JP2005189342A - Optical isolator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems of an optical isolator in which optical elements fall off, crack, decrease in joint strength, or degrade in optical characteristics. <P>SOLUTION: In the optical isolator 12 in which the optical elements 1 including a Faraday rotor 2 and polarizers 3 and 4 are joined to one another via joining members 5, each joining member 5 is such that the periphery of a resin core 6 is covered with a molten metal layer 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical isolator used for removing return light generated when light emitted from a light source is introduced into various optical elements and optical fibers.

  In an optical communication module or the like, light emitted from a light source such as a laser light source is incident on various optical elements or optical fibers, but a part of the incident light is reflected on the end surfaces or inside of the various optical elements or optical fibers. It is scattered. A part of the reflected or scattered light tries to return to the light source as return light, and an optical isolator is used to prevent the return light.

  Conventionally, this type of optical isolator is configured by installing a flat Faraday rotator between two polarizers and storing these three components in a cylindrical magnet via a component holder. It was. Normally, the Faraday rotator is adjusted to a thickness that rotates the polarization plane of light having a predetermined wavelength in the saturation magnetic field by 45 °, and the two polarizers rotate so that their transmission polarization directions are shifted by 45 ° rotation direction. Coordinated and configured.

  The optical isolator having such a configuration is fixed to each optical element of the Faraday rotator and the two polarizers with a metal holder with solder or the like, and the metal holders to which the optical element is fixed are then bonded to each other by YAG welding or the like. The manufacturing method to join is taken, and therefore the number of parts is increased and the number of assembling steps is increased, and the optical adjustment work between the parts is complicated, resulting in high cost. It was difficult to reduce the size.

  For this reason, an optical isolator has been proposed in which an optical isolator element having a configuration in which a plate-like polarizer is bonded and integrated on both surfaces of the optical surface of a plate-like Faraday rotator is arranged in the center of the cylindrical magnet. .

  Patent Document 1 shows a conventional miniaturized optical isolator 15 shown in FIG. 7, and the configuration thereof will be described below.

  The optical isolator 15 includes an optical isolator element 20 in which a Faraday rotator 16 and polarizers 17 and 18 are bonded with an optical adhesive 19 having a good light transmittance and a controlled refractive index, and a cylindrical magnet 21. Here, the polarizers 17 and 18 have a function of absorbing a polarization component in one direction of transmitted light and transmitting a polarization component orthogonal to the polarization component, and the Faraday rotator 16 has a saturation magnetic field strength. 1 has a function of rotating the polarization plane of light of a predetermined wavelength by about 45 degrees. The two polarizers 17 and 18 are arranged so that their transmission polarization directions are deviated by about 45 degrees.

  FIG. 8 is a view showing a method of manufacturing the conventional optical isolator element 20.

  First, as shown in FIGS. 8A and 8B, a large polarizer substrate 22 of about 10 mm square, a large Faraday rotator substrate 23, and a large polarizer substrate 24 are bonded and integrated. Here, the transmission polarization direction of the polarizer substrate 22 is set to a direction parallel to one side, and the transmission polarization direction of the polarizer substrate 24 is set to a direction of 45 degrees on one side. Each optical substrate is fixed by adhering the polarizer substrate 22, the Faraday rotator substrate 23, and the polarizer substrate 24 so that one side of each is parallel. Further, as described above, an optically transparent resin is used as an adhesive for bonding and integrating the optical elements, and generally an epoxy organic adhesive is used.

  Here, when high isolation is required for the optical isolator, the rotational deviation between the polarizer substrate 22 and the polarizer substrate 24 is precisely adjusted to 45-α degrees with respect to the polarization rotation angle 45 + α degrees of the Faraday rotator. There is a need to. Specifically, light is incident from the opposite direction (from the side of the polarizer substrate 24), and the polarizer substrate 22 and the polarizer substrate 24 are rotationally adjusted so that the transmitted light is minimized.

  Next, as shown in FIGS. 8C and 8D, the optical isolator element large substrate 25 is processed into a large number of small chip-like optical isolator elements 20 by dicing or the like.

When manufacturing the optical isolator element 20 in this way, large polarizer substrates 22 and Faraday rotator substrates 23 are alternately stacked, and after completion of bonding, a large number of optical isolator elements 20 are obtained. By using such a method, workability and production volume can be increased, and the number of parts can be reduced. Also, in Patent Document 2, solder is used as a bonding agent instead of an organic adhesive, and it is formed on an optical element. A method of directly joining and cutting through the metallized film has also been proposed.
JP-A-4-338916 Japanese Patent No. 3439279

  However, as shown in Patent Document 1 in FIG. 7, in the optical isolator element 20 in which the plate-like polarizers 17 and 18 are integrated with the adhesive 19 on both surfaces of the optical surface of the Faraday rotator 16, the adhesive 19 is organic. In the case of an adhesive, moisture resistance is inferior, and there is a problem that its use under high temperature and high humidity conditions is restricted. Further, when used for a long time or in a high-power laser beam, there is a risk of deterioration of the adhesive 19, and there is a problem in reliability.

  Further, when the optical isolator element 20 is incorporated into the laser module, the optical isolator 15 is exposed to a high temperature. However, when an organic adhesive is used as the adhesive 19, it is decomposed to generate bubbles, drop off members, etc. Occurs. Further, outgas from the organic adhesive 19 adheres to the surface of an optical component such as a laser chip or a lens, and there is a risk of deteriorating the optical characteristics.

  In addition, the method in which optical elements are directly bonded and cut by soldering through a metallized film is generally greatly different in the thermal expansion coefficient between the polarizer and the Faraday rotator. There is a problem that it occurs or the characteristics deteriorate due to residual stress. In particular, the larger the substrates to be joined, the more cracks are generated, resulting in poor yields and problems in practicality.

  The present invention has been made in view of the above problems, and the optical isolator of the present invention is an optical isolator in which optical elements including a flat Faraday rotator and a polarizer are bonded to each other via a bonding member. The bonding member is formed by covering the outer periphery of the resin core with a molten metal layer, and is bonded outside the region of the effective aperture diameter of the transmitted light of the Faraday rotator and the polarizer.

  Further, the Faraday rotator and the polarizer of the optical element have a rectangular shape with substantially the same plane, and a metallized film is formed at four corners of the Faraday rotator or the polarizer surface, and the bonding is performed via the metallized film. The members are joined.

  Furthermore, the region of the effective aperture diameter of the transmitted light of the optical element is a circle or an ellipse inscribed in the plane.

  According to the configuration of the present invention, the external stress can be received by the resin core by bonding the optical element of the optical isolator with the bonding member in which the outer periphery of the resin core is covered with the molten metal layer. The stress at the time of joining caused by the difference between the thermal expansion coefficients of the child and the Faraday rotator is reduced, the crack of the optical element, the crack of the joining member, the deterioration of the optical characteristics does not occur, and the joining strength increases. As a result, the reliability of the temperature cycle test and vibration shock test is also improved.

  Further, the interval between the optical elements can be made constant by the size of the resin core diameter d, and an optical isolator element can be manufactured as designed. Furthermore, since no resin adhesive is present on the optical path, it is possible to provide an optical isolator having excellent environmental resistance, particularly high temperature and high humidity characteristics, and light resistance. In addition, the area of the effective aperture diameter of the transmitted light of the optical element is configured to be a circle or an ellipse inscribed in the plane, thereby providing a miniaturized optical isolator having the above-described effects. Can do.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a perspective view showing an embodiment of an optical isolator element used in the optical isolator of the present invention, and FIG. 2 is a diagram showing an effective aperture diameter and metallized region of transmitted light of the optical element 1 which is a feature of the present invention. FIG. 3 is a cross-sectional view showing the structure of the joining member used in the present invention.

  Here, the effective aperture diameter refers to a region A through which light is transmitted without being blocked on the incident surface of the optical element. Since the spot shape of transmitted light is generally circular or elliptical, it is circular. Or an elliptical region.

  The optical isolator element 10 includes an optical element 1 including a polarizer 3, a Faraday rotator 2, and a polarizer 4, and a bonding member 5 that connects each of the optical elements 1.

  The polarizers 3 and 4 are made of, for example, polarizing glass having a structure in which ellipsoidal metal particles are dispersed in glass. This polarizing glass is a glass having polarization characteristics by arranging long stretched metal particles in one direction in the glass itself, light having a polarization plane perpendicular to the stretch direction of the metal particles is transmitted, Light with a parallel polarization plane is absorbed. For example, it is made of polarizing glass having a structure in which ellipsoidal metal particles are dispersed in glass. This polarizing glass is a glass having polarization characteristics by arranging long stretched metal particles in one direction in the glass itself, light having a polarization plane perpendicular to the stretch direction of the metal particles is transmitted, Light with a parallel polarization plane is absorbed.

  The Faraday rotator 2 is adjusted to have a thickness at which the polarization direction of light incident at room temperature rotates 45 degrees. The material is, for example, a bismuth-substituted garnet crystal. Generally, in order to rotate the plane of polarization, it is necessary to apply a sufficient magnetic field in the direction of the optical axis L of the incident light, and the optical isolator element 10 shown in FIG. When a sufficient magnetic field is applied to the optical isolator, it functions as an optical isolator having a configuration described later.

  By the way, as shown in FIGS. 1 and 2, the optical elements 1 of the polarizers 3 and 4 and the Faraday rotator 2 are all processed into a quadrangular shape having substantially the same shape. Metallized films are formed at the four corners excluding the area A of the effective opening. The material of this metallized film is generally formed as a layer made of one kind of metal of Cr, Ta, W, Ti, Mo, Ni, or Pt or an alloy containing at least one kind as an underlayer. Au, Ni, Pt or the like is used for the surface layer. Furthermore, a layer made of Ni, Pt or the like may be formed as an intermediate layer between the base layer and the outermost layer. Further, as a method for forming the metallized film 14, a wet process by plating, a dry process such as a vacuum deposition method, and a sputtering method are known. However, scratches and dust are generated on the optical surface of the optical element 1 or the antireflection film. A dry process is often used to prevent the adhesion of slag.

  The area A of the effective aperture diameter of the transmitted light of the optical element 1 is a circle or an ellipse inscribed in the four sides of the rectangular optical element 1, and the outer side of the area A of the effective aperture diameter of the transmitted light is a metallized area. 14 is preferable. That is, the metallized regions of the polarizer 3 and the Faraday rotator 2 of the optical element 1 are opposed to each other, and only this portion is joined via the joining member 5 covered with the molten metal layer 7 on the outer periphery of the minute resin core 6. Thus, since the dead space which is an optically unnecessary portion can be effectively used, the joining member 5 is not applied to the region A of the effective aperture diameter of the transmitted light, and the stress at the time of joining is the resin core 6. Therefore, the bonding area can be bonded with at least a large bonding strength. As a result, the miniaturized optical isolator element 10 can be provided.

  As shown in FIG. 3, the joining member 5 is a spherical microsphere in which a molten metal layer 7 is plated on a resin core 6. The resin core 6 has a high heat resistance and a small weight loss rate due to temperature. A resin having a heat resistance of 200 ° C. or higher from the melting step, specifically, a material such as divinylbenzene, a fluororesin (polytetrafluoroethylene, etc.), polystyrene, or the like may be used.

  Further, the molten metal layer 7 may be formed on the outer periphery of the resin core 6 preferably through the metal layer 8. Thereby, adhesiveness with the molten metal layer 7 can be improved. The metal layer 8 is plated with a metal such as copper by several μm in order to improve the adhesion of the molten metal layer 7. The molten metal layer 7 is formed with a thickness of several μm to several tens of μm from above. The molten metal layer 7 uses a solder material such as an Au—Sn alloy, a Pb—Sn alloy, or an Au—Ge alloy, and various brazing materials. The size of the bonding member 5 serving as the resin core 6 is preferably selected from about Φ0.5 mm to Φ0.05 mm according to the areas of metallization applied to the four corners of the optical element 1.

In order to relieve the stress applied to the resin core 6, the Young's modulus of the resin used is preferably 1 × 10 ¹⁰ Pa or less. The reason is that the Young's modulus of the Pb—Sn alloy is relatively soft as the molten metal 7 is 1.6 × 10 ¹⁰ Pa, but when the optical element is bonded only by the molten metal 7 without using the resin core 6, Due to the residual stress, the optical element 1 may be cracked or the metal layer 8 may be peeled off from the optical element 1. Therefore, it is essential that the resin core is smaller than at least 1.6 × 10 ¹⁰ Pa. As a result of elaborate research, when a 10 mm square optical element is bonded and cut out to 1 mm square, the Young's modulus of the resin core 6 is 1 × 10 6. It was found that there was no occurrence of cracks or cracks in the optical element or molten metal at ¹⁰ Pa or less.

  FIG. 4 is a partially enlarged cross-sectional view showing a bonding state between the polarizer 2 and the Faraday rotator 3 of the optical element 1.

  As shown in the figure, the joining member 5 is wetted on the entire surface of the metallized film, and a resin core 6 is disposed at the center of the joining member 5. Then, the polarizer 3 and the Faraday rotator 2 of the optical element 1 are joined via the joining member 5, and the polarizer 2 and the Faraday rotator are in the region A (not shown in FIG. 4) of the effective aperture for transmitted light. Only the air layer exists between the two. Although not shown, the connection between the Faraday rotator 2 and the polarizer 4 is the same as described above.

In this way, by using the bonding member 5 having the resin core 6 described above for bonding between the optical elements 1, the external adaptation force is received by the entire resin core 6, so that the thermal expansion coefficient of the Faraday rotator 2 is about 10.4. Bonding stress caused by the difference between the thermal expansion coefficient of about 6.5 × 10 ⁻⁶ / ° C. between 5 × 10 ⁻⁶ / ° C. and the polarizers 3 and 4 is reduced, and cracks, cracks in the bonding member, and optical characteristics are reduced. Less likely to occur. Furthermore, the reliability of the temperature cycle test and vibration shock test is also improved. Further, the distance between the optical elements 1 is constant with the size of the diameter d of the resin core 6, and the optical isolator element 10 can be manufactured as designed.

  FIG. 5 is a diagram showing a method for manufacturing the optical isolator element 10 of the present invention.

  First, as shown in FIG. 5A, metallized films are formed on each surface of the polarizer substrate 22 and the polarizer substrate 24 of about 10 mm square and both surfaces of the Faraday rotator substrate 23. Since the metallized films are formed at the four corners excluding the region A of the effective opening of the transmitted light of the optical isolator element 10, a number of metallized films having a substantially rhombus pattern are formed on the substrate. Here, the transmission polarization direction of the polarizer 22 is set to a direction parallel to one side, and the transmission polarization direction of the polarizer 24 is set to a direction of 45 degrees on one side. At this time, the optical isolator element 10 can be assembled with high accuracy by determining the relative alignment position of the polarizer substrate 22 and the polarizer substrate 24 by the formation position of the metallized film.

  Next, as shown in FIG. 5B, the bonding member 5 having a resin core 6 is sandwiched between the bonding member 5 in the order of the polarizer substrate 22, the Faraday rotator substrate 23, and the polarizer substrate 24. Were melted, solidified and joined. Four joining members 5 may be used in a size obtained by dividing one metallized pattern into four, or one joint member 5 may be used in the same size as one metallized pattern. When the bonding member 5 having the same size as that of one metallized pattern is used, the ratio of the bonding members in the bonding region is increased, and a larger bonding strength can be obtained. Further, the number of joining members is reduced, and there are effects of cost reduction and man-hour reduction. When one joining member 5 having the same size as that of one metallized pattern is used in this way, the resin core 6 is divided into four parts by dicing, but since processing stress tends to remain in the resin part, about 150 degrees after processing. It is desirable to perform the annealing process.

  Next, as shown in FIGS. 5C and 5D, the large substrate 25 of the optical isolator element 10 is processed into a large number of small chip-like optical isolator elements 10 by dicing or the like. Dicing is processed so as to cut approximately the center of the diamond-shaped metallized pattern. When one joining member 5 having the same size as that of one metallized pattern is used, the resin core 6 is divided into four parts by dicing processing. However, since processing stress tends to remain in the resin portion, an annealing process of about 150 degrees after processing is performed. It is desirable to do.

  As described above, when the optical isolator element 10 is manufactured, the large polarizer substrates 22 and 23 and the large Faraday rotator substrate 23 are alternately stacked, and after the completion of bonding, a large number of them are cut. By using the method of obtaining the optical isolator element 10, workability and production volume can be increased, and the number of parts can be reduced. Furthermore, by joining with the joining member 5 which formed the molten metal layer 7 in the outer periphery of the resin core 6, compared with the case where the polarizer 2 and the Faraday rotator 3 are joined only by the molten metal layer 7, they are joined by a large substrate. The occurrence of cracks, cracks, etc. is greatly reduced.

  Further, the polarizer substrates 22, 24 and the Faraday rotator substrate 23 are formed with a metallized film in a substantially rhombus pattern as in FIG. 4A, and then cut into a predetermined size in advance before bonding. You may assemble to. Assembling is performed by melting and solidifying the molten metal layer 7 in a heat treatment furnace with the bonding member 5 having the molten metal layer 7 formed on the outer periphery of the resin core 6 interposed therebetween. In the case of such a manufacturing method, the number of assembling steps is slightly increased, but it is possible to reduce dirt due to solder scraps during dicing and chipping of the optical element, and an improvement in yield can be expected.

  FIG. 6 is a sectional view showing the optical isolator 12 of the present invention.

A cylindrical magnet 9 is disposed around the optical isolator element 10 described with reference to FIG. 1, and the optical isolator element 10 and the magnet 9 are joined to a metal holder 11. For example, when a brazing material or a solder material is used, the metal holder is melted at a temperature lower than the melting temperature of the bonding member 5 used for bonding the optical isolator element 10. A resin adhesive or the like may also be used. The magnet is sized to give a sufficient saturation magnetic field strength to the Faraday rotator, and the material is Sm-Co magnet, and the shape of the magnet is not limited to a cylindrical shape, and if the Faraday rotator satisfies a predetermined magnetic field strength. The shape is not limited. When a Faraday rotator that does not require a magnet is used, the optical isolator element 10 of the present invention alone operates as an optical isolator.

  In the present embodiment, the case where both the resin core 6 and the molten metal layer 7 are spherical has been described. However, the present invention is not limited to this, and the resin core 6 may have other shapes such as a square shape and a plate shape.

  As described above, according to the configuration of the present invention, the polarizer and the Faraday rotator having different thermal expansion coefficients are joined via the joining member 5 in which the molten metal layer 7 is formed on the outer periphery of the resin core 6. Bonding stress caused by the difference in thermal expansion coefficient is reduced, and cracks in the optical element, cracks in the bonding member, and deterioration in optical characteristics do not occur. Furthermore, the reliability of the temperature cycle test and vibration shock test is improved. Further, the distance between the optical elements 1 is constant depending on the size of the diameter d of the resin core 6, and the optical isolator element 10 can be manufactured as designed. Furthermore, since no resin adhesive is present on the optical path, it is possible to provide an optical isolator having excellent environmental resistance, particularly high temperature and high humidity characteristics, and light resistance.

  As an example of the present invention, the optical isolator of the present invention shown in FIG. 6 was prototyped and its characteristics and temperature cycle test were conducted. Each component and configuration will be described below.

As the polarizer substrate, a polar core (product name) manufactured by Corning Inc. is used. The size is 11 mm square and the thickness is 0.2 mm. One side is a reference side, and the polarizer 3 on the incident side is parallel to the reference side. The polarization substrate on the output side was set to transmit a polarization direction of 45 degrees with respect to the reference side. The thermal expansion coefficient of the polarizer is 6.5 × 10 ⁻⁶ / ° C.

The Faraday rotator was a bismuth-substituted garnet, the size was 11 mm square, the thickness was 0.4 mm, and the polarization rotation angle in the saturation magnetic field strength was 45 degrees. Both are elements that operate with respect to light having a wavelength of 1.55 μm, and antireflection films for air (n = 1) are provided on both surfaces of the polarizer and the Faraday rotator. The thermal expansion coefficient of the Faraday rotator is 10.5 × 10 ⁻⁶ / ° C.

  Metallized films were formed on one surface of the polarizer substrate (the surface facing the Faraday rotator) and on both surfaces of the Faraday rotator. At this time, the metallized film was formed by RF magnetron sputtering, and the metal used was a three-layer film of Ti for the base, Pt for the intermediate layer, and Au for the surface. Next, each optical element substrate was cut into 1 mm square by dicing. The cut-out direction was substantially parallel to the reference side and perpendicular to the reference side, and the metallized film formation region was cut into four.

  Next, a polarizer, a Faraday rotator, and a polarizer were stacked in this order, and a bonding member serving as a resin core was placed at each of the eight metallized film portions facing each other, and melted and solidified in a heat treatment furnace to bond the optical elements. At this time, the joining member was Au-Sn, the resin core material was divinylbenzene, the diameter was 0.25 mm, and the diameter of the ball including the joining member was 0.3 mm.

  As shown in FIG. 6, the melted and fixed polarizer and Faraday rotator were attached with a metal holder and a magnet to produce five optical isolators, and the characteristics were evaluated.

Table 1 shows the insertion loss and isolation characteristics of five prototype optical isolators and their average values.

  The average value of the insertion loss was 0.21 dB and the average value of the isolation was 44.6 dB. All optical isolators were found to have good characteristics without variation. Further, there were no cracks in the optical element, cracks, cracks in the joining member, etc., and good results could be obtained.

  From the results of the above trial manufacture, 50 optical isolators were manufactured, characteristics were measured, and reliability was evaluated. The tests were conducted vibration test, impact test, temperature cycle test, high temperature holding test, low temperature holding test, high temperature high humidity test shown in Telcordia 1221. In all tests, the amount of change in insertion loss is ± 0.2 dB or less, A very good result was obtained in which the amount of change in isolation was ± 3 dB or less.

  By the above trial manufacture, it is possible to provide an optical isolator having stable optical characteristics, easy assembly, less man-hours, and excellent in reliability without dropping, cracking, and characteristic deterioration of optical elements.

It is a perspective view which shows embodiment of the optical isolator element of this invention. FIG. 2 is a diagram showing an effective aperture and a metallized region of the optical element. It is sectional drawing which shows the structure of the joining member used as a resin core. It is sectional drawing which shows the joining state of an optical element. It is a figure which shows the manufacturing method of the optical isolator element of this invention. It is sectional drawing which shows the optical isolator of this invention. It is a figure which shows the structure of the conventional optical isolator miniaturized. It is a figure which shows the manufacturing method of the conventional optical isolator element.

Explanation of symbols

1: Optical elements 15, 12: Optical isolators 2, 16: Faraday rotators 3, 4, 17, 18: Polarizer 5: Bonding member 6: Resin core 7: Molten metal layer 8: Metal layers 9, 21: Magnet 10 , 20: optical isolator element 11: metal holder 13: effective opening 14: metallized region 19: adhesive 22, 24: polarizer substrate 23: Faraday rotator substrate 25: large substrate of optical isolator element

Claims (4)

In an optical isolator in which optical elements including a flat Faraday rotator and a polarizer are bonded to each other via a bonding member, the bonding member is formed by covering the outer periphery of a resin core with a molten metal layer, and the Faraday rotation An optical isolator, wherein the optical isolator is bonded outside the region of the effective aperture diameter of the transmitted light of the polarizer and the polarizer. The Faraday rotator and the polarizer of the optical element have a rectangular shape with substantially the same plane, and a metallized film is formed at four corners of the Faraday rotator or polarizer surface, and the bonding member is interposed through the metallized film. The optical isolator according to claim 1, wherein the optical isolator is bonded. 3. The optical isolator according to claim 2, wherein the region of the effective aperture diameter of the transmitted light of the optical element is a circle or an ellipse inscribed in the plane. The optical isolator according to claim 1, wherein the joining member is a spherical body.

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