JP3196787B2 - How to use semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of using a multi-beam semiconductor laser used as a light source for optical disks, laser printers, optical communications, and the like.

[0002]

2. Description of the Related Art Semiconductor lasers are widely used as light sources for optical disks, laser printers, and optical communications. Recently, the transfer speed of optical disks has been increasing,
Alternatively, in order to increase the printing speed of a laser printer, a multi-beam semiconductor laser that emits a plurality of laser beams by independent driving has been actively developed.

A conventional multi-beam semiconductor laser has a plurality of laser resonators each having an independent drive structure including an oscillation region and a drive unit in one laser chip. A drive unit of the heater is selected, a predetermined voltage is supplied, and an operation current equal to or more than a threshold current is supplied. Thereby, the oscillation region of the laser resonator is excited to emit a laser beam. These laser beams are usually guided to a light receiving medium via an optical system or an optical fiber.

By the way, when driving a laser resonator,
Immediately after driving, the output level of the laser beam is large, and the output level decreases with time. This is because there is no heating element before driving, and the beam is easily excited with a small threshold current. On the other hand, after the beam is emitted, a predetermined amount of heat is generated and the laser chip is generated. Is increased, and the current required to continue laser oscillation increases. The% drop from the initial stage of laser oscillation is represented by the droop rate.

Therefore, conventionally, an increase in the droop rate has been prevented by taking measures such as bringing the vicinity of each laser resonator into contact with a heat sink.

[0006]

However, the conventional means is effective in the case of continuous operation of the semiconductor laser, but cannot suppress the fluctuation of the output level of the laser beam immediately after the driving.

In particular, in the case where a plurality of laser beams are used, if one of the laser resonators is driven intermittently while the other laser resonator is being driven, the output of the laser beam being emitted is affected by heat fluctuations and interference thereof. The level fluctuates greatly.

For this reason, for example, in a laser printer,
The density unevenness of the electrostatic latent image serving as a recording pattern occurs, causing problems such as shading of an image or a character.

Further, when used as a light source of an optical disk, recording / reproduction of the optical disk memory is not performed correctly,
When used as a signal generation light source for optical communication, there has been a problem that an error occurs during data demodulation due to fluctuations in the signal level.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a method of using a semiconductor laser for mitigating the influence of thermal interference between laser beams when a plurality of laser beams are used. Is to provide.

[0011]

According to the present invention, there is provided a method of using a semiconductor laser, comprising: a plurality of laser resonators each having a structure independently driven in a laser chip; A driving method for alternately driving at least one laser resonator selected from laser resonators and an adjacent remaining laser resonator, and applying heat generated during driving one laser resonator to the other laser resonator. Then, the semiconductor laser is driven as a signal generation source, and each laser beam emitted from one laser resonator and the other laser resonator is guided to a signal transmission path.

In a method for driving a semiconductor laser, in a semiconductor laser having at least one laser resonator in a laser chip, the temperature of each laser resonator immediately before driving is previously held at the temperature after driving, and the temperature before and after driving is measured. By keeping the temperature of the laser chip substantially constant, it is intended to suppress a drop in the droop rate.

Specifically, a heat generating means is provided for generating preliminary heat having substantially the same amount of heat as the heat generated when the laser resonator is driven,
While applying the preliminary heat to the laser resonator before driving,
After driving the laser resonator, the amount of preliminary heat is reduced.

The heat generating means may be a heat generating member newly added to the semiconductor laser, or a laser resonator in a laser chip may be used as it is. In the latter case, at least one laser resonator and an adjacent remaining laser resonator are alternately driven, and heat generated in one laser resonator being driven is given to the other laser resonator before driving.

In this case, the laser resonator serving as the heating means interrupts the emitted laser beam or supplies a current that does not exceed the threshold current before driving to emit a beam other than the effective laser beam. Prevent it, and arrange it so that it does not become an unnecessary light source.

Further, by making the sum of the amounts of current supplied to the laser resonator as the heat source and the laser resonator emitting the effective laser beam constant, the laser chip can be used regardless of whether the effective laser beam is emitted or not. The temperature becomes almost constant.

[0017]

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

(First Embodiment) FIG. 1 is a sectional view showing the structure of a semiconductor laser to which the present invention is applied. An active region of an active layer 13 sandwiched between cladding layers 12 and 14 on a semiconductor substrate 11 is formed as an oscillation region. And two laser resonators. This laser chip is manufactured by a known method using epitaxial growth, an etching technique, or the like.

When a current flows from the current-carrying terminals 18a and 18b toward the common current-carrying terminal 10 when these laser resonators are driven, carriers passing through the contact layers 17a and 17b pass through the gaps between the current blocking layers 15a to 15c to form cladding. Move to layer 14. At this time, the carriers are distributed in the form of a beam from the cladding layer 14 to the common electrode 10 due to the electric field, and the width across the active layer 13 is equal to the stripe region 16.
The width corresponds to the widths of a and 16b. Then, the regions of the active layer 13 corresponding to these widths oscillate to emit laser beams, respectively, and at the same time, oscillating heat of a predetermined calorie is generated.

In this embodiment, the width of the stripe regions 16a and 16b of the semiconductor laser is 4 [μm], the interval between the center portions is 15 [μm], and the length of each laser resonator in the paper plane is 250 [μm]. ] And use this as the light source of the laser printer.

Further, the semiconductor laser is provided with a heating means for generating preliminary heat having substantially the same amount of heat as oscillation heat generated when the laser resonator is driven. Specifically, a resistor that generates heat in proportion to the amount of energization is added near each laser resonator. Preferably, a plurality of resistors are provided in a dispersed manner.

Next, a method of driving the semiconductor laser will be described. When driving a laser beam serving as a light source, first, a heating unit is driven, and preliminary heat is applied to a laser resonator in advance. After the laser resonator is driven, the driving of the heating means is stopped to reduce the amount of the preliminary heat.

It is desirable that the amount of the preliminary heat is substantially the same as the amount of the oscillation heat, but it may be less. For example, in the case where two laser resonators are driven together, if the heat generating means generates heat of one laser beam, it is possible to at least reduce the influence of temperature crosstalk due to the mutual laser beams. In this case, the heat generation means stops the heat generation only when both laser resonators are being driven, and otherwise continues the heat generation.

In this way, regardless of whether the laser beam is driven or not, the temperature of the laser chip becomes substantially constant, and the temperature change before and after driving is suppressed. This allows
A laser beam having a uniform output level can be supplied to a recording system of a laser printer, and problems in conventional applications of this type are solved.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In this embodiment, the heat generating means is replaced by a laser resonator. Specifically, in the semiconductor laser having the structure shown in FIG. 1, one laser resonator and the other adjacent laser resonator are alternately driven by, for example, a binary signal, and the heat generated at the time of driving is preheated. To the other laser resonators before driving. At this time, only the laser beam emitted from one side is used as a light source, and the other laser beam is blocked.

FIG. 2 is a drive timing diagram of each laser resonator according to this embodiment. If the drive current for driving one laser resonator is as shown in FIG. Drives a drive current at the timing shown in FIG. That is, by alternately supplying the voltages of E [V], the timing is set such that the sum of the two drive currents becomes substantially constant.

When driven by such a method, the temperature of the laser chip can be kept constant at all times without separately providing a heat generating means in the semiconductor laser, and the drop of the droop rate can be suppressed by simple means. .

It is desirable that the characteristics of the two laser resonators be exactly the same, but they need not be strict. Therefore, the present invention can be applied to a multi-wavelength semiconductor laser described later. Further, even if there is a time when the drive current flows in both laser resonators in an overlapping manner, if the overlapping time is approximately 100 [ns] or less, no problem occurs in most applications.

(Third Embodiment) Next, a third embodiment of the present invention will be described. In the present embodiment, the second embodiment is improved to reduce the influence of the laser beam from the laser resonator used as the heating means.

FIG. 3 is a structural sectional view of a semiconductor laser used in this embodiment, and shows an example of a semiconductor laser having four laser resonators. This is manufactured using a well-known technique similarly to the semiconductor laser having the structure shown in FIG.

In this embodiment, the width of the central second and third stripe regions 36b and 36c is 4 [μm], and the width of the outer first and fourth stripe regions 36a and 36d is 8 [μm].
0 [μm], the interval between the stripe regions is 11 [μm],
The length of each laser resonator in the paper plane direction is 250 [μm].

In the semiconductor laser having the above structure, when only the protective film which does not change the reflectance is provided on the end face, 4 [μm]
The threshold current required to oscillate a 6 [mW] laser beam from an oscillation region having a width is about 30 [mA]. With such a current, an oscillation region having a width of 80 [μm] can emit a laser beam. Does not oscillate. Using this characteristic, 80
A laser resonator having [μm] stripe regions 36a and 36d (hereinafter referred to as a first laser resonator and a fourth laser resonator) is replaced with a 4 [μm] stripe region 36.
It is used as a heat generating means for applying preliminary heat to a laser resonator having b and 36c (hereinafter, referred to as a second laser resonator and a third laser resonator).

That is, the second and / or third laser resonators and the first and / or fourth laser resonators are alternately energized by using a drive current not exceeding the latter threshold current.
At this time, the latter laser resonator generates preliminary heat applied to the former laser resonator at the time of driving, but the output level of the emitted laser beam is extremely weak, and there is virtually no problem even if it is not blocked.

The driving sections of the first and fourth laser resonators are short-circuited to form a common driving section, and the sum of the driving currents flowing through the driving sections of the second and third laser resonators and the common driving section. Is constant, the temperature of the laser chip can always be kept almost constant. Also, the energization of the common drive unit is stopped only when the second and third laser resonators are energized simultaneously, and at other times, the same drive current as when the second or third laser resonator is driven flows. By doing so, power consumption can be reduced.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. In the present embodiment, one of the laser beams alternately emitted according to the second embodiment is actively used without blocking one of the laser beams. In the method of using the semiconductor laser, each laser beam driven as a heat generating means in the method of driving the semiconductor laser is used as one signal generation source for guiding the light beam to the light receiving device.

For example, the semiconductor laser driven according to the second embodiment is used as a signal generation light source for optical communication, and each laser beam is individually incident on a signal transmission line such as an optical fiber.
Since the semiconductor lasers are driven alternately, each laser beam contains the same information. Therefore, on the light receiving side, information sent from each optical fiber is detected, and the two are compared for their identity. Thereby, a more secure optical communication system with high redundancy can be configured.

In this case, by using a semiconductor laser that emits a multi-wavelength laser beam at the same time and detecting each wavelength, a system with higher accuracy can be constructed.

According to the method for driving a semiconductor device of the present invention,
Irrespective of whether or not the laser beam is emitted, the temperature of the laser chip becomes constant, and the effect of suppressing the drop of the droop rate immediately after driving is suppressed.

According to the present invention, at least one laser resonator and the remaining laser resonator are alternately driven, and heat generated in one laser resonator being driven is given to the other laser resonator before driving. With this configuration, the temperature fluctuation of the laser chip can be suppressed without providing any special heat generating means, and the droop rate can be easily reduced immediately after driving the laser beam.

In this case, since the sum of the driving currents flowing when driving alternately is fixed, if one increases, the other decreases, and the temperature of the laser chip is always constant. As a result, a high droop rate is obtained, and the operational reliability of the device or system using the same as a light source is significantly improved.

Further, at least one laser resonator serving as a heating means is supplied with a current not exceeding the threshold current at the time of driving, so that the influence of unnecessary laser beams is reduced.

[0042]

As described above, in the method of using a semiconductor laser according to the present invention, a plurality of laser beams driven by the driving method described above are used as signal generation light sources for optical communication, and these laser beams are used. Since the identity of the included information can be confirmed, an optical communication system with high operation reliability can be configured.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a semiconductor laser to which a first embodiment of the present invention is applied.

FIG. 2 is a drive timing diagram of two laser resonators according to a second embodiment of the present invention.

FIG. 3 is a sectional structural view of a semiconductor laser used in a third embodiment of the present invention.

[Explanation of symbols]

10 ... common energizing terminal, 11 ... semiconductor substrate, 12, 1
4 ... clad layer, 13, 33 ... active layer, 15a-1
5c: current blocking layer, 16a, 16b, 36a to 3
6d: stripe region, 17a, 17b: contact layer, 18a, 18b, 38a to 38d: energizing terminal.

Claims (1)

(57) [Claims] 1. A semiconductor laser in which a plurality of laser resonators each having a structure independently driven in a laser chip are formed in proximity to each other, and at least one laser resonator selected from the plurality of laser resonators is adjacent to the plurality of laser resonators. The semiconductor laser is driven as a signal generation source by a driving method of alternately driving the remaining laser resonators and applying heat generated during driving to one of the laser resonators to the other laser resonator, and driving the one laser. A method of using a semiconductor laser, wherein each laser beam emitted from a resonator and another laser resonator is guided to a signal transmission path.