JPH0974247A - Semiconductor optical amplifier module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the intensity of a laser beam, which is outputted by one semiconductor amplifier, by a method wherein the polarization direction of the laser beam on one side of laser beams, which are separated from each other and have polarization orientations vertical to each other, is rotated at a specified angle and the laser beam in the rotated polarization orientation is synthesized with the other laser beam separated from the laser beam in the rotated polarization orientation. SOLUTION: A laser beam entered into an optical fiber 1 is separated into two laser beams, whose polarization directions intersect orthogonally each other, using a polarizing prism 10. Then, the laser beam on one side of these separated laser beams is reflected by a mirror 13 and the polarization direction of the laser beam is rotated at 90 degrees by a λ/2 wavelength-plate 11. The laser beam in the rotated polarization direction is reflected by a mirror 13 and is led to a photosynthesizing means 12. On the other hand, the other laser beam separated by the prism 10 is inputted in the means 12 as it is and a synthesis of the two laser beams is conducted. The synthesized laser beam emitted by the means 12 is condensed by a lens 15 and the condensed laser beam is entered into a waveguide which gives a gain of a semiconductor amplifier 14 and is amplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization-independent semiconductor optical amplifier module for amplifying traveling-wave type semiconductor laser light mainly used as a light source for optical communication, optical applied measurement, optical information processing and the like. Is.

[0002]

2. Description of the Related Art FIG. 4 shows, for example, JP-A-5-299746.
FIG. 3 is a configuration diagram showing a conventional polarization-independent type semiconductor optical amplifier module disclosed in Japanese Patent Laid-Open Publication No. HEI-2003. In the figure, 1 is an optical fiber into which laser light is incident from the outside, and 2 is a wedge-shaped birefringent prism that separates the incident laser light according to the direction of the polarization plane. 3 is this wedge-shaped birefringent prism 2
Is a lens for converging each of the laser beams separated by 1., 4 is a first semiconductor optical amplifier that amplifies one of the laser beams condensed by the lens 3, and 5 is the other that is condensed by the lens 3. 2 is a second semiconductor optical amplifier that amplifies the laser beam. Reference numeral 6 is a lens for collecting the laser light amplified by each of the first semiconductor optical amplifier 4 and the second semiconductor optical amplifier 5, and 7 is a wedge-shaped birefringent prism for combining the collected laser light, Reference numeral 8 is an optical fiber for emitting the laser light combined by the wedge-shaped birefringent prism 7 to the outside. Reference numeral 9 denotes a package which incorporates these optical fibers 1 and 8, wedge-shaped birefringent prisms 2 and 7, lenses 3 and 6, and a first semiconductor optical amplifier 4 and a second semiconductor optical amplifier 5 to form the semiconductor optical amplifier module. is there.

[0003]

Since the conventional semiconductor optical amplifier module is configured as described above, two semiconductor optical amplifiers, a first semiconductor optical amplifier 4 and a second semiconductor optical amplifier 5, are used for amplifying laser light. Since each of the laser beams separated by the wedge-shaped birefringent prism 2 is incident on each of the semiconductor optical amplifiers 4 and 5, the intensity of the incident light must change from 0 to the maximum intensity. When the intensity of the incident light changes beyond the intensity that causes the gain saturation of the semiconductor optical amplifier, it is difficult to linearly amplify in the entire range, so the polarization direction of the laser light incident from the outside If the change occurs, there is a problem that the intensity of the laser light obtained by combining the amplified lights by the two semiconductor optical amplifiers 4 and 5 changes.

The present invention has been made in order to solve the above problems, and a single semiconductor amplifier is sufficient, and a polarization-independent semiconductor optical amplifier module in which the intensity of output laser light is stable is obtained. The purpose is to

[0005]

According to another aspect of the present invention, there is provided a semiconductor optical amplifier module in which one polarization direction of laser beams separated by polarization separation means and having polarization directions perpendicular to each other is polarized by polarization rotation means. It is rotated by 90 degrees, and the laser light and the other laser light separated by the polarization separation means are combined by the light combining means and amplified by the semiconductor optical amplifier.

A semiconductor optical amplifier module according to a second aspect of the present invention uses a polarization-maintaining fiber and one laser beam whose polarization direction is rotated by 90 degrees by a polarization rotating means,
The other laser beam that has been separated by the polarization separation means is guided to the photosynthesis means.

In the semiconductor optical amplifier module according to the third aspect of the present invention, when one of the laser beams separated by the polarization separating means is guided to the optical combining means by the polarization maintaining fiber, the polarization direction of the polarization maintaining fiber is changed. By twisting 90 degrees between the entrance and the exit, it also functions as a polarization rotation means.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below. Embodiment 1. 1 is a block diagram showing a semiconductor optical amplifier module according to Embodiment 1 of the present invention. In the figure, 1 is an optical fiber on which laser light from the outside is incident,
Reference numeral 8 is an optical fiber for emitting the laser light amplified by the semiconductor optical amplifier module to the outside, 9 is a package of the semiconductor optical amplifier module, and these are the same as those shown in FIG. Is equivalent to those of. Reference numeral 10 is a polarization prism as a polarization separation means for separating the laser light input from the optical fiber 1 into two laser lights having two polarization components whose polarization directions are orthogonal to each other. Reference numeral 11 is a λ / 2 wavelength plate as a polarization rotating means for rotating one polarization direction of the laser light separated by the polarization prism 10 by 90 degrees.
Reference numeral 12 is a light combining means for combining the laser light whose polarization direction is rotated by the λ / 2 wave plate 11 and the other laser light separated by the polarization prism 10. Reference numeral 13 reflects one of the laser light beams separated by the polarization prism 10 and
0 to λ / 2 wave plate 11 or λ / 2 wave plate 11
Is a mirror that guides the light from the photosynthesis means 12 to the photosynthesis means 12. Reference numeral 14 is a semiconductor optical amplifier that amplifies the laser light combined by the light combining means 12. Reference numeral 15 is a lens for focusing the laser light emitted from the light synthesizing means 12 on the optical semiconductor amplifier 14, and 16 is a lens for focusing the laser light amplified by the semiconductor optical amplifier 14 on the optical fiber 8. is there.

Next, the operation will be described. The small arrow in FIG. 1 indicates the polarization direction of the laser light, similarly to that in FIG. Here, when the semiconductor optical amplifier 14 is used, since the semiconductor optical amplifier 14 has a polarization characteristic for laser light, it is necessary to make the polarization direction of the incident laser light match the polarization direction of the semiconductor optical amplifier 14. . However, the laser light incident on the optical fiber 1 is randomly polarized, and the polarization direction thereof is the semiconductor optical amplifier 14.
Since they do not match the polarization directions of, the polarization directions of both must be matched in order to perform amplification with high gain.

Therefore, this embodiment 1 shown in FIG.
In the semiconductor optical amplifier module, the external laser light incident on the optical fiber 1 is first separated into two laser lights whose polarization directions are orthogonal to each other using the polarization prism 10. Next, one of the laser beams separated by the polarization prism 10 is reflected by the mirror 13 and guided to the λ / 2 wavelength plate 11, and the polarization direction of the λ / 2 wavelength plate 11 is changed by the polarization prism 10. It is rotated by 90 degrees so as to match the polarization direction of the other separated laser beam.
The laser light whose polarization direction is rotated by the λ / 2 wavelength plate 11 is reflected by the mirror 13 and guided to the light combining means 12. On the other hand, the other laser light separated by the polarization prism 10 is directly input to the light combining means 12. The light combining means 12 combines these two laser lights. In this way, laser light that matches the polarization characteristics of the semiconductor optical amplifier 14 is produced. The laser light emitted from the light synthesizing means 12 is condensed by the lens 15, is incident on the waveguide that gives the gain of the semiconductor optical amplifier 14, and is amplified. The laser light amplified by the semiconductor optical amplifier 14 is condensed by the lens 16, enters the optical fiber 8, and is emitted to the outside of the semiconductor optical amplifier module.

As described above, according to the first embodiment,
The polarization prism 10 separates the laser light into two laser lights whose polarization directions are perpendicular to each other, and one of the polarization directions is λ / 2.
The wavelength plate 11 rotates 90 degrees, and the light synthesizing means 12 synthesizes it with the other laser beam separated by the polarization prism 10 and then amplifies it by the semiconductor optical amplifier 14. Even if the polarization direction of the incident laser light changes, the intensity of the laser light having the same polarization direction incident on the semiconductor optical amplifier 14 does not change, so that a stable amplification factor can be obtained.

In the above description, the polarization prism is used as the polarization separating means and the λ / 2 wavelength plate is used as the polarization rotating means. However, the polarization separating means is a birefringent prism,
Other optical system equipment such as Fresnel ROM may be used as the polarization rotation means, and the same effects as those of the above-described embodiment are obtained. This also applies to Embodiments 2 and 3 described later.

Embodiment 2. 2 is a block diagram showing a semiconductor optical amplifier module according to a second embodiment of the present invention. As in the case of the first embodiment shown in FIG. 1, 1 is an optical fiber on which laser light is incident, and 8 is an optical fiber. An optical fiber for emitting laser light, 9 is a package, 10 is a polarization prism as a polarization separating means, and 11 is a λ as a polarization rotating means.
/ 2 wavelength plate, 12 is a light combining means for combining the laser light from the λ / 2 wavelength plate 11 and the laser light from the polarization prism 10, 14 is a semiconductor optical amplifier for amplifying the combined laser light, and 15 and 16 are lenses Is shown. Reference numeral 17 indicates a polarization direction of one of the laser beams separated by the polarization prism 10, which is rotated 90 degrees by a λ / 2 wavelength plate 11, and guides it to the light combining means 12 without changing the rotated polarization direction. It is a polarization maintaining fiber. Reference numeral 18 denotes a polarization plane maintaining fiber that guides the other laser beam separated by the polarization prism 10 to the light combining means 12 without changing its polarization direction. Reference numeral 19 is a lens that collects the laser light input from the optical fiber 1 and makes it enter the polarizing prism 10. Reference numeral 20 is a lens that collects the laser light whose polarization direction is rotated by the λ / 2 wavelength plate 11 and polarizes it. Reference numeral 21 denotes a lens which is incident on the wavefront holding fiber 17, and 21 is a lens which collects the other laser beam separated by the polarization prism 10 and makes it incident on the polarization maintaining fiber 18.

Next, the operation will be described. Optical fiber 1
The more incident laser light from the outside is condensed by the lens 19 and input to the polarization prism 10, and is separated into two laser lights having mutually perpendicular polarization directions. One of the laser beams separated by the polarization prism 10 has its polarization direction rotated by 90 ° by the λ / 2 wavelength plate 11, is condensed by the lens 20, and is incident on the polarization maintaining fiber 17. The polarization maintaining fiber 17 converts the incident laser light into
The light is guided to the photosynthesis means 12 without changing its polarization direction.
On the other hand, the other laser light separated by the polarization prism 10 is condensed by the lens 21 and is polarized by the polarization maintaining fiber 18
Is incident on. The polarization maintaining fiber 18 allows the incident laser light to be combined with the light combining means 1 without changing its polarization direction.
Lead to 2. Similarly to the case of the first embodiment, the two laser lights are combined by the light combining means 12 to produce a laser light that matches the polarization characteristics of the semiconductor optical amplifier 14, and the laser light is incident on the semiconductor optical amplifier 14. The light is amplified and emitted from the optical fiber 8 to the outside.

As described above, according to the second embodiment,
One of the laser beams whose polarization direction has been rotated by the λ / 2 wavelength plate 11 and the other laser beam which has been separated by the polarization prism 10 are respectively polarized plane maintaining fibers 17 or 18
Since the light is guided to the light combining means 12 by means of the above, there is no restriction on the arrangement of the polarization prism 10, the λ / 2 wavelength plate 11, the light combining means 12, etc. in the semiconductor optical amplifier module, and the adjustment of the optical system is facilitated. You can

Embodiment 3 3 is a block diagram showing a semiconductor optical amplifier module according to a third embodiment of the present invention. As in the case of the second embodiment shown in FIG. 2, 1 is an optical fiber on which laser light is incident, and 8 is An optical fiber for emitting a laser beam, 9 is a package, 10 is a polarization prism as a polarization separating means, 12 is a light combining means, 14 is a semiconductor optical amplifier, 15, 16, 19, 21 are lenses, and 18 is a polarization prism 10. A polarization-maintaining fiber that guides one of the separated laser beams to the light combining means 12 without changing the polarization direction thereof is shown. Further, 22 indicates that the polarization direction of the incident laser light is 90 degrees between the entrance and the exit.
The polarization prism 10 can be rotated by rotating
It is a polarization-maintaining fiber that guides the other laser beam separated by the above to the light combining means 12 by rotating the polarization direction thereof by 90 degrees, and this also realizes the function as the polarization rotating means. Reference numeral 23 denotes a lens that collects the other laser beam separated by the polarization prism 10 and makes it enter the polarization maintaining fiber 22.

Next, the operation will be described. Optical fiber 1
The more incident laser light from the outside is condensed by the lens 19 and input to the polarization prism 10, and is separated into two laser lights having mutually perpendicular polarization directions. One of the laser beams separated by the polarization prism 10 is condensed by the lens 21 and is incident on the polarization maintaining fiber 18. The polarization maintaining fiber 18 guides the incident laser light to the light combining means 12 without changing its polarization direction. On the other hand, the other laser beam separated by the polarization prism 10 is
It is condensed by the lens 23 and is incident on the polarization maintaining fiber 22. The polarization maintaining fiber 22 is twisted so that the polarization direction is rotated by 90 degrees between the entrance and the exit, so that the other laser light separated by the polarization prism 10 has its polarization direction. Is rotated 90 degrees and guided to the photosynthesis means 12. Similarly to the case of the first embodiment, the laser beam combining means 12 combines the two laser beams to produce a laser beam having the same polarization characteristic as that of the semiconductor optical amplifier 14, and the laser beam is generated.
It is amplified by 4 and emitted from the optical fiber 8 to the outside.

As described above, according to the third embodiment,
When one of the laser beams separated by the polarization prism 10 is guided to the light combining means 12 by the polarization maintaining fiber 22, the polarization direction of the polarization maintaining fiber 22 is 90 between the entrance and the exit.
Since the function as the polarization rotation means is realized by twisting the rotation, the polarization rotation means such as the λ / 2 wavelength plate 11 can be omitted and the adjustment can be facilitated.

[0019]

As described above, according to the first aspect of the present invention, one of the two laser beams separated by the polarization separation means and having mutually orthogonal polarization directions is polarized by the polarization rotation means. Since it is rotated by 90 degrees and sent to the photosynthesis means, the other laser light is sent to the photosynthesis means as it is without rotating the polarization direction and synthesized, and the obtained synthesized laser light is amplified by the semiconductor optical amplifier. Only one semiconductor optical amplifier is required, and since the laser light whose polarization direction and intensity are constant is incident on the semiconductor optical amplifier, the output stability of the amplified light is maintained and the incident laser light is polarization independent. This has the effect of obtaining a semiconductor optical amplifier module in which the output does not fluctuate depending on the polarization direction.

According to the second aspect of the present invention, one laser beam whose polarization direction is rotated by 90 degrees by the polarization rotating means and the other laser beam which is still separated by the polarization separating means are maintained in the polarization plane. Since the optical fiber is used to guide the light to the light synthesizing means, the degree of freedom in the arrangement position of the optical system device in the semiconductor optical amplifier module is increased, and the optical system can be easily adjusted.

According to the third aspect of the present invention, when one of the laser beams separated by the polarization splitting means is guided to the light combining means by the polarization maintaining fiber, the polarization directions of the polarization maintaining fiber are the entrance and the exit. Since the twisting is performed so as to rotate 90 degrees with respect to the mouth, this polarization-maintaining fiber also functions as a polarization rotating means, so that it is possible to reduce the number of parts of the optical system, It also has the effect of facilitating system adjustment.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a semiconductor optical amplifier module according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a semiconductor optical amplifier module according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a semiconductor optical amplifier module according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram showing a conventional semiconductor optical amplifier module.

[Explanation of symbols]

10 polarization prism (polarization separating means), 11 λ / 2 wavelength plate (polarization rotating means), 12 light combining means, 14 semiconductor optical amplifiers, 17, 18 polarization maintaining fiber, 22
Polarization preserving fiber (polarization rotating means).

Claims (3)

[Claims] 1. A polarization splitting means for splitting a laser light incident from the outside into two laser light having polarization components whose polarization directions are perpendicular to each other, and one polarization of the laser light split by the polarization splitting means. A polarization rotating means for rotating the direction by 90 degrees, a light combining means for combining the laser light whose polarization direction is rotated by the polarization rotating means and the other laser light separated by the polarization separating means, and the light combining means. Semiconductor optical amplifier module including a semiconductor optical amplifier that amplifies the generated laser light. 2. One of the laser beams separated by the polarized light separating means and having the polarization direction rotated by 90 degrees by the polarized light rotating means, and the other laser light separated by the polarized light separating means, The semiconductor optical amplifier module according to claim 1, wherein the polarization maintaining fiber guides the light to the optical combining means. 3. The polarization direction of the polarization maintaining fiber, which guides one of the laser beams separated by the polarization separation unit to the photosynthesis unit by the polarization rotation unit, is 90 degrees between the entrance and the exit. The semiconductor optical amplifier module according to claim 1, which is realized by twisting.