JPH11284266A - Optical pulse generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce timing jitter without degrading output pulse intensity. SOLUTION: A driving circuit 2 wherein a semiconductor laser 3 is made to perform gain switch operation at the repetition frequency of the repetition signal outputted from a signal generating means 1 for generating short beam pulse, and a phase changing means 4 wherein the phase of the repetition signal outputted from the signal generating means 1 is changed by a specified amount, are provided. A short beam pulse generating means 6 generates the short beam pulse synchronous with the output signal of the phase changing means 4, and an optical wave-synthesizing means 5 inputs the output of the short beam pulse generating means 6 into the semiconductor laser 3, with the output of the semiconductor laser 3 taken outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pulse generator having a semiconductor laser for generating short optical pulses used in measurement techniques such as ultrahigh-speed optical communication and optical sampling.

[0002]

2. Description of the Related Art There is a gain switching method as a method for generating a short light pulse using a semiconductor laser. The gain switching method is a method that can easily generate an optical pulse having a pulse width of several picoseconds simply by injecting a short current pulse into a semiconductor laser. However, there is a problem that when the repetition frequency of the generated optical pulse is reduced, the timing jitter increases. This is because the photon density in the semiconductor laser fluctuates due to spontaneous emission light randomly generated like noise in the semiconductor laser.

On the other hand, a method of injecting continuous light from another light source into a semiconductor laser to be gain-switched (hereinafter referred to as a continuous light injection method) or a part of output light of the semiconductor laser to be gain-switched is used. There is provided a method of suppressing the timing jitter by a method of returning the laser to its own laser after a certain time delay (hereinafter referred to as a self-injection method). The principle of these timing jitter suppression methods is that by inputting stimulated emission light of approximately the same wavelength from the outside to the semiconductor laser for gain switching,
The spontaneous emission light generated inside the semiconductor laser is suppressed, whereby fluctuations in photon density inside the semiconductor laser are suppressed, and as a result, timing jitter is suppressed.

[0004]

However, in the continuous light injection method among the two methods for suppressing the timing jitter, when the light intensity of the continuous light to be injected is increased, the timing jitter is suppressed. On the other hand, while the effect is improved, the injected continuous light consumes the injected current as stimulated emission light that does not become pulsed light, and the intensity of the light pulse is reduced. In the self-injection method, it is necessary to match the timing of the returning optical pulse with the timing of generating the optical pulse of the semiconductor laser. Furthermore, when the repetition frequency of the light pulse is changed,
The timing of the returning optical pulse must also be changed, and an optical delay circuit or the like that can change the amount of delay of light is required, and there has been a problem that timing control becomes complicated.

The present invention solves such a problem, and suppresses timing jitter while maintaining the intensity of an optical pulse high by injecting pulse light from a light source different from itself from outside the semiconductor laser. It is an object of the present invention to provide an optical pulse generator which can be performed and does not require complicated timing control.

[0006]

To achieve the above object, an optical pulse generator according to the first aspect of the present invention comprises a signal generator for generating a repetitive signal having a constant period, and a repetitive signal output by the signal generator. A drive circuit for causing a semiconductor laser to perform a gain switch operation at a repetition frequency of, and generating a short light pulse; and a phase change means for changing a phase of a repetition signal output by the signal generation means by a fixed amount. Generating a short light pulse synchronized with the output signal of the phase changing means, inputting the output of the short light pulse generating means to the semiconductor laser to the optical multiplexing means, and extracting the output of the semiconductor laser to the outside. It is like that.

According to a second aspect of the present invention, in the optical pulse generator, the timing of the short optical pulse input to the semiconductor laser by the short optical pulse generating means is such that the carrier density inside the semiconductor laser is set to a threshold value. It is time to reach.

According to a third aspect of the present invention, in the optical pulse generating apparatus, the short optical pulse generating means sets the peak of the short optical pulse input to the semiconductor laser to the carrier density inside the semiconductor laser as a threshold value. It is time to reach.

Further, in the optical pulse generating apparatus according to the present invention, an optical amplifier for increasing the light intensity of the short optical pulse outputted from the short optical pulse generating means is connected to the short optical pulse generating means.

In the optical pulse generator according to the invention, an optical band-pass filter for suppressing spontaneous emission noise is connected to the output side of the optical amplifier.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. FIG. 1 is a block diagram showing an optical pulse generating apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a signal generator as a signal generating means for generating a repetitive signal having a constant period; A drive circuit that generates a short optical pulse by causing the semiconductor laser 3 to perform a gain switch operation at the repetition frequency of the repetition signal output from the signal generator 1 changes the phase of the repetition signal output from the signal generator 1 by a fixed amount. A phase shifter 6 as a phase changing means for causing a short light pulse generating circuit as a short light pulse generating means for generating a short light pulse synchronized with an output signal of the phase shifter 4, and 5 is a short light pulse generating circuit 6 The output is input to the semiconductor laser 3 and the semiconductor laser 3
Is an optical multiplexer as an optical multiplexing means for taking out the output of the above.

Next, the operation will be described. First, an output of the signal generator 1 that generates a repetitive signal having a certain period is input to the drive circuit 2 and the phase shifter 4. The drive circuit 2 converts the DC current component for bias into a signal generator 1
And a short current pulse synchronized with the repetition frequency of the output is superimposed and output to the semiconductor laser 3. On the other hand, the phase shifter 4
Shifts the phase of the output of the signal generator 1 by a fixed amount, and outputs it to the short optical pulse generation circuit 6. Short light pulse generation circuit 6
Generates a short optical pulse in synchronization with the output signal of the phase shifter 4, and outputs the short optical pulse to the semiconductor laser 3 via the optical multiplexer 5. The semiconductor laser 3 generates a short optical pulse having a repetition frequency synchronized with the repetition frequency of the output of the signal generator 1 from the drive circuit 2 based on a gain switching method.
Output to the optical multiplexer 5. The optical multiplexer 5 outputs the output of the short optical pulse generation circuit 6 to the semiconductor laser 3, and outputs the output of the semiconductor laser 3 as an output signal of the optical pulse generation device of the present invention.

Here, the wavelength of the light pulse output from the short light pulse generation circuit 6 is set to be substantially equal to or slightly shorter than the wavelength of the short light pulse output from the semiconductor laser 3. FIG. 2B is an input light intensity characteristic diagram showing a temporal change in the intensity of the light pulse output from the short light pulse generation circuit 6 and input to the semiconductor laser 3, and FIG. FIG. 4 is a carrier density characteristic diagram showing a change in carrier density over time. The short light pulse generation circuit 6 outputs the semiconductor laser 3
The timing of the optical pulse input to the phase shifter 4 is such that the peak value of the optical pulse (optical input intensity) comes at the time when the carrier density inside the semiconductor laser 3 reaches the threshold value.
Adjust the shift amount of. By such a phase adjustment,
Unlike the continuous light injection method, the current injected into the semiconductor laser 3 is less consumed as stimulated emission light that does not become pulsed light, and the semiconductor laser 3 can output even if the intensity of the injected light pulse is increased. The light pulse intensity does not decrease. Further, even if the repetition frequency of the short light pulse generated by the short light pulse generation circuit 6 is changed, the timing of the light pulse to be injected into the semiconductor laser 3 is relatively constant by the phase shifter. There is no need for such complicated timing control. Further, timing jitter can be reduced.

Here, as the short light pulse generation circuit 6,
As shown in FIG. 3, a circuit in which a semiconductor laser 10 as a continuous wave single wavelength light source and an optical modulator 11 are combined, and as shown in FIG. 4, a short current pulse generating circuit 12 and a semiconductor laser 13 are combined. Alternatively, a circuit based on the gain switching method of the semiconductor laser 13 or a circuit in which the high repetition short current pulse generation circuit 14, the semiconductor laser 15, and the optical modulator 16 are combined as shown in FIG. 5 can be used. Further, as the optical multiplexer 5, an optical fiber coupler, a polarizing beam splitter, a non-polarizing beam splitter, an optical circulator, a half mirror, or the like can be used.

FIG. 6 is a block diagram showing an optical pulse generator according to another embodiment of the present invention. In the figure, parts corresponding to the respective parts in FIG. 1 are denoted by the same reference numerals, and redundant description thereof will be omitted. The embodiment shown in FIG. 6 differs from the embodiment shown in FIG. 1 in that the output of the short optical pulse generation circuit 6 is amplified by an optical amplifier 7. The optical amplifier 7 can increase the light intensity of the light pulse input to the semiconductor laser 3 and increase the effect of reducing timing jitter. An optical bandpass filter 8 is connected to the output side of the optical amplifier 7 in order to suppress spontaneous emission noise (ASE) generated by the optical amplifier 7. If the level of the spontaneous emission noise is sufficiently low and it is not necessary to reduce the timing jitter, it is not necessary to use the optical bandpass filter 8.

[0016]

As described above, according to the present invention, a semiconductor laser which generates and outputs a short optical pulse by the gain switching method is supplied with a pulse light from the outside during the time when the carrier density inside the semiconductor laser reaches the threshold value. Injection of the semiconductor laser can suppress spontaneous emission light generated inside the semiconductor laser, thereby suppressing fluctuation of the photon density inside the semiconductor laser, and as a result, obtaining an effect of suppressing timing jitter. Also, unlike the continuous light injection method, the pulsed light injected from the outside is injected only during the period when the carrier density of the semiconductor laser is high, so that the current injected into the semiconductor laser is consumed as stimulated emission light that does not become pulsed light. This is advantageous in that even if the intensity of the optical pulse to be injected is increased, the intensity of the optical pulse output from the semiconductor laser does not decrease. Also, even if the repetition frequency of the short light pulse to be generated is changed, the timing of the light pulse to be injected into the semiconductor laser is relatively constant by the phase shifter. The effect of not being obtained is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an optical pulse generator according to an embodiment of the present invention.

FIG. 2 is a carrier density characteristic diagram showing a temporal change of a carrier density inside a semiconductor laser according to the present invention, and an input light intensity characteristic diagram showing a temporal change of a light pulse intensity input to the semiconductor laser according to the present invention.

FIG. 3 is a block diagram showing a specific example of a short light pulse generation circuit in FIG. 1;

FIG. 4 is a block diagram showing another specific example of the short light pulse generation circuit in FIG. 1;

FIG. 5 is a block diagram showing another specific example of the short light pulse generation circuit in FIG. 1;

FIG. 6 is a block diagram showing an optical pulse generator according to another embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 signal generator (signal generating means) 2 drive circuit 3 semiconductor laser 4 phase shifter (phase changing means) 5 optical multiplexer (optical combining means) 6 short optical pulse generating circuit (short optical pulse generating means) 7 optical amplifier 8 light Bandpass filter

Claims (5)

[Claims] 1. A signal generating means for generating a repetitive signal having a constant period, a drive circuit for performing a gain switch operation of a semiconductor laser at a repetition frequency of the repetitive signal output by the signal generating means, and generating a short optical pulse; Phase change means for changing the phase of the repetitive signal output by the signal generation means by a fixed amount; short light pulse generation means for generating a short light pulse synchronized with the output signal of the phase change means; An optical pulse generator comprising: an optical multiplexing means for inputting an output to the semiconductor laser and extracting an output of the semiconductor laser to the outside. 2. The semiconductor device according to claim 1, wherein the timing of the short light pulse input to the semiconductor laser by the short light pulse generating means is a time at which a carrier density inside the semiconductor laser reaches a threshold value. An optical pulse generator according to any of the preceding claims. 3. The method according to claim 1, wherein the short light pulse input to the semiconductor laser by the short light pulse generating means has a peak at a time when a carrier density inside the semiconductor laser reaches a threshold value. Item 2. An optical pulse generator according to Item 1. 4. The short optical pulse generator according to claim 1, wherein an optical amplifier for increasing the light intensity of the short optical pulse output from the short optical pulse generator is connected to the short optical pulse generator. Optical pulse generator. 5. The optical pulse generator according to claim 4, wherein an optical bandpass filter for suppressing spontaneous emission noise is connected to an output side of the optical amplifier.