JPH03225326A - Semiconductor laser amplifying device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser amplification device that amplifies optical signals as they are without converting optical signals into electrical signals in optical communications.

(Prior Art) It has been known that by providing an antireflection film on both optical signal output end faces of a semiconductor laser device, the semiconductor laser device can be used not as an optical oscillator but as an optical signal amplifier.

FIG. 4 is a perspective view showing a simplified configuration of the semiconductor laser device 1 used as an amplifier. In FIG. 4, a semiconductor laser device 1 has a TE wave whose electric field is polarized in the direction of the junction surface 3 of the active layer 2 (width direction) and a magnetic field polarized in the direction of the junction surface 3 of the active layer 2 (width direction). ) polarized T
There are two propagation modes called M waves. 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 bonding surface), and the TE wave and T
Confinement coefficient rTE of semiconductor laser device 1 for M waves
and rTM are different. Therefore, in a semiconductor laser amplification device using a semiconductor laser element l having such shape characteristics, the gain GTE for TE waves is about 3 dB to 10 dB larger than the gain GTM for TM waves (for example, Journal of Optical Com.
communications 1989, Volume 4, page 57, or IEEE Journal of LigttWaV
e Technology, Vol. 6, p. 536, 1988). However, in commonly used single mode optical fibers, it is not possible to maintain a constant polarization state of the optical signal propagating within the optical fiber, and in conventional semiconductor laser amplification devices, the polarization state of the optical signal propagating in the optical fiber cannot be maintained constant. There was a drawback that the gain of the semiconductor laser amplification device varied greatly depending on the polarization state.

(Problems to be Solved by the Invention) The present invention eliminates the polarization dependence of the gain of an optical amplification device using a semiconductor laser element, which inevitably has an asymmetric shape, which occurs when propagating through a normal single mode optical fiber. An object of the present invention is to provide a semiconductor laser amplification device that always has a constant gain for an input optical signal in an arbitrary polarization state.

(Means for Solving the Problems) A semiconductor laser amplification device of the present invention splits an optical signal that has passed through an optical circulator into two beams, a first beam and a second beam whose polarization directions are orthogonal to each other, using a polarization beam splitter. , the first and second beams are passed through a polarization-maintaining fiber so that the polarization directions of these two beams are in the direction of the junction surface of the semiconductor laser device, which functions as an optical amplifier and has anti-reflection coatings on both end faces. The second beam is made to enter the active layer of the semiconductor laser device from both directions so that the first and second beams receive the same gain from the semiconductor laser device, and then are amplified by the semiconductor laser device. The first and second beams are combined by the polarization beam splitter via the polarization-maintaining fiber, passed through the optical circulator, and output, and the light incident on the semiconductor laser amplification device is To prevent the gain of an amplifier from depending on the polarization state of a signal.

The present invention is different from conventional semiconductor laser amplification devices in which the gain varies greatly depending on the polarization state of an incident optical signal.

(Example) Before describing the embodiments of the present invention in detail, first, an example of a polarizing beam splitter and an optical circulator, which are used in the optical circuit of the present invention and are important optical components, is shown in Figs. 2 and 3. The outline is explained below.

The polarizing beam splitter consists of a dielectric multilayer film 4 and two prisms 5.
, 6, the prism 5 is provided with an entrance lower part and an exit port 8, and the prism 6 is provided with an exit port 9. When light in an arbitrary polarization state is incident on the input lower part, the light component polarized perpendicular to the plane of the paper in FIG. It is emitted.

On the other hand, the light component polarized parallel to the plane of the paper in Figure 2 (hereinafter referred to as P
It's called a wave. ) passes through the dielectric multilayer film 4 and is emitted from the exit port 9 . By the way, conversely, when an S wave is incident on the emission aperture 8, it is reflected by the dielectric multilayer film 4, and when a P wave is incident on the emission aperture 9, it is transmitted through the dielectric multilayer film 4, and both of them are reflected by the dielectric multilayer film 4. It is emitted from. In this way, the polarization beam splitter 10 not only functions as a polarization splitter that splits light in any polarization state into S waves and P waves whose polarization directions are orthogonal to each other, but also functions as a polarization beam splitter that splits light in an arbitrary polarization state into S waves and P waves whose polarization directions are orthogonal to each other. S wave and P
It also functions as a polarization coupler that combines waves.

Next, the optical circulator 11 generally has four ports as shown in FIG.
Light incident from the third port 14 is emitted from the fourth port 15, light incident from the fourth port 15 is emitted from the first port 12, and light incident from the fourth port 15 is emitted from the first port 12. (The configuration of an optical circulator that has this function for light in any polarization state is, for example, Electronics Letters.
197B VO1, 15N (see page L25.83).

FIG. 1 is a block diagram of an embodiment of the present invention, in which an optical signal guided through an optical fiber 16 is inputted into the optical circulator 11 through the first port 12, outputted from the second port 13, and then optically transmitted through the optical fiber 16. The light is guided through a fiber 18 and input into the polarization beam splitter 10 from the input lower part. The optical signal input to the polarization beam splitter 10 is split into S waves and P waves whose polarization directions are orthogonal to each other. The light is bidirectionally input from 9 through a polarization maintaining fiber 20 to a semiconductor laser device 21 which has antireflection films on both end faces and functions as an optical amplifier. At this time, the two optical signals input to the semiconductor laser device 21 from both directions are connected to the polarization-maintaining fiber 19° so that the polarization directions of both optical signals are in the direction of the bonding surface of the active layer of the semiconductor laser device 21. The main axis direction of 20 is adjusted. Since the principal axes of the polarization-maintaining fibers 19 and 20 are adjusted as described above, the optical signal input from the polarization-maintaining fiber 19 to the semiconductor laser element 21 and amplified is guided through the polarization-maintaining fiber 20. After being waved, it enters the polarization beam splitter 10 as a P wave from the exit port 9. Similarly, an optical signal input from the polarization-maintaining fiber 20 to the semiconductor laser element 21 and amplified is input to the polarization beam splitter 10 from the output port 8 as an S wave.

As explained above, the polarization beam splitter lO
Since it also functions as a polarization coupler that combines waves, the two optical signals that are input from both directions to the semiconductor laser element 21 and amplified are combined by the polarization beam splitter IO and sent from the input lower to the optical fiber 18. The wave is guided and inputted into the optical circulator 11 through the second port 13, inputted into the optical fiber 17 through the third port 14, and guided through the optical fiber 17.

Pl is the power of the optical signal that passes through the optical circulator 11 from the optical fiber 16 and is input to the polarization beam splitter 10.
+, polarization maintaining fiber 19 by polarization beam splitter lO
If the power of the optical signal branched to the side is Pl, and the power of the optical signal branched to the polarization maintaining fiber 20 side by the polarization beam splitter IO is P2, then P +-= P ++ P
2 (1).

As described above, both the optical signal branched to the polarization-maintaining fiber 19 side and the optical signal branched to the polarization-maintaining fiber 20 side by the polarization beam splitter IO are output from the semiconductor laser element 21 with the same gain GTE. Since it is amplified, the power P of the optical signal that is multiplexed by the polarization beam splitter 10, passes through the optical circulator 11, and is input to the optical fiber 17
out is P out=GTxX P ++ GT
EX P is -CyrzX(P ++ Pz) = GTEX P l++ (2).

Depending on the various polarization states of the optical signal input from the optical fiber 16 to the optical circulator 11, the polarization maintaining fiber 1
The value of the power P1 of the optical signal branched to the polarization maintaining fiber 20 side and the value of the power P2 of the optical signal branched to the polarization maintaining fiber 20 side change, but the value of the power Ptn of the input optical signal is constant. Therefore, from equation (2), optical circulator 1
The power P of the optical signal output from 1 to the optical fiber 17,
. t is GTE times the input signal power Pin, and is always constant regardless of the polarization state of the optical signal input from the optical fiber 16 to the optical circulator 11.

When semiconductor laser amplification devices are connected in multiple stages in series and used, in one semiconductor laser amplification device, return light of the signal light due to reflection from the semiconductor laser amplification device in the next stage and subsequent stages,
It has also been pointed out that the amplified spontaneous emission light generated by the semiconductor laser element of the semiconductor laser amplification device in the next and subsequent stages is injected into the semiconductor laser element 21 of the semiconductor laser amplification device and generates noise. The above-mentioned light guided through the optical fiber 17 from the semiconductor laser amplification device in the next stage and subsequent stages is input to the optical circulator 11 from the third port 14, so it goes to the fourth port 15 as described above. , it does not reach the semiconductor laser element 21 of the semiconductor laser amplification device, and it is possible to prevent the above-described noise from occurring in the semiconductor laser element 21.

(Effects of the Invention) As explained above, the semiconductor laser amplification device of the present invention has a constant gain regardless 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, when semiconductor laser amplifier devices are connected in multiple stages, there is an effect that the present invention is not affected by return light from the semiconductor laser amplifier devices in the next stage and subsequent stages, which causes noise.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a simplified block diagram of a polarization beam splitter used in an optical circuit in a semiconductor laser amplifier, and Fig. 3 is a diagram of a semiconductor laser amplifier. FIG. 4 is a perspective view showing a simplified configuration of a semiconductor laser element used in a semiconductor laser amplification device. ■, 21... Semiconductor laser device 2... Active layer of semiconductor laser device 3... Bonding surface of active layer of semiconductor laser device 4... Dielectric multilayer film 5.6... Prism 7... - Inlet port 8.9 of polarized beam splitter...Output port 10 of polarized beam splitter...Polarized beam splitter 11...Optical circulator 12...First port 13 of optical circulator...Light Second port 14 of the circulator...Third port 15 of the optical circulator...Fourth port 16, 17.18 of the optical circulator...Optical fibers 19, 20...Polarization maintaining fiber Fig. 1 1O- (31 optical beam 4 interposer 11---optical circulator f6.f7.l#=-t77(/'( IQ, 20-(Jug degree relation special 7 eye 8. 21---1 sheep reso element Figure 2 7-4 Light do-A minute entrance port θ, q-it B 4-hibiki's baud ro

Claims (1)

[Claims] 1. Connect the second port of the optical circulator with the first port as the input port and the third port as the output port and the polarized beam splitter using an optical fiber, and convert the optical signal input from the optical fiber into the polarized beam. A splitter splits the beam into two beams whose polarization directions are orthogonal to each other, and the two split beams are sent from both sides to a semiconductor laser element with anti-reflection coatings on both end faces via polarization-maintaining fibers. A semiconductor laser amplification device characterized in that both beams are made incident such that their polarization directions are in the direction of a junction surface of an active layer of the semiconductor laser element.