JPH08234142A - Optical isolator and its production - Google Patents

Abstract

PURPOSE: To provide an inexpensive metal junction optical isolator having high characteristics and consistent quality by adopting a structure to allow a simultaneous treatment and to suppress the outflow of solder to optical paths at the time of fixing by soldering, unlike the conventional treatment method by each optical chip, and realizing the simplification of production stages and a process for producing such isolator. CONSTITUTION: The optical isolator featuring good mass productivity is provided by using the structure to join blanks for optical elements by interposing stress buffer plates 9, 10 between these blanks as means for relieving the stresses and strains generated among the optical elements including a polarizer 1, Faraday rotator 2 and analyzer 3 to be joined. In addition, parts for preventing the solder flow are formed around the apertures of the stress buffer plate 9 and patterned metallic thin film layers are formed on the joint surfaces of the blanks for the respective optical elements of a size to allow the layout of plural pieces and are joined by soldering and thereafter, the blanks are cut, by which the optical isolator is produced.

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 for an optical transmission system such as optical communication, 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 the oscillation characteristics of the semiconductor laser and increase of noise. An optical isolator is used to block this returning light.

FIG. 5 shows the basic structure of an optical isolator. In FIG. 5, after the incident light has passed through the polarizer 1, the Faraday rotator 2 rotates the plane of polarization by 45 degrees, and further, the plane of polarization inclined by 45 degrees with respect to the plane of polarization of the polarizer 1 is formed. It passes through the analyzer 3. On the other hand, in the reflected return light in the direction opposite to the incident light, only the component whose polarization plane matches that of the analyzer 3 passes through the analyzer 3, and then the polarization plane is rotated by the Faraday rotator 2. To be done.
Therefore, the reflected return light transmitted through the Faraday rotator 2 is
This means that the plane of polarization is rotated by 90 degrees with respect to the polarizer 1, and here 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 exerted. If the optical isolator having the basic configuration shown in FIG. 5 is configured in a plurality of stages, a greater isolation effect 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 bonding and fixing each component with an organic adhesive. Further, in the organic adhesive method, in many cases, the adhesive layer shrinks when the adhesive is cured. The shrinkage of the adhesive layer adversely affects the optical characteristics of the optical isolator and causes a problem. In particular, among the constituent parts, the optical element is bonded to the light transmitting surface side with an organic adhesive, so that the durability is remarkably poor in a use environment where temperature and humidity are severe.

For these reasons, in recent years, a metal bonding method having high reliability has become the mainstream in place of the optical isolator by the organic bonding method. The metal joining method is a method of joining each component using solder. AuSn alloy or the like is mainly used for the solder. The surface of the holder is preliminarily plated with Ni, Au, or the like so that the solder is easily attached to the surface. In addition, since it is difficult to perform plating treatment on the bonding surface of a magneto-optical element made of a non-metal material, a polarizer made of a polarizing glass, etc. Form a thin film. Each of the above optical elements is soldered to the holder via this metal film. Generally, soldering is performed by using an electric furnace and heating to a temperature at which the solder melts in an inert gas atmosphere. Further, after adjusting the optical axis of the soldered optical element, the holders are laser-welded to manufacture an optical isolator.

[0006]

As shown in FIG. 6, a metal-junction type optical isolator is usually composed of two parts. One is a polarizer-side portion 2 in which a polarizer 1, a Faraday rotator 2, and a magnet 8 are housed in a holder.
7 [left part of FIG. 6 (a)], and the other is an analyzer side part 28 [right part of FIG. 6 (a)] in which the analyzer 3 is housed in a holder. The polarizer side portion 27 and the analyzer side portion 28 are fixed to their respective holders after assembling and soldering steps. Further, the optical axes of the polarizer 1 and the analyzer 3 are adjusted in a state of being fixed to each holder, YAG laser welding of the holders is performed at a predetermined angle, and the metal junction type optical isolator shown in FIG. Is completed.

However, in the above-described conventional metal joining method, optical element materials having a large area capable of obtaining a plurality of optical elements are directly fixed by soldering without using a supporting material such as a holder. This is difficult due to the difference in thermal expansion coefficient between them. Conventionally, therefore, the optical isolator 1
After processing the optical element pieces having a small area for each piece, the optical element pieces are forced to be fixed by soldering with a holder which is an optical element supporting material, which causes a problem of high manufacturing cost. Further, in the conventional optical isolator that is joined by soldering only through the metal thin film, there is a problem that the stress strain at the time of joining cannot be sufficiently removed, and the characteristics change after the isolator is completed.

Further, when the optical element piece is fixed to the plated holder by soldering, there is a problem that the melted solder flows out to the optical path other than the joint portion (metal thin film portion). The solder that has flowed out into the optical path causes scattering of the light that passes through the optical isolator. Therefore, it is necessary to control the solder wettability when the solder is melted, but it is difficult to control by the conventional method.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an inexpensive optical isolator which is free from the above-mentioned problems, has mass productivity, and has stable optical characteristics, and a manufacturing method thereof.

[0010]

SUMMARY OF THE INVENTION The present invention is a metal-junction type optical isolator capable of solving the above-mentioned problems by bonding and fixing optical elements by soldering. A processed metal thin film layer, a solder layer in contact with the metal thin film layer, and an optical isolator comprising a stress strain buffer plate in contact with the solder layer, wherein in the optical isolator, the stress The strain buffer plate is made of Cu, Ti, Pt, Al ₂ O ₃
An optical isolator characterized by comprising at least one kind of
An optical isolator characterized in that a solder flow preventive portion having reduced solder wettability near the aperture on the surface of the stress-strain buffer plate is provided, and a metal-junction type optical isolator for fixing an optical element by soldering is manufactured. By the way
A metal thin film is formed on at least one surface of an optical element material having an area capable of obtaining a plurality of the optical elements, and a solder sheet, a stress buffer plate, a solder sheet, on at least one surface of the optical element material. Similarly to the optical material, another optical element material having a metal thin film formed on one surface thereof is sequentially stacked and joined by solder, and the joined body is thickened to a predetermined size. It is a method for manufacturing an optical isolator, which is characterized in that an isolator chip is manufactured by cutting in the vertical direction, and an optical isolator is constructed using this isolator chip.

[0011]

[Operation] In manufacturing a metal junction type optical isolator,
The fixing of the optical element is performed by melting the solder between the individual members to be joined. There is a problem of stress strain of the joint portion which occurs when the optical element is joined by soldering. The main factor of these stress strains is the difference in thermal expansion coefficient between the joining materials. According to the present invention, the solder joint layer has a structure of optical element-metal thin film-solder-stress strain buffering material-solder-metal thin film-optical element, whereby the joint strain (stress strain) of the optical element is obtained.
Can be reduced. As a result, it is possible to prevent the characteristic deterioration due to the bonding strain. Further, by patterning the metal thin film 22 as shown in FIG. 2 on the optical element material and forming the bonding layer with the above structure, the optical element material 15 corresponding to each optical element can be used without using a holder. It becomes possible to solder joints between them, and by cutting at a predetermined cut portion 24, it becomes possible to mass-produce a large number of optical isolator elements (optical isolator chips).

Stress-strain buffer plates 9 and 10 (see FIGS. 1 and 3)
Is made of a soft thin plate having a large Young's modulus, and is made of, for example, at least one kind of material such as Cu, Ti, Pt, and Al ₂ O ₃ , and stress strain generated at the time of solder joining of the optical element material, It is possible to absorb and mitigate the effects of shrinkage of the bonding layer caused by changes in the outside air temperature.

Further, the molten solder generally exhibits wettability with respect to the metal-plated surface, but the wettability may be lowered on the surface not subjected to the plating treatment. As shown in FIG. 3, in the stress-strain buffering plate 9 of the present invention, the metal plating layer in the vicinity of the aperture 18 (light transmitting hole) is removed, or conversely, a layer having poor wettability is processed to remove solder flow. By forming the prevention portion 20, it is possible to prevent the solder from flowing out to the aperture. That is, as shown in FIG. 3B, the solder flow prevention portion 20 has a structure larger than the diameter (L1) of the aperture 18, that is, the molten solder does not flow into the aperture. vice versa,
For example, when a stress-strain buffer plate made of a thin metal plate having good solder wettability, such as Cu, is used, the same effect can be obtained by forming an oxide film or an organic resin film on the solder wettability preventing portion 20. Therefore, by controlling the solder wettability, it is possible to prevent incident light scattering and the like due to the solder flowing out, and to manufacture an optical isolator having stable characteristics.

In the manufacture of the optical isolator according to the present invention, a plurality of isolator chips can be manufactured at a time by using a large optical element material capable of producing a plurality of isolator chips. Therefore, the optical axis adjustment can be performed for each isolator chip. It is not necessary to carry out, and the washing process etc. can be reduced. Therefore, the manufacturing cost can be reduced, and a large number of optical isolators having stable characteristics can be provided at low cost.

[0015]

EXAMPLES Examples and comparative examples of the present invention will be described below.

The isolator chip used in the optical isolator according to the present invention, as shown in FIG.
Stress-strain buffer plate 9, Faraday rotator 2, stress-strain buffer plate 1
0, each of the optical element materials forming the analyzer 3 and the stress-strain buffer plate material. The Faraday rotator 2, the polarizer 1, the analyzer 3, and the two stress-strain buffer plates 9 and 10 were each 10 mm square. As shown in FIG. 1A, the polarization axis 13 of the polarizer 3 and the analyzer is tilted by 45 degrees with respect to the polarization axis 13 (polarization direction) of the polarizer 1 in advance. The cut optical element material was used as described above.

As shown in FIG. 2, the optical element material 15 for forming the Faraday rotator and the optical element material 15 using the polarizing glass for forming the polarizer 1 and the analyzer 3 are shown in FIG. ), It is difficult to apply a patterned plating treatment. Therefore, a plurality of layers of metal thin film 22 as shown in FIG. 2B were formed. These metal thin films 22 were patterned on the fixed portion of each optical element by combining a masking method and a sputtering method. The patterned metal thin film 22 is composed of three layers, as shown in FIG.
As shown in (b), the layers are laminated, and the film thicknesses of Cr are 0.10 μm, Ni is 0.30 μm, and Au is 0.15 μm.
And The metal thin film 22 may be a single metal layer, but a combination of a plurality of metal thin film layers is preferable in order to obtain sufficient bonding strength and solderability.

The stress strain buffer plate 9 is made of a material of 0.1 m.
An m-thick Cu plate was used, the shape was as shown in FIG. 3, and the dimensions were 10 mm square, like the optical element material. The light-transmitting portion (aperture 18) was subjected to hole processing, and its surface was plated with NiAu in order to enable soldering. Further, in solder joining, the solder flow prevention portion 20 without plating is provided to prevent the solder from flowing into the vicinity of the aperture 18.
Was provided. In this solder flow prevention unit 20, a photoresist is applied near the aperture, and after the plating process and after the plating is finished, the resist portion is removed with a processing solvent so that the vicinity of the aperture is prevented from being plated. As shown in FIG. 4B, a solder sheet 17 having an outer dimension of 10 mm square as shown in FIG. 4A was used for joining the optical element material 15 and the stress-strain buffer plate 9. PbSn
Eutectic solder (38% / 62% by weight, melting point 18)
3 ° C.), and the thickness of the solder sheet 17 was set to 50 μm in consideration of the required volume of solder.

As shown in FIGS. 1 (a), 3 (b) and 4 (b), metal thin films were processed on these components using a carbon jig (not shown). Material 15 for optical element for polarizer, solder sheet 17, stress buffer plate 9, solder sheet 17, material 15 for optical element for Faraday rotator, solder sheet 17, stress strain buffer plate 9,
The solder sheet and the optical element material 15 for the analyzer were superposed in this order, and the side surfaces of each component were aligned, and a load of 20 g was applied. 20 in the electric furnace together with the carbon jig
Heated to 0 ° C. The atmosphere in the electric furnace was bonded by soldering in a reducing atmosphere (95% nitrogen, 5% hydrogen) so that the solder was easily wetted, and an isolator wafer 11 as shown in FIG. 1B was produced.

The isolator wafer is cut by a cutting machine.
The isolator chip 12 as shown in FIG. 1C was obtained by cutting the metal thin film along the cutting gap 24 shown in FIG. 2A into a predetermined shape. Isolator chip 12
Is inserted into a plastic magnet 8 as shown in FIG. 1D, the side surfaces other than the optical surface of the isolator chip 12 are fixed to the inner surface of the magnet 8 with an organic adhesive, and the light transmitting surface is organically bonded. A drug-free optical isolator was obtained.

[0021]

Comparative Example In order to compare and confirm the effects of the above examples,
Two comparative examples are shown below.

(Comparative Example 1) As shown in FIG. 7, a material 2 for a Faraday rotator having metal thin film patterns formed on both surfaces.
The polarizer material 1 and the analyzer material 3 each having a pattern of a metal thin film formed on one side thereof are superposed on both sides of the sheet, and a solder sheet (not shown) is inserted between them to absorb stress and strain. An optical isolator of Comparative Example 1 was manufactured by the same method as that of the above-described example without using a plate.

(Comparative Example 2) As shown in FIG. 6, an optical isolator having a structure including a polarizer side portion 27 and an analyzer side portion 28 according to the above-mentioned conventional technique was manufactured. The polarizer-side portion 27 is configured such that the first end holder 4 and the outer holder 6 are arranged in advance.
It is composed of a polarizer 1, an inner ring 7, a Faraday rotator 2, and a magnet 8 which are welded by AG laser and bonded inside. On the other hand, the analyzer-side portion 28 has the second end holder 5
And an analyzer 3 (second polarizer). Inside these metal holders, NiA
u plating treatment is applied. In addition, a metal thin film is formed on the surfaces of the Faraday rotator, the polarizer, and the analyzer in order to enable soldering, as in the embodiment. These constituent parts were individually laminated for each of the polarizer side portion and the analyzer side portion, and in the laminated state, soldering was performed in the electric furnace in the same manner as in the above-described example. After soldering and joining is completed, the polarizer side part and the analyzer side part are combined, the polarization axes (polarization directions) of the two parts are aligned to a predetermined angle, and the external holder and the second end holder are YAG laser welded. An optical isolator of Comparative Example 2 was obtained.

In Example, Comparative Example 1 and Comparative Example 2, each 5
The forward insertion loss and the reverse insertion loss of zero optical isolator were evaluated. The evaluation results are shown in Table 1 below.

[0025]

[Table 1]

As is apparent from Table 1, Comparative Example 1 is significantly inferior in both the forward insertion loss and the reverse insertion loss. It is considered that the optical characteristics are deteriorated without relaxing or absorbing the thermal stress strain between the materials due to the solder joining.

The forward insertion loss and the reverse insertion loss of the example and the comparative example 2 are almost at the same level. It is considered that this is because in Comparative Example 2, the optical axis is individually adjusted for all the optical isolators, and thus the strict optical axis adjustment is possible. In the optical isolator of this embodiment, a plurality of equivalent products are obtained by performing the optical axis adjustment once. Further, it was found that the joint strain between the optical elements was relieved by the stress strain buffer plate, and the optical isolator had sufficient characteristics. Further, as a result of a visual inspection, it was found that solder did not flow into the optical path. This is the effect of removing the plating layer near the apertures of the stress-strain buffer plates 9 and 10.

Ten optical isolators produced in each of Example and Comparative Example 2 were sampled and subjected to a heat cycle test. The conditions were temperature −20 to + 70 ° C., 4.5 hours / cycle, and 100 cycles. Table 2 shows the amount of fluctuation (maximum value of 10) of the forward insertion loss and the backward insertion loss before and after the test of the optical isolator in Example and Comparative Example 2.

[0029]

[Table 2]

From Table 2, in both Example and Comparative Example 2, no significant deterioration in characteristics was observed. Also, in the appearance inspection, no cracks or the like on the optical surface were observed. It was found that the optical isolators produced in Example and Comparative Example 2 had sufficient reliability.

In the present embodiment, the Cu plate was used as the stress buffer plate, but a Ti, Pt, Al ₂ O ₃ plate or a stress buffer plate in which these are combined has the same effect as the Cu plate. Was given.

Further, in this embodiment, the isolator chip is bonded and fixed to the holder by using an organic adhesive, but the isolator chip is bonded and fixed to the holder via the solder layer to improve weather resistance. A good optical isolator was obtained. In this case, the solder used has a melting point lower than that of the solder used for joining the isolator chip. Further, in the case where the holder uses a non-metallic material, a holder in which a metal thin film is processed on the joint surface is used.

[0033]

As described above, by adopting the means for alleviating the stress strain generated between the optical elements to be bonded according to the present invention, the optical element members are bonded together and a large number of optical elements are collectively manufactured. It became possible to obtain. Therefore, it has become possible to omit the step of adjusting the optical axis, which has conventionally been required for the total number of optical isolators to be manufactured. Furthermore, we solved the problem of solder outflow, which was a problem in soldering, and solved the problem of transmitted light scattering. As a result, according to the present invention, it is possible to mass-produce the optical isolators having uniform characteristics all at once, and the manufacturing process is significantly shortened to realize the low cost.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a structure and a manufacturing procedure of an optical isolator according to an embodiment of the present invention. FIG. 1A is a diagram showing constituent materials. FIG. 1B is a view showing an assembled state of the isolator wafer. FIG. 1C is a view showing a cutout of the isolator chip. FIG. 1D is a sectional view of the assembled optical isolator.

FIG. 2 is a perspective view showing a metal thin film formed on the surface of a material for an optical element. FIG. 2A is a diagram showing the entire optical element material.
FIG. 2B is a sectional view of the metal thin film portion.

FIG. 3 is a view showing a stress buffer plate used according to the present invention and a state in which the stress buffer plate is assembled. FIG. 3A is an external perspective view of the stress-strain buffer plate. FIG. 3B is a cross-sectional view showing the bonding structure around the light transmitting portion.

FIG. 4 is a diagram showing a solder sheet used according to the present invention and a state in which the solder sheet is assembled. FIG. 4A is an external view of the solder sheet. FIG.4 (b) is sectional drawing which shows a joining structure.

FIG. 5 is an explanatory diagram showing a basic configuration of an optical isolator.

FIG. 6 is an exploded cross-sectional view illustrating the configuration of a conventional metal-bonded optical isolator. FIG. 6A is a diagram showing a polarizer-side portion and an analyzer-side portion before assembling. FIG.6 (b) is a figure which shows assembly completion.

FIG. 7 is an explanatory view showing a structure and a manufacturing procedure of an optical isolator manufactured in Comparative Example 2. FIG. 7A is a diagram showing constituent materials. FIG. 7B is a view showing an assembled state of the isolator wafer. FIG.7 (c) is a figure which shows the cutting out of an isolator chip. FIG. 7D is a sectional view of the assembled optical isolator.

[Explanation of symbols]

 1 Polarizer (Material) 2 Faraday Rotor (Material) 3 Analyzer (Material) 4 First Part End Holder 5 Second Part End Holder 6 External Holder 7 Inner Holder 8 Magnet 9, 10 Stress Buffer Plate (Materials) 11,31 Isolator wafer 12,32 Isolator chip 13 Polarization axis 14 Optical element 15 Optical element material 16 Solder 17 Solder sheet 18 Aperture 19 Ni, Au plated portion 20 Solder flow prevention portion 21 Plating layer 22 Metal thin film 23 Adhesive layer 24 Cutting margin 25 Light transmitting surface 26 Bonding layer 27 Polarizer side part 28 Analyzer side part 29 YAG laser welding part 30 Solder fixing part

Claims (4)

[Claims] 1. In a metal-junction type optical isolator for bonding and fixing optical elements by soldering, a metal thin film layer in which a bonding portion between the optical elements is processed on the surfaces of both optical elements, and a solder contacting the metal thin film layer An optical isolator comprising a layer and a stress-strain buffer plate in contact with the solder layer. 2. The optical isolator according to claim 1, wherein the stress-strain buffer plate is made of Cu, Ti, Pt, Al ₂ O _3.
An optical isolator comprising at least one type of 3. The optical isolator according to claim 1, further comprising a solder flow preventive portion for reducing solder wettability near an aperture on the surface of the stress-strain buffer plate. 4. A method of manufacturing a metal-junction type optical isolator for fixing an optical element by soldering, wherein a metal thin film is formed on at least one surface of an optical element material having an area capable of obtaining a plurality of the optical elements. Then, on at least one surface of the optical element material, a solder sheet, a stress buffer plate, a solder sheet, and another optical element material having a metal thin film formed on one surface in the same manner as the optical material are sequentially formed. Superimpose them, join them with solder, and join the joined pieces together.
A method for manufacturing an optical isolator, which comprises cutting an isolator chip to a predetermined size in the thickness direction to produce an isolator chip, and constructing an optical isolator using the isolator chip.