JPH01232782A - Method of driving array-type semiconductor laser device - Google Patents

Abstract

PURPOSE:To decrease the effect of adjacent light sources on each other by a method wherein light sources are driven by a periodically modulated current whose frequency is higher than a specified value, where a threshold current which starts generating an oscillation is between the maximum and the minimum amplitude of the modulated current. CONSTITUTION:In a usual semiconductor laser, the optical output is nearly proportional to the variation of a drive current when the drive current is equal to or larger than a threshold current Ith. Therefore, provided that a drive direct current required for obtaining an average optical output P denotes (Ip+Ith), the average optical output of a laser driven by a square pulse of 50% duty whose minimum and maximum value are Ith and (2XIp+Ith) respectively is also equal to P. If the drive current is less than the threshold current Ith, the laser does not start oscillating, so that the optical output is the same even if the minimum value of a drive pulse is less than Ith. On the other hand, if the minimum value is made smaller than Ith, the average drive current becomes smaller than (Ip+Ith). Therefore, the rise of temperature becomes small. If the period of a pulse is smaller than a time constant of the heat interference, the rise of temperature can be considered to be nearly the same as a direct current drive, so that it is sufficiently effective if the period of a pulse is 1kHz or more.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a driving method for an array type semiconductor laser device.

[Conventional technology]

Because semiconductor lasers are small, they are widely used in place of gas lasers as light sources for optical disk devices, laser printers, and the like. Also in recent years? An array type semiconductor laser device including a light emitting source capable of independently driving iR has been developed. By using such an array type semiconductor laser device, it is possible to obtain a device with better characteristics than conventional devices.

For example, the data processing speed of optical disk devices, laser printers, etc. is improved.

Conventionally, in such an array type semiconductor laser device,
When a certain light emitting source generates a certain amount of output light, it is driven by applying a certain amount of direct current.

[Problem to be solved by the invention]

Conventional drive systems using direct current have had the problem that when current is applied to adjacent light emitting sources, the light emitting output decreases due to the influence of the upper temperature limit. FIG. 3 shows the decrease in the output of the light source LDI when the current of the light source 1 and D2 adjacent to the light source LDI is turned on. The time constant t of the output decrease depends on the distance between the light emitting sources and the heat sink material, but it is from several 100 μs to several ms at a practical distance between the light sources of several tens of μm to several 100 μm.

Automatic power control (APC) can be performed by monitoring the output of each light source independently, but the time constant of feedback control needs to be sufficiently faster than the output reduction time constant t in t. The configuration will be restricted.

An object of the present invention is to provide a driving method for an array type semiconductor laser device that is less influenced by adjacent light emitting sources as described above.

[Means to solve the problem]

The present invention provides a driving method for an array type semiconductor laser device having a plurality of independently drivable light emitting sources, in which each light emitting source is driven at a frequency of 1 kHz, which has a maximum value and a minimum value between which a threshold current that causes laser emission is sandwiched. It is characterized by being driven with the above periodic modulated current.

[For production]

FIG. 2 shows an example of measuring the drive current and temperature rise of adjacent light emitting sources. It can be seen that the temperature rise is proportional to the current value of the adjacent light emitting sources and is not dependent on the light output of the adjacent light emitting sources.

In a general semiconductor laser, the optical output is approximately proportional to the amount of change in the drive current when the threshold current is 11 or more. Therefore, the DC drive current required to obtain the average optical output P is (Ir +1th
), then the minimum value ILh and the maximum value (2XIP+I)
The average optical output when driving with a square pulse with a duty of 50% is also P.

Since laser light is not emitted with a current below the threshold value I, the optical output is the same even if the minimum value of the previous pulse drive is set below I.

On the other hand, if the average drive current is set below the minimum value (Ip
+rth). Therefore, the temperature rise is also reduced.

If the pulse period is smaller than the time constant of thermal interference, it can be considered that the temperature rise is almost the same as that of DC drive, so a pulse period of 1 kHz or more is sufficient.

Note that the drive current may be a sine wave instead of a pulse.

By adding such periodic modulation to the drive current, can the influence of adjacent light emitting sources be reduced? f[l can be done.

〔Example〕

FIG. 1 shows a driving method according to an embodiment of the present invention.
The relationship between the optical output of the light emitting source of the array type semiconductor laser device and the rectangular pulse drive current is shown. The threshold value 1th of this light emitting source is 50 mA, and when driven with DC current, an average of 1 mW
The direct current required to obtain the optical output of 55 mA is 55 mA.

Therefore, in this embodiment, the maximum value of the square pulse drive current is set to 6.
0mA, the minimum value is OmA, and the duty is 50%.

The average value of this drive current is 30 mA, and the average drive current can be reduced to nearly half that of DC drive.

Therefore, although the optical output is the same as that of 55 mA DC drive, the temperature rise is smaller, so that the decrease in the light emitting output due to thermal interference can be suppressed to a small level.

When this embodiment is applied to an optical disk device, the frequency of the drive current only needs to be sufficiently higher than the data recording frequency, for example, 10MHz for an IMHz recording frequency.
A drive current cycle of about

〔Effect of the invention〕

According to the present invention, in an array type semiconductor laser device, the influence of thermal interference between adjacent light emitting sources on light emission output can be suppressed to a small level.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating an embodiment of the present invention, FIG. 2 is a diagram illustrating the principle of the present invention, and FIG. 3 is a diagram illustrating a reduction in output due to the influence of adjacent light emitting sources in a conventional drive system. Agent Patent Attorney Yoshi Iwasa Koden J square Figure 1 ↑ Figure 2 ← ------→ B square Figure 3

Claims (1)

[Claims] (1) In a driving method for an array type semiconductor laser device having a plurality of light emitting sources that can be driven independently, each light emitting source is
A driving method for an array type semiconductor laser device, characterized in that it is driven with a periodic modulation current of 1 kHz or more having a maximum value and a minimum value with a threshold current that causes laser emission in between.