JPH01115184A - Ultrashort optical pulse generator - Google Patents

Abstract

PURPOSE:To realize a light source having a high timing coherence by integrating a mode synchronous optical pulse oscillator with means for frequency- discriminating an output optical pulse light from the oscillator. CONSTITUTION:The output optical pulse 20 of a mode synchronous semiconductor laser 10 generates an ultrashort optical pulse train, and its optical spectrum is oscillated in longitudinal multimodes at the round-trip frequency interval of a resonator. Then, the pulse 20 is incident to an optical frequency discriminator 30, thereby easily obtaining a desired oscillation optical spectrum. The output optical pulse 40 of the discriminator 30 is oscillated in an ultrashort pulse, and has a high timing coherence. Thus, a light source having an ultrashort optical pulse and a high timing coherence can be easily realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultrashort optical pulse generator for use in optical communications, optical information processing, optical computers, and the like.

(Prior art) Generating short pulses on the order of ρsec (picoseconds) using a semiconductor laser is an important technology, and mode-locking is a conventional method for generating short pulses using a semiconductor laser. . The mode locking can be roughly divided into two types: active mode locking and passive mode locking. The former modulates the current injected into the semiconductor laser with the round-trip frequency of the resonator, and the latter involves inserting a saturable absorber into the resonator. In both cases,
A mode-locked semiconductor laser 10 as shown in FIG. 5(a)
The output light pulse 101 of 0 oscillates as a short pulse as shown in FIG. 5(b), and its pulse width is about 1 to 20 psec. At this time, the oscillation light spectrum exhibits longitudinal multimode oscillation at intervals corresponding to the round trip frequency of the resonator, as shown in FIG. 5(c).

On the other hand, with the progress of research on making semiconductor laser devices coherent, it has become possible to realize a light source that oscillates in a single longitudinal mode and has an extremely narrow spectral wave width in the CW state.

(Problems to be Solved by the Invention) Even in such a coherent semiconductor laser, when current modulation is performed, spectrum broadening called wavelength chirping is induced. Therefore, there is no light source that generates ultrashort optical pulses using a semiconductor laser modulated at ultrahigh speed and has high temporal coherence.

In view of the above points, the present invention aims to realize a light source that is a semiconductor laser that oscillates with ultra-high-speed short pulses and has high temporal coherence.

(Means for Solving the Problems) In order to realize the above-mentioned light source, that is, an ultrashort pulse generator, the present invention provides a mode-locked optical pulse oscillator including a semiconductor laser, and an output light source from the oscillator. This is to integrate means for frequency discrimination of pulsed light.

(Function) By performing the integration in this manner, it is possible to easily realize an ultrashort optical pulse generator whose output light is temporally coherent.

(Example) An example of the present invention will be explained using FIGS. 1 and 2, and an example of an experiment that was actually conducted to provide the basis of the present invention will be explained using FIGS. I will explain.

FIG. 1 is a block diagram of an ultrashort optical pulse generator according to the present invention, in which the output optical pulse 2 of a mode-locked semiconductor laser 10 is
0 generates an ultrashort optical pulse train, but its optical spectrum is longitudinally multimode oscillated at the round trip frequency interval of the resonator. Therefore, by inputting this output light pulse 20 into an optical frequency discriminator 30, a desired oscillation light spectrum can be easily obtained.
The output optical pulse 40 is an ultrashort pulse oscillation and has high temporal coherence.

This situation will be explained using FIG. 2. The optical frequency spectrum of the output optical pulse 20 of the mode-locked semiconductor laser 10 oscillates in multiple modes as shown in FIG. As shown in FIG. 2(b), it is possible to select only one arbitrary mode, and oscillates in a single mode. Further, the output optical pulse 40 at this time is ultrashort optical pulse oscillation as shown in FIG. 2(C).

Next, an example of an experiment that provides the basis of the present invention will be described using FIGS. 3 and 4.

In order to configure the mode-locked semiconductor laser 10, A I
The light 2 emitted from one end surface of the GaAs semiconductor laser 1 is converted into parallel light 4 by a lens 3, and this is made incident on a diffraction grating 5.
The parallel light 4 is passed through the lens 3 again.

It is fed back to the semiconductor laser 1. At this time, the injected current is modulated at a frequency equal to the round trip frequency of this resonator using a power supply 6 having a built-in modulation circuit. The end face of the semiconductor laser 1 on the lens 3 side is coated with an anti-reflection film, and the threshold current of a single mode-locked semiconductor laser in the CW state is 20 mA. When performing pulse modulation, the bias current was set to 0.7 times the threshold current, and the peak current value was set to 2.5 times the threshold current. Further, the temperature of the semiconductor laser 1 was stabilized by a temperature stabilizer 7 having a built-in Peltier element. Emitted light 8 from the opposite end facet of the semiconductor laser
is made into an output optical pulse 20 by the lens 9, and the frequency discriminator 3
0. Here, a Fapley-Perot etalon was used as the frequency discriminator 30. This output light pulse 40
led to an optical system to measure its properties. First, an optical isolator 41 is used to eliminate the influence of reflected light from the measurement optical system. This isolator uses two stages with an isolation ratio of 30 dB, ensuring a total of 60 dB. The output light 42 from the isolator 41 is transmitted through three beam splitters 50, 70, 80 and a reflecting mirror 9.
0, the four measured beams 51.71.81.91
divided into. Beam 51 is directed to autocorrelator 52 to measure the optical pulse width. Its configuration is that a beam 51 is divided into two beams 54 by a beam splitter 53.
Divided into ゜55, corner cube mirror 56.57
The beams 54 and 55 are reflected by the beam splitter 53 into a collinear beam 58. The beam 58 is passed through a lens 59 to a crystal L for second harmonic generation.
The second harmonic light 61 enters the lens 6
2, an image is formed on a photomultiplier tube 63. At this time, only the second harmonic light was guided to the photomultiplier tube using Blue Filter Taro 4. The corner cube mirror 56 is mounted on a motor 65, and the motor position change corresponds to the delay time, and its electrical output 66 and the output 67 of the photomultiplier tube 63 are
was recorded and observed using a pen recorder 68. The optical spectrum of the beam 71 was measured using a high-resolution Fapley-Perot interferometer 72 and an oscilloscope 73. Beam 81 passes through lens 82 to high speed PIN photodiode 83
The waveform was observed using a sampling oscilloscope 84. Beam 91 passes through lens 92 and monochromator 93
The optical spectrum was observed using a TV camera 94 and a monitor TV 95.

While changing the bias conditions of the mode-locked semiconductor laser 10 and observing the waveform of the sampling oscilloscope 84, measurements were taken at the shortest pulse width. Since the diffraction grating 5 is used to configure the mode-locked semiconductor laser, a single longitudinal mode is observed on the monitor television 95.

The measurement results are shown in Figure 4. Figure 4(a) shows the second-order correlation waveform measured with an autocorrelator. It was confirmed that ultra-short pulse oscillation was occurring. At this time, the output cuff 3 of the Fapley-Perot interferometer 72 is shown in FIG. 4(b). As shown in the figure, it was found that it oscillated very clearly in one mode, and could be used as a light source with high temporal coherence.

In this experiment, a Farpley-Perot etalon was used as the frequency discriminator 30, but it may be a diffraction grating with high resolution, or a combination of both.

(Effects of the Invention) As described above, according to the present invention, it is possible to easily realize a light source having ultra-short optical pulses and high temporal coherence. Therefore, the influence of wavelength dispersion of fiber can be easily removed in long-distance optical fiber communications.

Furthermore, detection methods such as heterodyne and homodyne become possible, and the consequences of these methods are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an ultrashort optical pulse generator according to the present invention;
Fig. 2 is a characteristic diagram showing the effects of the present invention, Fig. 3 is a diagram showing an example of an experiment providing the basis of the present invention, Fig. 4 is a characteristic diagram showing the experimental results, and Fig. 5 is a characteristic diagram showing the results of the experiment. FIG. 2 is an explanatory diagram of a short optical pulse generator. 1... Semiconductor laser, 2, 8... Emitted light, 3.
9... Lens, 4... Parallel light, 5... Diffraction grating, 6... Power supply, 7... Temperature stabilizer, lO...
・Mode-locked semiconductor laser, 20° 40... Output optical pulse, 30... Frequency discriminator, 41... Isolator, 42... Outgoing light, 50, 53.70.80...
Beam splitter, 51, 54.55.58.71.
81.91... Beam, 52... Autocorrelator, 56.57... Corner cube mirror, 59
．． 62.82.92... Lens, 60... Li
IO3 crystal, 61...Second harmonic light, 63...Photomultiplier tube, 64...Blue filter, 65...Motor, 66, 67...Electric output, 68...Pen recorder , 72...Fapley-Perot interferometer, 73...
Oscilloscope, 83...PIN photodiode, 8
4... Sampling oscilloscope, 93... Monochromator, 94... TV camera, 95... Monitor TV. Patent applicant Matsushita Electric Industrial Co., Ltd. Figure 1 20, 40 ・Tsuchikamaru Palace Figure 2 Figure 4! Kusaima (psec) 5th (b) (C) Kuyō Ronen

Claims (1)

[Claims] 1. An ultrashort optical pulse generator characterized by integrating a mode-locked optical pulse oscillator comprising a semiconductor laser and means for frequency discrimination of the output optical pulse light from the oscillator.