JPS6170516A - Semiconductor laser module with optical isolator - Google Patents

Abstract

PURPOSE:To couple a laser light with an optical fiber easily by piling up successively and fixing individual constituting elements of a semiconductor laser module including an optical isolator while adjusting them so that the deviation of the optical axis is reduced. CONSTITUTION:The semiconductor laser module with the optical isolator consists of a semiconductor laser 1 and the lens 2 are attached to a supporting tool 15 as one body so that a laser parallel beam is discharged from the end face in the vertical direction. A supporting tool 23 to which a permanent magnet 22 giving 45 deg. Farady rotation and the rotator 3 are added is moved on the end face and is so adjusted that the optical output is maximum, and the supporting tool 23 is fixed to the supporting tool 15 by an adhesive. Similarly, supporting tools 32, 42, and 52 provided with the analyzer 4, the lens 5, and the optical fiber 6 respectively are fixed successively and are fixed in a cylindrical cap 16 by an adhesive. The laser light and the optical fiber are coupled easily and surely by this successive piling and fixing.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a semiconductor laser module with an optical isolator, and in particular, it is easy to couple to an optical fiber while fully utilizing the characteristics of the optical isolator, and is easy to manufacture and stable. Concerning the structure of a small and versatile module.

[Background of the invention]

The stability of the oscillation frequency of semiconductor lasers used in optical communications and optical disks becomes one of the more important factors as the performance of the system increases. It is known that the oscillation frequency of a semiconductor laser becomes extremely unstable when the emitted light is reflected from the end face of an optical fiber and returns to the end face of the optical fiber.As a countermeasure, an optical isolator is installed between the semiconductor laser and the optical fiber. It is also known to insert a light beam to reduce the return light.

For example, in Japanese Patent Application Laid-Open No. 57-173992, a Faraday rotator such as YIG is used in the first condensing lens to reduce the return of light and to reduce the size.

Further, Japanese Patent Application Laid-Open No. 57-66686 describes a method for efficiently introducing light emitted from a semiconductor laser into an optical fiber by appropriately arranging a first condenser lens and a second condenser lens.

Although these are factors for stable operation of a semiconductor laser, there is no description of optical axis alignment, which has a greater influence than these.

[Purpose of the invention]

An object of the present invention is to insert optical components such as an optical isolator and a lens between a semiconductor laser and an optical fiber.

It is an object of the present invention to provide a structure of a semiconductor laser module with an optical isolator that can easily couple a laser beam and an optical fiber.

[Summary of the invention]

The installation of an optical isolator is essential for stable semiconductor laser modules used in optical communications and optical disks, but in this case the optical isolator f211! As a result of various studies regarding the method and conditions for related components to further enhance the performance of the optical isolator, the following conclusions were reached.

1. As shown in FIG. 1, the semiconductor laser module includes at least a semiconductor laser 1. It is composed of a first condensing lens 2, a Faraday rotator 3, an analyzer 4, a second condensing lens S, and an optical fiber 6.

2. In order to reduce the coupling loss between the semiconductor laser and the optical fiber to 3 dB or less in the semiconductor laser module, the optical axis misalignment must be 4 μm or less.

3. In order to reduce the coupling loss to 3 dB or less, and to keep the module length within 40 m and the outer diameter within 15 m, the first condenser lens should be made of sapphire (AQ, O,) or lead glass (
It must be a spherical lens with a diameter of 1 cm or less and made of a material with a high refractive index such as PBO).

4. In order to increase the extinction ratio (rate of reducing returned light) of the optical isolator, it is necessary to make the light propagating inside the Faraday rotator uniform within the optical path length plane in the optical axis direction.

5. In order to set the extinction ratio to 30 to 40 dB, a rotation adjustment function is required so that the polarization direction of the analyzer forms an angle of 45 degrees with the polarization direction of the semiconductor laser.

6. When fixing the components, the easiest method is to stack them one after another starting from the laser and fix the optical axis while adjusting the optical axis, so the components must be mounted on a support that allows them to be stacked.

7. In order to reduce the light reflected in the optical axis direction by the optical isolator surface and the fiber input end surface, these surfaces must be tilted with respect to the optical axis so that they are not perpendicular to the optical axis.

The angle is preferably 5 degrees, but any angle between 4 and 9 degrees is practical.

8. If the component or support is axially symmetrical, such as a cylinder, or spherical, thermal expansion will be axially symmetrical and no distortion will occur on the optical axis.

9. The positional accuracy of each component in the optical axis direction is several tens of microns
There is no problem with m.

With the above conclusions in mind, semiconductor lasers,
The optimal method is to install components such as optical lenses, Faraday rotators, and optical fibers in a cylindrical support, and then stack and fix them one after another on top of the semiconductor laser, aligning the shoulders to minimize misalignment of the optical axis. I found out something.

The optical axis misalignment is 4 μm or less if the loss is to be 3 dB or less, but 10 μm may be sufficient depending on the purpose of use.For example, for general communication use, it is 5 μm (loss about 6 dB).
Below, 1μm (loss approximately 1dB) or less is desirable for high-level communications, and 10μm for applications where the transmission distance is shorter.
m (with a loss of approximately 10 dB), but if the thickness exceeds 10 μm, the optical output from the semiconductor laser module becomes small and the practicality becomes poor.

In addition, when inserting a polarizer between the first condensing lens and the Faraday rotator, it has a rotation fine adjustment function around the optical axis, and its end surface is tilted with respect to a plane perpendicular to the optical axis. Bye.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

As optical components, semiconductor laser 1, semiconductor laser 1
a first condenser lens 2 for collimating the light emitted from the
a second condenser lens 5 for better coupling of light to the
Single mode optical fibers 6 are arranged in sequence. A magnetic field is applied to the Faraday rotator 3 in the optical axis direction by a cylindrical magnet 22. Faraday rotator 3. and analyzer 4,
The optical fiber 6 has an angle of 5 degrees for the first two, and an angle of 8 degrees for the optical fiber so that the reflected light at the end face does not return to the semiconductor laser.

The end face was tilted with respect to the optical axis. Each optical component is held by cylindrical supports 15, 23, 32, 42, and 52. The first condenser lens 2 is a ball lens 2 made of AΩ2O3 with a diameter of 0.8m+ and anti-reflection coated, and the semiconductor laser 1 is an embedded semiconductor that operates at a wavelength of 1.5μrn and has a direct vA polarized wave output. A laser (BH laser) was used.

The full width at half maximum of the semiconductor laser beam is 30 to 40 degrees, and by separating it from the ball lens 2 by about 0.06 m++, a parallel beam with a diameter of about 0.3 on was obtained. Note that the semiconductor laser 1 and the first condensing lens 2 are adjusted and integrated in advance so that the emitted parallel beam is substantially perpendicular to the front end surface of the support 15.

The Faraday rotator 3 mounted on the support 23 consists of YIG CY, F f3*ols) with a length of 2.6 mm and a diameter of 1 mm, and is IKOed by a permanent magnet 22 so as to give a Faraday rotation of 45 degrees.
A magnetic field of e is applied to the Faraday rotator 3. Note that the Faraday rotator 3 is arranged at an angle of 5@ with respect to the optical axis. The support 23 has approximately the same diameter 12 as the support 15.
It has a cylindrical shape with a diameter of +m, and both end faces are parallel and spaced apart by 5.5 cm. The parallel light from the first condensing lens 2 is transmitted to the Faraday rotator 3.
In order to emit radiation more efficiently, hold the support 15,
The analyzer support 23 is moved over the end face using a fine movement table,
Supports 15 and 23 were fixed with adhesive at the location where the light output was maximum.

Next, a cylindrical support 32 with an analyzer 4 installed in the center with the same inclination as the Faraday rotator 3 is moved on the surface of the support 23 using a fine movement table to efficiently emit parallel light, and the Faraday rotation is performed. In order to facilitate the one-rotation function of rotating the support 32 within the end face of the support 23 so that the polarized light wave tilted by 45 degrees can propagate without loss in the cylindrical support 23, the central portion is approximately 1111 degrees inside the cylindrical support 23. It has a structure with uneven protrusions for insertion.

The optical axis of the parallel light emitted from the analyzer is BK-7 with a diameter of 3 m.
Optical axes are aligned by slightly moving the ball lens support 42.

After the alignment of each optical component is completed, adhesive is flowed into the gap between each cylindrical support and fixed to the Faraday rotating section B, the analyzer section C1, the condensing lens section, and the optical fiber section E in sequence. Finally, the optical fiber 6 was moved in the optical axis direction to the optimum position so that the deviation of the optical axis was within 3 μm, and then fixed. After the above-mentioned optical components were fixed, a cap 16 was put on and fixed to the laser section A or the Faraday rotator section B to protect the entire module.

This semiconductor module with an optical isolator was small with a length of 39 mm and an outer diameter of 14 mm, and had high performance with optical isolation of 25 dB and insertion loss of 2.9 dB.

FIG. 3 shows the measurement results of the relationship between the deviation of the optical axis of the optical fiber and the optical output of the semiconductor module in the semiconductor laser module with an optical isolator.

In the figure, the horizontal axis represents the amount of optical axis deviation of the optical fiber, and the vertical axis represents the optical output of the semiconductor laser module. 4 μm
No significant decrease in coupling power was observed up to 4 μ
When the amount of leakage becomes larger than m, it is observed that the optical output of the semiconductor laser module suddenly decreases. However, as described above, depending on the purpose of use, for example, in communication systems with short transmission distances, even a deviation of 10 μm may be practical.

In this example, a single mode optical fiber was used, but similar results were obtained using a multimode optical fiber such as a graded index type optical fiber.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of the present invention, and FIG. 2 is a diagram for explaining an embodiment. FIG. 3 is a diagram showing the relationship between the deviation of the optical axis of an optical fiber and the optical output in joules of a semiconductor laser. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... First condensing lens or ball lens, 3... Faraday rotator, 4... Analyzer. 5... Second condensing lens or ball lens, 6... Optical fiber, 13.14... Electrical terminal, 15... Semiconductor laser and first condensing lens support, 16... Cap, 22... Cylindrical magnet, 23... Faraday rotator support, 32... Analyzer support, 42... Second condensing lens support, 52... Optical fiber support, A...
・Semiconductor laser section, B... Faraday rotator section, C.
・・Analyzer direction 1 Figure 3 Figure light 7r i8° ri force/) r"4 V") Procedural amendment 'Ii l'l Size of 1981 Patent Application No. 191549 Name of the invention f Filter 7L/-Semiconductor module; city +1:
, a long time ago lll1 axis1'li, i To the patent applicant f+
□51011'1 Ceremony meeting 111 tate)2 Production fee
1 person from Tokyo + 1 person from Ig

Claims (1)

[Claims] 1. A group of optical components consisting of at least a semiconductor laser, a first lens for condensing, an optical isolator, an analyzer, a second lens for condensing, and an optical fiber are held by respective supports,
A semiconductor laser module with an optical isolator, characterized in that the group of component parts is arranged in the order described above so that optical axis deviation of each of the component parts is below a predetermined value. 2. The semiconductor laser module with an optical isolator according to claim 1, wherein the supports are fixed to each other using an adhesive. 3. The semiconductor laser module with an optical isolator according to claim 1, wherein the optical isolator is a Faraday rotator. 4. The semiconductor laser module with an optical isolator according to claim 1, wherein the first condensing lens is a spherical lens made of fire or lead glass and having a diameter of 1 mm or less. 5. The semiconductor laser with an optical isolator according to claim 1, wherein the support for the analyzer is provided with a mechanism capable of rotating the analyzer within a left plane perpendicular to the optical axis of the analyzer. module. 6. The semiconductor with an optical isolator according to claim 1 or 3, wherein the end faces of the optical isolator, the Faraday rotator, the analyzer, and the optical fiber are not in a plane perpendicular to the optical axis. laser module. 7. A semiconductor laser module with an optical isolator according to claim 1 or 2, wherein the support is axially symmetrical. 8. The semiconductor laser module with an optical isolator according to claim 1, wherein the optical axis deviation is set to a predetermined value of 10 μm or less. 9. The semiconductor laser module with an optical isolator according to claim 1, wherein the predetermined value of the optical axis deviation is 5 μm or less. 10. The semiconductor laser module with an optical isolator according to claim 1, wherein the predetermined value of the optical axis deviation is 4 μm or less. 11. The semiconductor laser module with an optical isolator according to claim 1, wherein the predetermined value of the optical axis deviation is 1 μm or less. 12. The semiconductor laser module with an optical isolator according to claim 1 or 2, wherein the support is cylindrical. 13. Claim No. 1, characterized in that the angle between the end face of the optical isolator, the Faraday rotator, the analyzer, and the optical fiber and a plane perpendicular to the optical axis is in the range of 4 degrees to 9 degrees. A semiconductor laser module with an optical isolator according to item 1, 3 or 6. 14. The semiconductor laser module with an optical isolator according to claim 1, wherein the arrangement is performed by stacking.