JPH0222619A - Optical isolator and its production - Google Patents

Abstract

PURPOSE:To facilitate assembling and adjustment by adhering and fixing an analyzer and a Farady rotator to a spacer fitted to the inside of a magnet by a solder and fixing the magnet and the spacer by welding after adjustment of the plane of polarization. CONSTITUTION:An analyzer 2, a Farady rotator 3, and a polarizer 7 are adhered and fixed to spacers 1 and 6 by a solder. Brass is used as materials of spacers 1 and 6 and is metallized with Ni/Au with 1,000Angstrom thickness, and they are fixed by an eutectic solder of Pb-Sn. The outside surface of the cylinder part of the spacer 6 is brought into contact with the inside surface of a magnet 4 and is fitted to it, and a semiconductor laser beam is made incident on the polarizer 7 fixed to the space in this manner, and a polarizing prism having a sufficiently high polarization ratio is used and the spacer 6 is rotated in the fitting part while observing the power intensity of the transmitted light by a photodetector, and the spacer 6 and the magnet 4 are fixed at such rotation angle that the power intensity is maximum. Thus, assembling and adjustment are facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical isolator and a method for manufacturing the same, and more particularly to an optical isolator for a semiconductor laser module having a plurality of optical components and a method for manufacturing the same.

[Conventional technology]

In an optical transmission communication system, when reflected return light from optical components such as connectors and switches installed in the middle of a transmission path enters the oscillation region of a semiconductor laser crystal, the oscillation state of a laser diode (hereinafter referred to as LD) changes. As a result, there is a problem that response characteristics deteriorate and noise increases. This becomes a major obstacle when performing high-speed long-distance transmission, and an optical isolator that eliminates reflected return light is essential.

Conventionally, as optical isolators for optical communication, T. Sugie (T, Sugie) + M. Sarwatari (M, S.
``An Effective Non-Reciprocal Circuit'' was published by Mr.
Four Semiconductor Laser-to-Fiber Coupling Using an Effective Non-reci-pr
ocal C1rcuit for Sem1co
conductor La5er-to-F-iber C
Upling Using a YIG 5pher
)” Journal of Lightwave Technology (
JOURNAL OF LRGHTWAVE TECHN
OLOGY), Volume LT-1, No. 1, 1983, 3
The structure of an optical isolator equipped with a semiconductor laser module is shown on the moon.

This optical isolator uses a YIG sphere with the function of converting it into a convergent beam as the Faraday rotation element, a calcite plate as the analyzer, and a ring-shaped magnet placed around the YIG sphere. The configuration is such that a magnetic field in the optical axis direction is applied to the YIG sphere.

In this case, since the light beam emitted from the semiconductor laser is primarily TE polarized light, the polarizer is omitted, and the light beam emitted from the companion laser has its polarization direction rotated by 45 degrees by the YIG sphere. It is then input to an analyzer.

The polarization plane of the analyzer is set at an angle that allows ordinary light to pass through, and the light beam is not separated but coupled into the fiber.

Since the polarization direction of the return light from the fiber is indeterminate, an analyzer can distinguish between ordinary light and extraordinary light, whose polarization planes differ by 90 degrees.
separated into two light beams.

When the ordinary light passes through the YIG sphere again, its polarization plane is rotated by 45 degrees, so when it returns to the semiconductor laser, it is rotated by 90 degrees and becomes TM polarized light, which does not affect the operation of the semiconductor laser.

In addition, the abnormal light is laterally shifted in position by the analyzer, and when it returns to the semiconductor laser, it returns to a position shifted from the light emitting point, and does not affect the operation of the semiconductor laser.

In addition, a paper titled "DFB-LD module with built-in optical isolator" was recently published by Mr. Chika, Mr. Watanabe, Mr. Goto, Mr. Miura, and Mr. Toge.
The isolator described in 1985 IEICE Semiconductor/Materials National Conference 305 is composed of a rutile prism polarizer and analyzer, a YIG crystal Faraday rotation element, and a magnet.

In this case, the optical paths of the returning reflected light are bent by the two prisms for both the ordinary light and the extraordinary light so that they do not return to the LD end face.

As for the required performance for the practical use of an optical isolator mounted on such an LD module, firstly, it is important that the optical isolator has excellent reliability against environmental tests and changes over time. Therefore, metal fixing is especially essential for fixing the parts that make up the optical isolator.

In addition, in order to obtain high isolation, it is necessary that the performance of each individual optical component is high, but what is more important is that the individual polarization plane angle settings can be easily adjusted when assembling and adjusting the optical isolator. Must be able to do it with high precision.

[Problem to be solved by the invention]

Both of the above-mentioned conventional optical isolators use YIG as a Faraday rotation element, and the latter has a configuration with two prisms, so both are expensive, and the latter requires assembly and adjustment. The drawback is that it is difficult and difficult to reduce in size and weight.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical isolator that is easy to assemble and adjust, can be made smaller and lighter, and has excellent reliability, which can reduce costs, and a method for manufacturing the same.

[Means to solve the problem]

The optical isolator of the first invention includes a first spacer made of a cylindrical non-magnetic material having a flange-like protrusion on the first opening surface, and adhesively fixed to the first and second opening surfaces of this spacer, respectively. The analyzer and the Faraday rotator element are mated with the inner surface in contact with the outer surface of the cylindrical part of the spacer, and the first opening surface is in contact with the protruding part of the spacer so that the Faraday rotator element is inserted into the spacer at approximately the center thereof. and a cylindrical magnet that fixes the spacer and applies a predetermined magnetic field to the Faraday rotation element.

In addition to the optical isolator of the first invention, the optical isolator of the second invention has a flange-like protrusion on the first opening surface, the outer surface of the cylindrical part contacts and engages with the inner surface of the magnet, and the protrusion a second spacer made of a cylindrical non-magnetic material that is fixed in contact with a second opening surface of the magnet; and a polarizer that is adhesively fixed to a first opening surface of the second spacer. have.

A method for manufacturing an optical isolator according to a third aspect of the invention is to solder an analyzer, a Faraday rotation element, and a polarizer to the first and second parts.
After adjusting the angle of the polarization plane of the analyzer and polarizer by rotating the first and second spacers, the first and second spacers are fixed to a spacer with a temperature lower than the melting point of the solder. It has a structure in which it is fixed to a magnet by high-temperature YAG welding.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the first invention.

This embodiment utilizes the polarization property of the semiconductor laser itself, and includes a cylindrical non-magnetic spacer 1 having a flange-like projection in the first opening, and a first and second spacer of this spacer 1. The analyzer 2 and the Faraday rotation element 3 are respectively adhesively fixed to the openings of the spacer 1, and the inner surface thereof is in contact with the outer surface of the cylindrical portion of the spacer 1, and the first opening surface is in contact with the protrusion of the spacer 1. A cylindrical magnet 4 is provided, in which a Faraday rotation element 3 is arranged approximately in the center of the interior, and this spacer 1 is fixed with a YAG weld 5 to apply a magnetic field to the Faraday rotation element 3 in the axial direction of the light beam 10. The structure is as follows.

FIG. 2 is a sectional view showing an embodiment of the second invention.

In this embodiment, in addition to the embodiment of the first invention shown in FIG. and a cylindrical non-magnetic spacer 6 whose protrusion is in contact with the second opening surface of the magnet 4 and fixed by the YAG welding part 5;
The polarizer 7 is adhesively fixed to the first opening surface of the polarizer 7.

In these embodiments, a bismuth-substituted (GdBi) garnet thick film is useful as the Faraday rotation element 3. This bismuth-substituted garnet thick film is excellent in mass production, reaches a saturation magnetic field with a small magnetic field, and has a large optical rotation ability, so it is advantageous in that it is inexpensive and compact.

Calcite, titanium dioxide (rutile), and the like can be used as the polarizer 7 and analyzer 2, but titanium dioxide is more useful in the case of solder fixation because calcite tends to crack due to thermal shock.

Next, an embodiment of the third invention will be described, taking as an example the case where the optical isolator shown in FIG. 2 is manufactured.

First, the analyzer 2, Faraday rotation element 3, and polarizer 7 are adhesively fixed to the spacer 1.6 with solder.

These optical elements are fixed by soldering after performing AR co-coating, then masking the light beam passing portion on the adhesive surface side, and performing metallization processing. Although various films can be used as the metallized film, in this example, two layers of Mo/Cu were deposited each with an thickness of about 100 OA.

Spacers 1 and 6 are made of brass and N i / A u
is metallized to 1000A and fixed with Pb-3n eutectic solder. Polarizer 7 at this time. There is no need to consider the angle of the plane of polarization when the analyzer 3 is fixed with adhesive.

The polarizer 7 fixed to the spacer 6 in this way is brought into contact with the outer surface of the cylindrical part of the spacer 6 on the inner surface of the magnet 4, and a semiconductor laser beam is made incident on the polarizer 7, and the transmitted light is polarized with a sufficiently large polarization ratio. Using a prism, for example, a Grand Thomson prism, the spacer 6 is rotated at the joint while observing the power intensity of the transmitted light with a photodetector, and the spacer 6 and the magnet 4 are fixed at an angle that maximizes the angle.

Next, the spacer 1 to which the Faraday rotation element 3 and the analyzer 2 are fixed is inserted through the opening of the magnet 4 on the opposite side of the polarizer 7 and engaged, and the polarization angle of the Grand Thomson prism is measured in advance. Faraday rotating element 3
The spacer 1 is rotated at a rotation angle (ideal value of 45 degrees) at the joint, and the spacer 1 and the magnet 4 are fixed at an angle that maximizes transmitted power.

At this time, for fixing, it is necessary to use a solder having a melting point lower than that of the solder used to fix the optical elements such as the polarizer 7 and the Faraday rotation element 3. For example, if the optical element is Pb-
If it is fixed with 3n solder, the combination is to use In-3n solder.

Therefore, considering reliability and workability, YAG laser spot welding is useful.

Next, the operation of the optical isolator shown in FIG. 2 will be explained.

The light beam 10 is transmitted through the polarizer 7, the plane of polarization is rotated by 45 degrees by the Faraday rotation element 3, and the analyzer 2 is transmitted as is since it has been rotated by 45 degrees and fixed in advance.

The return reflected light is separated into an ordinary beam and an extraordinary beam by the analyzer 2 due to the birefringence effect, and the extraordinary beam is laterally shifted.

For this ordinary beam, the Faraday rotation element 3 is used again.
, the polarization plane is further rotated by 45 degrees, and the beam enters the polarizer 7 as a beam with a polarization plane rotated by 90 degrees, and is laterally shifted and emitted as an abnormal beam.

Further, since the extraordinary light beam from the analyzer 2 passes through the Faraday rotator 3 again, it is similarly rotated by 45 degrees and enters the polarizer 7 as a beam with a polarization plane rotated by 0 degrees or 18080 degrees, and is emitted as an ordinary beam.

Therefore, the configuration is such that the return reflected light of any polarization plane is not injected into the semiconductor laser because the beam is laterally shifted.

〔Effect of the invention〕

As explained above, in the present invention, a polarizer, an analyzer, and a Faraday rotation element are fixed by soldering to a spacer that engages with the inside of a magnet, and after adjusting the plane of polarization, the magnet and spacer are fixed by YAG welding. By using a configuration in which the Faraday rotation element is made of GdBi garnet and the polarizer and analyzer are made of titanium dioxide, the plane of polarization can be adjusted by simply rotating the space, making assembly and adjustment easy and reducing the size and weight. Moreover, it is possible to obtain an optical isolator with excellent reliability at a low cost.

[Brief explanation of the drawing]

1 and 2 are sectional views showing an embodiment of the first and second inventions. DESCRIPTION OF SYMBOLS 1... Spacer, 2... Analyzer, 3... Faraday rotation element, 4... Magnet, 5... YAG welding part, 6... Spacer, 7... Polarizer.

Claims (4)

[Claims] (1) A first spacer made of a cylindrical non-magnetic material with a flange-like protrusion provided on the first opening surface, and first and second spacers of this spacer.
an analyzer and a Faraday rotator, each of which is adhesively fixed to the opening surface of the spacer, and the inner surface of the spacer is in contact with and engaged with the outer surface of the cylindrical portion of the spacer, and the first opening surface is in contact with the protrusion of the spacer, and the faraday rotation element is fixed with adhesive. 1. An optical isolator comprising: a rotating element disposed approximately in the center thereof; and a cylindrical magnet that fixes the spacer and applies a predetermined magnetic field to the Faraday rotating element. (2) A cylindrical shape in which a flange-like protrusion is provided on the first opening surface, the outer surface of the cylindrical portion contacts and mates with the inner surface of the magnet, and the protrusion is fixed in contact with the second opening surface of the magnet. Claim comprising: a second spacer made of a non-magnetic material; and a polarizer adhesively fixed to the first opening surface of the second spacer.
1) The optical isolator described above. (3) The optical isolator according to claims (1) and (2), wherein the Faraday rotation element is made of thick film GdBi garnet, and the polarizer and analyzer are made of titanium dioxide crystal. (4) An analyzer, a Faraday rotation element, and a polarizer are adhesively fixed to the first and second spacers by soldering, and the angles of the polarization planes of the analyzer and polarizer are changed by rotating the first and second spacers. A method for manufacturing an optical isolator, comprising: adjusting the first and second spacers, and then fixing the first and second spacers to the magnet by YAG welding at a temperature lower than the melting point of the solder.