JP2002204037A - High-frequency signal generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a high-frequency signal such as a high-frequency period signal, a pseudo-random signal or a chaos signal having a frequency exceeding a relaxation oscillation frequency of a semiconductor laser with a simple circuit configuration. SOLUTION: A high-frequency signal generator comprises two semiconductor lasers 1, 2 freerunning with a prescribed freerunning wavelength so that the freerunning wavelengths approach to each other. In this case, a light is injected from one semiconductor laser 1 to another semiconductor laser 2, a light signal generated by the laser 2 is reflected by an external mirror 5 and fed back to the laser 2, and a light signal generated by the laser 2 is photoelectrically converted by a photodiode 7. Thus, for example, the high-frequency signal such as the period signal, pseudo-random signal or the like of a high frequency having the high frequency exceeding the relaxation oscillation frequencies of the lasers 1 and 2 is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-frequency signal generator for generating a high-frequency signal using a semiconductor laser.

[0002]

2. Description of the Related Art It has been studied to generate a signal by performing injection locking on a semiconductor laser. For example, in the specification of US Pat. An apparatus for expanding a modulation band and reducing noise by injection locking (hereinafter, referred to as a first conventional example) is disclosed.

In this first conventional example, a first optical signal is generated by a slave semiconductor laser, and an optical modulator modulates the intensity of the generated first optical signal according to an input microwave signal. Output. The other master semiconductor laser generates a second optical signal for injection locking with the slave semiconductor laser, where
Has a large power level such that the photon density in the slave semiconductor laser is sufficiently increased during injection locking. Then, the second optical signal is injected into the slave semiconductor laser, thereby increasing the modulation bandwidth of the first optical signal and reducing the broadband noise of the first optical signal.

In Japanese Patent No. 2961898, a semiconductor laser and a photodiode for receiving a laser beam oscillated from the semiconductor laser are provided, an input side is connected to an anode of the photodiode, and an output side is provided. A chaos generator (hereinafter referred to as a second conventional example) including a nonlinear amplifier connected to the anode of the semiconductor laser is disclosed.

In the second conventional example, optical chaos can be generated by using a semiconductor laser, and the optical chaos changes a voltage applied to a photodiode such as an avalanche photodiode. For this reason, it can be easily controlled with high controllability, and has a unique effect that no fine optical adjustment is required as in the related art.

[0006]

However, in the first conventional example, the modulation band is expanded and noise is reduced by injection locking of the semiconductor laser, and a high-speed response characteristic to current modulation of the semiconductor laser is obtained. However, vibration of a high frequency of, for example, several tens of GHz or more cannot be expected by itself.

In a second conventional example, a semiconductor laser,
Although a chaos signal can be generated by a photodiode, a nonlinear amplifier, or the like, there is a problem that the band of the generated signal is limited by the relaxation oscillation frequency of the laser and the response characteristics of the electronic circuit.

An object of the present invention is to solve the above-mentioned problems, to have a very simple circuit configuration as compared with the conventional example, to provide a high-frequency periodic signal having a frequency exceeding the relaxation oscillation frequency of a semiconductor laser, a pseudorandom signal, and the like. It is an object of the present invention to provide a high-frequency signal generator capable of generating a high-frequency signal of the above.

[0009]

According to the present invention, there is provided a high-frequency signal generator according to the present invention, comprising: a first semiconductor laser for generating a first optical signal having a single wavelength; A second semiconductor laser which is close to the wavelength of the first optical signal and has a predetermined free-running oscillation wavelength difference to generate a second optical signal; and a second light generated by the second semiconductor laser. A light reflecting means for reflecting a signal and returning the signal to the second semiconductor laser;
And photoelectric conversion means for generating a high-frequency signal by photoelectrically converting the optical signal.

In the above high frequency signal generator,
Preferably, when the first optical signal is optically injected into the second semiconductor laser, the second optical signal is transmitted to the first semiconductor laser.
And the frequency of the high-frequency signal is higher than the relaxation oscillation frequency of the second semiconductor laser when the optical signal is not optically locked.

Further, in the high-frequency signal generator, preferably, by changing the reflectance of the light reflecting means, any one of a high-frequency periodic signal and a pseudo-random signal is used as the high-frequency signal. Is selectively generated.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a high-frequency signal generator according to an embodiment of the present invention. In general, the configuration of the high-frequency signal generator according to this embodiment includes two semiconductor lasers 1 and 2 that have free-running oscillation wavelengths that are close to each other but have a predetermined free-running oscillation wavelength difference and that self-run. One semiconductor laser 1 to the other semiconductor laser 2
The optical signal generated by the semiconductor laser 2 is reflected by the external mirror 5 and returned to the semiconductor laser 2, and the optical signal generated by the semiconductor laser 2 is photoelectrically converted by the photodiode 7. For example, it is characterized by generating a high-frequency signal such as a high-frequency periodic signal, a pseudo-random signal, and a chaos signal having a frequency exceeding the relaxation oscillation frequency of the semiconductor lasers 1 and 2.

Here, the relaxation oscillation of the semiconductor lasers 1 and 2 is a natural oscillation due to the non-linear characteristics of the laser mechanism. When the injection currents of the semiconductor lasers 1 and 2 are pulse-modulated, phenomena such as damping oscillation observed at the rise of the output power and frequency peaks in the noise spectrum of the free-running semiconductor laser represent relaxation oscillation. The frequency of the relaxation oscillation, that is, the relaxation oscillation frequency Ω, is expressed by the number of photons P of the semiconductor lasers 1 and 2,
2 and a linear gain coefficient G representing the dependence of the gain on electron carriers as shown in the following equation.
_N.

[0015]

[Number 1] Ω = √ _(GG N P)

## EQU2 ## G _N = ∂G / ∂N

Here, N is the number of carriers.

Next, the configuration of the high-frequency signal generator will be described in detail with reference to FIG.

In FIG. 1, semiconductor lasers 1 and 2 are, for example, distributed feedback drag type (DFB type) semiconductor lasers or surface emitting semiconductor lasers, respectively. Oscillates with a free-running oscillation wavelength difference of While the semiconductor laser 1 generates a first optical signal of a single wavelength, the semiconductor laser 2 can perform optical injection locking substantially the same as or close to the wavelength of the first optical signal (the wavelength range of the optical injection locking range). A second optical signal of a wavelength. Here, the first optical signal is injected into the semiconductor laser 2 via the optical isolator 10 to inject light. At this time, the semiconductor laser 2 enters a light injection mode or a light injection lock mode which is not the synchronous mode according to the light injection amount, generates a second optical signal, and outputs the second optical signal via the collimator lens 3 and the beam splitter 4. The light is made incident on an external mirror 5 having a reflecting surface perpendicular to the optical axis of the collimating lens 3 and constituting light reflecting means. Here, when the light injection amount is sufficiently large, the light injection locking mode is set, and the semiconductor laser 2 converts the light injection locked second optical signal that is substantially the same as the wavelength of the first optical signal and is coherent. appear.

Next, the external mirror 5 reflects the incident optical signal and returns it to the second semiconductor laser 2 via the beam splitter 4 and the collimating lens 3. On the other hand, the optical signal generated by the second semiconductor laser 2 is taken out by the beam splitter 4 and made incident on the photodiode 7 via the focus lens 6. In response, the photodiode 7 photoelectrically converts the incident optical signal into an electric signal and outputs the electric signal via the high-frequency amplifier 8. Here, the generated electric signal is, as described later, for example, a high-frequency periodic signal having a frequency higher than the relaxation oscillation frequency of the semiconductor laser 2 when not performing optical injection locking, and a kind of pseudo-random signal. And a high-frequency signal such as a chaos signal.

In the high-frequency signal generator configured as described above, the optical system from the semiconductor laser 2 to the external mirror 5 constitutes a feedback oscillation system. Changes the operation mode. (A) The injection current Jb of the semiconductor laser 2. (B) The delay amount τ determined by the distance from the emission surface of the semiconductor laser 2 to the reflection surface of the external mirror 5. (C) Reflectance of external mirror 5 ξext.

By changing these operating parameters, as will be described later in detail, the oscillation frequency and signal waveform (specifically, the periodic waveform) of the high-frequency signal intensity-modulated by the optical signal generated by the feedback oscillation system are changed. Signal, a pseudo-random signal, and a pseudo-random periodic pattern). The high-frequency signal generator according to the present embodiment can selectively generate high-frequency signals such as a high-frequency periodic signal and a chaotic signal that is a pseudo-random signal according to the operation mode by changing the operation parameter. it can.

As described above, according to this embodiment, the circuit configuration is extremely simple as compared with the conventional example.
For example, a high-frequency signal such as a high-frequency periodic signal, a pseudo-random signal, or a chaotic signal having a frequency exceeding the relaxation oscillation frequency of the semiconductor laser can be generated.

FIG. 2 is a block diagram showing the configuration of a high-frequency signal generator as a first comparative example used in the embodiment.
In the first comparative example of FIG. 2, compared to the embodiment of FIG.
The semiconductor laser 1 for light injection is not provided, and no light is injected. That is, the semiconductor laser 2 operates in a free-running oscillation state.

FIG. 3 is a block diagram showing a configuration of a high-frequency signal generator as a second comparative example used in the embodiment.
In the second comparative example of FIG. 3, compared to the first embodiment,
The optical signal generated by the semiconductor laser 2 is incident on the photodiode 7 via the focus lens 9 without providing the beam splitter 4 and the external mirror 5. That is, the semiconductor laser 2 is in a light injection state, but does not constitute a feedback oscillation system.

[0025]

FIG. 4 is a signal waveform diagram showing an output signal in a high-frequency oscillation mode as a result of a numerical experiment of a high-frequency signal generator according to a first comparative example. In this numerical experiment, the operation parameter was set to the injection current Jb = (1 + 2/3) Jth
(Where Jth is a threshold current), the delay amount τ
= 1 ns and the reflectance ξext = 0.006. As is clear from FIG. 4, a high-frequency periodic signal having a frequency of 2.7 GHz substantially equal to the relaxation oscillation frequency was observed.

FIG. 5 is a signal waveform diagram showing an output signal in the chaos oscillation mode, which is a result of a numerical experiment of the high-frequency signal generator according to the first comparative example. In this numerical experiment, the operating parameter was set to the injection current Jb = (1 + 2/3) Jt
h, the delay amount τ = 1 ns, and the reflectance ξext = 0.012. As is clear from FIG. 5, a high-frequency chaotic signal having a maximum frequency of 2.7 GHz substantially equal to the relaxation oscillation frequency was observed.

FIG. 6 is a numerical experiment result of the high-frequency signal generator according to the second comparative example, showing the output signal of the laser by light injection, the vibration frequency, and the vibration possibility. And a graph of the stability coefficient. Here, the light injection coefficient ξinj (no unit) represents the intensity (relative value) of the injected light standardized by the photon attenuation coefficient inside the resonators of the semiconductor lasers 1 and 2. When the stability coefficient shown in FIG. 6 is negative, the laser is stabilized, and when it is positive, the laser vibrates at a predetermined frequency. As is clear from FIG. 6, as indicated by hatching, the oscillation region oscillates at an oscillation frequency of about 3 to about 7 GHz when the intensity (relative value) of the injected light is in the range of 0.02 to 0.18. However, the range of vibration frequencies is very limited.

FIG. 7 is a signal waveform diagram showing an output signal in a high-frequency oscillation mode, which is a result of a numerical experiment of the high-frequency signal generator according to the embodiment. In this numerical experiment, the operating parameters were: injection current Jb = (1 + 2/3) Jth, delay amount τ = 1 ns, reflectance ξext = 0.05, light injection intensity ratio ξinj = 0.25, free-running oscillation wavelength difference Ω. = 3 GHz
Set to. As is clear from FIG. 7, a high-frequency periodic signal having a frequency of 13 GHz exceeding the relaxation oscillation frequency was observed.

FIG. 8 is a signal waveform diagram showing an output signal in the chaos oscillation mode, which is a result of a numerical experiment of the high-frequency signal generator according to the embodiment. In this numerical experiment, the operating parameters were: injection current Jb = (1 + 2/3) Jth, delay amount τ = 1 ns, reflectance ξext = 0.125, light injection intensity ratio ξinj = 0.25, free-running oscillation wavelength difference Ω. = 3GH
z. As is clear from FIG. 8, a high-frequency chaotic signal having a maximum frequency of 14 GHz exceeding the relaxation oscillation frequency was observed.

Here, the signal waveforms of FIGS. 7 and 8 according to the embodiment are respectively similar to FIGS. 4 and 5 according to the first comparative example, but the horizontal axis and the vertical axis are completely different. Please be careful.

FIG. 9 is a graph of a numerical experiment result of the high-frequency signal generator according to the embodiment, showing a vibration frequency of a laser caused by light injection and a vibration frequency with respect to a light injection coefficient ξinj. In this numerical experiment, the operating parameters were set as injection current Jb = (1 + 2/3) Jth and delay amount τ =
1 ns, the reflectance ξext = 0.075, and the free-running oscillation wavelength difference Ω = 3 GHz. As is clear from FIG. 9, as the intensity of the injected light increases, the vibration frequency initially becomes
Vibrates at the relaxation oscillation frequency corresponding to the free-running oscillation wavelength difference, but when the threshold value exceeds about 0.14, the oscillation frequency becomes
Vibration at a frequency of about 12 GHz or higher, which exceeds the relaxation oscillation frequency, was observed. In other words, it can be said that, for the first time, generation of a high-frequency signal oscillating at a frequency exceeding the relaxation oscillation frequency can be observed by combining light injection with the feedback oscillation system.

[0032]

As described above in detail, according to the high-frequency signal generator of the present invention, two semiconductor lasers having free-running oscillation wavelengths close to each other are provided, and light is injected from one semiconductor laser to the other semiconductor laser. Then, the optical signal generated by the other semiconductor laser is reflected and returned to the other semiconductor laser, and the optical signal generated by the other semiconductor laser is photoelectrically converted to generate a high-frequency signal. Therefore, the circuit configuration is extremely simple as compared with the conventional example, and high-frequency signals such as high-frequency periodic signals and pseudo-random signals having a high frequency exceeding the relaxation oscillation frequency of the semiconductor laser can be generated.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a high-frequency signal generator according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a high-frequency signal generator according to a first comparative example.

FIG. 3 is a block diagram illustrating a configuration of a high-frequency signal generator according to a second comparative example.

FIG. 4 is a signal waveform diagram showing an output signal in a high-frequency oscillation mode, which is a result of a numerical experiment of a high-frequency signal generator according to a first comparative example.

FIG. 5 is a signal waveform diagram showing an output signal in a chaos oscillation mode, which is a numerical experiment result of the high-frequency signal generator according to the first comparative example.

FIG. 6 is a numerical experiment result of a high-frequency signal generator according to a second comparative example, showing an output signal of a laser by light injection, a vibration frequency and a vibration possibility, and a vibration frequency and a stability coefficient with respect to a light injection coefficient Δinj. It is a graph of.

FIG. 7 is a signal waveform diagram showing an output signal in a high-frequency oscillation mode, which is a numerical experiment result of the high-frequency signal generator according to the embodiment.

FIG. 8 is a signal waveform diagram showing an output signal in a chaos oscillation mode, which is a numerical experiment result of the high-frequency signal generator according to the embodiment.

FIG. 9 is a graph showing a result of a numerical experiment of the high-frequency signal generator according to the embodiment, showing a vibration frequency of a laser caused by light injection and a vibration frequency with respect to a light injection coefficient ξinj.

[Explanation of symbols]

 1, 2, semiconductor laser, 3: collimating lens, 4: beam splitter, 5: external mirror, 6: focus lens, 7: photodiode, 8: high-frequency amplifier, 10: optical isolator.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Peter Davis 2-1-2 Koikodai, Seika-cho, Soraku-gun, Kyoto Pref. ATR Co., Ltd. Environmentally Adaptive Communication Laboratory (72) Inventor Tajin Aida Kyoto, Kyoto F-term (Reference) 5F073 AA89 AB21 AB29 EA02 EA29

Claims (3)

[Claims] A first optical signal generating a single wavelength first optical signal;
And a second semiconductor that is optically injected with the first optical signal and generates a second optical signal having a predetermined free-running oscillation wavelength difference close to the wavelength of the first optical signal. A laser; a light reflecting means for reflecting a second optical signal generated by the second semiconductor laser and returning to the second semiconductor laser; a second light generated by the second semiconductor laser A high-frequency signal generator comprising: a photoelectric conversion unit that generates a high-frequency signal by photoelectrically converting a signal. 2. The high-frequency signal generator according to claim 1, wherein when the first optical signal is injected into the second semiconductor laser, the second optical signal is changed to the first optical signal. Wherein the frequency of the high-frequency signal is higher than the relaxation oscillation frequency of the second semiconductor laser when the light is not injection-locked. 3. The high-frequency signal generating device according to claim 1, wherein the high-frequency signal includes a high-frequency periodic signal by changing a reflectance of the light reflecting means.
A high-frequency signal generation device for selectively generating any one of a pseudo-random signal and a pseudo-random signal.