JP2500604B2 - Ultra high speed optical oscillator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrafast optical oscillator for generating ultrafast repeating ultrashort optical pulse trains useful for optical communication and optical information processing.

[0002]

2. Description of the Related Art In recent years, as a basic technology for ultra-high-speed optical communication and optical information processing, there is an increasing demand for a technology capable of generating an optical pulse train having a repetition frequency exceeding several tens GHz to 100 GHz. One example of an ultrafast optical oscillator that generates a high-speed optical pulse train is an ultrafast optical oscillator that uses a mode periodic operation of a semiconductor laser having a two-electrode or three-electrode structure. In this device, a reverse bias is applied to one section separated by electrodes,
By acting as a saturable absorption region, 100G
It has been reported that self-pulsation is realized at a repetition frequency of Hz or higher. This technique is described, for example, in P. of Journal of Quantum Electronics, Vol. 28, No. 10, by YK Chen et al. 2176 to P.M. It is described in a paper published over 2185. Up to 350 in this paper
It is reported that an optical pulse having a time width of about 0.6 ps was obtained at a repetition frequency of GHz.

[0003]

In the mode period of the above semiconductor laser, the repetition frequency is increased by shortening the cavity and shortening the circulation time of the optical pulse.
However, since this semiconductor laser has a multi-electrode structure,
The resonator length of about μm is almost the limit, and it becomes difficult to make the resonator shorter than that. Further, even if the length can be further shortened, there is a lack of certainty that a normal mode cycle operation is performed on the operating mechanism. Further, since the mode cycle operation is caused by a delicate balance between gain and saturable absorption, the average light output from the semiconductor laser device is usually about 1 mW.

An object of the present invention is to provide an ultra-high-speed optical oscillator which can eliminate the above-mentioned drawbacks of the conventional ultra-high-speed optical oscillator and can operate at ultra-high speed and can obtain high output.

[0005]

An ultrafast optical oscillator according to the present invention has a first semiconductor laser device having a plurality of electrodes and a resonator length which is a fraction of the resonator length of the semiconductor laser device. A second semiconductor laser device and means for optically coupling the first and second semiconductor lasers are provided.

[0006]

The present invention utilizes the resonance amplification of the optical pulse train obtained by the mode-locked oscillation of the first semiconductor laser by the second semiconductor laser. For example, assuming that the cavity length of the first semiconductor laser is L, the frequency f = c / 2η
Assuming that a mode-locking operation of L (c is the speed of light and η is a group refractive index) is performed, this optical output is coupled to a second semiconductor laser having a cavity length of L / m (m is an integer) for amplification. As a result, an optical pulse train having a frequency of m times f is generated. This situation will be described in the frequency domain with reference to the operation principle diagram of FIG. In the mode-locked state, the optical output of the first semiconductor laser has the frequency spectrum of the first semiconductor laser having a frequency interval of c / 2ηL as shown in FIG. When this light output is coupled to the second semiconductor laser, the frequency spectrum of the light output is filtered by the resonator of the second semiconductor laser and, as shown in FIG. 2B, a mode with a frequency interval of mc / 2ηL Second with structure
Has the frequency spectrum of a semiconductor laser. Correspondingly, the repetition frequency is initially f at a time interval of 2ηL / c.
The optical pulse train of the first semiconductor laser (Fig.
After being amplified by the second semiconductor laser, (c) is an optical pulse train of the second semiconductor laser having a repetition frequency of mf at a time interval of 2ηL / mc as shown in FIG. 2 (d). . Moreover, although the number of modes decreases in the second semiconductor laser, the light intensity of each oscillation mode can be increased by laser amplification, and as a result, the average light output can also be increased.

[0007]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 schematically shows an example of the configuration of an ultrahigh-speed optical oscillator to which the present invention is applied. In this example, a two-electrode parallel-plane Fabry-Perot type GaAs / AlGaAs multiple quantum well buried hetero semiconductor laser is used as the first semiconductor laser 1, and a one-electrode parallel-plane Fabry-Perot type GaAs / AlGaAs is used as the second semiconductor laser 2. AlGaAs
A multiple quantum well buried hetero semiconductor laser was used. In the first semiconductor laser 1, a forward current was injected from one electrode to act as a gain region 101, and a reverse bias was applied to the other electrode to act as a saturable absorption region.

A collimation lens 21, an optical isolator 22, and a condenser lens 23 are provided between the first semiconductor laser 1 and the second semiconductor laser 2.

In this embodiment, the cavity length of the first semiconductor laser 1 is about 300 μm, the length of the gain region 101 is about 240 μm, and the saturable absorption region 102 is about 60 μm.
And The cavity length of the second semiconductor laser 2 is about 7
5 μm, 1/4 of the cavity length of the first semiconductor laser 1
It was set so that

Next, the operation of this embodiment will be described.

In the first semiconductor laser 1, a forward current of about 60 mA was injected into the gain region 101, and a reverse bias of 1 V was applied to the saturable absorption region 102. As a result, an average output of about 1 mW was obtained in a mode-locked operation with an optical pulse width of about 1 ps and a repetition frequency of about 120 GHz.

The light output 11 of the first semiconductor laser 1 is made into a parallel beam by the collimation lens 21, then passed through the optical isolator 22, and is coupled to the second semiconductor laser 2 by the condenser lens 23.

The operating current of the second semiconductor laser 2 is set to about 50.
By setting to mA, the repetition frequency of the optical pulse is about 48
The frequency was increased to 4 times at 0 GHz, and the average light output could be about 10 mW.

In this embodiment, the first semiconductor laser 1
Although the two-electrode type is used as the above, the point is that an optical pulse train can be generated by mode locking, and it is clear that the two-electrode type is not limited from a theoretical viewpoint. Similarly, from a theoretical point of view, the first semiconductor laser 1 and the second semiconductor laser 2 are not limited to Fabry-Perot resonators using parallel plane mirrors.

[0016]

As described above, according to the present invention, it is possible to obtain an ultrafast optical pulse repetition frequency and a high average optical output, which cannot be realized by the conventional ultrafast optical oscillator.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of an ultrafast optical oscillator to which the present invention is applied.

FIG. 2 is a diagram showing the operating principle of the optical oscillator according to the present invention.

[Explanation of symbols]

 1 1st semiconductor laser 2 2nd semiconductor laser 11 optical output 21 collimation lens 22 optical isolator 23 condensing lens 101 gain area 102 saturable absorption area

Claims (3)

(57) [Claims] 1. A first semiconductor laser device having a plurality of electrodes, a second semiconductor laser device having a cavity length that is an integer fraction of the cavity length of the semiconductor laser device, and first and second semiconductor laser devices. And a means for optically coupling the semiconductor laser of 1. with an ultrahigh-speed optical oscillator. 2. The ultrafast light as claimed in claim 1, wherein the means for optically coupling the first and second semiconductor lasers comprises a collimation lens, an optical isolator, and a condenser lens. Oscillator. 3. The first semiconductor laser is a two-electrode parallel plane Fabry-Perot type multiple quantum well buried hetero semiconductor laser, and the second semiconductor laser is a one-electrode parallel plane Fabry-Perot type multiplex semiconductor laser. 3. A quantum well-embedded hetero semiconductor laser.
The described ultrafast optical oscillator.