JPH0961751A - Optical isolator - Google Patents

Abstract

(57) [Abstract] [Problem] It is possible to perform bonding in a low distortion state without using an organic adhesive that causes a decrease in adhesive strength during assembly, prevent cracks, etc. To provide an inexpensive optical isolator having a simplified structure. SOLUTION: An optical element including a Faraday rotator 2, a polarizer 1, and an analyzer 3 and a permanent magnet 4 for applying a magnetic field to the Faraday rotator 2 are supported and fixed in a support member, and the support is provided. The member is an optical isolator including a polarizer support member that supports and fixes the polarizer 1, the Faraday rotator 2, and the permanent magnet 4, and an analyzer support member that supports and fixes the analyzer, the Faraday rotation Child 2
Is directly solder-fixed to one of the polarizer 1 and the analyzer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an optical isolator utilizing the Faraday effect used in optical transmission equipment.

[0002]

2. Description of the Related Art Conventionally, when a semiconductor laser is used as a light source for an optical transmission system such as optical communication, a part of light emitted from the semiconductor laser is reflected by a transmission line or optical components for transmission and returned to the semiconductor laser. This may cause instability of the oscillation characteristics of the semiconductor laser and increase of noise. Optical isolators are used to block such return light.

FIG. 6 is an explanatory diagram shown for explaining the basic structure and operation of a conventional optical isolator. Figure 6
(A) is explanatory drawing regarding operation | movement in case incident light injects in a forward direction. FIG. 6B is an explanatory diagram regarding the operation when the return light of the incident light is incident in the opposite direction.

This optical isolator is used as an optical element.
A polarizer 1, a Faraday rotator 2, and an analyzer 3 are arranged in this order from the incident side, and a magnetic field is applied to these in a forward direction. The analyzer 3 is the same as the polarizer 1.

When the incident light as shown in FIG. 6 (a) is incident on the optical isolator in the forward direction, the incident light is transmitted through the polarizer 1 and then its polarization plane is changed by the Faraday rotator 2. Rotate 45 degrees. Further, emitted light is obtained by passing through the analyzer 3 having a polarization plane whose angle θ is inclined by 45 degrees with respect to the polarization plane of the polarizer 1.

On the other hand, as shown in FIG. 6B, when the return light is incident on the optical isolator in the opposite direction, only the component whose polarization plane matches that of the analyzer 3 is returned. Passes through the analyzer 3. After that, the plane of polarization is rotated by the Faraday rotator 2. Therefore, the return light that has passed through the Faraday rotator 2 has its polarization plane rotated by 90 degrees with respect to the analyzer 3, which means that the analyzer 3 has blocked its transmission.

As described above, the optical isolator has an isolation effect as a basic function of blocking return light by reflection. However, if the optical isolators are formed in a plurality of stages, the isolation effect is further increased.

By the way, when assembling the optical isolator, an organic bonding method and a metal bonding method can be cited as a method of fixing each component.

The organic adhesive method is a method of fixing each component with an organic adhesive. In the case of this organic adhesive method, the adhesive layer always shrinks when the adhesive is cured.

The shrinkage of the adhesive layer has a great influence on the optical characteristics, and significantly deteriorates the durability in a severe environment of use.

Therefore, recently, a metal bonding method which can ensure high reliability has become mainstream.

The metal bonding method is a method of bonding the respective components using metal solder. Further, as the material of the solder used, an AuSn alloy is mainly used. For this reason,
The surface of the metal holder, which is a supporting member of the optical isolator, is previously made of Ni, Au in order to make it easy to attach solder.
Etc. are plated.

Further, it is impossible to perform plating treatment on an optical element which is not a metal, that is, a magneto-optical crystal forming a Faraday rotator, a polarizing glass of a polarizer and an analyzer. Therefore, the metal thin film is formed by the physical vapor deposition method.

As a result, the optical element is soldered to the metal holder at the metal thin film portion.

Soldering is generally carried out by heating and melting in an inert gas atmosphere using an electric furnace.

Further, after adjusting the optical axis of the soldered optical element, the metal holders accommodating the optical elements are laser-welded to complete the production of the optical isolator.

[0017]

In the case of the conventional optical isolator, the organic isolator is used to bond and fix the optical isolator to the support holder of the optical element. However, when the optical isolator thus obtained is used as an optical communication component of an optical transmission system, the optical characteristics are deteriorated due to the above-mentioned problem of shrinkage occurring in the adhesive layer and the decrease in adhesion (adhesion) due to water absorption. Then, it becomes impossible to meet the demand for long-term reliability.

In particular, even in the case of an optical isolator manufactured with high precision, the adhesive layer is likely to contract and the optical characteristics are deteriorated under use conditions where the temperature environment is severe. For this reason, when manufacturing an optical isolator, a joining method that does not use an organic adhesive on a solder fixing portion, a low melting point glass portion, or the like is desired.

Further, in order to enable laser welding and fixing when the optical isolator is incorporated in the optical transmission system, stainless steel is generally used as the material of the metal holder on the outer peripheral portion which is the target of the laser welding. Is.

However, the coefficient of thermal expansion of stainless steel is C used as a magneto-optical crystal forming a Faraday rotator.
The coefficient of thermal expansion of dMnTe single crystal or CdMnHgTe single crystal is greatly different from the coefficient of thermal expansion of the polarizing glass forming the polarizer and the analyzer or the polarizing beam splitter.
Therefore, if the Faraday rotator is directly fixed to the holder made of stainless steel, the optical characteristics of the Faraday rotator may be deteriorated or a crack may be induced at the joint surface.

Further, in the optical isolator, the permanent magnet for applying the magnetic field to the optical element is made of Nd-Fe which is a ferromagnetic material.
A -B type composition or the like is used.

However, the Faraday rotator of the optical isolator has physical properties that are greatly affected by changes in the strength of the applied magnetic field. Therefore, when a metal holder for fixing an optical element such as a Faraday rotator is made of a material having a high magnetic permeability, the leakage magnetic field of the permanent magnet is reduced, so that CdMnTe which is a magneto-optical crystal forming a Faraday rotator is reduced. The strength of the magnetic field applied to the single crystal or the CdMnHgTe single crystal is reduced.

As a result, in the Faraday rotator, the Faraday rotation angle is relatively reduced, which causes deterioration of the characteristics of the optical isolator.

An object of the present invention is to solve such problems, and it is possible to join in a low distortion state without using an organic adhesive which causes a decrease in adhesive strength at the time of assembly, and to prevent cracks and the like. Another object of the present invention is to provide an inexpensive optical isolator which can be manufactured without causing deterioration in characteristics in terms of structure and which has a simplified structure.

[0025]

According to the present invention, an optical element including a Faraday rotator, a polarizer, and an analyzer and a permanent magnet for applying a magnetic field to the Faraday rotator are supported and fixed in a support member. In the optical isolator, the support member includes a polarizer support member that supports and fixes the polarizer, the Faraday rotator, and the permanent magnet, and an analyzer support member that supports and fixes the analyzer. An optical isolator is obtained in which the rotator is directly solder-fixed to one of the polarizer and the analyzer.

In the optical isolator described above, either one of the polarizer support member and the analyzer support member is
An optical isolator is obtained which has a multiple structure in which local parts made of different materials are combined with each other.

In the optical isolator described above, at least one of the polarizer support member and the analyzer support member is made of a non-magnetic material, thereby obtaining an optical isolator.

In the optical isolator described above, one of ceramics, titanium, platinum and rhodium is used as a material for directly supporting a polarizer and an analyzer among local parts made of different materials. Is obtained.

In the optical isolator according to any one of the items (1) to (3), an optical isolator can be obtained in which a solder fixing metal thin film is formed on the end portion and the side surface of the surface of the optical element for solder fixing.

In the optical isolator described above, an optical isolator characterized in that the metal thin film is formed by using a masking method and a sputtering method in combination is obtained.

When assembling the optical isolator, in the conventional metal bonding method, when fixing the optical element composed of the Faraday rotator, the polarizer and the analyzer, the solder is melted between different metal holders. However, the stress distortion of the joint portion that occurs during the solder joint becomes a problem. The main factor of stress strain is the difference in thermal expansion coefficient between the joining material and the materials to be joined.

In the optical isolator of the present invention, by utilizing the fact that the difference in thermal expansion coefficient ΔαT between the Faraday rotator and the polarizer is small, the Faraday rotator and the polarizer are directly soldered to reduce the junction distortion. It is possible.

Therefore, without using an intermediate material for matching the thermal expansion coefficient between the Faraday rotator and the polarizer,
The optical element can be fixed to the support member.

Since the stress strain of the above-mentioned joint can be reduced and the structure can be simplified, the optical isolator can be manufactured at low cost.

However, since either the polarizer or the analyzer requires the optical axis adjustment, it is necessary to join and fix the polarizer support holder or the analyzer support holder made of metal having a rotating mechanism.

In the present invention, the analyzer support member supporting and fixing the analyzer has a multiple structure in which local parts made of materials having different thermal expansion coefficients are combined with each other. In addition, the local parts of the multiple structure are each made of a non-magnetic material. Further, a material that directly supports the optical element has a thermal expansion coefficient close to that of the optical element. As described above, during assembly, it is possible to reduce the joint distortion that occurs at the time of solder joint and prevent the characteristic deterioration due to the joint distortion.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION The optical isolator of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the basic structure of an optical isolator according to one embodiment of the present invention. FIG.
The internal structure diagram and FIG. 1B are exploded views in which the internal structure is partially disassembled.

As shown in FIG. 1, this optical isolator comprises an optical element forming an optical system, that is, a Faraday rotator 2 composed of a magneto-optical crystal such as a CdMnTe single crystal or a CdMnHgTe single crystal, a polarizing glass or a polarizing beam splitter. Polarizer 1 and analyzer 3 and Faraday rotator 2
And a permanent magnet (magnet) 4 which is applied to the inside of the supporting member.

The supporting member here is composed of a polarizer 1, a Faraday rotator 2 and a polarizer supporting holder 5 for accommodating the magnet 4, and an analyzer supporting member for supporting and fixing the analyzer 3. The optical isolator is configured by combining these polarizer support members and analyzer support members. However, the analyzer support member here has a double structure in which local parts made of materials having different thermal expansion coefficients α are combined with each other.

2A and 2B show the basic structure of the analyzer support member. FIG. 2A is a plan view thereof, and FIG.
It is a side view which shows the internal structure which fractured | ruptured a part.

The analyzer support member is formed by melting and joining the first analyzer support holder 6 outside and the second analyzer support holder 7 inside with AuSn eutectic solder 8. .

Here, both the first analyzer support holder 6 and the second analyzer support holder 7 are non-magnetic materials, but the first analyzer support holder 6 is made of metal, and the analyzer A material having a thermal expansion coefficient α close to that of the polarizer 1 / analyzer 3 is used for the second analyzer support holder 7 that directly supports 3 of the polarizers.

Incidentally, as the material of the second analyzer support holder 7, for example, one kind of ceramics, titanium, platinum or the like may be used.

Therefore, a method for manufacturing such an optical isolator will be specifically described below with reference to Examples and Comparative Examples.

First, regarding the optical element of the optical isolator according to the embodiment of the present invention, the Faraday rotator having the characteristics and standards shown in Table 1 was used.

[0047]

Polarizing glass was used for the polarizer and the analyzer, and those having a shape of 2.0 mm square were used for these shapes, as in the case of the Faraday rotator.

Regarding the polarizer and the polarizing glass of the analyzer, those having a thermal expansion coefficient α of 6.5 × 10 ⁻⁶ / K were used.

In general, it is difficult to plate an optical element. Therefore, as shown in FIG. 3 (a), the Faraday rotator 2 has four corners and side surfaces (light transmitting direction) of the light transmitting surface 14, and a polarizer as shown in FIG. 3 (b). 1. In the analyzer 3, metal thin films 13 were formed on the four corners of the surface by a sputtering device for soldering.

The metal thin film 13 on the light transmitting surface 14 is patterned by combining the masking method and the sputtering method at the four corners at the ends of the surface of the optical element, avoiding the light transmitting surface 14 which is the fixed portion. It was obtained.

As shown in FIG. 3 (c), the metal thin film 13 is composed of three layers of Cr, Ni, and Au.
The thickness of the r layer is 0.35 μm, and the thickness of the Ni layer is 0.35 μm.
The thickness of the Au layer was 0.15 μm.

Further, the magnet 4 shown in FIG.
Ni plating treatment was performed on the entire surface so that the fixing with solder was possible by using a -B type composition.

Regarding the double-structured analyzer support member, the material of the second analyzer support holder 7, which is the inner part, is ceramics having a thermal expansion coefficient α of 6.5 × 10 ⁻⁶ / K. , So that it can be fixed by soldering with Cr,
The surface was plated with Au.

Further, the material of the first analyzer support holder 6 which is the outer portion has a coefficient of thermal expansion α of 17 to 19 × 10.
SUS304 which is a metal non-magnetic material of ^-6 / K was used.
Further, in order to fix the second analyzer support holder 7 by soldering, the underlayer on the inner surface side was plated with Ni and the surface was plated with Au.

In addition, the polarizer support holder 5, which is a metal support member, includes the first analyzer support holder 6 and YAG.
SUS304 was used to enable welding.

In this way, the components necessary for producing the optical isolator as shown in FIG. 1 are obtained.

Therefore, when assembling and manufacturing the optical isolator, first, in the step of fixing the solder, as shown in FIG.
As shown in FIG. 4 (b), the polarizer 1, the polarizer support holder 5, the Faraday rotator 2, and the permanent magnet 4 are fixed by soldering AuSn eutectic solder 8 on the side of the polarizer 1 as shown in FIG. The analyzer 3, the first analyzer support holder 6, and the second analyzer support holder 7 were divided into parts on the side of the analyzer 3 which were fixed by soldering with AuSn eutectic solder 8. Then, the polarizer 1 side portion and the analyzer 3 side portion are soldered for each configuration and fixed to each supporting member. Note that AuS
The n eutectic solder 8 contains AuSn of 80%, S
n20% eutectic solder was used.

Next, in a state in which the polarizer side portion and the analyzer side portion were laminated, they were heated and melted to 320 ° C. in an electric furnace. After obtaining the optical isolator member before optical axis adjustment as shown in FIG. 1B, the optical axes of the polarizer 1 and the analyzer 3 fixed to the respective support members were adjusted. That is, the polarizer support holder 5 and the first analyzer support holder 7 were YAG-welded and integrated at a predetermined angle to obtain an optical isolator as shown in FIG.

On the other hand, an optical isolator as a comparative example is
As shown in FIG. 5, the polarizer support member and the analyzer support member do not have a double structure, and a polarizer support holder 9, an analyzer support holder 10 and a cylindrical holder 11 which are made of the same material and have a single structure are used. Except for the points described below, the procedure was basically the same as that of the example.

In the optical isolator of Comparative Example 1, the materials of the polarizer support holder 9, the analyzer support holder 10, and the cylindrical holder 11 were the same as those of the inner ring 12, and SUS3.
04 was used.

In the optical isolator of Comparative Example 1, each component was heated with an organic adhesive in a thermostatic chamber at 100 ° C. for 2 hours to cure and bond the organic adhesive before the optical axis adjustment. After obtaining the optical isolator member (1), the optical axis was adjusted and obtained.

In the optical isolator of Comparative Example 2, the metal thin film 1 for solder bonding was formed on the surface of the optical element as in the case of the example.
3 was deposited.

The supporting member for supporting the optical element and the inner ring 12 were made of the same material and had the same shape as in Comparative Example 1.

Ni was applied to the base and Au was applied to the surface of the support member so that the surface could be fixed by soldering.

As in the case of the embodiment, each component was heated to 320 ° C. in an electric furnace, and the joint portion indicated by the hatched portion in FIG. 5 was fixed by soldering. In other respects, an optical isolator was obtained in the same manner as in the example.

Under the conditions as described above, the optical isolators according to the example and the comparative examples 1 and 2 are respectively used for 10 times.
Each was produced. With respect to the characteristics of the forward insertion loss and the backward insertion loss, a total of 30 optical isolators were statistically evaluated, and the evaluation results are shown in Table 2.

[0068]

From Table 2, the forward insertion loss and the reverse insertion loss of the example and the comparative example 1 which is a conventional manufacturing method are at the same level and have good characteristics. However, it can be seen that Comparative Example 2 is significantly deteriorated.

In Comparative Example 2, some cracks were found in the solder joints after soldering.

The main cause of the occurrence of cracks is the difference in thermal expansion coefficient α between the optical element and its supporting member. As a result, stress distortion occurs in the solder joint portion, and the characteristics of the optical element deteriorate.

Next, a thermal shock test was carried out on the example and the comparative example 1 having good optical characteristics. The conditions of the thermal shock test were that the extreme temperatures were −40 ° C. and + 85 ° C., the holding time was 30 minutes at each extreme temperature, the moving time was within 2 minutes, and the number of cycles was 50. When the amounts of fluctuations in the forward insertion loss and the reverse insertion loss before and after the test of these optical isolators were examined, the results shown in Table 3 were obtained.

[0073]

From Table 3, in the examples, no characteristic deterioration was observed before and after the test. On the other hand, in Comparative Example 1, it can be seen that characteristic deterioration was observed.
In Comparative Example 1 which is a conventional manufacturing method, when a rapid temperature change occurs, the optical characteristics are deteriorated because the bonding tank contracts.

The shape of the support member, the type of solder, and the composition and thickness of the metal thin film in the optical isolator described in the embodiments of the present invention are not limited to these. Further, in the optical isolator of the embodiment, the analyzer supporting member has a double structure, but these structures may have a multiple structure of a triple structure or more. Further, the polarizer support member may have a multiple structure.

[0076]

As described above, according to the present invention, a polarizer having a small thermal expansion coefficient difference ΔαT among optical elements and a Faraday rotator are directly solder-fixed, and in addition, optical axis adjustment is required. The support member that supports a simple analyzer has a multiple structure in order to further match the coefficient of thermal expansion with a non-magnetic material, so that the optical element is solder-bonded to the support member in a low bonding distortion state during assembly. Therefore, the optical isolator can be manufactured without deterioration in characteristics in terms of structure.
Further, the structure is simplified, so that the cost is reduced.

Since the support member is made of a non-magnetic material,
A sufficient leakage magnetic field is secured by the permanent magnet, a sufficient magnetic field is applied to the Faraday rotator, and even when a rapid temperature change is applied using solder to fix the optical element,
Sufficient reliability is secured in the long term. Therefore, it is possible to guarantee good optical characteristics even under severe operating environment.
It becomes possible to provide a highly reliable optical isolator.

[Brief description of drawings]

FIG. 1 is a structural diagram showing a basic configuration of an optical isolator according to an embodiment of the present invention. FIG. 1A is a sectional view showing the internal structure. FIG. 1B is an exploded sectional view in which the internal structure is partially disassembled.

FIG. 2 is a diagram showing a basic configuration of an analyzer support member as a support member used in the optical isolator shown in FIG. FIG.
(A) is the top view. FIG. 2B is a side view in which a part thereof is broken.

3 is an explanatory diagram shown for explaining a metal thin film for solder bonding, which is formed on an end portion and a side surface of a surface of an optical element used in the optical isolator shown in FIG. FIG. 3A is a schematic perspective view of a film formation pattern of the Faraday rotator. FIG.
(B) is a schematic perspective view of the film-forming pattern of a polarizer and an analyzer. FIG. 3C is a side view in which the metal thin film portion of the film formation pattern is cut away for explaining the metal thin film composition.

4A and 4B are views for explaining a manufacturing process (solder fixing process) of the optical isolator shown in FIG. FIG. 4A is an exploded cross-sectional view of a polarizer-side constituent portion. FIG. 4B is an exploded cross-sectional view of the analyzer-side constituent portion.

FIG. 5 is a cross-sectional view showing the basic structure of optical isolators according to Comparative Examples 1 and 2 with a part thereof broken away.

FIG. 6 is an explanatory diagram shown for explaining the basic configuration and operation of a conventional optical isolator. FIG. 6A is an explanatory diagram regarding an operation when incident light is incident in the forward direction. Figure 6
(B) is explanatory drawing regarding operation | movement when the return light of incident light injects in a reverse direction.

[Explanation of symbols]

 1 Polarizer 2 Faraday Rotor 3 Analyzer 4 Permanent Magnet (or Magnet) 5,9 Polarizer Support Holder 6 First Analyzer Support Holder 7 Second Analyzer Support Holder 8 AuSn Eutectic Solder 10 Analyzer Support Holder 11 Cylindrical holder 12 Inner ring 13 Metal thin film 14 Light transmitting surface

Claims (6)

[Claims] 1. An optical element including a Faraday rotator, a polarizer, and an analyzer and a permanent magnet for applying a magnetic field to the Faraday rotator are supported and fixed in a supporting member, and
In the optical isolator, wherein the support member includes the polarizer, the Faraday rotator, and a polarizer support member that supports and fixes the permanent magnet, and an analyzer support member that supports and fixes the analyzer, the Faraday rotator, An optical isolator, which is directly soldered to either the polarizer or the analyzer. 2. The optical isolator according to claim 1, wherein either one of the polarizer support member and the analyzer support member has a multiple structure in which local parts made of different materials are combined with each other. Optical isolator. 3. The optical isolator according to claim 2, wherein at least one of the polarizer support member and the analyzer support member is a non-magnetic material. 4. The optical isolator according to claim 2, wherein a material for directly supporting the polarizer and the analyzer among the local parts made of different materials is ceramics.
An optical isolator comprising at least one of titanium, platinum and rhodium. 5. The optical isolator according to claim 1, wherein a solder fixing metal thin film is formed on an end portion and a side surface of a surface of the optical element where the solder is fixed. Optical isolator. 6. The optical isolator according to claim 5, wherein the metal thin film is formed by using a masking method and a sputtering method in combination.