JPH0954284A - Method for manufacturing optical isolator - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: By collectively performing optical axis alignment and joint fixing of optical elements such as a Faraday rotator, a polarizer and an analyzer, the width, depth, pattern, solder shape of a grating groove, To provide an inexpensive optical isolator which is not limited by the type and thickness of the metallized film, has excellent optical characteristics and durability, has high reliability, and has high productivity. SOLUTION: Faraday rotator 2 such as garnet single crystal, CdMnTe single crystal, CdMnHgTe single crystal
And a polarizer such as a polarizing glass or a polarizing beam splitter 1
.Optical element composed of analyzer 2 and Faraday rotator 2
A method for bonding and fixing the optical element of an optical isolator comprising a permanent magnet for applying a magnetic field to the optical isolator, wherein the Faraday rotator 2, the polarizer 1 and the analyzer 3 are collectively soldered and fixed. Production method.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art When a semiconductor laser is used as a light source of an optical transmission system for optical communication or the like, when 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 laser oscillation characteristics and increase of noise. An optical isolator is used to block this returning light.

FIG. 4 shows the basic structure of an optical isolator. In FIG. 4, after the incident light has passed through the first polarizer 1, the Faraday rotator 2 rotates the polarization plane thereof by 45 degrees, and further the polarization plane is inclined by 45 degrees with respect to the polarization plane of the polarizer 1. The second polarizer (analyzer) 3 having a surface is transmitted.

On the other hand, in the reflected return light in the opposite direction to the incident light, only the component whose polarization plane matches that of the second polarizer 3 is transmitted through the second polarizer 3, and then the Faraday rotator. 2, the plane of polarization is rotated.

Therefore, the reflected return light transmitted through the Faraday rotator 2 has a polarization plane of 90 degrees with respect to the second polarizer 3.
This means that the reflected return light is blocked from being transmitted.

In this way, the return light reflected by the optical isolator is blocked and the function of the optical isolator is exhibited.

If the optical isolator having the basic structure shown in FIG. 4 is composed of a plurality of stages, a larger isolation can be obtained.

When assembling the optical isolator, there are an organic bonding method and a metal bonding method as a method of fixing each component. The organic bonding method is a method of fixing each component with an organic adhesive.

As a conventional method for producing an optical isolator,
The organic bonding method is used. As shown in FIG. 5, the light transmissive resin 4 is used as a polarizer 1, a Faraday rotator 2, and an analyzer 3.
Is applied to the light-transmitting surface of the optical element consisting of, and the optical element is bonded via the organic adhesive 4. After the bonding is completed, the light-transmissive resin 4 is thermoset in the constant temperature layer.

The organic adhesive type optical isolator is shown in FIG.
20 to 30 optical isolator chips 9 can be obtained at a time by cutting out an optical isolator chip 9 [FIG. 5B] of a predetermined size from the optical element wafer 8.

The cut out optical isolator chip 9 is
The Faraday rotator 2 is bonded and fixed to the permanent magnet 5 that applies a magnetic field, and the organic bonding type optical isolator 10 as shown in FIG. 5C is manufactured. Therefore, the organic bonding method is a manufacturing method that can be easily mass-produced.

[0012]

However, when it is used as an optical communication component of an optical transmission system, long-term reliability is required. In the 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 properties, and the durability is remarkably poor in a severe environment of use. Solder fixing, to obtain a highly reliable optical isolator,
There is a demand for a bonding method using a low melting point glass or the like without using an organic adhesive.

As a method of manufacturing an optical isolator that does not use an organic adhesive, there is a metal bonding method.

The conventional metal bonding method is a method of bonding each optical element to a metal holder using metal solder. As the solder, as shown in FIG. 1, mainly AuSn solder 14 is used. The surface of the metal holder (supporting material) is preliminarily plated with Ni, Au, or the like in order to make it easy for solder to adhere.

Further, since plating treatment is not possible on a Faraday rotator which is not a metal, and a polarizing glass which is a polarizer and an analyzer, a metal thin film is formed by a physical film forming method. The optical element is soldered to the holder based on this metal film. Generally, soldering is performed by heating and melting in an inert gas atmosphere using an electric furnace. Further, the optical axis of the soldered optical element is adjusted, and the holders are laser-welded to manufacture an optical isolator.

In the method of manufacturing an optical isolator by the metal bonding method, it is necessary to individually fix the optical element chips and align the optical axes. Therefore, it is a manufacturing method that is difficult to mass-produce, and it is difficult to provide an inexpensive optical isolator.

The object of the present invention is to perform the optical axis alignment and the bonding and fixing in an optical element such as a Faraday rotator, a polarizer, and an analyzer at the same time, so that the width and depth of the grating groove can be improved.
An object of the present invention is to provide an inexpensive optical isolator that is not limited by the pattern, the shape of solder, the type of metallized film, and the thickness, has excellent optical characteristics and durability, is highly reliable, and has high productivity.

[0019]

As means for solving the above problems, according to the present invention, a Faraday rotator, a polarizer, an analyzer, and a permanent magnet for applying a magnetic field to the Faraday rotator are used. In the method for joining optical isolators according to the present invention, there is obtained a method for producing an optical isolator characterized by simultaneously performing optical axis alignment and solder fixing of the Faraday rotator, polarizer and analyzer.

According to the present invention, a Faraday rotator,
Polarizer, an optical element consisting of an analyzer, and a bonding method of an optical isolator consisting of a permanent magnet for applying a magnetic field to the Faraday rotator, on the surface of the optical element,
A method of manufacturing an optical isolator characterized by forming a grating groove is obtained.

According to the present invention, in the method for manufacturing an optical isolator described above, a metal thin film for solder bonding is formed on an end portion and a lattice groove portion of the surface of the optical element by a vapor deposition method. A method for manufacturing an isolator is obtained.

According to the present invention, in the method of manufacturing an optical isolator described above, AuSn is formed on the surface of the metal thin film.
A method for manufacturing an optical isolator, which is characterized in that a solder layer is formed by vapor deposition, is obtained.

By using the method for manufacturing an optical isolator according to the present invention, each of the constituent optical elements can be fixed together as in the manufacturing method using an organic adhesive. Further, as shown in FIG. 2, by using the Faraday rotator 2 in which the polarization axis of the polarizer 1 and the polarization axis of the analyzer 3 are tilted by 45 degrees in advance, optical axis alignment and solder fixing can be simultaneously performed. Therefore, the process can be shortened and mass production is possible.

Further, as shown in FIG. 1A, a grating groove is formed on the surface of the optical element to form an optical element grating groove pattern 11 (polarizer 1, Faraday rotator 2, analyzer 3). The metallization pattern 12 shown in FIG. 1 (b) is formed by sputtering to reduce chipping and chipping that occur during cutting, and the metallized film 7 is applied to the surface of the optical element. ,
The metal thin film (metallized film) 7 is prevented from peeling from the surface of the optical element when the element is cut. At the time of cutting, by using a cutting blade narrower than the width of the grating groove, it is possible to reduce impact and cutting strain on the metallized film portion and prevent peeling and scratches on the metallized film portion.

Sufficient adhesion strength can be secured by forming three layers of the metallized composition 13 consisting of a metal thin film (metallized film) for solder bonding as shown in FIG. 1C on the surface of the optical element. . Cr layer 15 that is the first layer
Secures the adhesion with the optical element, and the Ni layer 16 as the second layer prevents the diffusion of the solder. Furthermore, the third layer A
The u layer 17 promotes solder wettability and forms a solder joint layer,
Stable soldering is possible.

Further, as shown in FIGS. 1 (c) and 3, the wire is compared with the grating groove (shape □ 0.3 mm) formed by the polarizer 1, the Faraday rotator 2, and the analyzer 3, respectively. The volume of solder 6 (shape 0.3 mm) is small, and
Due to the grooving process, the groove cross section and the bottom portion have a larger surface roughness than the light transmitting surface. Therefore, the amount of solder coating is small for melting the solder, sufficient solder diffusion does not occur, and stable adhesion strength cannot be obtained.

However, the AuSn solder 14 having the same composition as the wire solder 6 is deposited on the cross section and the bottom of the lattice groove by using a sputtering device to assist the wire solder adhesive layer and ensure the necessary adhesion strength. You can

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Examples and comparative examples of the present invention will be described below.

In the optical isolator according to the present invention, as shown in FIG. 1A, a cutting machine is used for the polarizer 1 (first polarizer), the Faraday rotator 2, and the analyzer 3 (second polarizer). Then, the grating grooving process was performed to produce the optical element grating groove pattern 11. During the grooving process, a resist was spin-coated on the surface of the optical element so as to protect the surface of the optical element and prevent contaminants from remaining in the grooved portion, and heat-treated at 85 ° C. for 20 minutes.

The width of the grating grooves on the surface of the optical element was 0.3 mm, the depth was 0.2 mm for the polarizer and analyzer, and the Faraday rotator was 0.1 mm square. The shape of each optical element is 11
It was set to mm square.

After grooving, ethanol hot bath treatment was carried out at 80 ° C. for 15 minutes to remove the resist residue on the surface. Furthermore,
For the lattice groove, spray ethanol shower,
Washed.

For each grooved optical element obtained as described above, a thin metal film was formed on the surface of the optical element using a sputtering device manufactured by Nichiden Anelva. Since a metal thin film cannot be formed on the light transmitting surface of the optical element, metallization as shown in FIG. 1B, which is an enlarged view of A shown in FIG. 1A, is performed by using a sputtering method and a masking method. Membrane 7
To give a metallized pattern 12. The sputtering conditions are RF power of 200 W and sputtering pressure of 0.5 P.
a, the distance between the substrates was 50 mm, and the substrates were rotated.

The solder fixing metal film formed on the optical element is
It consists of 3 layers. That is, as a base on the surface of the optical element, as shown in FIG.
As shown in (c), the Cr layer 15 is 0.3 μm, the Ni layer 16 is 0.35 μm as an intermediate layer, and the Au layer 17 is 0.15 μm.
A metal thin film of μm was formed.

Further, an AuSn target (composition AuSn eutectic solder; 80/20%) was used as the solder layer, and AuSn solder 14 was formed on the surface of the metal thin film for solder joining. The film thickness formed was 5 μm.

As shown in FIG. 1B, the solder fixing metal thin film (CrNiAu3 layer film) and the solder layer (AuSn solder layer) formed by the above-mentioned process, as shown in FIG. , And also on the bottom. That is, the optical element surface, the cross section of the lattice groove portion, and the bottom portion can be fixed by soldering.

AuSn formed by sputtering
The film has almost the same temperature as the melting point of AuSn eutectic solder.

As shown in FIG. 2, the polarizer 1, the garnet 2 and the analyzer 3 which form the optical isolator form respective optical elements and a grating groove pattern 11 (see FIG. 1). The analyzer used was one in which the crystal axis was tilted in advance by 45 degrees with respect to the polarizer.

Further, as shown in FIG. 3, wire solder 6 (φ0.3 mm × L11 mm) is inserted into the grating groove portions between the polarizer 1 and the garnet 2 and between the garnet 2 and the analyzer 3 to align the optical axes. The jig was used to finely adjust the optical axis of the optical isolator, and the jig was heated in an electric furnace.
At that time, a load of about 200 g was applied.

The above sample was heated and melted up to 320 ° C. in an electric furnace, and fixing of each optical element by soldering was completed. After fixing the solder, the optical isolator wafer 8 (see FIG. 5) is
It was cut into 1.8 mm square. The optical isolator chip 9 (see FIG. 5) obtained by cutting was inserted into a permanent magnet to manufacture an optical isolator.

(Comparative Example) Optical elements such as a Faraday rotator 2, a polarizer 1 and an analyzer 3 which constitute an optical isolator,
As shown in FIG. 5, they were bonded together via an organic adhesive 4. The organic adhesive 4 was heated and cured at 100 ° C. for 2 hours in a constant temperature bath. After the completion of curing of the organic adhesive, it was cut and inserted into a permanent magnet in the same manner as in the example to obtain an optical isolator.

The forward insertion loss and the reverse insertion loss of the 10 optical isolators manufactured in the examples and comparative examples were evaluated. The evaluation results are shown below in Table 1.

[0042]

As a result of Table 1, it was found that the forward insertion loss and the backward insertion loss of the example and the comparative example which is the conventional manufacturing method are at the same level and have good characteristics.

Next, a thermal shock test was carried out on the optical isolators produced in Examples and Comparative Examples having good optical characteristics. The conditions for the thermal shock test are a temperature of −40 ° C. and +85.
C, holding time, 30 min at each extreme temperature, moving time 2 mi
Within n, the number of cycles was 100.

Table 2 shows the fluctuation amounts of the forward insertion loss and the reverse insertion loss before the test and after the test of the optical isolators in Examples and Comparative Examples.

[0046]

As a result of Table 2, the optical isolators manufactured in the examples did not show the characteristic deterioration before and after the test. However, the optical isolator produced in the comparative example was found to have characteristic deterioration. In the comparative example, which is a conventional manufacturing method, it is considered that when a rapid temperature change occurs, the adhesive layer contracts, and as a result, the optical characteristics deteriorate.

In addition, the optical isolator obtained in the embodiment of the present invention is
It was found that the optical characteristics were not significantly affected. Therefore, it was found that an optical isolator having good optical characteristics and high reliability can be manufactured by using the example of the present invention.

Although the garnet single crystal was used as the Faraday rotator in both the examples and the comparative examples, similar results can be obtained by using the CdMnTe single crystal and the CdMnHgTe single crystal.

[0050]

According to the present invention, an optical isolator which has good durability, long-term reliability, high productivity, and good optical characteristics can be provided at low cost. In addition, the present invention
Faraday rotator, a polarizer, an optical element such as an analyzer is to collectively process optical axis alignment and bonding and fixing, and the width and depth of the grating groove according to Examples of the present invention and Comparative Examples.
The pattern, the shape of the solder, the type of the metallized film, and the thickness are not limited.

[Brief description of drawings]

FIG. 1 is an external view of an optical element according to the present invention and a structural diagram showing a metallized composition. FIG. 1A is a perspective view showing an optical element lattice groove pattern. FIG. 1B is a perspective view showing a metallized pattern. FIG. 1C is a configuration diagram showing a metallized composition.

FIG. 2 is an external perspective view showing a lattice groove pattern of each optical element used in the present invention. FIG. 2A is a perspective view of the polarizer. FIG.
(B) is a perspective view of a garnet. FIG. 2C is a perspective view of the analyzer.

FIG. 3 is a cross-sectional view showing a method for soldering each optical element according to the present invention.

FIG. 4 is a perspective view showing a basic configuration of an optical isolator. FIG.
FIG. 6A is a perspective view of the optical isolator in the forward direction. Figure 4 (b)
FIG. 3 is a perspective view of the optical isolator in the reverse direction.

FIG. 5 is a perspective view showing a method for manufacturing an organic adhesive optical isolator. FIG. 5A is a perspective view showing an optical isolator wafer. FIG. 5B is a perspective view showing the optical isolator chip.
FIG. 5C is a perspective view showing an organic adhesive optical isolator.

[Explanation of symbols]

 1 Polarizer (First Polarizer) 2 Faraday Rotator (Garnet) 3 Analyzer (Second Polarizer) 4 Organic Adhesive (Light-Transparent Resin) 5 Permanent Magnet 6 Wire Solder 7 Metallized Film (Metal Thin Film) 8 Optics Element wafer (optical isolator wafer) 9 Optical isolator chip 10 Organic adhesive type optical isolator 11 Optical element lattice groove pattern 12 Metallized pattern 13 Metallized composition 14 AuSn solder 15 Cr layer 16 Ni layer 17 Au layer

Claims (4)

[Claims] 1. A method of joining an optical isolator comprising a Faraday rotator, a polarizer, an analyzer, and a permanent magnet for applying a magnetic field to the Faraday rotator, wherein the Faraday rotators for a plurality of optical isolators are provided. A method of manufacturing an optical isolator, which comprises simultaneously performing optical axis alignment of a polarizer and an analyzer and solder fixing. 2. A method of joining an optical isolator comprising a Faraday rotator, an optical element including a polarizer and an analyzer, and a permanent magnet for applying a magnetic field to the Faraday rotator. A method for manufacturing an optical isolator, which comprises forming a grating groove in the substrate. 3. The optical isolator manufacturing method according to claim 2, wherein a metal thin film for solder bonding is formed on the end portion and the lattice groove portion of the surface of the optical element by a vapor deposition method. Manufacturing method. 4. The method for manufacturing an optical isolator according to claim 3, wherein an AuSn solder layer is formed on the surface of the metal thin film by a vapor deposition method.