JPH0368915A - Optical isolator and semiconductor laser module incorporated with optical isolator - Google Patents

Abstract

PURPOSE:To enhance reliability, to attain miniaturization and to allow the hermetic sealing over the entire part of a coupling optical system by making the effective use of holders for a Faraday rotating element, polarizer and analyzer as structural members for the optical system before and behind an optical isolator. CONSTITUTION:A magnet 32 of the optical isolator has three grooves for holding and fixing the polarizer 33, the Faraday rotating element 31 and the analyzer 34 and the peripheral part thereof is soldered to the holder 35. The polarizer 33, the element 31, the analyzer 34 are cut out to a square chip shape from a crystal. The optical isolator 30 is welded to the front end of a base 4 of the semiconductor laser module and an optical fiber 20 protected by a ferrule 9 is welded via a slide ring 8 to the front end of the isolator 30. The light from the semiconductor laser 1 is introduced to the fiber 20.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical isolator and a semiconductor laser module with a built-in optical isolator, which is particularly economical, can be miniaturized, has excellent temperature characteristics, and is easy to assemble. The present invention relates to an optical isolator and a semiconductor laser module with a built-in optical finlayer, which are also easy to mount.

[Traditional technology]

Semiconductor lasers used in optical fiber communications are often supplied as modules equipped with a fiber for optical output, and are often provided with a connector at the end thereof to connect to a fiber for transmission. In this case, it is known that the reflected return light generated at the connector portion is reinjected into the semiconductor laser, destabilizing the operating state of the semiconductor laser. This becomes a particularly serious problem when performing high-speed, long-distance transmission. For this reason, semiconductor laser modules have been developed that include a built-in optical isolator that eliminates reflected and returned light.

Figure 3 shows the paper rAn Effective Nonrec-ip published by Sugie (T) and Saruwatari (M).
local C1rcuit for Sem1con
ductor La5er-to-Fiber Couu
plinga YIG 5phereJ (JOURN
AL OF LIGHTWAVE TECHNO-LO
GY, VOL, LT-1, No, I, MARCH198
3) shows the structure of the optical isolator built-in semiconductor laser module described in 3). In the figure, the light beam emitted from the semiconductor laser 1 is YIG
It is converted into a convergent beam by a sphere 21, and further by a lens 22.
and is coupled to the optical fiber 2° via the polarizer 23. A ring-shaped magnet 19 arranged around the YIG ball 21
As a result, a magnetic field in the optical axis direction is applied to the YIG sphere 21, and the polarization direction of the beam passing through the YIG sphere 21 is rotated by 45 degrees due to the Faraday effect. As the polarizer 23, a calcite plate is used.

In a semiconductor laser module with this type of structure, the light emitted from the semiconductor laser is efficiently coupled into the optical fiber, but on the other hand, the light that returns in the opposite direction inside the optical fiber does not return to the semiconductor laser, resulting in stable operation. . The principle will be explained below. The beam emitted from the semiconductor laser is generally TE polarized, and is polarized in a direction perpendicular to the plane of the paper in FIG. The polarization direction of this beam is rotated by 45 degrees by the YIG sphere 21 and then enters the polarizer, but at that time only the ordinary refractive index is sensed, so the light beam is not separated and is coupled to the optical fiber as it is. On the other hand, since the polarization direction of the light traveling in the opposite direction through the optical fiber is indeterminate, the polarizer 23 divides the light into two beams: one having only the ordinary refractive index and the other having the extraordinary refractive index. Of these, the light that only senses the ordinary refractive index is rotated by 45 degrees with respect to the polarization direction of the semiconductor laser, but it is rotated an additional 45 degrees when passing through the YIG sphere, so when it returns to the semiconductor laser, it is rotated by a total of 90 degrees. It becomes TM polarized light and does not affect the operation of the semiconductor laser.In addition, the beam of light that senses the extraordinary refractive index is shifted laterally, and when it returns to the semiconductor laser, it is shifted from the light emitting point. Since the light returns to , it does not affect the operation of the semiconductor laser. Therefore, this module is free from the influence of reflected return light and can operate stably.

Figure 4 is explained in the paper ``DFB-LD module with built-in optical isolator'' (1985 IEICE Semiconductor and Materials National Conference 305) presented by Chika, Watanabe, Goto, Miura, Toge et al. This figure shows the structure of a semiconductor laser module with a built-in optical isolator.

In the figure, a light beam emitted from a semiconductor laser 1 is converted into a parallel beam by a first lens 15, passes through an optical isolator 25 formed from a rutile prism, a YIG crystal, and a magnet 19, and then is converged by a second lens 14. and is coupled to the optical fiber 20. This case differs from the case shown in FIG. 3 in that two prisms are used in the optical isolator 25.

[Problem to be solved by the invention]

By the way, it is generally known that when the temperature of a semiconductor laser changes, the oscillation threshold, differential quantum efficiency, and oscillation wavelength change. In particular, when the oscillation wavelength changes, noise is generated from the semiconductor laser or the dispersion of the optical fiber changes, which has an unfavorable effect on the transmission characteristics. Furthermore, although it depends on the material of the Faraday rotation element, the Faraday rotation angle changes due to temperature changes, and it is conceivable that the isolation against reflected return light may deteriorate. Therefore, it is desirable that the temperature of the semiconductor laser and Faraday rotation element be controlled by a Peltier element built into the module.
The module mentioned above cannot do that.

At the same time, the aforementioned semiconductor laser module with a built-in optical isolator has a coaxial type, and when compared with a DIP type module, it is not only difficult to miniaturize but also has poor mountability when installed in communication equipment.

In addition, all of the above-mentioned conventional semiconductor laser modules with a built-in optical isolator use YIG crystal as a Faraday rotation element, but the price thereof is high.

In addition, the aforementioned semiconductor laser module with built-in optical isolator,
- The optical isolator and the parts before and after it are not hermetically sealed, making it difficult to prevent condensation under low-temperature conditions, resulting in poor reliability.

Also, compared to modules without optical isolators,
The relative rotation angle between the polarizer and analyzer must be adjusted.

In contrast, the present invention is economical and can be miniaturized,
Another object of the present invention is to provide a semiconductor laser module with a built-in optical finlayer and optical isolator that has excellent temperature characteristics and no need to adjust the relative rotation angle between the polarizer and the analyzer and is highly reliable.

[Means to solve the problem]

The optical isolator of the present invention has a Faraday rotation element, a polarizer, an analyzer, two sets of magnets each having three parallel grooves on one side, a through hole on the central axis, and an open top. Rather than using a box-shaped holder, two sets of magnets are placed in close contact with the inner walls on both sides of the holder, sandwiching the central axis, the valley grooves are arranged in correspondence, and the Faraday rotation element is inserted into the groove in the center of the magnet. , a polarizer and an analyzer are inserted into the grooves on both sides, and the Faraday rotation element is sandwiched between the polarizer and the analyzer, and the Faraday rotation element, polarizer, and analyzer are sandwiched between two sets of magnets from both sides. The structure is characterized by being arranged and fixed in such a way that the

The semiconductor laser module with a built-in optical isolator of the present invention includes a semiconductor laser, a chip carrier, a metal base, a condensing lens, the optical fiber whose tip end is protected by a metal tube, and a slide having an inner diameter slightly larger than the metal tube. It consists of a ring, the metal case having an introduction hole in the side wall through which the optical fiber passes, and the above-mentioned optical isolator, the metal base having a flat part and a vertical surface, and a through hole extending from the flat part to the vertical surface, The semiconductor laser is fixed within a metal case, the semiconductor laser is mounted on a flat part of the metal base via the chip carrier, the condensing lens is fixed inside a through hole of the metal base, and the optical isolator is mounted on a flat part of the metal base. The optical fiber is fixed to the vertical surface of the base, and the metal tube at the tip of the optical fiber is bonded and fixed to the end face of the optical isolator via the slide ring, and passes through the introduction hole and is sealed with solder. The structure is characterized by the following.

When assembling the optical isolator of the present invention, the magnet is inserted into the holder, and then the optical member of each optical isolator is inserted into the groove of the inserted magnet, so it is simple, highly reliable, and compact.

In addition, the semiconductor laser module with a built-in optical isolator is
By utilizing a metal holder that supports an optical isolator optical component such as a Faraday rotation element as a structural member that supports the coupling optical system of the entire module, reliability can be improved and miniaturization can be achieved. At the same time, by incorporating a Peltier element, the temperature of the isolator can be controlled, and the entire coupling optical system can be hermetically sealed.

[Example 1] FIGS. 1(a) and 1(b) are structural diagrams of an embodiment of the optical isolator of the present invention, in which (a) is a plan view and (b) is a plan view.
It is a sectional view taken along AA' of FIG. The optical isolator in the figure is a Faraday rotation element 31. Magnet 32. Polarizer 33.
Analyzer 34. It consists of a holder 35 and is assembled in the manner described below.

First, Hibiya (T, Hi
The paper rGrawth published by Mr. biya) et al.
and Magneto-Optic Property
es of Liquid Phase Epitax
ialBi-3ubstituted Garnet
Films for 0ptical l5olato
rJ (NECRes, & Develop, No.
80. A bismuth-substituted garnet thick film introduced in January 1986) is useful.

This garnet thick film is excellent in mass production, reaches a saturation magnetic field with a small magnetic field, and has a large rotational ability, so it is advantageous in realizing an economical and compact semiconductor laser module with a built-in optical isolator.

The magnet 32 has three grooves for holding and fixing a polarizer, a Faraday rotation element, and an analyzer, the grooves and the surrounding area are metallized, and the surrounding area is soldered to the holder 35. A non-magnetic material such as SUS 304 is used as the material of the holder.

Polarizer 33. The Faraday rotation element 31 and the analyzer 34 are cut into square chips from a crystal.

At this time, the polarizer 33 is cut out so that the polarization direction is parallel to the sides, and the analyzer 34 is cut out so that the polarization direction is parallel to the diagonal line (relative angle between polarizer and analyzer 45°). As the material for the polarizer 33 and the analyzer 34, a uniaxially anisotropic optical crystal such as rutile is used. Each optical member of the optical isolator (polarizer, Faraday rotation element, analyzer) cut out into a square chip shape is metalized at its peripheral portion, and then fitted into the groove of the magnet 32 and soldered. In this way, simply by storing the polarizer and analyzer in the groove of the magnet, the relative rotation angle will automatically become 45° (self-alignment).
The assembly process is simple, each member has a simple shape such as a square, and it is easy to process, making it highly economical.

[Example 2] Figures 2 (a) and 2 (b) are structural diagrams of an example of the semiconductor laser module incorporating the optical isolator of Example 1, where (a) is a plan view and (b) is a cross-sectional view. It is. In the figure, a semiconductor laser 1 is mounted on a base 4 together with a monitor photodiode 5 via a heat sink 2 and a chip carrier 3. The base 4 includes a lens 7, and the optical isolator 30 of the first embodiment is fixed to the tip of the base 4 by welding. Furthermore, the tip of the optical isolator 30 is attached to a ferrule 9.
An optical fiber 20 protected by a slide ring 8 is fixed by welding via a slide ring 8. The output light from the semiconductor laser 1 is guided to the optical fiber 20 by this series of structures. The base 4 is connected to the case 11 via the Bertier element 10.
The ferrule 9 and the case 11 are connected and sealed with solder 12. The thermistor 6 is in the form of a chip, and is mounted on the chip carrier 3 adjacent to the semiconductor laser 1.

In this structure, the support system from the base 4 on which the chip carrier 3 is mounted to the ferrule 9 is assembled by welding using metal parts, and the Faraday rotation element, polarizer, and analyzer are made of metal parts. It has excellent mechanical strength because it is attached directly to the component. In other words, the holder that supports the Faraday rotation element, polarizer, and analyzer is also used as a structural member that mechanically connects the optical systems before and after the optical finlayer, so it takes up less space when incorporated into the module. It is possible to reduce the size by saving on the amount of energy.

Furthermore, in this case, since the optical isolator is connected to the base installed on the Bertier element, it is possible to compensate to a comparable extent for variations in characteristics of the optical isolator due to changes in ambient temperature.

Furthermore, in the case of a semiconductor laser module with a built-in optical isolator having this structure, the entire optical system from the semiconductor laser 1 to the end face of the optical fiber 20 is DI? Hermetically sealed inside the package prevents the risk of condensation under low temperature conditions.

〔Effect of the invention〕

As explained above, when assembling the optical isolator of the present invention, simply by inserting the optical components of each optical isolator into the grooves of the magnet, the optical relative angle is automatically set (
(Selfline), no complicated optical angle adjustment is required.

In addition, since the Faraday rotation element, polarizer, analyzer, and magnet can be easily processed using a simple processing method, the processing accuracy is excellent and it is also economically advantageous.

Further, the semiconductor laser module with a built-in optical isolator of the present invention has high reliability, is easy to downsize, and can be temperature compensated and completely hermetically sealed to prevent dew condensation.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are structural diagrams showing an example of the structure of the optical isolator of the present invention, and FIGS. 2(a) and (b) are structural diagrams showing an example of the structure of the semiconductor laser module with a built-in optical isolator of the present invention. FIG. 3 is a diagram showing the structure of a conventional optical isolator, and FIG. 4 is a cross-sectional view showing the structure of a conventional semiconductor laser module with a built-in optical isolator. 1...Semiconductor laser, 2...Heat sink, 3...Chip carrier, 4...
Base, 5... Monitor photodiode, 6
... Group thermistor, 7... Lens, 8...
... Slide ring, 9 ... Ferrule, 1
0... Peltier element, 11... Case, 12... Solder, 14... Second lens, 15... First lens, 19...Magnet, 2o...Optical fiber, 21...Y
IG bulb, 22...lens, 23...polarizer, 30...optical isolator, 31...
...Faraday rotating element, 32... Magnet, 33
...Polarizer, 34...Analyzer, 35.
·····holder.

Claims (2)

[Claims] (1) A Faraday rotation element, a polarizer, an analyzer, two sets of magnets with three parallel grooves on one side, and a box-shaped holder with a through hole on the central axis and an open top. The two sets of magnets are brought into close contact with the inner wall surfaces on both sides of the holder across the central axis, the respective grooves are arranged in correspondence with each other, the Faraday rotation element is inserted into the central groove of the magnet, and the The polarizer and the analyzer are inserted into the grooves on both sides, respectively, and the Faraday rotation element, the polarizer, and the analyzer are arranged and fixed so as to be sandwiched between the two sets of magnets from both sides. optical isolator. (2) A semiconductor laser, a chip carrier, a metal base, a condensing lens, an optical fiber whose tip is protected by a metal tube, a slide ring with an inner diameter slightly larger than the metal tube, and an optical fiber that passes through the side wall. The optical isolator comprises the metal case having an introduction hole and the optical isolator according to claim 1, wherein the metal base has a flat part and a vertical surface, and has a through hole extending from the flat part to the vertical surface, and the metal base has a through hole extending from the flat part to the vertical surface. the semiconductor laser is mounted on the flat part of the metal base via the chip carrier, the condensing lens is fixed inside the through hole of the metal base, and the optical isolator is mounted on the flat part of the metal base through the chip carrier. The optical fiber is fixed to the vertical surface, and the metal tube at the tip of the optical fiber is bonded and fixed to the end face of the optical isolator via the slide ring, and is penetrated through the introduction hole of the metal case and sealed with solder. A semiconductor laser module with a built-in optical isolator.