JPH03273208A - Semiconductor laser module - Google Patents

Abstract

PURPOSE:To facilitate production by providing a rectangular prism which can monitor forward reflected return light and a photodiode in a module and constituting the Faraday rotator of an optical isolator by winding a coil, etc. CONSTITUTION:This module is constituted of a semiconductor laser 11, a 1st lens 12 which converts the laser beam emitted from the semiconductor laser 11 to collimated beams of light of a prescribed diameter, the rectangular prism 13, a polarizer 14 which is formed by using a double refractive material having the moving distance of extraordinary light exceeding the prescribed diameter of the collimated beams of light, the Faraday rotator 15, an analyzer 16 which has the plane of polarization inclined by about 45 deg. with the plane of polarization of the polarizer 14, a 2nd lens 17 which converges the collimated beams of light, an optical fiber 18, the photodiode 19 which monitors the reflected light from the rectangular prism 13 and generates the photocurrent corresponding to the reflected light thereof, and the coil 20 which is wound on the Faraday rotor 15 and excites a DC magnetic field H by the DC current I passed according to the photocurrent from the photodiode 19. The difficulty in the optical axis adjustment of the Faraday rotator is decreased in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser module that is applied to optical communication, optical measurement, etc., and converts an electrical signal into an optical signal.

[Conventional technology: It is well known that semiconductor lasers are conventionally used in image transmission systems using high-speed PCM transmission or analog direct modulation. However, in such systems, the influence of reflection noise caused by the reinjection of reflected light from optical connectors and other optical devices into the semiconductor laser is significant, so semiconductors with built-in isolators to prevent the reinjection of reflected light have a large effect. A laser module has been developed.

FIG. 2 shows the configuration of such a conventional semiconductor laser module with a built-in optical isolator. The emitted light from the semiconductor laser 1 is converted into parallel light by a lens 2, passes through an optical isolator consisting of a polarizer 3, a 45° Faraday rotator 4, and an analyzer 5, is converged by a lens 6, and is transmitted to a fiber 7. The structure is such that the reflected light is prevented from being reinjected.

[Problem to be solved by the invention]

However, in the above-described conventional semiconductor laser module with a built-in optical isolator, the light emitted from the semiconductor laser is converted into parallel light by the first lens 2, and the light emitted from the semiconductor laser is converted into parallel light by the polarizer 3, the 45° Farade rotator 4, and the analyzer 5. After passing through an optical isolator, it is converged by a second lens 6 and coupled to a fiber 7.
A fixed DC magnetic field is applied to the Farade rotor 4 by a magnet or the like. For this reason, when constructing a semiconductor laser module, high precision is required to adjust the optical surfaces of the polarizer 3 and analyzer 5, which causes problems such as extremely high manufacturing difficulty and a long manufacturing time. be.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a semiconductor laser module that can shorten the manufacturing time by reducing the difficulty in adjusting the optical axis of a Faraday rotator during manufacturing and increasing the degree of freedom. With the goal.

[Means to solve the problem]

The present invention provides a semiconductor laser, a first lens that converts laser light emitted from the semiconductor laser into parallel light of a predetermined diameter, a right-angle prism that separates a part of the parallel light as reflected return light, and an abnormality. A polarizer using a birefringent material that allows light to travel a distance equal to or greater than a predetermined diameter of parallel light, a Faraday rotator equipped with means for changing the rotation angle, and a polarizer whose polarization plane is approximately 45 degrees with respect to that of the polarizer. It includes an inclined analyzer, a second lens that converges parallel light, an optical fiber from which the converged light is emitted, and a means for monitoring the reflected return light separated by a right-angle prism. The degree of difficulty in adjusting the optical axis can be reduced, feedback control can be realized, and the above-mentioned objects can be achieved.

Note that the means for changing the rotation angle of the Faraday rotator is a coil.

Further, the means for monitoring the reflected return light separated by the right-angle prism is a photodiode.

〔Example〕

Hereinafter, one embodiment of a semiconductor laser module according to the present invention will be described with reference to FIG.

The semiconductor laser module of this embodiment has a semiconductor laser 1
1, a first lens 12 that converts the laser light emitted from the semiconductor laser 11 into parallel light having a predetermined diameter, and a right angle prism 13, so that the traveling distance of the extraordinary light is equal to or greater than the predetermined diameter of the parallel light. A polarizer 14 using a birefringent material, a Faraday rotator 15, an analyzer 16 whose polarization plane is inclined at approximately 45 degrees with respect to that of the polarizer 14, and a second polarizer that converges parallel light.
lens 17, optical fiber 18, and right angle prism 13
A photodiode 19 that monitors the reflected light from the photodiode 19 and generates a photocurrent according to the reflected light; and a photodiode 19 that is wound around the Faraday rotator 15 and receives a direct current r in accordance with the photocurrent from the photodiode 19 to generate a direct current magnetic field. Coil 2 that excites H
0.

However, the light emitted from the semiconductor laser 11 is transmitted through the first lens 1.
2, the light passes through a right-angle prism 13, passes through a polarizer 14 and a Faraday rotator 15, passes through an analyzer 16, and is converged by a second lens 17.
The light is input into the optical fiber 18. At this time, since a coil 20 is wound around the Faraday rotator 15, which excites an III-flow magnetic field H when a DC current I is passed through it, when this DC current ■ is controlled and the DC magnetic field H is changed, the Faraday rotation The Faraday rotation angle θ of the child 15 can be changed while satisfying the relationship of the following equation (1).

θ=VH・1 (1) (v: Verdet constant, 1: length of Faraday rotator 15) Now, there is a reflection point in front of the polarizer 14 (output side), and the reflected light Assuming that the reflected light returns, the reflected light is not incident on the semiconductor laser 11 but is incident on the photodiode 19 at the right angle prism 13, and a photocurrent corresponding to the reflected light incident on the photodiode 19 is generated. If a circuit is provided externally to monitor this photocurrent and detect its average value, and a control circuit is provided externally to the module to convert the detected voltage into a current, and is fed back to the Faraday rotator 15, The rotation angle of the Faraday rotator 15 is automatically adjusted to the optimum value so that reflected return light is eliminated.

Therefore, in the past, the optical surface was semi-fixed using magnets, etc., making it difficult to adjust the optical surface, and there was no way to compensate for axis deviation due to some external factor. Since the light can be monitored and the rotation angle of the Faraday rotator 15 can be changed continuously, the difficulty in adjusting the optical axis of the Faraday rotator during manufacturing can be reduced, and feedback control can be realized, increasing the degree of freedom. This makes it possible to realize semiconductor laser diodes with large diameters.

〔Effect of the invention〕

As described above, according to the present invention, a rectangular prism, a photodiode, etc. that can monitor the forward reflected return light are provided in the module, and a coil etc. is wound around the Faraday rotator of the optical isolator. , the difficulty in adjusting the optical axis of the Faraday rotator can be reduced, feedback control can be realized, and a semiconductor laser diode with a large degree of freedom can be realized, which is an excellent effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional example. 11... Semiconductor laser, 12... Lens, 13... Right angle prism, 14...
Polarizer, 15... Faraday trochanter, 16...
...Analyzer, 17...Lens, 18...Optical fiber, 19...Photodiode, 20...Coil.

Claims (1)

[Claims] 1. A semiconductor laser, a first lens that converts the laser light emitted from the semiconductor laser into parallel light of a predetermined diameter, and a right angle lens that separates a part of the parallel light as reflected return light. a prism; a polarizer using a birefringent material such that the travel distance of the extraordinary light is equal to or greater than a predetermined diameter of the parallel light; a Faraday rotator having a means for changing the rotation angle; The analyzer is provided with an analyzer tilted at approximately 45 degrees with respect to the analyzer, a second lens that converges parallel light, an optical fiber from which the converged light is emitted, and means for monitoring reflected return light separated by the right angle prism. A semiconductor laser module characterized by: 2. The semiconductor laser module according to claim 1, wherein the means for changing the rotation angle of the Faraday rotator is a coil. 3. The semiconductor laser module according to claim 1, wherein the means for monitoring the reflected return light separated by the right-angle prism is a photodiode.