JPS61133688A - Semiconductor laser-wavelength controller - Google Patents

Abstract

PURPOSE:To suppress mode hopping, by superimposing high frequency pulses, in which at least one of frequency, amplitude and duty cycle is adjusted, on an applied signal, when light is emitted or not emitted, or at both timings. CONSTITUTION:High frequency pulses 2 have the same amplitude as that of an input signal 1. The pulses are vibrated at a frequency higher than that of the input signal 1 on the positive side with the low level of the input signal as a reference. The high frequency pulses are superimposed on the input signal 1 at either timing when a semiconductor laser emits light or does not emit light. Therefore, the junction part of the semiconductor laser is hard to become high temperature, and more stable single longitudinal mode oscillation can be obtained. At least one of the frequency, amplitude and duty cycle of the high frequency pulses 2 is adjusted. Thus, mode hopping can be prevented, and the occurrence of multiple modes can be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a single wavelength semiconductor laser device in which mode hops are suppressed, and particularly to a semiconductor laser wavelength control device for controlling the wavelength thereof.

[Conventional technology]

In recent years, research and development of optical application devices using semiconductor lasers, such as laser printers, optical disk memories, and POS barcode leagues, has been actively conducted. In these devices, techniques have recently been developed that use holograms to deflect, converge, and condense light based on the principle of double diffraction. but.

The wavelength of the semiconductor laser depends on the applied current9 ambient temperature, etc.
Since the light that is diffracted by the hologram changes discontinuously and does not have a fixed single wavelength, it changes depending on the wavelength. In order to use a semiconductor laser device in an optical application device,
This is a practical problem.

Further, in optical disks, there is a problem in that mode hop noise occurs due to wavelength transition (mode hop) during semiconductor laser modulation, and this causes deterioration of the S/N ratio.

To solve these problems, distributed feedback lasers (Distributed feedback 1a) capable of producing a single wavelength have been developed.
ser) is being developed, but it is difficult and expensive to manufacture, so it has not yet been commercially available. FIGS. 2 and 3 show examples of changes in optical output and wavelength mode with respect to applied current, respectively. When a dark value current (approximately 50m^) or more is applied, light emission in laser mode occurs.

After that, the mode changes discontinuously. The manner in which this mode changes varies depending on the individual semiconductor laser, and also varies depending on the ambient temperature and applied current. As shown in FIG.
When a pulse current of is applied, Fig. 3 (a), (b),
c), (d), (e).

Six vertical modes (to) occur. In the case of a laser printer using a hologram, the occurrence of such multimodes becomes a big problem because the beam position cannot be determined.

It is also known that index-guided semiconductor lasers become single-mode when applied with a current above a certain value, but as shown in Figure 4, at a constant optical output the ambient temperature When changed, a discontinuous change in mode occurs, similar to FIG.

In this case, the transition between adjacent modes is about 0.3 nm.

Mode hops occur at a rate of one mode every 2°C.

In a scanner for a laser printer using a hologram, this mode hop causes the beam position to jump, resulting in deterioration of print quality.

Incidentally, as shown in FIGS. 2 and 3, there is a continuous fluctuation in wavelength with respect to changes in current and temperature.

Approximately 0. Although it occurs at a rate of 07 nm/'C, this does not pose a practical problem in optical application devices such as laser printers.

In view of the above-mentioned conventional drawbacks, the present invention changes the parameters of the 5-superimposed pulse and superimposes the 5-superimposed pulse on the input signal. It is an object of the present invention to provide an inexpensive semiconductor laser wavelength control device that can prevent changes, that is, mode hops, and suppress the occurrence of multimode.

[Means for solving problems]

The conventional mode hop caused by changes in current and ambient temperature as described above is due to temperature changes at the semiconductor laser junction.
This is thought to be because the bandgap changes and the wavelength that provides the maximum gain changes. Therefore, in order to prevent mode hopping, it is first necessary to reduce the temperature change at the junction. For this purpose, it is sufficient to apply a high frequency that cannot be followed by temperature changes at the junction.

In view of the above points, the present invention provides a semiconductor laser device including:
means for superimposing a high-frequency pulse on a signal to be applied, and at least one of the frequency, amplitude, and duty of the high-frequency pulse;
and a superimposition control means for controlling the high-frequency pulse to be superimposed on the applied signal at one or both of the timings when the semiconductor laser emits light and when it does not emit light. An object of the present invention is to provide a semiconductor laser wavelength control device.

[For production]

According to the present invention, in a semiconductor laser device.

As shown in FIG.
By superimposing a high-frequency pulse 2 with a higher frequency at the timing when the semiconductor laser is emitting light, that is, when the input signal 1 is at a high level, or at the timing when the semiconductor laser is not emitting light, that is, when the input signal 1 is at a low level, the semiconductor laser can be −
In a refractive waveguide semiconductor laser that oscillates in a longitudinal mode, multi-modes are suppressed from occurring. Since the semiconductor laser has a stable single-longitudinal mode, when used in a laser printer or the like, it is possible to obtain a product with good application quality.

〔Example〕

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

As shown in FIG. 5, the power spectrum of the semiconductor laser tends to fluctuate as the applied current changes at one ambient temperature. Therefore, a high frequency pulse 2 is superimposed on the input signal 1 as shown in FIG. At this time, the parameters of the high-frequency pulse, that is, the frequency, amplitude, and duty, are adjusted to values that can suppress mode hops.

FIG. F shows an embodiment of the present invention in which the input signal 1
A high-frequency pulse 2 is used which has the same amplitude as the input signal 1 and oscillates at a higher frequency than the input signal on the positive side with the low level of the input signal 1 as a reference. and.

This high frequency pulse 2 is superimposed on the input signal 1 both when the semiconductor laser emits light and when it does not emit light. Therefore, the junction of the semiconductor laser is less likely to reach a high temperature than in the case shown in FIG. 6, so that more stable single-longitudinal mode oscillation can be obtained. and,
Each parameter of the frequency, amplitude, or duty of the high-frequency pulse 2 is adjusted to a value that does not cause mode hops in the semiconductor laser even when the ambient temperature fluctuates.

When the current value applied to the semiconductor laser fluctuates in a pulsed manner, 9
Correspondingly, the temperature at the junction of the semiconductor laser changes with a slight time delay, and the optical output also changes. When a high-frequency pulse is superimposed on the input signal, the temperature change cannot follow the current value fluctuation, and the temperature at the junction can be kept constant. However, when a high-frequency pulse with such a duty is used, the optical output decreases, and the optical output is changed to a high-frequency When using a high-frequency pulse with a duty that is the same as when no superimposition is applied, the maximum applied current is large, so the temperature of the junction increases.

Therefore, in order to keep the temperature of the junction constant and the optical output constant, it is necessary to increase the bias current to the semiconductor laser.

FIG. 7 shows another embodiment of the present invention, in which the high frequency pulse 2
is superimposed on the input signal when the semiconductor laser is not emitting light. As the high frequency pulse 2, a signal generated on the positive side with respect to the low level of the input signal 1 is used.

FIG. 8 shows another embodiment of the present invention. As the high frequency pulse 2, a signal that oscillates in the negative side with respect to the low level of the input signal 1 is used, and this high frequency pulse is applied when the semiconductor laser is not emitting light. , to be superimposed on input signal 1.

FIG. 9 shows still another embodiment of the present invention, in which a high frequency pulse 2 that oscillates on the negative side with respect to the input signal 1 is superimposed on the input signal 1 when biasing the semiconductor laser.

In FIG. 10, the high frequency pulse 2 oscillates to the negative side with respect to the input signal 1, and its amplitude is such that the current value reaches 0 both when the input signal is at a low level and when the input signal is at a high level. Then, similar to the embodiment shown in FIG. 9, this high frequency pulse 2 is superimposed on the input signal 1 at the timing when the semiconductor laser emits light and when it does not emit light, and when the semiconductor laser is biased.

FIG. 11 shows the relationship between drive current and optical output.

The relationship between input signal 1 and high frequency pulse 2 is shown.

The optical output of the semiconductor laser is such that the drive current has a dark value current value of 47m.
In method A, a high frequency pulse 2 with the same amplitude as the input signal is superimposed on the input signal 1, which increases from the vicinity of A. In method A, a high frequency pulse 2 with the same amplitude as the input signal is superimposed only when two light emissions are made, and in method B, the amplitude of the high frequency pulse 2 is set as the drive current value. is selected so that it reaches close to O, and in method C, a high frequency pulse 2 whose amplitude is smaller than that of the input signal 2 is used when the semiconductor laser is not emitting light.

FIG. 12 is a chart showing oscillation modes for each drive method shown in FIG. 11. Here, the input signal 1 can obtain frequencies from DC to 2 Mllz, and the duty ratio is between 0 and 100%. Furthermore, a high frequency pulse of 5 MIIz or 10 MIIz is used. That is, in FIG. 12, when a DC 101 is used as the drive current, a single mode occurs, and when only an input signal is used, a multi-mode occurs, and in the drive method A shown in FIG. Since a high-frequency pulse is superimposed when emitting light, single mode occurs at the shorter wavelength.

In driving method C, a high-frequency pulse is superimposed during non-emission and fora bias, so a single mode appears in the longer superimposition. In driving method B, the high frequency pulse is oscillated to near the O level, so in this case, a multi-mode occurs, which is not desirable.

That is, when the high frequency pulse has an amplitude close to the dark value, stable single mode laser oscillation can be performed.

〔Effect of the invention〕

According to the present invention, by superimposing a high-frequency pulse on an input signal when a semiconductor laser is emitting light and/or not emitting light, the frequency, amplitude, and duty of the high-frequency pulse can be maintained in a single longitudinal mode even when the ambient temperature fluctuates. I used a hologram because it can be adjusted to be stable and mode hops are suppressed.

A semiconductor laser device suitable for laser printer scanners and the like can be provided.

[Brief explanation of drawings]

FIG. 1 is a waveform diagram showing input signals and superimposed high-frequency pulses in an embodiment of the semiconductor laser wavelength control device according to the present invention. FIG. 2 is a characteristic diagram showing the relationship between applied current and optical output. Figure 3 is a conventional characteristic diagram of applied current and wavelength when the ambient temperature is constant. FIG. 4 is a characteristic diagram showing the relationship between ambient temperature and wavelength in a conventional device. FIG. 5 is a diagram showing the relationship between wavelength and power spectrum showing mode hops. FIG. 6 is a waveform diagram in which a high-frequency pulse is superimposed on an input signal. FIG. 7, FIG. 8, FIG. 9, and FIG. 10 are waveform diagrams of other embodiments of the present invention. FIG. 11 is a waveform diagram showing the relationship among drive current, optical output, input signal, and high-frequency pulse. FIG. 12 is a chart showing a comparison of each drive method shown in FIG. 11. 1...Input signal. 2...High frequency pulse. Width board 9. Kakeha ≧ E 6 Kusa - Senbei 1 - Seventy-one swords - Hard bronze board trade

Claims (2)

[Claims] (1) In a semiconductor laser device, a means for superimposing a high-frequency pulse on an applied signal, a means for adjusting at least one of the frequency, amplitude, and duty of the high-frequency pulse, and a means for when the semiconductor laser emits light and when it does not emit light. A semiconductor laser wavelength control device comprising: superimposition control means for controlling the high-frequency pulse to be superimposed on the applied signal at either or both timings. (2) The semiconductor laser wavelength control device according to claim 1, wherein the superimposition control means superimposes a high frequency pulse on the applied signal when biasing the semiconductor laser.