JP4403239B2 - Optical isolator - Google Patents

Description

  The present invention relates to an optical isolator suitable as a passive optical device such as an optical communication module, a semiconductor laser module, and an optical amplifier mainly used in an optical communication system.

  An optical isolator is one of key devices in an optical communication system using an optical fiber. In an optical communication module, a semiconductor laser module, an optical amplifier, and the like, a laser diode (hereinafter referred to as LD) light source side from an optical component in an optical path system is used. This is used to prevent the reflected return light of the light and the occurrence of light resonance inside the optical amplifier. These optical isolators are optical elements of a polarizer, a Faraday rotator, and another polarizer (also referred to as an analyzer) between an LD light source and an optical fiber or between two opposed optical fibers. The elements are combined, and a magnet for saturation magnetization of the Faraday rotator is arranged around the Faraday rotator.

  For example, in the case of a “single-stage type” configuration of a polarization-dependent optical isolator (hereinafter referred to as an optical isolator), the relative angle of the polarization transmission direction on the optical signal transmission surface of the two polarizers is about 45. The two Faraday rotators with a thickness of about 45 degrees at a given wavelength in a saturated magnetic field are placed between the polarizers so that they face each other, and are held and fixed together. It is made up of. With the above configuration, the forward optical signal is transmitted and the reverse optical signal is blocked.

In the above optical isolators, recently, there has been a strong demand for cost reduction by downsizing and mass production, which reduces the number of assembly steps at the time of manufacture or reduces the rotation adjustment work of the polarization transmission direction between the polarizers. For example, an optical isolator having a structure in which, for example, a plate-shaped polarizer and a Faraday rotator and a rectangular parallelepiped magnet are fixed on a plate-shaped mounting substrate has been proposed (for example, Patent Documents). 1).
JP-A-10-227996 (page 2-4, FIG. 1)

  FIG. 4 is a schematic perspective view showing such an optical isolator 100. The two polarizers 1a and 1b constituting the optical isolator 100 are cut out in a flat plate shape so that the polarization transmission direction is set in a predetermined direction in advance, and the Faraday rotator 2 is cut out in a flat plate shape as well. In more detail, first, the polarizer 1a is cut out so that the polarization transmission direction is set in a predetermined direction, and then, when the polarization direction of the optical signal is rotated in the predetermined direction in the saturation magnetic field, the polarization direction is changed to the polarizer. The Faraday rotator 2 is cut out so as to be 45 degrees different from the polarization transmission direction of 1a. Finally, the polarizer 1b is cut out so that its polarization transmission direction is 45 degrees different from the polarization transmission direction of the polarizer 1a and coincides with the rotation direction of the Faraday rotator 2.

  The cut out polarizers 1a and 1b and the Faraday rotator 2 (hereinafter referred to as an optical element if necessary) and the magnets 3 and 3 are mounted on one flat mounting substrate 4 by a fixing means such as solder (not shown). Fixed to. At that time, the magnets 3 and 3 are magnetized so that the magnetization direction thereof is parallel to the optical axis of the optical isolator 100. Thus, the optical isolator 100 is formed.

  However, in the configuration of the optical isolator 100 as shown in FIG. 4, the optical element and the magnets 3 and 3 are arranged on the same plane of the single mounting substrate 4, so that there are some problems as described below.

  First of all, since the mounting substrate 4 has a flat plate shape, there is no structure or reference position for determining the fixing position of the optical element and the magnets 3 and 3 on the surface to which the optical element and the magnets 3 and 3 are fixed. Furthermore, since the fixing surface of the optical element and the mounting substrate 4 and the fixing surface of the magnets 3 and 3 and the mounting substrate 4 are on the same plane, it is difficult to position the optical element and the magnets 3 and 3 one by one. The optical element and the fixing position of the magnets 3 and 3 on the surface of the substrate 4 varied for each optical isolator 100, and the optical characteristics were not stable.

  Further, since each optical element is individually fixed to the mounting substrate 4 with a gap, it is very difficult to adjust the gap between the optical elements so as to obtain an optimum position with good characteristics. Therefore, the reverse insertion loss of optical signal transmission, which is an important characteristic as an optical isolator, is difficult to reach the maximum state in each optical isolator.

  Second, since the applied magnetic field strength at the end of the Faraday rotator 2 is relatively weaker than that at the center, desired optical characteristics cannot be obtained for the optical signal passing through the end.

In order to solve these problems, an optical isolator has been devised in which an optical element is fixed on a mounting substrate having a step portion so that the height of the plane of the optical element fixing part is different from the plane height of the peripheral part. (See Patent Document 2).
JP 2001-264695 (page 2-4, Fig. 1)

  FIG. 5 is a schematic perspective view showing such an optical isolator 101. In addition, the same number is attached | subjected to the same location as the optical isolator 100, and the overlapping description is abbreviate | omitted or simplified.

  The optical isolator 101 fixes the optical element on the optical element fixing surface 4′C of the mounting substrate 4 ′ having a step 4′D in the center, and the magnets 3 and 3 on the magnet fixing surfaces 4′A and 4′B, respectively. It has a structure. By providing a step in the magnet fixing part plane 4'A, 4'B and the optical element fixing part plane 4'C, the optical element is arranged on the stepped surface in the center of the mounting substrate 4 ', and this is arranged on the magnets 3 on both sides. 3 makes it easy to position the magnets 3 and 3 and the optical element, and allows the optical element to be arranged at the center of the magnets 3 and 3 in the height direction. It is said that the shortage of magnetic field strength against can be solved.

  However, since the optical isolator 101 is configured to fix the polarizers 1a and 1b and the magnets 3 and 3 (hereinafter, collectively referred to as “components” as needed) to the mounting substrate 4 ′, each component is attached to the mounting substrate 4 ′. When fixing on the top, due to the difference between the thermal expansion coefficient of each component and the thermal expansion coefficient of the mounting substrate 4 ′, contraction occurs in each component or the mounting substrate 4 ′, resulting in stress distortion. appear. Such stress strain is desirably removed because it has various adverse effects such as deterioration of the optical characteristics of the entire optical isolator.

  As an effective means for that purpose, it is possible to select the material of the mounting substrate 4 ′ for fixing the respective components as a material having a thermal expansion coefficient close to the thermal expansion coefficient of the respective components. By making the mounting substrate 4 ′ a material having an approximate thermal expansion coefficient, it is intended to suppress various adverse effects by reducing the stress strain generated inside each component.

  However, in the configuration of the optical isolator 101, the optical element and the magnets 3 and 3 are fixed on the mounting substrate 4 ′ made of one material. The material close to the thermal expansion coefficient must be selected to form the mounting substrate 4 ′.

In such a case, in most cases, a material having a thermal expansion coefficient approximate to that of the optical element is often selected for the mounting substrate 4 ′. The reason is that the optical element is glassy and very fragile to stress strain. The thermal expansion coefficient of the polarizers 1a and 1b generally used in the optical isolator is about 6.5 × 10 ⁻⁶ / ° C., whereas the thermal expansion coefficient of the Faraday rotator 2 is about 10.2 to 11.0 × 10 ⁻⁶ / In order to prevent the occurrence of stress distortion occurring inside these optical elements because of the temperature of about 0 ° C., intermediate values of the respective thermal expansion coefficients of the polarizers 1a and 1b and the Faraday rotator 2 are used as the material of the mounting substrate 4 ′. It is optimal to select a material having a thermal expansion coefficient of

  However, if the material of the mounting substrate 4 ′ is made to have a coefficient of thermal expansion that is an intermediate value between the polarizers 1a and 1b and the Faraday rotator 2, the difference from the coefficient of thermal expansion of the magnets 3 and 3 must be opened. Disappear. Therefore, the increase in the thermal expansion difference between the mounting substrate 4 ′ and the magnets 3 and 3 causes a situation where the magnets 3 and 3 are separated from the mounting substrate 4 ′.

  Furthermore, mounting the optical isolator 101 on an external device such as an optical communication module, a semiconductor laser module, or an optical amplifier is performed by mounting the mounting substrate 4 ′ on the external device. Therefore, if the material of the mounting substrate 4 ′ is selected to be close to the thermal expansion coefficient of the optical element, it is not necessarily a material with high toughness, high rigidity or high strength against deformation caused by external stress or external force applied during mounting. The shrinkage occurs inside the mounting substrate 4 ′ and stress strain is generated. This stress strain is transmitted to the optical element and causes stress strain inside the optical element. There is also a problem that cracks, cracks, etc. occur in the mounting substrate 4 ′ due to deformation due to external force.

  However, if the mounting substrate 4 ′ is selected as a material having high toughness, high rigidity or high strength against deformation due to external stress or external force, this time, the difference between the thermal expansion coefficient of the mounting substrate 4 ′ and the thermal expansion coefficient of the optical element. Becomes larger, and stress distortion is likely to occur in the optical element. That is, it was very difficult to satisfy two conflicting requirements with one kind of material.

  Further, in the optical isolator 101, the optical element is arranged at the center in the height direction of the magnets 3 and 3 according to the height dimension of the step 4'D, so that the step 4'D with respect to the magnet fixing surfaces 4'A and 4'B The machining accuracy required for the height dimension is very strict, and the magnet fixing surfaces 4'A and 4'B are separated from each other, so both sides of 4'A and 4'B are the same in the horizontal direction. If the height is not processed, the center of the two magnets 3 and 3 is displaced in the height direction, so that the required processing accuracy is very severe.

  Furthermore, since the outer shape of the step 4'D and the continuous surface of the step 4'D and the magnet fixing surfaces 4'A and 4'B must be processed at 90 degrees, the entire processing of the mounting substrate 4 'itself In addition to being complicated, there is also a problem that deformation due to burrs, burrs, cracks, etc. is likely to occur in the 90-degree processed part. In particular, when a plastic material such as stainless steel SUS304 is used for the mounting substrate 4 ', burrs, chips, cracks, and the like are likely to occur during cutting and cutting. Further, when a brittle material having excellent workability is used for the mounting substrate 4 ′, as described above, the toughness, rigidity, or strength against deformation due to external stress / external force when mounting the optical isolator is insufficient.

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide an optical isolator in which at least two or more polarizers and one or more Faraday rotators are fixed on a mounting substrate. By reducing stress distortion generated in each component when fixing each component to the board, and providing an optical isolator with high toughness, high rigidity, or high strength against deformation due to external stress or external force applied when mounting external equipment is there. It is another object of the present invention to provide a high-quality and highly reliable optical isolator excellent in workability and adhesion of each component to the mounting substrate.

In order to solve the above problems, an optical isolator according to a first aspect of the present invention, the optical element and the magnet preparative comprising at least two or more polarizers and one or more Faraday rotator fixed on the mounting substrate In this optical isolator, the mounting substrate is composed of a first substrate made of a brittle material and a second substrate made of a plastic material, and the first substrate and the second substrate are fixed and integrated. In this optical isolator, the optical element is fixed on the first substrate and the magnet is fixed on the second substrate.

  Furthermore, in the optical isolator according to claim 2 of the present invention, the first substrate is made of oxide ceramics, and the second substrate is made of any of ferritic stainless steel, austenitic stainless steel, copper tungsten alloy, and tungsten. This is an optical isolator characterized by comprising one of these.

  In the optical isolator according to claim 3 of the present invention, a metal film layer is formed on the first substrate and the second substrate, and the first substrate and the second substrate are further formed. A solder layer is formed on one or both of the metal film layers, the metal film layer of the first substrate and the metal film layer of the second substrate are in surface contact, and the surface contact is made. As an optical isolator optical isolator characterized in that a part is locally heated by spot welding of an Nd: YAG laser to melt a solder layer and integrate the first substrate and the second substrate Yes.

  According to a fourth aspect of the present invention, in the optical isolator according to the fourth aspect of the present invention, grooves are formed on the first substrate to which the optical element is fixed so as to have an inclination angle with respect to the optical axis of the optical signal. The optical isolator is formed in a divided manner and fixed on the first substrate by inserting the optical element into the groove.

  According to the optical isolator of the present invention, the mounting substrate is composed of substrates made of two different materials. Therefore, the first substrate for fixing the optical element is made of a brittle material and has a thermal expansion coefficient of the polarizer and the Faraday. It is possible to use materials that are intermediate values of the coefficient of thermal expansion of the rotor. Therefore, it becomes possible to suppress the stress strain generated in the optical element, and furthermore, since a brittle material is used, it is excellent in workability such as cutting and cutting, and prevents deformation due to burrs, cracks, cracks, etc. It becomes possible.

  In addition, when the optical isolator is mounted on an external device, the second substrate that is contacted / fixed to the external device uses a plastic material and is resistant to deformation of external stress and external force when mounted on the external device. An optical isolator can be formed. In addition, since a material having a thermal expansion coefficient close to that of the magnet and excellent in laser weldability can be used for the second substrate, peeling of the magnet from the mounting substrate due to a difference in thermal expansion coefficient is prevented. As a result, the adhesiveness can be improved.

  Further, the first substrate and the second substrate are integrated by spot welding with an Nd: YAG laser in advance before fixing the optical element and the magnet. By integrating the first substrate and the second substrate, it is possible to form an attachment substrate that satisfies the two conflicting requirements by combining the effects of the first substrate and the effects of the second substrate. Thus, an optical isolator using the mounting substrate can be formed. Also, by integrating the first substrate and the second substrate in advance, the occurrence of misalignment when the optical element is fixed on the first substrate can be prevented, and the optical characteristics of the entire optical isolator can be made to the desired characteristics. It becomes possible to do.

  Furthermore, the spot weld mark after welding can be used as a marking indicating the forward direction or the reverse direction in the optical axis direction of the optical isolator.

  Further, since the outer shapes of the first and second substrates can be formed in a flat plate shape, the processing of the two substrates can be simplified and the required processing accuracy can be moderated. . Further, by making the second substrate into a flat plate shape, it becomes very easy to process the height of the fixed surfaces of the two magnets in the horizontal direction, and the required processing accuracy is also moderated. In addition, it is possible to form the mounting substrate 7 that satisfies all the above conditions at a low price.

  Further, grooves are formed for the number of optical elements so as to have an inclination angle with respect to the optical axis of the optical signal on the first substrate, and the optical elements are fixed on the first substrate by being inserted into the grooves. This makes it possible to automatically place and fix the polarizer and the Faraday rotator obliquely so as to have an inclination angle with respect to the optical axis only by inserting the polarizer and the Faraday rotator into the groove. Furthermore, by setting the groove interval in advance to the optimum position between the optical elements, the interval between the optical elements is automatically adjusted to an optimum position that provides good characteristics simply by inserting the optical element into the groove. It becomes possible.

<First Embodiment>
Hereinafter, an optical isolator according to the present invention will be described in detail with reference to FIGS. FIG. 1 is a schematic perspective view showing an example of the optical isolator of the present invention, FIG. 2 is a schematic perspective view showing an example of a mounting substrate forming the optical isolator of FIG. 1, and FIG. It is a top view of an optical isolator when it sees from. The same parts as those of the conventional optical isolator 100 or 101 are denoted by the same reference numerals, and redundant descriptions are omitted or simplified.

  As shown in FIG. 1, the optical isolator 1 of this embodiment will be described by taking a “one-stage type” (configuration with two polarizers and one Faraday rotator) as an example, and polarization transmission of two polarizers 1a and 1b. The directions are configured to differ by 45 degrees relative to the optical signal incident direction I, respectively.

  As shown in FIG. 2, a mounting substrate 7 on which the components of the polarizers 1a and 1b and the magnets 3 and 3 are placed and fixed is a first substrate 5 (hereinafter referred to as a substrate 5 if necessary) and a first substrate. Two flat-plate substrates of two substrates 6 (hereinafter referred to as substrate 6 as needed) are fixed and integrated. First, a metal film layer is formed on both surfaces 5a and 5b of the substrate 5 so that the solder can be fixed, and a metal film layer for fixing solder is also formed on at least one surface 6a of the substrate 6 in the same manner. Then, a solder layer is formed by sputtering on one or both of the substrate 5 and the substrate 6. Next, the one surface 5b of the substrate 5 and the one surface 6a of the substrate 6 are brought into surface contact, and a part of the surface contact is locally heated to intervene between the metal film layers of both the substrates 5 and 6. The solder layer is melted, the substrate 5 and the substrate 6 are partially bonded and fixed, and an integrated mounting substrate 7 is formed.

  The substrate 5 and the substrate 6 are fixed before the optical element is fixed on the substrate 5. If the optical element unit composed of the optical element and the substrate 5 is fixed to the substrate 6 after the optical element is fixed to the substrate 5, the optical element unit is slightly misaligned when placed and fixed on the one surface 6 a of the substrate 6. This is because it becomes difficult to obtain desired optical characteristics as the entire optical isolator 1.

  As a means for locally heating the solder fixing surfaces of the substrate 5 and the substrate 6, spot welding with an Nd: YAG laser is optimal. In addition, when spot welding of the Nd: YAG laser is performed in this way, the spot welding mark 8 generated after welding is forward or reverse in the optical axis a direction of the optical isolator 1 (direction of arrow I in FIG. 1) or reverse. It can also be used as a marking indicating the direction.

  Next, a metal film layer is formed on the side surfaces of the light transmission surfaces of the polarizers 1a and 1b and the Faraday rotator 2 by a sputtering method and a masking method so that the solder can be fixed. A solder layer is formed on the layer by vapor deposition. Then, on the surface of the substrate 5, the polarizer 1a, the Faraday rotator 2, and the polarizer 1b are arranged in this order on the basis of one side of each optical element. At that time, similarly to the optical isolator 100 or 101, the polarization transmission directions of the polarizers 1a and 1b are relatively different by 45 degrees.

  Polarizers 1a and 1b are flat glass polarizers, including a type in which dielectric particles are encapsulated in a glass substrate and a type in which dielectrics are laminated on a glass substrate. For example, a “Polar core” manufactured by Corning Co., Ltd. can be used.

  On the other hand, the Faraday rotator 2 is incident when a single magnetic plate such as a bismuth-substituted rare earth iron garnet manufactured by a liquid phase epitaxial growth method (LPE method) is used, and a saturation magnetic field in the optical signal incident direction is applied. In order to accurately rotate the polarization direction of the optical signal around the optical axis by 45 degrees, the optical signal is configured to have a predetermined thickness with respect to the traveling direction of the optical signal.

  With the optical element placed on the substrate 5, the mounting substrate 7 is inserted into an electric furnace and heated in an inert gas to a temperature equal to or higher than the melting temperature of the solder layer to form a film on the side surface of the optical element. The solder layer melts and the substrate 5 and the optical element are fixed and integrated. While the solder layer is melted, a certain load is applied to the optical element. And after melting and solidifying, it cools gradually to room temperature. The inert gas is preferably nitrogen that is a reducing atmosphere. As shown in FIG. 3, each optical element is disposed and fixed on the substrate 5 so as to have a predetermined inclination angle θ with respect to the direction perpendicular to the optical axis a. By arranging the optical elements obliquely so as to have the inclination angle θ, it is possible to prevent the optical signal reflected by the optical signal transmission surface of each optical element from returning to the LD light source.

  Next, a metal film layer is formed on one surface of the rectangular parallelepiped magnets 3 and 3 by a wet method, and a solder layer is further formed on the metal film layer, and then the magnets 3 and 3 are formed on the surface of the substrate 6. 3, the solder layer is melted in the electric furnace, and the magnets 3 and 3 are fixed and integrated on the substrate 6. After the integration, the magnets 3 and 3 are magnetized in parallel with the direction of the optical axis a to obtain the optical isolator 1.

  As the magnets 3 and 3, for example, a samarium cobalt (Sm-Co) -based magnet, a neodymium (Nd-Fe-B) -based magnet, a ferrite magnet, or the like can be used. In particular, a samarium-cobalt magnet has high magnetic characteristics. Therefore, it is suitable for downsizing, and is optimal because it is excellent in temperature stability and oxidation resistance.

As a material constituting the first substrate 5, it is desirable to use a brittle material such as zirconia ceramics or oxide ceramics such as alumina ceramics. In particular, zirconia ceramics have high toughness, high rigidity, high strength, and high weatherability, and are resistant to changes in the thermal environment. Furthermore, their thermal expansion coefficients (9.2 × 10 ^-6 / ° C) are the polarizers 1a and 1b This is desirable because it is an intermediate value of the thermal expansion coefficient of the Faraday rotator 2. Furthermore, since the first substrate 5 is a brittle material, it has excellent workability such as cutting and cutting, and can prevent deformation due to burrs, cracks, cracks, and the like.

Further, as a material constituting the second substrate 6, it is desirable to use a stainless steel SUS430 (magnetic material, good laser weldability) which is a plastic material. Although SUS430 is not a non-magnetic material, it is not easily affected by a magnetic field, has a thermal expansion coefficient very close to that of an optical element, and has a thermal expansion coefficient of the magnets 3 and 3 compared to the oxide ceramics of the first substrate 5. It is suitable for the substrate 6 because it has a thermal expansion coefficient close to the coefficient (samarium cobalt type: about 13 × 10 ⁻⁶ / ° C.) and is excellent in laser weldability. In addition, plastic material stainless steel SUS304 (non-magnetic material, good laser weldability, thermal expansion coefficient: about 16 × 10 ^-6 / ° C), which has a relatively large thermal expansion coefficient, is close to the thermal expansion coefficient of magnets 3 and 3 Can be used. Further, tungsten steel, tungsten alloy (for example, Cu20W80) or the like is also suitable as a plastic material other than the stainless steel having a low thermal expansion coefficient. An alloy containing tungsten as a main component is slightly inferior in laser weldability as compared with tungsten steel, but can be welded by laser welding at high energy. Furthermore, since the plastic material is more resistant to deformation of external stress and external force than the brittle material, it is optimal as a substrate material used when the optical isolator 1 is mounted on an external device.

  Thus, in the optical isolator according to the present invention, the mounting substrate 7 has a structure in which the two substrates 5 and 6 made of two different materials are integrated, so that the substrate for fixing the optical element and the magnet are fixed. It becomes possible to divide the material of the substrate. Therefore, it is possible to select materials close to the respective thermal expansion coefficients, it is possible to suppress the occurrence of stress distortion in the optical element, and the magnet from the mounting substrate 7 due to the difference in thermal expansion coefficient. The peeling of 3, 3 can also be prevented.

  Further, by forming the outer shapes of the two substrates 5 and 6 into a flat plate and integrating them, a step can be formed between the optical element fixing surface 5a and the magnet fixing surface 6a. Accordingly, the processing of the two substrates 5 and 6 can be simplified and the required processing accuracy can be moderated. Moreover, it becomes very easy to process the height in the horizontal direction of the fixed surface of the two magnets 3 and 3 by making the board | substrate 6 flat form. In addition, it is possible to form the mounting substrate 7 that satisfies all the above conditions at a low price.

  The metal film layer is preferably composed of three layers of Cr / Pt / Au. The Cr layer formed in the first layer is formed in order to ensure adhesion with the optical element, and the Pt layer formed in the second layer is formed in order to prevent diffusion of the solder layer. The Au layer formed on the third layer promotes the wettability of the solder layer, forms a bonding layer for the solder layer, and enables stable soldering. Note that the metal film layer only needs to be able to ensure sufficient adhesion strength, so that not only Cr / Pt / Au but also a metal film layer of another configuration such as Cr / Ni / Au or Ti / Pt / Au may be used. good.

  Further, for example, Au / Sn can be used for the solder layer, and the thickness is set to about 5 μm. The solder layer is not limited to Au / Sn, and a eutectic solder material having another composition such as Au / Ge can be used as a solder layer having a melting temperature higher than that of Au / Sn.

  Note that the optical signal transmitting surfaces of the polarizers 1a and 1b and the Faraday rotator 2 prevent Fresnel reflection caused by the refractive index difference between each optical element and the air layer interposed between the optical elements. In order to reduce the optical signal insertion loss into the air, it is desirable to provide a non-reflective coating (not shown) for the air layer.

  Instead of the solder layer, a solder bed may be melted and solidified on the metal film layer, and the optical elements and the magnets 3 and 3 may be fixed on the surface of the mounting substrate 7. Further, each component may be fixed by low melting glass instead of solder. In this way, by using an inorganic material such as solder or low melting point glass for fixing the components constituting the optical isolator 1, the moisture resistance under high temperature and high humidity conditions is improved, and laser light with a long time or high output is obtained. It is possible to improve the reliability in use in the environment and prevent the outgassing from affecting each part.

<Second Embodiment>
The optical isolator according to the present invention will be described in detail below with reference to FIG. FIG. 4 is a schematic perspective view showing an example of a mounting substrate of the optical isolator according to the second embodiment. In addition, the same number is attached | subjected to the same location as the attachment board | substrate 7 of 1st Embodiment, and the overlapping description is abbreviate | omitted or simplified and described.

  As shown in FIG. 4, the mounting substrate 7 ′ according to the second embodiment has a predetermined inclination with respect to the optical axis a of the optical signal on the one surface 5 b that is the optical element fixing surface of the first substrate 5. As many grooves 5c as the number of the optical elements are formed so as to have an angle θ. When the number of optical elements is “one-stage type”, there are three polarizers and two Faraday rotators, so three grooves 5c are also formed.

  By forming the groove 5c so as to have an inclination angle θ, it is possible to automatically have the inclination angle θ with respect to the optical axis a only by inserting the polarizers 1a, 1b and the Faraday rotator 2 into the groove 5c. It becomes possible to fix the arrangement at an angle. Furthermore, by setting the interval between the grooves 5c in advance to the optimum position between the optical elements, it is possible to automatically set the gap between the optical elements to the optimum position with good characteristics by simply inserting the optical element into the groove 5c. It is also possible to adjust. The groove 5c is formed by an etching method or the like.

  In the first and second embodiments, the configuration of the single-stage type (two polarizers and one Faraday rotator) optical isolator is shown, but the present invention is not necessarily limited to the single-stage type. The present invention can be applied to various optical isolator configurations such as a so-called 1.5-stage type (three polarizers and two Faraday rotators) or a two-stage type (four polarizers and two Faraday rotators).

  By using the optical isolator of the present invention for passive optical devices such as optical communication modules, semiconductor laser modules, and optical amplifiers used in optical communication systems, it is possible to prevent reflected return light to the LD light source side, It is possible to prevent the occurrence of light resonance.

The schematic perspective view which shows an example of the optical isolator of this invention. (First embodiment) The schematic perspective view which shows an example of the attachment board | substrate which forms the optical isolator of FIG. (First embodiment) The top view of an optical isolator when FIG. 1 is seen from the arrow U direction. (First embodiment) The schematic perspective view which shows an example of the attachment board | substrate of the optical isolator which concerns on 2nd Embodiment. (Second Embodiment) The schematic perspective view which shows an example of the conventional optical isolator. The schematic perspective view which shows another form of the conventional optical isolator.

Explanation of symbols

1 Optical isolator
1a, 1b Polarizer 2 Faraday rotator 3 Magnet 7, 7 'Mounting board 8 Spot welding mark

Claims (4)

In the optical isolator at least two or more polarizers and optical elements and the magnet preparative consisting of one or more Faraday rotators, which are fixed on the mounting substrate, a first substrate on which the mounting substrate is made of brittle material, A second substrate made of a plastic material, and after the first substrate and the second substrate are fixed and integrated, the optical element is fixed on the first substrate and the An optical isolator comprising a magnet fixed on the second substrate.   2. The first substrate is made of oxide ceramics, and the second substrate is made of any one of ferritic stainless steel, austenitic stainless steel, copper tungsten alloy, and tungsten. Optical isolator.   A metal film layer is formed on the first substrate and the second substrate, and a solder layer is further formed on one or both of the first substrate and the second substrate. The metal film layer of the first substrate and the metal film layer of the second substrate are brought into surface contact with each other, and a part of the surface contact is locally heated by spot welding with an Nd: YAG laser. The optical isolator according to claim 1, wherein the first substrate and the second substrate are integrated by melting the solder layer.   On the first substrate to which the optical element is fixed, grooves are formed by the number of the optical elements so as to have an inclination angle with respect to the optical axis of the optical signal, and the optical elements are inserted into the grooves. The optical isolator according to claim 1, wherein the optical isolator is fixed on the first substrate.

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