JPH043004A - Semiconductor laser module - Google Patents

Abstract

PURPOSE:To suppress the incident quantity of the reflected return light on a light emitting point by constituting the lens system of a 1st lens group which images the exit light from a semiconductor laser to a space and a 2nd lens group which forms the image of the 1st lens group to the end face of an optical fiber and disposing an optical isolator within the optical axis of the image space of the 1st lens group. CONSTITUTION:The lens system is constituted of the 1st lens group 7 which images the exit light from the semiconductor laser 5 to the space and the 2nd lens group 8 which forms the image of this 1st lens group 7 to the end face of the optical fiber 6. The optical isolator 9 is disposed in the optical axis of the image space of the 1st lens group 7. The image magnification of the lens image 7 of the 1st lens group is set freely and the distance between the light emitting point of the semiconductor laser 5 and the reflected light imaging position from the optical fiber 6 is equaled to the moving quantity of the optical axis of the reflected light in the optical isolator 9. The incident quantity of the reflected return light on the light emitting point of the semiconductor laser 5 is suppressed in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser module equipped with an optical isolator.

[Prior Art] Generally, in optical communication systems such as high-speed digital communication using semiconductor lasers or analog direct brightness modulation, noise is generated due to the influence of reflected light from devices inserted into the transmission path, such as optical connectors. This often causes various problems in system configuration.

The noise caused by this reflected light is caused because the reflected light disturbs the stable emission state of the semiconductor laser, and there are two methods to solve this problem. (1) Take anti-reflection measures for optical devices such as optical connectors to suppress the occurrence of reflected light. (11) Preventing the generated reflected light from being reinjected into the laser cavity.

However, applying complete anti-reflection measures to all optical devices inserted into the optical transmission path leaves many unresolved technical issues and at the same time causes a significant increase in system cost. Therefore, an effective and efficient method for preventing noise generation due to reflected light is to use an optical isolator, which prevents reflected light from being reinjected into the laser cavity and maintains stable laser emission. be. In other words, the re-injected light is removed by using an optical isolator, which is a device with a so-called tragic reciprocal propagation function that transmits light in the forward direction (light transmission direction) but not in the reverse direction. It is.

In conventionally proposed optical isolators, the optical axis of the reflected return light from the optical fiber 2 to the semiconductor laser 3 is normally aligned with the optical axis of the light from the semiconductor laser 3 to the optical fiber 2, as shown by the broken line in FIG. A device that has the function of moving parallel to the axis is used. Since the image of this reflected return light by the lens 4 is focused at a position away from the light emitting point of the semiconductor laser, the amount of the reflected return light that enters the light emitting portion of the semiconductor laser 3 is suppressed.

[Problem to be solved by the invention]

By the way, the conventional semiconductor laser module mentioned above is
It has a structure in which an optical isolator 1 is placed between a lens 4 and an optical fiber 2. Therefore, if the image magnification of the lens 4 is m, then the distance between the image formation position of the reflected return light from the optical fiber 2 by the lens 4 and the light emitting point of the semiconductor laser 3 is calculated. is the amount of movement of the optical axis at the reflection return destination in optical isolator 1■
, against ■. =1.7m. Therefore, in order to reduce the amount of reflected light incident on the semiconductor laser 3, the distance I is required. Therefore, it is desirable to make the magnification m small≧ On the other hand, the image magnification m of the lens 4 is determined by the emission point radius rL of the semiconductor laser 3 (l and the core radius r of the optical fiber 2).

It is determined by the following equation (1).

rF m= ...(1) LD Here, rF is usually about 1 μm, so the image magnification m
is determined by r, the core radius r.

Even the smallest single mode mode fiber with r.

-, 5 μm, the image magnification m cannot be larger than 5. Therefore, it is difficult in principle to make the distance I0 larger than l515.

That is, the conventional semiconductor laser module has a drawback in that it is difficult to sufficiently suppress the amount of reflected light incident on the semiconductor laser 3.

SUMMARY OF THE INVENTION An object of the present invention was made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide a semiconductor laser module that can sufficiently suppress the amount of reflected light incident on the light emitting point of a semiconductor laser.

[Means to solve the problem]

In the present invention, in a semiconductor laser module including a semiconductor laser, an optical fiber into which light emitted from the semiconductor laser is input, and a lens system that optically couples the semiconductor laser and the optical fiber, the lens system includes: It is composed of a first lens group that forms an image of the light emitted from the semiconductor laser in space, and a second lens group that forms an image of the first lens group on the end face of the optical fiber. The optical isolator is arranged within the optical axis of the image space of the lens group.

[Effect]

In this way, in the present invention, the lens system is composed of a first lens group and a second lens group, and an optical isolator is arranged between the first lens group and the second lens group. By doing so, the image magnification of the first lens group can be freely set,
If the distance between the light emitting point of the semiconductor laser and the imaging position of the reflected light from the optical fiber is made equal to the amount of optical axis movement of the reflected light at the optical isolator, this will ensure that the amount of reflected light incident on the light emitting point of the semiconductor laser is sufficient. can be suppressed to achieve the above objectives.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of a semiconductor laser module according to the present invention. This semiconductor laser module includes a semiconductor laser 5, an optical fiber 6 which is arranged facing the semiconductor laser 5 at a predetermined distance and into which light emitted from the semiconductor laser 5 is input, and a semiconductor laser 5.
and the optical fiber 6, and the semiconductor laser 5
A first lens group 7 that forms an image in space of light emitted from It has a configuration including a second lens group 8 that forms an image on the end surface of the lens, and an optical isolator 9 provided within the optical axis between the first lens group 7 and the second lens group 8. .

By the way, in this embodiment, a DFB laser is used as the semiconductor laser 5, a single mode fiber with a core system of 5 μm is used as the optical fiber 6, and one distributed refraction type is used as the first lens group 7 and the second lens group 8. Each uses a rod lens. The optical isolator 9 is composed of a YfG crystal 10 and two rutile polarizing plates 11 sandwiching the YfG crystal 10, and the optical axis of the reflected light from the optical fiber 6 is directed to the semiconductor laser 5.
It has the function of moving the beam parallel to the optical axis of the beam heading from the optical fiber 6 to the optical fiber 6.

Now, the light emitted from the semiconductor laser 5 is once condensed by the first lens group 7 arranged so that the image magnification m is 1.
After passing through the optical isolator 9, the light is again focused by the second lens group 8 and imaged onto the optical fiber 6. Further, the reflected light from the optical fiber 6 is condensed by the second lens group 8 and enters the optical isolator 9, and its optical axis is moved in parallel by a distance fs. Thereafter, the light is focused on the first lens group 7 and is imaged on a plane including the light emitting point of the semiconductor laser 5. At this time, since the first lens group 7 is set so that the image magnification m is 1,
Distance between the light emitting point of the semiconductor laser 5 and the imaging position of the reflected light■
. is equal to the amount of parallel movement of the optical axis of the reflected light at the optical isolator 9.

That is, the distance I0 between the light emitting point of the semiconductor laser 5 and the imaging point of the reflected light is determined only by the beam shift amount 1 at the optical isolator 9, regardless of the image magnification of the second lens group 8. Therefore, the amount of reflected return light incident on the light emitting point of the semiconductor laser 5 can be sufficiently suppressed.

In the above-described embodiment, the first lens group 7 and the second lens group 8 are composed of one rod lens, but it goes without saying that they do not need to be one rod lens.

〔Effect of the invention〕

As explained above, in the semiconductor laser module according to the present invention, the lens system includes a first lens group that images the light emitted from the semiconductor laser in space, and an image of this jJl lens group that forms an image on the end face of an optical fiber. Since it is composed of a second lens group for imaging, and an optical isolator is arranged within the optical axis of the image space of the first lens group, the image magnification of the first lens group can be freely set. By setting the distance between the light emitting point of the semiconductor laser and the imaging position of the reflected light from the optical fiber to be equal to the amount of movement of the reflected optical axis in the optical isolator,
This provides an excellent effect in that the amount of reflected light incident on the light emitting point of the semiconductor laser can be sufficiently suppressed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of a semiconductor laser module according to the present invention, and FIG. 2 is a schematic diagram showing an example of a conventional semiconductor laser module. 5... Semiconductor laser, 6... Optical fiber, 7... First lens group, 8... Second lens group, 9... ... Optical isolator, 10 ... YIG crystal, 11 ... Rutile polarizing plate.

Claims (1)

[Claims] 1. A semiconductor laser module including a semiconductor laser, an optical fiber into which light emitted from the semiconductor laser enters, and a lens system that optically couples the semiconductor laser and the optical fiber. , the lens system includes a first lens group that images the light emitted from the semiconductor laser in space;
and a second lens group that forms an image of the lens group on the end face of the optical fiber, and an optical isolator is disposed within the optical axis of the image space of the first lens group. semiconductor laser module. 2. The semiconductor laser module according to claim 1, wherein the first and second lens groups are comprised of at least one distributed refraction type rod lens. 3. The semiconductor laser module according to claim 1, wherein the optical isolator is composed of a YIG crystal and rutile polarizing plates disposed on both sides of the YIG crystal.