JPH0943556A - Optical semiconductor pulse light source and light pulse generating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the generating of a pulse having a high frequency and also to obtain a fixed pulse oscillation by forming a semiconductor modulator part at the end part of one side of a light resonator or at the vicinity of the resonator. SOLUTION: A light resonator 3 is composed in such a way that a semiconductor modulator part 1 and a semiconductor gain part 2 are arranged and formed in the inside of the resonator. A DC voltage source 4 being an impression voltage source is connected to the modulation part 1 and als a high frequency power source 5 supplying a signal for modulation is connected to it. Moreover, a DC current source 6 supplying an injecting current is connected to the gain part 2. Then, light pulses are generated with the same repetition as a basic frequency by superposing a sine wave voltage having the half frequency of the basic frequency to be determined by the reciprocal of the light reciprocating time of the light resonator 3 on the semiconductor modulator part 1 on which a fixed bias voltage is impressed from the DC voltage source 4 by using a high frequency power source 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor pulse light source device and an optical pulse generation method required for optical communication and optical signal processing. More specifically, it is easy to generate a pulse having a high repetition frequency. The present invention relates to an optical semiconductor pulse light source device and a method for generating an optical pulse.

[0002]

2. Description of the Related Art Conventionally, as a light pulse light source, a light source using a gain switching method for a semiconductor laser, a passive mode locking method for a semiconductor laser, an active mode locking method for a semiconductor laser, an active mode locking method for a fiber ring laser, etc. has been used. Mainly under consideration.

The light source according to the passive mode-locking method of the semiconductor laser utilizes self-excited oscillation by a semiconductor saturable absorber, and pulse oscillation can be obtained without adding a modulation signal from the outside, which is higher than 100 GHz. The repetition frequency is also obtained. However, when this light source is applied to optical communication, signal processing, etc., there is a drawback in that it is difficult to obtain synchronization.

Therefore, an active mode locking method in which an external high frequency power source is used for modulation is indispensable. However, due to the limitation of the modulator band and the limitation of the external high frequency power source, the frequency is about 40 GHz. Further, there is a problem that the external high frequency power source of 40 GHz or more is expensive and the cost is increased.

[0005]

By the way, in the optical semiconductor pulse light source device, the repetition frequency of the generated pulse is the fundamental frequency given by the reciprocal of the time required for the optical pulse to reciprocate through the resonator, or an integer thereof. Double the frequency. Therefore, in order to obtain a high repetition frequency, the band of the modulator must be increased to about the fundamental frequency. For example, at a frequency of 40 GHz or higher, it is conventionally necessary to create a modulator having such a high band. Was difficult. Further, in the active mode locking, if the modulation frequency is slightly deviated from the resonance frequency, the pulse width increases and the pulse power also decreases.

Therefore, an object of the present invention is to easily generate a high-frequency pulse, to enable a frequency which has been impossible in the past due to the limitation of the bandwidth of the modulator and the limitation of the high-frequency power source to be driven, and yet stable. An object of the present invention is to provide an optical semiconductor pulse light source device capable of obtaining pulse oscillation and a method of generating an optical pulse.

[0007]

FIG. 1 is a diagram showing a basic configuration of an optical semiconductor pulse light source device according to the present invention. In the figure, 1 is a semiconductor modulator section in which a light absorption coefficient for a certain wavelength region is increased by applying a voltage, 2 is a semiconductor gain section adjacent to the semiconductor modulator section 1, and this semiconductor gain section 2 Has a gain for the certain wavelength range. At least the semiconductor modulator unit 1 and the semiconductor gain unit 2 are arranged and formed inside, so that the optical resonator 3
Is configured. A DC voltage source 4 which is an applied voltage source is connected to the modulator section 1, and a high frequency power source 5 which supplies a signal for modulation is connected to the modulator section 1. A DC current source 6 for supplying an injection current is connected to the gain section 2. The semiconductor modulator unit 1 has a voltage range in which the change of the light absorption coefficient with respect to the applied voltage increases monotonically.
Further, it has a characteristic that the second derivative of the light absorption coefficient with respect to the voltage is positive.

In the method of generating an optical pulse by the optical semiconductor pulse light source device having such a configuration, the sine wave voltage having a half frequency of the fundamental frequency determined by the reciprocal of the optical round trip time of the optical resonator 3 is applied to the high frequency. The power source 5 is used to superimpose it on the semiconductor modulator 1 to which a constant bias voltage is applied from the DC voltage source 4, and generate an optical pulse with the same repetition as the fundamental frequency.

FIG. 2 schematically shows the principle of pulse generation. The fundamental frequency determined by the reciprocal of the optical round trip time τ of the optical resonator 3 is f0. By applying a sinusoidal voltage having a frequency half that of the fundamental frequency f0 from the high frequency power source 5 to the modulator section 1, the absorption coefficient of the optical resonator 3 changes, and the loss changes with time.

FIG. 2 (a) shows the case where the frequency of the modulation voltage is f0 and the pulse train generated is generated only at the frequency of f0 or an integral multiple thereof. Therefore, the optical pulse is synchronized with the time when the loss is minimum. And occurs at frequency f0.
This is the conventional active mode locking method.

FIG. 2 (b) shows the method according to the present invention, in which the frequency of the modulation voltage is ½ of the fundamental frequency. At this time, the states of (1) and (2) shown in the figure are possible in the time arrangement of the light pulse. Of these, oscillation will occur in a state where the loss is small. In the state of (1), the pulse intensity is constant. Since the optical pulse is stabilized by being applied to the shoulder where the loss changes abruptly, the restoring force works even if the frequency f0 is slightly shifted, and stable pulse oscillation can be obtained. In the state of (2), the loss repeats large and small for each optical pulse, so that the intensity of the pulse also repeats large and small. In order to realize the state of (1), it is necessary to reduce the ratio of the time region in which the loss is large in the curve showing the time change of the loss.

This is realized by adjusting the bias voltage as shown in FIG. 3, that is, as shown in FIG. 3 (a), the voltage dependence of the loss of the modulator unit monotonically causes loss. As shown in FIG. 3B, the bias voltage Vb is set in the voltage region where the second derivative is increased and is positive, and the sine wave voltage is superposed within the range. As a result, the time change of the loss as shown in FIG. 3C is obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of an optical semiconductor pulse light source device of the present invention is a semiconductor gain section having a gain for a certain wavelength range, and an optical absorption coefficient for the wavelength range with respect to an applied voltage. A semiconductor modulator section having a voltage range that increases monotonically and having a positive second-order derivative with respect to the voltage of the optical absorption coefficient in the voltage range is disposed inside the optical resonator, and the semiconductor modulator section has the optical resonance. It is characterized in that it is formed at one end of the container or in the vicinity thereof.

The second embodiment of the optical semiconductor pulse light source device of the present invention is the same as the first embodiment, but a voltage source for applying a constant bias voltage is connected to the semiconductor modulator section. At the same time, a high frequency voltage source for superimposing a sine wave voltage having a half frequency of a fundamental frequency determined by the reciprocal of the optical round trip time of the optical resonator on the semiconductor modulator section to which the constant bias voltage is applied. It is characterized by being connected.

In a third embodiment of the optical semiconductor pulse light source device of the present invention, a semiconductor gain section having a gain and a semiconductor modulator section having a multiple quantum well as a light absorption layer are arranged and formed inside an optical resonator. A multi-quantum well optical modulator type optical semiconductor pulse light source device in which the semiconductor modulator section is formed at one end of the optical resonator or in the vicinity thereof, wherein the semiconductor modulator section has a constant Is connected to a voltage source for applying the bias voltage, and the semiconductor modulator section to which the constant bias voltage is applied has a frequency half the fundamental frequency determined by the reciprocal of the optical round-trip time of the optical resonator. A high-frequency voltage source for superposing a sine wave voltage is connected.

The optical semiconductor pulse light source device of the present invention is characterized in that, in any of the first to third embodiments, a wavelength filter made of a diffraction grating is provided in the resonator. .

The first method of generating an optical pulse of the present invention
The embodiment has a semiconductor gain section having a gain in a certain wavelength range and a voltage range in which the light absorption coefficient in the wavelength range monotonically increases with respect to the applied voltage, and the light absorption coefficient in the voltage range. A semiconductor pulse light source device in which a semiconductor modulator section having a positive second derivative with respect to the voltage is placed inside the optical resonator, and the semiconductor modulator section is formed at one end of the optical resonator or in the vicinity thereof. By using a sinusoidal voltage having a frequency of half the fundamental frequency determined by the reciprocal of the optical round-trip time of the optical resonator, superposed on the semiconductor modulator portion to which a constant bias voltage is applied, at the fundamental frequency. It is characterized by generating an optical pulse.

In the second embodiment of the optical pulse generating method of the present invention, a semiconductor gain section having a gain and a semiconductor modulator section having a multiple quantum well as a light absorption layer are arranged and formed inside an optical resonator. , A reciprocal of the optical round-trip time of the optical resonator using a multiple quantum well optical modulator type optical semiconductor pulse light source in which the semiconductor modulator section is formed at one end of the optical resonator or in the vicinity thereof. The sine wave voltage having a half frequency of the fundamental frequency determined by is superposed on the semiconductor modulator section to which a constant bias voltage is applied, and an optical pulse is generated at the fundamental frequency.

The third embodiment of the optical pulse generating method of the present invention is the same as the first or second embodiment,
A wavelength filter made of a diffraction grating is provided in the resonator.

[0020]

【Example】

(Embodiment 1) FIG. 4 shows a first embodiment of the present invention. The semiconductor gain section 2 and the electro-absorption modulator section 1 are integrated on the same semiconductor substrate made of InP, and the optical resonator 3
Is formed. In the gain section 2, the well layer is made of InPGaAs or IGaAsP and the barrier layer is made of InGaAsP multiple quantum wells, and its photoluminescence wavelength is around 1.55 μm. In the modulator section 1, the well layer is made of InGaAs or InGaAsP and the barrier layer is made of InGaAsP multiple quantum wells, and its photoluminescence wavelength is around 1.49 microns. The modulator section 1 has a length of 120 microns and the gain section 2 has a length of 706 microns.

Electrodes are formed on the modulator section 1 and the gain section 2, and these electrodes are separated by a length of 50 μm and are electrodes 10 and 11, respectively. The length of the resonator 3 is 876 microns.

In this structure, the fundamental frequency determined by the optical round trip time is about 48 GHz. In the optical semiconductor pulse light source device having this configuration, the modulator unit 1 includes a DC voltage source 4
A bias voltage and a sine wave voltage of 24 GHz, which is half the fundamental frequency, are superimposed and applied by a bias TEE 7 and a high frequency power source 5. At this time, the bias voltage is set to a relatively shallow point as shown in FIG. On the other hand, the gain unit 2
, A constant current is applied from the DC current source 6.

As a result, an optical pulse train of 48 GHz with a pulse width of 3 ps was obtained from the end face of the optical resonator 3.

(Embodiment 2) FIG. 5 shows a second embodiment of the present invention. This embodiment has the same structure as that of the first embodiment.
In order to narrow the spectral width of the pulse, the diffraction grating 1
The optical filter unit 12 is formed of three.

The filter 12 limits the spread of the wavelength and suppresses the wavelength chirping that occurs when the optical pulse is generated. This is important for reducing the influence of chromatic dispersion in long-distance optical fiber communication.

[0026]

According to the optical semiconductor pulse light source device and the optical pulse generating method of the present invention, since it is possible to drive at a frequency voltage of 1/2 of the pulse repetition frequency, it becomes easy to generate a high frequency pulse. Now, it has become possible to achieve frequencies that could not be realized by the limitation of the modulator band and the limitation of the driving high frequency power source. Since the pulse is stabilized by being applied to the shoulder where the loss changes abruptly, the restoring force works even if the frequency f0 is slightly shifted, and stable pulse oscillation can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a basic configuration of an optical semiconductor pulse light source device according to the present invention.

FIG. 2 is a graph for explaining one of the actions of the optical semiconductor pulse light source device according to the present invention.

FIG. 3 is a graph for explaining one of the actions of the optical semiconductor pulse light source device according to the present invention.

FIG. 4 is a first optical semiconductor pulse light source device according to the present invention.
It is a block diagram which shows the Example of.

FIG. 5 is a second optical semiconductor pulse light source device according to the present invention.
It is a block diagram which shows the Example of.

[Explanation of symbols]

 1 Semiconductor Electroabsorption Type Optical Modulator Section 2 Semiconductor Gain Section 3 Optical Resonator 4 DC Voltage Source 5 High Frequency Power Supply 6 DC Current Source 7 Bias TEE 8 Multiple Quantum Well for Modulator 10 Modulator Electrode 11 Gain Section Electrode 12 Wavelength Filter Section 13 Diffraction grating

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yamamoto ▲ Mitsu ▼ Husband 1-16, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (7)

[Claims] 1. A semiconductor gain section having a gain in a certain wavelength range, and a voltage range in which the light absorption coefficient in the wavelength range monotonically increases with respect to an applied voltage, and the light absorption coefficient of the light absorption coefficient in the voltage range. A semiconductor modulator section having a positive second derivative with respect to a voltage is arranged inside the optical resonator, and the semiconductor modulator section is formed at one end of the optical resonator or in the vicinity thereof. Optical semiconductor pulse light source device. 2. A voltage source for applying a constant bias voltage is connected to the semiconductor modulator section, and the semiconductor modulator section to which the constant bias voltage is applied is connected to a light source of the optical resonator. The optical semiconductor pulse light source device according to claim 1, further comprising a high-frequency voltage source connected to superimpose a sine wave voltage having a half frequency of a fundamental frequency determined by the reciprocal of the round-trip time. 3. A semiconductor gain section having a gain and a semiconductor modulator section having a multi-quantum well as an optical absorption layer are arranged and formed inside an optical resonator, and the semiconductor modulator section is one end of the optical resonator. Is a multi-quantum well optical modulator type optical semiconductor pulse light source device formed in or near the portion, and a voltage source for applying a constant bias voltage is connected to the semiconductor modulator portion, A high frequency voltage source for superimposing a sine wave voltage having a half frequency of a fundamental frequency determined by the reciprocal of the optical round trip time of the optical resonator is connected to the semiconductor modulator section to which a constant bias voltage is applied. An optical semiconductor pulse light source device characterized in that 4. The optical semiconductor pulse light source device according to claim 1, wherein a wavelength filter made of a diffraction grating is provided in the resonator. . 5. A semiconductor gain section having a gain in a certain wavelength range, and a voltage range in which the light absorption coefficient in the wavelength range monotonically increases with respect to an applied voltage, and the light absorption coefficient in the voltage range is increased. A semiconductor pulse light source device in which a semiconductor modulator section having a positive second derivative with respect to a voltage is arranged inside an optical resonator, and the semiconductor modulator section is formed at one end of the optical resonator or in the vicinity thereof. Using a sinusoidal voltage having a frequency of half the fundamental frequency determined by the reciprocal of the optical round-trip time of the optical resonator, is superimposed on the semiconductor modulator portion to which a constant bias voltage is applied, and light is emitted at the fundamental frequency. A method of generating an optical pulse, which comprises generating a pulse. 6. A semiconductor gain section having a gain and a semiconductor modulator section having a multiple quantum well as a light absorption layer are arranged and formed inside an optical resonator, and the semiconductor modulator section is one end of the optical resonator. Using a multi-quantum well optical modulator type optical semiconductor pulse light source formed in the part or in the vicinity thereof, a sinusoidal voltage having a frequency of half the fundamental frequency determined by the reciprocal of the optical round-trip time of the optical resonator, A method of generating an optical pulse, characterized in that the optical pulse is superposed on the semiconductor modulator section to which a constant bias voltage is applied, and the optical pulse is generated at the fundamental frequency. 7. The optical pulse generating method according to claim 5, wherein a wavelength filter made of a diffraction grating is provided in the resonator.