JPH06169124A - Short optical pulse generating device - Google Patents

Abstract

PURPOSE:To provide a short optical pulse generator which generates a very short optical pulse by a small construction and by conducting a multimode or single mode operation. CONSTITUTION:A double waveguide structure semiconductor laser 3, having an electrically separated double waveguide structure, is laser-oscillated by a DC current source 1, the loss of the laser resonator of the double waveguide structure semiconductor laser 3 is changed into a pulse state by a pulse generating circuit 2, an oscillating operation is ON-OFF controlled, and a short-beam pulse is generated by a Q-switching operation. Besides, a gainswitching method is combinedly used. Also, a double waveguide structure semiconductor laser, having no diffraction grating, is laser-oscillated by the DC current source 1, and a short-beam pulse is generated using a mode synchronization method. Besides, a gain switching method is combinedly used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique using an optical pulse or an electromagnetic pulse.
The present invention relates to a short light pulse generator used in the fields of optical communication and measurement technology.

[0002]

2. Description of the Related Art A semiconductor laser has excellent basic characteristics as an ultra-small optical pulse generator. In particular, the generation of short optical pulses by a semiconductor laser using the Q-switching method (active Q-switching) is low power, the pulse width is small,
A pulse with a large peak output is obtained.

Next, FIG. 8 shows the configuration of a short optical pulse generator using a two-electrode structure type quantum well laser. In FIG. 8, 1 is a direct current source, 2 is a pulse generation circuit, and 10 is a two-electrode structure type quantum well laser. Two-electrode structure quantum well laser 1
0 is the waveguide 10A, the optical switch unit 10B, and the optical amplification unit 1
With 0C. In FIG. 8, when an electric field is applied to the optical switch 10B inside the semiconductor laser resonator, the amount of light absorption changes due to the electro-optical effect, the Franz-Keldish effect, the quantum confined Stark effect, or a combined effect of these effects. Optical switches are integrated in the direction of the light beam 10D.

Since the absorption change of the optical switch section 10B changes the loss of the laser resonator, the Q switch operation of the laser is performed when the loss change is such that the laser oscillation operation is turned on and off. Therefore, from the pulse generation circuit 2,
By applying a pulsed electric field having a repetition frequency of several hundred MHz to several GHz to the optical switch unit 10B, the amount of light absorbed by the optical switch unit 10B is changed, and an optical pulse having a pulse width of about 20 picoseconds is generated. For such technology, see Y. Arakawa et al., Appl.Phys.Lett.,
Vol.48, No.9,561 (1986), it is explained in detail.

[0005]

In the prior art using the Q-switching method, an optical switch section for changing the loss in the waveguide direction of the resonator is integrated. Therefore, it is not possible to use a distributed feedback (DFB) structure for imparting wavelength selectivity, and most laser oscillations occur in multiple modes. Further, since the optical switch section is integrated in the optical waveguide direction, the resonator length becomes long and the structure becomes large. Further, there is a problem in that the life of the photon is lengthened by the lengthening of the resonator and the width of the generated optical pulse is widened. An object of the present invention is to provide a short optical pulse generator having a small configuration and generating an extremely short optical pulse in multimode or single mode operation.

[0006]

To achieve this object, according to the present invention, a double-waveguide structure semiconductor laser 3 having an electrically-separated double-waveguide structure and a double-waveguide structure semiconductor are provided. A direct current source 1 which is connected between the active layer side anode electrode 3A and the common cathode electrode 3E of the laser 3 and causes a laser oscillation operation by flowing a current equal to or more than an oscillation threshold current, a modulation layer side anode electrode 3D and a common cathode electrode. A pulse generation circuit 2 connected between 3E is provided, the loss of the laser resonator of the double-waveguide structure semiconductor laser 3 is changed in a pulse shape, the oscillation operation is turned on and off, and a short optical pulse is generated by the Q switching operation. To do. Furthermore, the gain switch method is also used. In addition, a double waveguide structure semiconductor laser 31 which is electrically separated and has a double waveguide structure without the diffraction grating 3H,
The direct current source 1 for connecting the active layer side anode electrode 3A and the common cathode electrode 3E of the double-waveguide structure semiconductor laser 31 and the common cathode electrode 3E to cause a current equal to or more than the oscillation threshold current to perform laser oscillation operation, and the modulation layer side anode The pulse generation circuit 2 connected between the electrode 3D and the common cathode electrode 3E is provided, and the mode-locking method is also used. Furthermore, the gain switch method is also used.

[0007]

Next, the structure of the present invention will be described with reference to FIG. In FIG. 1, 1 is a direct current source, 2 is a pulse generation circuit, and 3 is a double-waveguide structure semiconductor laser. As the double waveguide structure semiconductor laser 3, for example, a TTG-DFB laser is used. The TTG-DFB laser is a semiconductor laser having an electrically separated double waveguide. For TTG-DFB laser, see E. Yamamoto et al., Appl. Phys. Lett., Vo.
l.60, No. 7,805 (1992) and JP-A-3-87086.

The double-waveguide structure semiconductor laser 3 shown in FIG.
The active layer side anode electrode 3A, the active layer side cladding layer 3F, the diffraction grating 3H, the active layer 3B, the common cathode electrode 3E, the modulation layer 3C, the modulation layer side cladding layer 3G, and the modulation layer side anode electrode 3D are arranged in this order from the top. It is configured. In Figure 1,
A direct current source 1 is connected between the active layer side anode electrode 3A and the common cathode electrode 3E of the double waveguide structure semiconductor laser 3. Modulation layer side anode electrode 3D and common cathode electrode 3
The pulse generation circuit 2 is connected between E.

Next, the operation of FIG. 1 will be described. A current for laser oscillation operation is supplied from the direct current source 1 to one of the waveguides of the double-waveguide structure semiconductor laser 3. That is, since the double-waveguide structure semiconductor laser 3 performs the laser oscillation operation, the active layer side anode electrode 3A and the common cathode electrode 3E are
A current greater than the oscillation threshold current is passed between them.

Next, when a negatively biased voltage pulse as shown in FIG. 2 is applied from the pulse generation circuit 2 to the modulation layer side anode electrode 3D, the electro-optical effect, the Franz-Keldish effect, the quantum confined Stark effect, Alternatively, the absorption of the waveguide changes like a pulse due to a combined effect of these effects.

Since the laser light in the double-waveguide structure semiconductor laser 3 is guided through these two waveguides as a whole, the loss of the laser resonator of the double-waveguide structure semiconductor laser 3 changes in a pulsed manner. At this time, when the loss changes so as to exceed the gain of the double-waveguide structure semiconductor laser 3, the oscillation operation is turned on and off, so-called Q switching operation is performed, and
Light pulses of 0 picoseconds or less are generated. The bias value at this time is a magnitude at which the laser operation stops, and for example, −2 to
-3V, and the voltage pulse width is about 100 nanoseconds.
Generates short light pulses. Further, distributed feedback of light is obtained by the diffraction grating 3H inside the double-waveguide structure semiconductor laser 3, and a single-mode optical pulse is generated.

Next, the configuration of the second embodiment of the present invention is shown in FIG. A double-waveguide structure semiconductor laser 31 having no diffraction grating 3H is used as the semiconductor laser used. In Figure 3,
As shown in FIG. 4, the pulse period of the pulse generating circuit 2 is
By matching the time τ (= 2 × laser resonance length / speed of light) for the optical pulse to make one round trip in the resonator, mode locking is applied, and an even shorter optical pulse can be generated.

For example, if the laser resonance length L is 1 cm, mode synchronization is achieved by setting the pulse period of the pulse generating circuit 2 to about 70 picoseconds. However, the reflecting mirror 7 and the lens 8 of FIG. 3 are not always necessary, and in this case, the double waveguide structure semiconductor laser 31 itself serves as a laser resonator.

Next, the configuration of the third embodiment of the present invention is shown in FIG. In FIG. 5, 5 is a second pulse generating circuit, and 6 is a pulse phase adjusting line. In the configuration of FIG. 5, a pulse generation circuit 5 is connected instead of the direct current source 1 between the active layer side anode electrode 3A and the common cathode electrode 3E. The pulse generation circuit 5 sends a current pulse in which a current flows in the forward direction.

Next, an example of the operation of FIG. 5 will be described with reference to FIGS. 6 and 7. First, as shown in FIG. 6, the peak value of the pulse of the pulse generation circuit 5 is set to be equal to or higher than the oscillation threshold current (usually several to ten times the oscillation threshold) and the pulse width is set to several tens.
When it is set to 0 picoseconds or less, a gain switching operation is caused similarly to a normal semiconductor laser, and a short optical pulse is generated (20 to several tens of picoseconds in a normal semiconductor laser). If a voltage (for example, −2 to −3 V) that stops the oscillation of the pulse generation circuit 2 is applied during the time when the intensity of the optical pulse is maximized, the photon density in the laser resonator is rapidly reduced and the Q switch operation is performed. As a result, the falling edge of the optical pulse becomes steep as indicated by 61, and the optical pulse width becomes short.

Further, as shown in FIG. 7, when the rise time of the pulse of the pulse generation circuit 2 is matched with the rise time of the optical pulse, the photon density in the laser resonator rapidly increases, and the optical pulse is generated by the Q switch operation. Rises steeply as shown at 71, and the optical pulse width becomes shorter.

[0017]

According to the present invention, since the semiconductor laser having the double waveguide structure is used to generate the short optical pulse,
A diffraction grating can be easily integrated, a short-wave pulse generator that oscillates in a single mode can be easily configured, and long-distance transmission can be performed. Further, since the resonator length can be shortened, the photon life can be shortened, the pulse width can be shortened, and the device can be downsized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment according to the present invention.

2 is an output voltage waveform of a pulse generation circuit 2 of FIG.

FIG. 3 is a configuration diagram of a second embodiment according to the present invention.

4 is an output voltage waveform of the pulse generating circuit 2 of FIG.

FIG. 5 is a configuration diagram of a third embodiment according to the present invention.

FIG. 6 is an output voltage waveform showing the first operation of FIG.

7 is an output voltage waveform showing the second operation of FIG.

FIG. 8 is a configuration diagram of an optical pulse generator using a Q switch method according to a conventional technique.

[Explanation of symbols]

 1 DC Current Source 2 Pulse Generation Circuit 3 Double Waveguide Structure Semiconductor Laser 3A Active Layer Side Anode Electrode 3D Modulation Layer Side Anode Electrode 3E Common Cathode Electrode 3H Diffraction Grating 4 Ground 5 Pulse Generation Circuit 6 Pulse Phase Adjustment Line 7 Reflector 8 lens

Claims (4)

[Claims] 1. A double-waveguide structure semiconductor laser (3) having an electrically-separated double-waveguide structure, and an active layer side anode electrode (3A) of the double-waveguide structure semiconductor laser (3). Connected between the common cathode electrodes (3E), and flowing a current higher than the oscillation threshold current to operate the laser oscillation, between the modulation layer side anode electrode (3D) and the common cathode electrode (3E) The pulse generation circuit (2) connected to the laser is used to change the loss of the laser resonator of the double-waveguide structure semiconductor laser (3) in a pulse shape to turn the oscillation operation on and off, and the short optical pulse by the Q switching operation. A short light pulse generator characterized in that 2. A double-waveguide structure semiconductor laser (31) which is electrically separated and has a double-waveguide structure without a diffraction grating (3H).
DC current for operating the laser oscillation by connecting between the anode electrode (3A) on the active layer side and the common cathode electrode (3E) of the double-waveguide structure semiconductor laser (31) and applying a current above the oscillation threshold current. Source (1) and a pulse generation circuit (2) connected between the modulation layer side anode electrode (3D) and common cathode electrode (3E), using a mode-locking method together . 3. A double-waveguide structure semiconductor laser (31) electrically isolated and having a double-waveguide structure, and an active layer side anode electrode (3A) of the double-waveguide structure semiconductor laser (31). Connected between the common cathode electrodes (3E), and flowing a current higher than the oscillation threshold current to operate the laser oscillation, between the modulation layer side anode electrode (3D) and the common cathode electrode (3E) The short optical pulse generator according to claim 1, further comprising a pulse generating circuit (2) connected to the optical switch, and using the gain switch method together. 4. A double-waveguide structure semiconductor laser which is electrically separated and has a double-waveguide structure without a diffraction grating (3H).
DC current for operating the laser oscillation by connecting between the anode electrode (3A) on the active layer side and the common cathode electrode (3E) of the double-waveguide structure semiconductor laser (31) and applying a current above the oscillation threshold current. The source (1) and a pulse generation circuit (2) connected between the modulation layer side anode electrode (3D) and the common cathode electrode (3E) are provided, and the gain switching method is used together. Short optical pulse generator.