JPH0335576A - Semiconductor laser amplifier - Google Patents

Abstract

PURPOSE:To see that the gain of an amplifier does not depend on the polarized conditions of an incoming optical signal by entering each beam, where the polarizing direction of the diverged beam crosses each other at right angles, into a semiconductor laser element while rotating it so that the direction of polarization may be the same, and uniting the wave of each amplified output after rotating it so that the polarizing direction may cross each other at right angles, and then outputting it. CONSTITUTION:First and second polarized beam couplers 12 and 15 are arranged so that the polarizing direction of a beam, which is diverged with a polarized beam divider 10 and has passed the first polarized beam coupler 12, and the polarizing direction of a beam, which is diverged with the polarized beam divider 10 and has passed the second polarized beam coupler 15, may accord with each other. A semiconductor laser element 27, where nonreflective films are provided at both ends, is arranged on a light axis, where the emission port of the first polarized beam coupler 12 and the emission port of the second polarized beam coupler 15 are according with each other, so that the junction face may make an inclination of 45 deg. with the polarizing directions of the beams which have passed the first and second polarized beam couplers 12 and 15, and first and second Faraday rotation elements 28 and 29 of 45 deg. in rotation angle are arranged between the semiconductor laser element 27 and the first beam coupler 12 and between the semiconductor element 27 and the second polarized beam coupler 15, respectively.

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention relates to a semiconductor laser amplification device that amplifies an optical signal as it is without converting it into a commercial signal in optical signal transmission. "Prior Art" It has long been known that by providing an anti-reflection film on both end faces of a semiconductor laser device that outputs optical signals, the semiconductor laser device can be used not as an optical oscillator but as an optical signal amplifier. ing. FIG. 5 is a simplified configuration diagram of a semiconductor laser element l used as an amplifier. In the propagation mode of the semiconductor laser device 1, the electric field is polarized in the width direction of the junction surface 3 of the active layer 2.
There are two types: a wave propagation mode and a TM wave propagation mode in which the magnetic field is polarized in the width direction of the bonding surface 3 of the active layer 2. In general, the active layer 2 of the semiconductor laser device 1 has an asymmetric shape in which the width is several times the thickness (in the direction perpendicular to the junction surface 3), and the confinement coefficient I of the semiconductor laser device 1 for TE waves and TM waves is 'TE and FTM are different. Therefore, in a semiconductor laser optical amplification device using a semiconductor laser element l having such shape characteristics, the gain G for the TE wave is
TE has a gain of 3 to 10 dB compared to GTM for TM waves.
It's getting bigger. In addition, this matter is 4, for example, Jo
Urnal of 0ptical Com5unic
ations 1989, Vol. 4, p. 57, or IEE
E Journal or Lightwava Tec
hnology, Vol. 6, p. 536, 1988. ``Problem to be solved by the invention'' However, with the commonly used single mode optical fiber, it is not possible to maintain a constant polarization state of the optical signal propagating within the optical fiber. When amplifying the output light of a single mode optical fiber using an optical amplifier, the amplification gain varies greatly depending on the polarization state of the incident optical signal. There was a problem with doing so. This invention was made in view of the above-mentioned circumstances, and it eliminates the polarization dependence of the gain of an optical amplification device using a semiconductor laser element that inevitably has asymmetrical shape characteristics, and propagates through a normal single mode optical fiber. It is an object of the present invention to provide a semiconductor laser amplification device that always has a constant gain for an input optical signal in an arbitrary polarization state generated when ``Means for Solving the Problems'' In order to solve the above problems, the first invention provides a system in which a manually generated optical signal is divided into two beams whose polarization directions are orthogonal to each other using a polarization beam splitter.
One beam is guided to the first entrance of the first polarization beam combiner by a waveguide capable of maintaining the polarization state, and the other beam is guided to the first entrance of the first polarization beam combiner by a waveguide capable of maintaining the polarization state. A waveguide capable of maintaining the polarization state connects the second input port of the first polarized beam combiner to the first input port of a third polarized beam combiner. to form an optical circuit that connects the second input port of the second polarization beam combiner to the second input port of the third polarization beam combiner using a waveguide capable of maintaining the polarization state.
The optical axes of the exit of the polarized beam combiner and the exit of the second polarized beam combiner are aligned, and the polarization direction of the beam split by the polarized beam splitter and passed through the first polarized beam combiner and the above The first and second polarized beam combiners are arranged so that the polarization directions of the beams split by the polarized beam splitter and passed through the second polarized beam combiner are the same, and the exit port of the first polarized beam combiner is A semiconductor laser element having anti-reflection films on both end faces is placed on the optical axis where the output apertures of the first and second polarized beam combiners coincide with each other, and the bonding surface thereof is connected to the first
and the second polarization beam combiner so as to form an inclination of 45 degrees with the polarization direction of the beam that has passed through the second polarization beam combiner, and the rotation angle is 45 degrees.
a first and a second Faraday rotary element of a degree are respectively disposed between the semiconductor laser element and the first polarization beam combiner and between the semiconductor laser element and the second polarization beam combiner; It is characterized by Further, a second invention provides a structure between the semiconductor laser element provided with a non-reflection film on both end faces and the first Faraday rotation element, and between the semiconductor laser element and the second Faraday rotation element. The present invention is characterized in that first and second analyzers that transmit only light polarized in the direction of the bonding surface of the semiconductor laser element are respectively disposed. "Operation" According to the first invention, the beams split by the polarizing beam splitter and having orthogonal polarization directions are rotated so that the polarization directions are the same, and are incident on the semiconductor laser element. The amplified outputs are rotated so that their polarization directions are orthogonal to each other, and then combined and output. Therefore, the gain of the amplifying device does not depend on the polarization state of the optical signal incident on the conductive laser amplifying device. Further, according to the semiconductor laser amplification device of the second invention, when a plurality of stages of the semiconductor laser amplification devices are connected in cascade, even if there is return light from the subsequent stage amplifier to the previous stage amplifier, this return light Since the light based on the above is blocked by the first and second analyzers, it does not enter the semiconductor laser element. Therefore, generation of noise due to returned light is prevented. r Real 1111JN Hereinafter, the present invention will be described in detail with reference to the drawings.

First Embodiment FIG. 1 is a block diagram of a semiconductor laser amplification device according to a first embodiment of the present invention. Furthermore, FIG. 2 shows an example of a polarization light beam combiner, which is a large number of important optical parts used in this apparatus. First, with reference to FIG. 2, the outline of the polarization beam combiner will be explained. In the polarized beam combiner, a dielectric multilayer film 4 is sandwiched between two prisms 5 and 6, and the prism 5 is provided with a first entrance port 7 and an exit port 9, and the prism 6 is provided with a second entrance port 8. It is. In Figure 2, light polarized perpendicular to the plane of the paper (
When an S wave (hereinafter referred to as an S wave) is incident on the first entrance port 7 , it is reflected by the dielectric multilayer film 4 and exits from the exit port 9 . Next, in FIG. 2, when light polarized parallel to the plane of the paper (hereinafter referred to as P wave) is incident on the second entrance port 8, this P wave is transmitted through the dielectric multilayer film 4, and the P wave is transmitted through the dielectric multilayer film 4. The light is combined with the S wave that is incident on the input aperture 7 and reflected by the dielectric multilayer film 4, and is emitted from the output aperture 9. By the way, when light having an arbitrary polarization state is incident on the exit port 9 of the polarized beam combiner, the component of the incident light polarized perpendicularly to the plane of the paper is sent to the first entrance port 7 of the prism 5 as an S wave.
The component of the incident light that is emitted from and polarized parallel to the plane of the paper is P
The light is emitted from the second entrance 8 of the prism 6 as a wave. In this way, the polarization beam combiner not only functions as a combiner for S waves and P waves whose polarization directions are orthogonal to each other, but also functions as a combiner for S waves and P waves whose polarization directions are orthogonal to each other.
Light with any polarization state is S whose polarization directions are orthogonal to each other.
It also has the ability to branch into waves and P waves. Next, the present embodiment will be described with reference to FIG. The input optical signal is split into two beams whose polarizations are perpendicular to each other by a polarization beam splitter IO, and one beam is sent to a first polarization beam combiner 1 by a polarization-maintaining fiber 11.
Guided by 2. Here, the polarizing beam combiner 1
The light is input to the first entrance port 13 of No. 2. The other beam B is guided to a second polarization beam combiner 15 by a polarization maintaining fiber 14. Here, the beam is input to the first entrance 16 of the polarization beam combiner 15 l 5 such that the polarization direction of the beam becomes the S-wave direction of the polarization beam combiner 15. The input port 17 of the second polarization beam combiner 18 and the second input port 19 of the third polarization beam combiner 18 are connected by a polarization-maintaining fiber 20, and at this time, the polarization-maintaining fiber 20 12 Ps
The wires are connected so that the wave direction is the P wave direction of the third polarization beam combiner 18. The second entrance 2t of the second polarization beam combiner 15 and the first entrance of the third polarization beam combiner 18
is connected to the input port 22 of the polarization-maintaining fiber 23, and at this time, the polarization-maintaining fiber 23 connects the P-wave direction of the second polarization beam coupler 615 to the third polarization beam coupler 1.
The wires are connected in the direction of the S wave of 8. The exit port 24 of the first polarized beam combiner 12 and the exit port 25 of the second polarized beam combiner 15 are on the same optical axis 26, and the S-wave direction and the exit port 25 of the first polarized beam combiner 12 are located on the same optical axis 26. The two polarization beam couplers 15 are arranged so that the S-wave directions of the two polarization beam combiners 15 coincide with each other. Arranged on the optical axis 26 are a semiconductor laser element 27 which has anti-reflection films on both end faces and acts as an optical amplifier, and two Faraday rotary elements 28 and 29 having a rotation angle of 45 degrees. At this time, the direction of the bonded surface of the semiconductor laser element 27 is 45.degree.
It is placed so that it has an inclination of degrees. FIG. 3 shows the beam propagation situation between the exit port 24 of the first polarized beam combiner 12 and the exit port 25 of the second polarized beam combiner 15. In FIG. 3, the optical axis 26 is the Z axis, and the P wave direction of the first and second polarization beam combiners 12.15 is the X axis.
Axial, first and second polarization beam combiner 12. l 5
The S wave direction is taken as the Y axis. The bonding surface of the semiconductor laser element 27 is perpendicular to the plane of the paper, and in FIG. 3, the direction of this bonding surface is indicated by a broken line. The beam split by the polarization beam splitter 1O and incident on the first entrance port 13 of the first polarization beam combination 512 is polarized in the Y-axis direction at the exit port 24 of the polarization beam combination 512 (Fig. 3). (a)
condition). When this beam passes through the Faraday rotation element 28, the polarization direction of the beam is rotated by 45 degrees and becomes the direction of the broken line (the state shown in FIG. 3(b)), and the semiconductor laser element 2
Since this beam coincides with the junction surface of No. 7, when this beam propagates within the active layer of the semiconductor laser element 27, it is amplified by the gain GTE. When the beam that has propagated through the active layer of the semiconductor laser element 27 passes through the Faraday rotation element 29, the polarization direction of the beam is further rotated by 45 degrees and becomes aligned with the X axis (
Figure 3 (C) state). In this way, the beam is polarized in the X-axis direction, that is, in the P-wave direction of the second polarized beam combiner 15, and enters the exit port 25 of the second polarized beam combiner 15, so that Thus, the light is emitted from the second entrance 21 of the second polarization beam combiner 15 in a state polarized in the P-wave direction. On the other hand, the other beam split by the polarization beam splitter 10 and incident on the first entrance port 16 of the second polarization beam combiner 315 is polarized in the Y-axis direction at the exit port 25 of the polarization beam combiner 15. There is (3rd
Figure (a) state). When this beam passes through the Faraday rotary element 29, the polarization direction of the beam becomes the direction of the broken line (the state shown in FIG. 3(b)) and coincides with the bonding surface of the semiconductor laser element 27, so that this beam passes through the semiconductor laser element 27.
When the signal propagates through the active layer of No. 7 by 4°, it is amplified by the gain GTE. When the beam propagated through the active layer of the semiconductor laser device 27 passes through the Faraday rotation element 28, the polarization direction of the beam changes to X! becomes d+ (state shown in Fig. 3(c)). In this way, the other beam enters the exit port 24 of the first polarized beam combiner 12 while being polarized in the X-axis direction, that is, in the P-wave direction of the first polarized beam combiner 12. As mentioned above, the second polarization beam combination of the first polarization beam a12
The light is emitted from the entrance 17 in a polarized state in the P-wave direction. The beam emitted from the second input port 21 of the second polarized beam combiner 15 in a polarized state in the P-wave direction propagates through the polarization maintaining fiber 23, and its polarization direction is changed to the third polarized beam combiner 2Sts. is inputted into the first entrance 22 of the third polarization beam combiner 18 in the S-wave direction. Furthermore, the beam that is polarized in the P-wave direction and exits from the second entrance 17 of the first polarized beam combiner 12 propagates through the polarization-maintaining fiber 20, and its polarization direction becomes the third polarized beam. The beam becomes the P-wave direction of the coupler 18 and is input to the second entrance 19 of the third polarized beam coupler 18 . In this way, the two beams whose polarization directions are perpendicular to each other, split by the polarization beam splitter 10, are amplified with the same gain GTE from the semiconductor laser element 27, which is provided with an anti-reflection film on both end faces and acts as an optical amplifier. are received, combined by a third polarization beam combiner 18, and output. The power of the optical signal input to the polarization beam splitter lO is P
in, polarization maintaining fiber 1 by polarization beam splitter 10
If the power of the optical signal branched to the polarization maintaining fiber 14 side is P3, and the power of the optical signal branched to the polarization maintaining fiber 14 side by the polarization beam splitter Bto is P, then Pin=Pl+P, (1 ). As described above, both the optical signal branched to the polarization-maintaining fiber 11 side by the polarization beam splitter 10 and the optical signal branched to the polarization-maintaining fiber 14 side are amplified by the same gain GTE from the semiconductor laser element 27. Therefore, the power P out of the optical signal output from the third polarization beam combiner 18 is P out = G'rEX P , + GTE X P
2-〇TEX (P, + P = GTExPin - (2). Depending on the various polarization states of the optical signal input to the polarization beam splitter IO, Although the values of the power P of the optical signal to be branched and the power Pt of the optical signal branched to the polarization maintaining fiber 14 side change, the power Pin of the input optical signal is constant, and therefore, the formula From (2), the power P out of the optical signal output from the third polarization beam combiner 18 is GTE times the input signal power Pin, and is dependent on the polarization state of the optical signal input to the polarization beam splitter IO. It is always constant.

[Second Embodiment] FIG. 4 shows a second embodiment of the present invention, in which two analyzers 30 and 31 that transmit only the light polarized in the direction of the junction surface of the semiconductor laser element 27 are connected to the semiconductor laser element 27. 27 and Faraday rotary elements 28 and 29, respectively, the other configurations are the same as the embodiment shown in FIG. When using semiconductor laser amplification devices connected in tandem in multiple stages, in a certain semiconductor laser amplification device,
The return light of the signal light that returns by reflection from the semiconductor laser amplification device in the next stage and the subsequent stage and the amplified natural number destination generated by the semiconductor laser element of the semiconductor laser amplification device in the next stage and subsequent stages are the semiconductor of the semiconductor laser amplification device. It has been pointed out that it is injected into the laser device and generates noise. When light from the semiconductor laser amplification device of the next stage and subsequent stages as described above enters the semiconductor laser amplification device of the embodiment shown in FIG.
This light is branched by the third polarization beam combiner 18 into first light (P wave) and second light (S wave) whose polarization directions are orthogonal to each other, and each is connected to a polarization maintaining fiber 20. Propagating within the fiber 23, the first polarized beam combiner 12
and enters the second polarized beam combiner 15. At this time,
The first light incident on the first polarized beam combination 512 is
as a P wave to the polarization beam combiner 12;
The second light incident on the polarization beam coupler 15 is incident on the polarization beam coupler 15 as a P wave. The first light incident on the polarization beam coupler 12 as a P wave is output from the polarization beam coupler 12 in the polarization state shown in FIG. 3(c), and is rotated by 45 degrees by the Faraday rotation element 28. , the analyzer 30 includes a semiconductor laser element 27.
The incident polarized light is perpendicular to the junction surface of the analyzer 30.
is blocked and does not reach the semiconductor laser element 27. The second light incident on the polarization beam combiner 12 as a [l] wave passes through the analyzer 3 as in the case of the first light described above.
It is blocked by I and does not reach the semiconductor laser element 27. "Effects of the Invention" As explained above, the semiconductor laser amplification device of the first invention has a constant gain independent of the polarization state of the input optical signal. Therefore, it has the great effect of being applicable to optical communication systems using ordinary single mode optical fibers that cannot maintain the polarization state of optical signals. Furthermore, according to the second invention, when semiconductor laser amplifier devices are connected in multiple stages, it is possible to block the return light from the semiconductor laser amplifier devices in the next stage and subsequent stages, which causes noise.

[Brief explanation of drawings]

1 is a block diagram showing the configuration of a semiconductor laser amplification device according to a first embodiment of the present invention; - FIG. 2 is a diagram showing a simplified configuration of a polarization beam combiner used in the same embodiment; FIG. 3 is a diagram explaining the beam propagation situation between the first and second polarization beam couplers in the same embodiment, and FIG. 4 is a block diagram showing the configuration of a semiconductor laser amplification device according to the second embodiment of the present invention. , FIG. 5 is a diagram showing a simplified configuration of a semiconductor laser element used in a semiconductor laser amplification device. 1.27... Semiconductor laser device, 2... Active layer of semiconductor laser device, 3... Active junction surface of semiconductor laser device, 4... Dielectric multilayer film, 5.6... Prism , 7.13, 16.
22... First entrance port of polarized beam combiner, 8.17.19.21... Second entrance port of polarized beam combiner, 9 24.25... Output port of polarized beam combiner , lO
... Polarization beam splitter, 11 14 20.23 ... Polarization maintaining fiber, 12
．． 15.18...Polarization beam coupler, 26...Optical axis,
28.29... Faraday rotation element, 3031...
analyzer

Claims (2)

[Claims] (1) The input optical signal is split into two beams whose polarization directions are orthogonal to each other by a polarization beam splitter, and one of the beams is sent to the first polarization beam combiner using a waveguide that can maintain the polarization state. The other beam is guided to the first entrance of the second polarized beam combiner by a waveguide capable of maintaining the polarization state, and the second beam of the first polarized beam combiner is guided to the first entrance of the second polarized beam combiner.
The input port of the second polarization beam combiner is connected to the first input port of the third polarization beam combiner by a waveguide capable of maintaining the polarization state, and the second input port of the second polarization beam combiner is connected by a waveguide capable of maintaining the polarization state. An optical circuit is formed that connects the second input port of the third polarized beam combiner, and the output port of the first polarized beam combiner connects to the second input port of the third polarized beam combiner.
The optical axes of the output ports of the polarized beam splitter are made to coincide with each other, and the polarization direction of the beam split by the polarized beam splitter and passed through the first polarized beam splitter and the second polarized light split by the polarized beam splitter are The first and second polarized beam combiners are arranged so that the polarization directions of the beams passing through the beam combiners match, and the exit port of the first polarized beam combiner and the exit port of the second polarized beam combiner are arranged. A semiconductor laser element with anti-reflection films on both end faces is placed on the coincident optical axes of the semiconductor laser element, and its bonded surface is tilted at 45 degrees with the polarization direction of the beam that has passed through the first and second polarization beam combiners. A first and a second Faraday rotary element having a rotation angle of 45 degrees are arranged between the semiconductor laser element and the first polarized beam coupler, and between the semiconductor laser element and the second polarized beam combiner. A semiconductor laser amplification device characterized in that the semiconductor laser amplification device is arranged between a beam combiner and a beam combiner. (2) A semiconductor laser element is provided between the semiconductor laser element provided with a non-reflection film on both end faces and the first Faraday rotation element, and between the semiconductor laser element and the second Faraday rotation element. 2. The semiconductor laser amplification device according to claim 1, further comprising first and second analyzers that transmit only light polarized in the direction of the junction surface.