coefficient acts on the bonded portion of the two materials in the direction of being pressed inward. To solve this problem, as shown in FIG. 1 (c), a total of four slits 5 as shown in FIG. 1 (a) are formed in the adhesive portion of the housing of the cylindrical A holder 2 made of stainless steel. As shown in FIG. 1 (c), by bonding, the strain stress due to the difference in the thermal expansion coefficient is absorbed by the deformation of the stainless-steel cylindrical A holder 2 on the housing side, and a ceramic plate, which is a buffer plate, is absorbed. Of the donut plate-shaped A holder 1 is prevented. By the above method, it is possible to assemble the optical isolator using a bonding material such as gold-tin solder or low melting point glass that does not cause internal damage of the optical element.

[0009]

【Example】

An embodiment of the optical isolator of the present invention is shown in FIG. FIG. 1A is an assembled perspective view of the optical isolator. FIG. 1 (b) shows a comparative example in which a donut-shaped plate-shaped A holder 1 made of ceramics and a cylindrical A-shaped holder 2 made of stainless steel are used together with a split type housing, but when there is no slit portion, they are made of a stainless steel cylindrical shape. A sectional view showing that the strain application direction 7 of the A holder 2 is as shown by an arrow and a stress is applied to the glass polarizer 3 so that the glass polarizer 3 is cracked 8. FIG. 1C is a cross-sectional view showing that the glass polarizer is not cracked when the slit portion is formed in the stainless-steel cylindrical A holder 2. FIG. 1B shows a comparative example in which a ceramic donut plate A holder 1 is inserted as a cushioning material between the stainless steel cylindrical A holder 2 made of SUS304 and the glass polarizer A31. The glass polarizer 31 is attached to the plate-shaped A holder 1 to avoid direct joining of the cylindrical A holder 2 made of stainless steel and the glass polarizer A31. The coefficient of thermal expansion of the glass polarizer 31 is 6 × 10 ⁻⁶ / ° C., and the coefficient of thermal expansion of the ceramic is about 8 × 10 ⁻⁶ / ° C. in the case of the embodiment. In this case, the difference in the coefficient of thermal expansion between the ceramic donut plate-shaped A holder 1 and the glass polarizer 31 is small, and the joint portion will not be damaged if the two are jointed together. When a cylindrical A holder 2 made of stainless steel (note that there is no slit part) is added, the ceramic donut plate-shaped holder 1 is heated by the stainless steel cylindrical A holder 2 as shown in FIG. 1 (b). The strain application direction 7 acting on the inside due to the expansion coefficient differential works, that is, it is deflected by the strain stress, and as a result, a peeling stress is generated at the joint portion of the glass polarizer 31 and a crack 8 is generated. Therefore, in order to solve this problem, the slit portion 5 is cut on the side of the stainless steel cylindrical A holder 2. In the example of FIG. 1 (a), four slits 5 are inserted, and the slits 5 are formed by a highly reliable bonding material between the stainless cylindrical A holder 2 and the ceramic donut plate A holder 1. Join. As shown in Fig. 1 (c), the direction of strain stress 7 (see Fig. 1 (b)) at the joint between the stainless steel cylindrical A holder 2 and the ceramic donut plate A holder 1 acts on the inner side. Due to the presence of the slit portion 5, the strain stress acts in the direction in which the stainless steel cylindrical A holder 2 is expanded outward, that is, in the strain stress direction 71, so that the ceramic donut plate-shaped holder 1 is not deformed. Therefore, no damage occurs in the bonded portion of the glass polarizer 31, and the purpose is achieved. Here, if gold-tin solder with a melting point of 280 ° C. is used as the joining material, the outward bulge of the slit of the cylindrical A holder made of stainless steel is about 4 mm on one side (the outer diameter of the optical isolator is about φ5 mm. If). The same thing can be said when Kovar is used for the ceramic donut plate-shaped A holder 1. The coefficient of thermal expansion of Kovar is about 4 × 10 ^-6 / ° C. That is, it is understood that a material having a very small difference in thermal expansion coefficient from that of the glass polarizer may be used. The same principle can be applied to the principle of the cylindrical B holder 4, the Faraday rotator 9, and the donut plate B holder 11, and the description thereof will be omitted.

[0010]

[Effect of device]

 As described above, there is a difference in the thermal expansion coefficient of the optical elements used in the outer housing of the optical isolator, and internal temperature breakage may occur in any of the optical isolator joints during temperature rising assembly using a highly reliable bonding material. If it occurs, a buffer material with a coefficient of thermal expansion close to that of the optical element used is added during the construction, and a slit is provided at the joint with the buffer material on the outer casing side. Absorb strain stress. As a result, it is possible to assemble an optical isolator that does not cause internal damage even if a highly reliable bonding material such as gold-tin solder or low melting point glass is used.

[Brief description of drawings]

1A is an assembled perspective view of an optical isolator according to an embodiment of the present invention, and FIG. 1B is a perspective view of FIG. 1C.
3 is a vertical cross-sectional view showing a case where there is no slit portion of the stainless steel cylindrical A holder 2 of FIG. 1, showing the behavior of the ceramics holder, the direction of stress at the joint portion, and the position of cracks that occur. FIG. 1C is a vertical cross-sectional view of the disassembled portion on the left side of the optical isolator in FIG.

2 (a) and 2 (b) are conventional explanatory views of an optical isolator by soldering. 2A is an external perspective view, and FIG. 2B is a vertical sectional view of the same.

[Explanation of symbols]

 1 Donut Plate A Holder 2 Cylindrical A Holder 3 Glass Polarizer 4 Cylindrical B Holder 5 Slit 6 Optical Axis 7,71 Strain Stress Direction 8 Crack 9 Faraday Rotor 10 Permanent Magnet 11 Donut Plate B Holder 12 Holder A 13 Holder B 14 Holder C 31 Glass Polarizer A 32 Glass Polarizer B

Claims (2)

[Scope of utility model registration request] 1. An optical isolator comprising a housing consisting of a plurality of glass polarizers, a Faraday rotator and a permanent magnet, a holder A, a holder B and a holder C. It is characterized in that it has a structure in which it is divided into a cylindrical A holder having a slit portion, and the holder B is also divided into a doughnut-shaped B holder and a cylindrical B holder having a plurality of slit portions. Optical isolator. 2. The optical isolator according to claim 1, wherein the donut plate-shaped A holder, the cylindrical A holder, the donut plate-shaped B holder, and the cylindrical B holder have a difference in thermal expansion coefficient between the glass polarizer and the Faraday rotator. An optical isolator characterized by using few metallic and ceramic materials.