JPS59117285A - Optical amplifier circuit - Google Patents

Abstract

PURPOSE:To make it possible to ease dependency on wavelengths, by utilizing semiconductor laser, which indicates optical bistability. CONSTITUTION:An injecting DC Ib is applied to a P side electrode 101 of a semiconductor laser 100 by an electric circuit 200, so that the Ib is set in the vicinity of a laser oscillation starting current threshold value I1 between I1 and a stopping current threshold value I2. A light signal 103 is branched by a branching circuit 104. An injecting light signal 105 is injected into a cleavage surface 108 in an active layer 107 by a coupling circuit 201. When the transduced value of a current by light excitation exceeds the difference between I1 and Ib, laser oscillation occurs and an ON state is obtained. Meanwhile, a trigger pulse current generating light signal 106 generates a trigger pulse current Ip, whose sign is reverse to that of Ib, through an electric circuit 202. The current Ip is delayed by a 1/4 period of the first light signal from the maximum value of the light signal 106. The current Ip is applied to the P-side electrode 101. By the trigger pulse current Ip, the semiconductor laser 100 is changed into the OFF state from the ON state. By the repetition of this procedure, the light signal is amplified by about several hundred times - thousand times.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical amplification circuit for surface amplifying optical signals. In optical fiber communication systems capable of long-distance, high-capacity transmission, 5.5
Can transmit over distances of 0 km or more without relaying. As a result, the use of submarine optical transmission for communication between remote islands and the main island is being put into practical use.

In order to use this for intercontinental communications, repeaters must be installed between the optical fibers to amplify the weakened optical signals. In this case, the complicated method of converting the optical signal into an electrical signal, amplifying it, and then converting it back into an optical signal is used. For this reason, repeaters, which are essential for long-distance optical communications, are complex, large, and consume high power, and they also perform optical-to-electrical conversion, creating problems in improving reliability. Therefore, as a countermeasure to this problem, without converting the optical signal into an electrical signal,
A method of directly amplifying the light is being considered. For example, as reported by Mr. Mukai et al. in the 1982 National Conference of the Institute of Electronics and Communication Engineers, Volume 4, No. 820, a normal Optical amplification is achieved by optically injecting and synchronizing an optical signal from an optical fiber into a semiconductor laser. This made it possible to realize a small repeater with low power consumption, but it was necessary to match the axial mode of the wavelength of the semiconductor laser and the optical signal to be injected, and to do so, temperature control was required with an accuracy of about ±001°C. Is required. Therefore, such optical repeaters that are extremely sensitive to temperature have reliability problems.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide an optical amplification circuit that is less dependent on wavelength.

The configuration of the optical amplification circuit according to the present invention is as follows: Laser oscillation starting current threshold (1); An optical bistable semiconductor laser having a smaller laser oscillation stop current threshold value, and a DC current Ib in the vicinity of 11 between the semiconductor laser's current value and I2.
'(r a first electrical circuit that applies voltage to the semiconductor laser;
A part of the optical signal is detected, and after a time delay of less than half a period of the optical signal from its thickest value, a trigger pulse current with a sign opposite to Ib and larger than the difference between Ib and I2 is applied to the semiconductor laser. It is characterized in that it includes at least a second electric circuit.

In this invention, an optical amplification circuit is constructed using a semiconductor laser that exhibits optical bistability in the relationship between injection current and optical output and the relationship between optical input and optical output.

Optical bistability is something that has a binary optical output in response to an injected current or optical input, and exhibits one of the two optical output values in response to a change in externally injected current or optical input. It is. In semiconductor lasers that exhibit optical bistability,
The width of the injected current indicating a binary optical output is usually around 19 mA. For example, if this width is 10 mA, set the injection current to a value in the middle of the width and use an external positive/negative trigger of 5 mA or more.
When a pulse current is applied, the device repeats on/off operations in response to changes in the pulse current. On the other hand, when a certain optical input has a binary optical output, the optical input can be set to a value midway between the width of the optical input that indicates the binary optical output, similar to the application of positive and negative trigger pulse currents. Even if a binary optical trigger pulse is superimposed externally, the on/off operation will be repeated in response to the change. However, when the width of the optical input indicating a binary optical output is wide, in order to turn the semiconductor laser on and off, an on-off response cannot be obtained unless the intensity of the optical input is extremely increased.

In this respect, in the case of positive and negative pulse currents, the wide width allows operation with almost no problem. Therefore, in the present invention, the injection current is set to an optical bistable value near the laser oscillation starting current threshold so that the semiconductor laser is turned on even when a weak optical signal is injected into the semiconductor laser. In addition, by detecting individual optical signals from the outside and providing a time delay within a half period of the optical signal from each maximum value, a trigger pulse current of opposite sign to the injected current is applied to the semiconductor laser. This changes the on state to the off state, that is, resets it. Semiconductor lasers exhibiting optical bistability exhibit a sharp response in optical output to changes in optical input or injected current. Therefore, when a weak optical signal is injected from the outside using the injection current as described above, optical excitation occurs due to the optical injection, and the semiconductor laser is turned on and an optical output of several mW or more is obtained.

As a result, the amplification factor of the light intensity can be expected to be several hundred times to a thousand times. However, since the amplification mechanism of this semiconductor laser is based on optical excitation, it is not necessary to match the axial mode of the wavelength as in optical injection locking, and it is not necessary to match the wavelength.

For this reason, temperature control of semiconductor lasers is limited to ±0.
Accuracy of 0.1°C is no longer required. With the above, an optical amplification circuit with mild wavelength dependence can be realized.

Next, the present invention will be explained in detail using examples.

FIG. 1 shows a block diagram of an embodiment of the present invention. FIG. 2 is a diagram showing the relationship between the injection current and the optical output, showing the optical bistability of the semiconductor laser used in the present invention.

The semiconductor laser 100 receives a DC injection current Ib from the first electric circuit 200, which is a DC power supply, between the laser oscillation start current threshold 1 and the laser oscillation stop current threshold I2, and is set near the P-side electrode. 101. The first optical signal 10 transmitted through the first optical fiber 102
3 is branched into an optical signal 105 for injection into the semiconductor laser 100 and an optical signal 106 for generating a trigger pulse current by a branch circuit 104 configured with a half mirror. Optical signal for injection 1
05, the first arm opening 1 is formed in the active layer 107 of the semiconductor laser 100 by the lens system which is the first coupling circuit 201.
Injected from 08. If the conversion value of the injection optical signal 105 into a current due to optical excitation is greater than or equal to the difference between 11 and Ib, the laser oscillates and enters the on state. On the other hand, the optical signal 106 for generating a trigger pulse current is converted to the maximum value of the optical signal by a second electric circuit 202 composed of a photodetector and a resistor and a capacitor for delaying the photocurrent pulse detected by the photodetector. With a time delay of 1030% period of the first optical signal,
Generate a trigger pulse current IP of opposite sign to Ib,
The voltage is applied to the P-side electrode 101.

This trigger pulse magnetic current IP functions as a so-called electrical signal for resetting the optical signal. Therefore, the '1 current value needs to be larger than the difference between Ib and ■. This trigger pulse current IP changes the semiconductor laser 100 from an on state to an on state. By repeating this process, the semiconductor laser 100 amplifies the first optical signal 103 by several hundred to one thousand times.

The amplified second original signal 109 is coupled from the second arm opening 110 to the second optical fiber 111 through a second coupling circuit 203 constituted by a lens system and transmitted. The semiconductor laser 100 used here has an I of 35 mA and an I2
It is an InP-InGaAsP quaternary semiconductor laser with a current of 25 mA and an oscillation wavelength of 1.31 μm. At this time, Ib was 34.5 mA, and Ip was still -12 mA. Therefore, the first optical signal 103 only needs to have a magnitude that is converted into a photocurrent of 0.5 mA or more, and the coupling efficiency from the first fiber 102 to the semiconductor laser 100 is determined by the signal 103.
5 is enough. Still, the first and second optical fibers 1
02.111. The core diameter is 8 μm and the cutoff wavelength is 1.
A 1 μm single mode fiber was used.

The first optical signal 1030 wavelength is 1.21 μm.

The optical bistability of a semiconductor laser changes somewhat with respect to temperature changes. Therefore, it was necessary to suppress the temperature of the semiconductor laser 100 to ±0.1°C. As a result of the above, we have realized an optical amplification circuit that is one order of magnitude looser in accuracy control than the conventional one and has warm wavelength dependence.

Note that in the above embodiments, a tandem structure semiconductor laser or a semiconductor laser in which a non-excited region is provided in a part of the active layer may be used, although no particular specifications are given as the semiconductor laser 100 exhibiting optical bistability. can. In addition, as a means for injecting the first optical signal 103 into the active layer 107 of the semiconductor laser 100, in the actual optical system, the first optical signal 103 is injected from the first arm opening 108; Alternatively, the injection optical signal 105 may be injected into the removed portion. Also,
In the above demonstration example, the trigger pulse current generation optical signal 1
Although the trigger pulse current IP is generated as a reset electric signal after a time delay of % period of the first optical signal 103 when 06 is detected, any period may be used as long as it is within 3 A period.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between injection current and optical output showing the optical bistability of the semiconductor laser used in the embodiment. In the figure, 100... Semiconductor laser, 101... P-side electrode, 102...
......First optical fiber, 103...
. . . first optical signal, 104 . . . branch circuit, 105 . . . optical signal for injection, 106.
......Trigger pulse current generation optical signal, 1
07...--Active layer, 108...
...First arm opening plane, 109...Second original signal, 110...Second arm opening plane, 111
......Second optical fiber, 200...
...10th direct air circuit, 201...-
・The first coupling circuit, 202...second electrical circuit, and 203...second coupling circuit are respectively arranged. Procedural amendment (method) 6 The Palace of the Commissioner of Licensing Agency ■, Indication of the case 1982 Patent Application No. 2316
No. 21 7゜2, Title of the invention: Optical amplifier circuit conversion 3, Relationship to the amended case: Applicant: 5-33-1 Shiba, Minato-ku, Tokyo (423) NEC Corporation Representative: Tadahiro Sekimoto 4; Agent 5, date of amendment order: March 29, 1980 (shipment date) column for the title of the invention in the specification to be amended. Claims section of the specification. A detailed description of the invention in the specification. Pages 1 to 3 of the statement of contents of the amendment may be attached to the attached document. (
No changes to content. )

Claims (1)

[Scope of Claims] An optically bistable semiconductor laser having a laser oscillation start current threshold value and a laser oscillation stop current threshold value smaller than 11, and I and I of the semiconductor laser. and (1) detecting a part of the optical signal, and after a time delay within half a period of the optical signal from its maximum value, Ib. an optical amplification circuit including at least a second electric circuit that applies a trigger pulse current to the semiconductor laser with opposite signs and which is larger than the difference between Ib and I;