JPS61133684A - Semiconductor laser-wavelength controller - Google Patents

Abstract

PURPOSE:To suppress mode hopping and to make printing quality homogeneous when the controller is used for a laser printer hologram scanner, by superimposing high frequency pulses, whose power per pulse is made constant, on an input signal. CONSTITUTION:A sawtooth wave and a control voltage V are applied on a comparator 11. An output signal 12, whose duty cycle corresponds to the voltage value, is outputted. The output signal 12 is applied on a VCA13. A controllable voltage V is applied to the VCA13 through a sensitivity setting circuit 14. Therefore, the product of the pulse width and the amplitude value becomes constant in the output voltage OUT. Such frequency pulses are superimposed on an input signal (not shown), and the result is applied on a semiconductor laser. Thus, mode hopping can be suppressed, and the printing quality of a laser printer can be made homogeneous.

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.

[Prior Art] In recent years, research and development of optical application devices using semiconductor lasers, such as laser printers, optical disk memories, and POS barcode leagues, have been actively conducted. In these devices, a technique has recently been developed that uses a hologram to perform optical deflection, optical convergence, and condensation based on the principle of single diffraction. but.

The wavelength of a semiconductor laser depends on the applied current, 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, a distributed feedback laser capable of producing a single wavelength (Distributecl feedback 1
Aser) is being developed, but it has not yet been commercially available because it is difficult and expensive to manufacture. FIGS. 2 and 3 show examples of changes in optical output and wavelength mode with respect to applied current, respectively. Dark value current (approx. 50mA)
When the above voltage is applied, light emission occurs in a laser mode, and thereafter 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. In this semiconductor laser, as shown in FIG.

When a pulse current is applied to 20 m with a bias current of 50 mA, Fig. 3 (a), (b), (c), and (d).

Six vertical modes (E) and (E) are generated. In the case of laser printers that use holograms, such multi-modes occur because the beam position is not fixed.

It becomes a big problem.

Furthermore, it is known that refractive waveguide type semiconductor lasers become single-mode when applied with a current above a certain value, but as shown in Figure 4, it is possible to change the ambient temperature at a constant optical output. When this happens, a discontinuous change in mode occurs similar to that shown in FIG.

In this case, the transition between adjacent modes is approximately 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 pop causes the beam position to jump, resulting in deterioration of print quality.

As shown in FIGS. 2 and 3, continuous fluctuations in wavelength occur 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.

The applicant has developed the frequency and amplitude of high-frequency pulses in order to eliminate the above-mentioned drawbacks of semiconductor laser devices.

We have developed a technology in which parameters such as duty are adjusted so that the semiconductor laser can stably oscillate a single longitudinal mode without being affected by ambient temperature, and this high-frequency pulse is superimposed on the input signal.

That is, in order to prevent the power spectrum from fluctuating toward longer wavelengths as shown in FIG. 5 due to changes in ambient temperature, the input signal 1 as shown in FIG.
A high-frequency pulse is superimposed on the At this time, the high frequency pulse is changed by changing the pulse width T1 by T1' while keeping one frequency constant, for example, as shown in FIG. 7, so that the semiconductor laser performs stable single longitudinal mode oscillation.

Change the duty from T+/T2 to T+'/T
Change it to 2. When such a semiconductor laser is applied to a hologram scanner for a laser printer as shown in FIG.

Since the energy changes at positions P1 and P2 on the photoconductor drum 4, the density of the dots is no longer constant. For this reason, there was a problem that the print quality was not uniform.

In view of the above-mentioned drawbacks, the present invention provides a method for adjusting the duty even if the pulse width of the high-frequency pulse is changed.

It is an object of the present invention to provide a semiconductor laser oscillation control device that can obtain uniform printing quality because the energy of the irradiated laser light does not vary depending on the irradiation position. In laser equipment.

means for superimposing a high-frequency pulse on an input signal; means for adjusting at least one of the frequency, amplitude, and duty ratio of the high-frequency pulse to obtain a single longitudinal mode; Provided is a semiconductor laser wavelength control device comprising means for keeping the amount of light constant.

[For production]

According to the present invention, as shown in FIG. 1, a high-frequency pulse having a higher frequency than the input signal is superimposed on the input signal, and the applied current is adjusted such that the product of the power Pa and the pulse width Ta of the high-frequency pulse is constant. By changing , the amount of light will be constant for any laser light pulse, and when used in a hologram scanner for a laser printer, the printing quality will also be uniform.

Of course, at this time, the frequency, amplitude, and duty ratio of the high-frequency pulse including the pulse width Ta are adjusted to perform stable single mode oscillation.

〔Example〕

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

In FIG. 1, in order to fix the product of the pulse width Ta and the laser power Pa of the high-frequency pulse 61, which is a pulse superimposed on the input signal and has a higher frequency than the input signal, to a constant value S, the pulse When the width Ta changes.

The laser power Pa may be controlled so as to satisfy Pa=S/Ta. For this purpose, the current applied to the semiconductor laser is changed.

That is, in FIG. 1, when the pulse width Ta is large (that is, the duty Ta / T 2 is large), the laser power Po, that is, the current applied to the semiconductor laser is small, and when the pulse width Ta is small, the laser The power Pa, that is, the applied current is controlled to be large.

Here, the relationship between duty, laser power, and applied current is as follows.

kD Hop - I b ) = P k T b (1 - I b / I op) = P
Here, k is a constant, D is a duty, Iop is a maximum current value of applied current, Ib is a bias current value (dark value), and P is a laser power. Since Ib/Iop is nothing but the duty D, if the duty D is changed to select the optimum value, the laser power will also change. Therefore, in order to keep the power constant, the duty must also be constant.

Therefore, the temperature of the semiconductor laser will change slightly.

Furthermore, if the junction temperature of the semiconductor laser is constant, the optical output will decrease, and if the optical output is constant, the junction temperature will increase, so in order to keep both the junction temperature and the optical output constant, the bias current rb is increased. I have to let it happen.

FIG. 9 shows a block diagram of a control circuit of the present invention that performs the above-mentioned control.

A saw-tooth signal is input to one input of the comparator 11, and a controllable voltage (2) is applied to the other input. According to this voltage value, the comparator 11 outputs an output signal 12 whose duty, ie, pulse width, is controlled, and this output signal 12 is applied to the VCA 13. vC
Since the controllable voltage (■) is applied to A13 via the sensitivity setting circuit 14, this controllable voltage V causes VCA1
The amplitude value of the output voltage OUT of No. 3 is determined. At this time, the duty or pulse width of the output voltage OUT corresponds to the pulse width of the output of the comparator 11.

Therefore, comparator 12. VCA13. Sensitivity setting circuit 1
The characteristic No. 4 may be set so that the product of the pulse width and the amplitude value of the output voltage OUT is constant.

In this way, the light intensity of each pulse of laser light can be made equal, and the integrated power can be kept constant. Then, the pulse width of the high-frequency pulse is controlled so that the mode of the laser light is not affected by ambient temperature, etc., and the laser power, that is, the current applied to the laser, is controlled in accordance with the change in the pulse width.

By superimposing such a high frequency pulse on the input signal to the semiconductor laser, mode hopping can be prevented and even if the pulse width of the high frequency pulse changes, uniform laser light energy can be obtained.

〔Effect of the invention〕

According to the present invention, it is possible to provide a semiconductor laser wavelength control device that can prevent mode hops and obtain uniform printing quality when used in a laser printer hologram scanner.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram illustrating the operation of an embodiment of the semiconductor laser wavelength control device of the present invention. FIG. 2 is a characteristic diagram showing the relationship between applied current and optical output. FIG. 3 is a characteristic diagram showing the relationship between the applied current and the wavelength of laser light when the ambient temperature is kept constant. FIG. 4 is a characteristic diagram showing the relationship between ambient temperature and wavelength. FIG. 5 is a power spectrum diagram showing mode hops. FIG. 6 is a waveform diagram in which a high-frequency pulse is superimposed on an input signal. FIG. 7 is a waveform diagram showing variations in duty. FIG. 8 is a configuration diagram of a program scanner of a laser printer. FIG. 9 is a block diagram of one embodiment of the present invention. 1...Input signal. 2...High frequency pulse. 3...Hologram. 4... Photocon drum. Pa...Laser power. Ta...Pulse width. Fig. 1 Fig. 2 f-FJ vmouth t no shuku mA)

Claims (2)

[Claims] (1) In a semiconductor laser device, means for superimposing a high-frequency pulse on an input signal, means for adjusting at least one of the frequency, amplitude, and duty of the high-frequency pulse to obtain a single longitudinal mode; A semiconductor laser wavelength control device comprising means for keeping the amount of light per pulse constant. (2) The wavelength of the semiconductor laser according to claim 1, wherein the means for obtaining a constant amount of light is controlled so that the product of the pulse width and the power of the semiconductor laser light is constant for each pulse. Control device.