JPH11251681A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser device from which speckle noise is remarkably reduced and which is reduced in size and can operate stably. SOLUTION: A semiconductor laser device is provided with a semiconductor laser 2 integrally formed on a base 1, at least one external mirror 4 which is provided at a prescribed position on the base 1 so that the mirror 4 may be separated from the end face 2a of the laser 2 by a prescribed distance S, and has a reflecting surface formed in parallel with the end face 2a of the laser 2, and an oscillating means which oscillates the mirror 4 at a prescribed frequency in a direction which is nearly parallel to the stripe electrodes 2c of the laser 2. The temporal coherence of the laser device is remarkably reduced and speckle noise can be suppressed considerably, because the phase of the light which returns to the active layer of the laser 2 after being reflected by the mirror 4 periodically changes at the oscillation frequency of the mirror 4 and the oscillation wavelength of the light largely changes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a semiconductor laser device.

[0002]

2. Description of the Related Art Semiconductor lasers include, for example, gas lasers,
Compared with other light output devices such as light-emitting diodes, they have features such as small size, light weight, long life, low operating voltage and current, high efficiency and high brightness.
Such a semiconductor laser is used for, for example, a multimode optical fiber transmission system, a display device, and various optical measurement devices.

[0003]

However, a semiconductor laser has a large amount of speckle noise due to too high temporal and spatial coherence, and the above-mentioned multimode optical fiber transmission system, display device, and various optical measuring devices. Difficult to use. Conventionally, several techniques for reducing the above-described speckle noise of a semiconductor laser have been proposed. For example, JP-A-56-46589 and JP-A-57-124
Japanese Patent Publication No. 493 discloses a technique in which a part of light emitted from a semiconductor laser is returned to an active layer of the semiconductor laser by a reflection mirror which is provided outside the semiconductor laser and vibrates at a predetermined frequency. In the above configuration, speckle noise is reduced by setting up a plurality of longitudinal modes by the vibrating reflection mirror.

However, in the above-mentioned technique, an ultrasonic transducer is used as a driving source for driving the reflection mirror, and the driving frequency can be increased only up to about several tens of kHz. In addition, there is a disadvantage that the size of the semiconductor laser device is increased due to the use of the ultrasonic transducer. Further, since high precision is required for the alignment accuracy between the reflecting mirror driven by the ultrasonic transducer and the semiconductor laser, it is difficult to stabilize the operation, and there is a disadvantage that the assembly cost is increased.

As another technique for reducing the speckle noise of a semiconductor laser, for example, a frequency modulation method using current modulation (Caesar Saloma et.al., Appl. Opt. Vo.
l.29, No.6, p.741 (1990)), a high-frequency superposition method, a self-pulsation method, and the like.In these methods, the substantial wavelength spread is, for example, It is 1 to several nm, for example, it is difficult to use it for a display device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a semiconductor laser device in which speckle noise is significantly reduced, the size is reduced, and the operation is stable.

[0007]

According to the present invention, there is provided a semiconductor laser having two resonator end faces integrally formed on a base, and a semiconductor laser having a predetermined distance from one end face of the semiconductor laser. At least one external mirror provided at a predetermined position and having a reflecting surface substantially parallel to one end face of the semiconductor laser, and the external mirror is positioned at a predetermined position in a direction substantially parallel to a cavity length direction of the semiconductor laser. Vibrating means for vibrating at a frequency.

In the present invention, the laser light emitted from the semiconductor laser toward the external mirror enters the external mirror,
Since the external mirror is vibrating, the distance between the end face of the semiconductor laser and the external mirror changes. Therefore, the phase of the light reflected by the external mirror and returning to the active layer of the semiconductor laser periodically changes at the oscillation frequency of the external mirror, and the oscillation wavelength greatly changes. As a result, temporal coherence is greatly reduced, and speckle nozzles are significantly suppressed. In addition, by providing the semiconductor laser and the external mirror on the same base, the alignment accuracy between the semiconductor laser and the external mirror can be easily improved, and the operation of the semiconductor laser device can be stabilized. The size can be reduced.

The vibrating means includes an elastic plate provided with the external mirror, and an electrostatic means for causing the elastic plate to undergo elastic deformation of a predetermined period by an electrostatic force.

[0010] The electrostatic means generates an elastic deformation with a period substantially coincident with the resonance frequency of the elastic plate. With such a configuration, if the resonance frequency (natural frequency) of the elastic plate is designed to have a desired value, the external mirror can be vibrated at an arbitrary frequency, and a very high frequency can be obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a perspective view showing one embodiment of a semiconductor laser device of the present invention. The semiconductor laser device shown in FIG. 1 includes a mount base 1, a semiconductor laser 2 integrally formed on the mount base 1, and a distance S on the mount base 1 substantially parallel to one end surface 2a of the semiconductor laser 2. And an oscillating means (not shown).

The semiconductor laser 2 has, for example, a wavelength of 0.8.
This is a semiconductor laser having a stripe structure composed of an AlGaAs system and oscillating at μm, and emits laser light L from one end face 2a and the other end face 2b. One end face 2a of the semiconductor laser 2 is in a non-coated state,
Is about 250 μm. The other end surface of the semiconductor laser 2 is a cleavage reflection surface having a predetermined reflectance.

The external mirror 4 is disposed at a distance S from one end face 2a of the semiconductor laser 2 and substantially parallel to the end face 2a. The distance S is preferably set to any value within the range of 10 μm, but is set to about 2 μm in the present embodiment. The external mirror 4 has a reflection surface 4a formed on one end surface 2a side of the semiconductor laser 2, and the reflection surface 4a is
The laser beam L emitted from one end face 2a of the semiconductor laser 2 is reflected and enters the active layer of the semiconductor laser 2. Further, the reflecting surface 4a of the external mirror 4 has an area of 1 [mu] m ² 10 .mu.m ² schematically. The external mirror 4 is made as compact and lightweight as possible. This is because, when the external mirror 4 is vibrated, the inertia of the external mirror 4 is reduced, and the vibration at the highest possible frequency is enabled.

[0014] vibrating means, not shown, small amplitude A ₀ of the external mirror 4, at a predetermined frequency f1, the laser stripe 2c substantially parallel to the direction of the semiconductor laser (arrow B1 and B
(Direction 2). The vibration means will be described later. The vibration amplitude A ₀ of the external mirror 4 is, for example, about ± 0.4 μm to ± 0.5 μ
m. The driving frequency f1 is not particularly limited, but can be 100 kHz or more.

In the semiconductor laser device configured as described above, the laser light L emitted from the semiconductor laser 2 toward the external mirror 4 is incident on the reflection surface 4a of the external mirror 4. External mirror 4, the frequency f1, because it vibrates at an amplitude A _0, the distance S of the reflecting surface 4a of the end face 2a and the external mirror 4 of the semiconductor laser 2 is changed. Therefore, the amount and phase of light reflected by the reflection surface 4a of the external mirror 4 and returning to the active layer of the semiconductor laser 2 periodically changes at the frequency f1.
Therefore, the oscillation wavelength oscillated between the other end face 2b of the semiconductor laser 2 and the reflection surface 4a of the external mirror 4 changes greatly. The amount of change in the oscillation wavelength depends on the structure of the semiconductor laser.
It changes with a width of 0 nm or more. This change is, for example,
This is a much larger value than the case using the high frequency superposition method or the self-pulsation method.

In the present embodiment, as a result of the change in the oscillation wavelength, the temporal coherence of the laser light L output from the end face 2b of the semiconductor laser 2 can be greatly reduced, and in a frequency band lower than the frequency f1. Can be greatly suppressed. In addition, in the semiconductor laser device of the present embodiment, when the oscillation wavelength changes, a certain degree of change in the laser output may occur, which may cause a problem. There is no problem if the frequency f1 is sufficiently higher than the response speed of the photodetector that detects the laser beam.

In this embodiment, an external mirror 4 that can vibrate substantially parallel to the laser stripe 2c of the semiconductor laser 2 formed on the mount base 1 is formed on the mount base 1, so that the semiconductor laser 2 The alignment accuracy can be easily improved, the operation of the semiconductor laser device can be stabilized, and the size of the semiconductor laser device can be reduced.

Further, in this embodiment, the semiconductor laser 2
Since the external mirror 4 is arranged at a position close to the one end face 2a and vibrated, a laser wavelength change that can sufficiently suppress speckle noise can be obtained even with a minute amplitude modulation of about the wavelength of the laser beam.

Further, the semiconductor laser device according to the present embodiment includes a red semiconductor laser having a wavelength of about 0.635 μm, a green semiconductor laser having a wavelength of about 0.525 μm, and a wavelength of about 0.47 μm.
The present invention is also applicable to a blue semiconductor laser of m, for example, to a full-color laser display device in which speckles are not substantially visible.

Second Embodiment FIG. 2 is a perspective view showing another embodiment of the semiconductor laser device according to the present invention. In the semiconductor laser device according to the present embodiment, as shown in FIG. 2, a combination of the semiconductor laser 2 and the external mirror 4 described in the first embodiment is integrated on the mount base 1 at regular intervals in a predetermined direction. Have been. With such a configuration, interference between laser beams emitted from the respective semiconductor lasers 2 is reduced, and spatial coherence is reduced. Therefore, speckle noise can be further reduced. Further, by optimizing the arrangement of the semiconductor lasers 2, the position of the external mirror 4, and the modulation method, for example, a high-output semiconductor laser device with reduced speckle noise that can be used as a light source of a laser display device is provided. Can be.

Third Embodiment FIG. 3 is a perspective view showing still another embodiment of the semiconductor laser device according to the present invention. In the semiconductor laser device according to the present embodiment, as shown in FIG. 3, a wide stripe type semiconductor laser 2 having a wide stripe 2c is provided on a mount base 1, and as described in the first embodiment. A similar external mirror 4 is installed on the mount base 1. The wide stripe type semiconductor laser 2 has a feature that the laser output is relatively large. Each external mirror 4 is vibrated by a vibration means (not shown) in the same manner as in the first and second embodiments.

In the semiconductor laser device having the above structure, the end face 2a of the semiconductor laser 2 is
Is returned to the active layer 2d of the semiconductor laser 2, the temporal coherence and the spatial coherence of the laser light L output from the end face 2d of the semiconductor laser 2 are simultaneously reduced. As a result, a high-output semiconductor laser device with reduced speckle noise is obtained.

Fourth Embodiment FIG. 4 is a view for explaining another example of a method of driving the external mirror 4 in still another embodiment of the semiconductor laser device according to the present invention. In the present embodiment, as shown in FIG. 4, different amplitudes A ₁ and A from the rest position of the external mirror 4 arranged at a distance S from the end face 2 a of the semiconductor laser 2 provided on the mount base 1. Shake with ₂ . That is, the center position of the vibration of the external mirror 4 is adjusted, and the vibration of the external mirror 4 is performed asymmetrically with respect to the rest position (position of the distance S). The amplitudes A ₁ and A ₂ are appropriately adjusted.

By applying such vibration to the external mirror 4, the center wavelength of the change in the oscillation wavelength of the semiconductor laser 2 changes according to the amplitudes A ₁ and A ₂ . Accordingly, the oscillation wavelength of the semiconductor laser 2 can be adjusted, and the color of the laser light can be adjusted. In particular, when the semiconductor laser device of the present embodiment is applied to a display device, the color adjustment can be performed. Become.

Fifth Embodiment FIGS. 5 and 6 are views showing a specific configuration example of a vibrating means for vibrating the external mirror 4 of the above-described semiconductor laser device. FIG. 5 is a plan view and FIG. Is a perspective view. 5 and 6, a semiconductor laser 2 and first to third electrodes 11, 12 and 13 are provided on a mount base 1.
An elastic plate 15 having an external mirror 4 formed on one surface;
A stopper 17 is provided.

On the surface of the elastic plate 15 on the semiconductor laser 2 side,
The external mirror 4 is formed, and the elastic plate 15 elastically deforms to give vibration to the external mirror 4. The elastic plate 15 is held between the first electrode 11 and the third electrode 13 by joining both ends to the first electrode 11 and the third electrode 13. Are arranged substantially parallel to one end surface 2a. On the opposite side of the elastic plate 15 to the semiconductor laser 2, a second electrode 12 is arranged at a predetermined distance. The elastic plate 15 is, for example,
It can be formed from polysilicon. The restoring force of the elastic plate 15 can be determined from the Young's modulus of the material forming the elastic plate 15 and the shape of the elastic plate 15.

Between the elastic plate 15 and the second electrode 12,
A pin-shaped stopper 17 is provided at a predetermined distance from the elastic plate 15. The stopper 17 is connected to the elastic plate 15
Is elastically deformed toward the second electrode 12, the elastic plate 15
And serves to regulate the amount of deformation of the elastic plate 15 and prevent the elastic plate 15 from contacting the second electrode 12.

In the semiconductor laser device having the above configuration, the first
When a voltage is applied between the third electrode 13 and the second electrode 12, an electrostatic force is generated between the elastic plate 15 and the second electrode 12. Elastic plate 15 and second electrode 1
When an electrostatic force is generated between the second electrode 12 and the second electrode 12, the elastic plate 15 is attracted to the second electrode 12 side.
Fold to the side. As a result, the distance between the external mirror 4 and the end face 2a of the semiconductor laser 2 changes.

As the voltage applied between the first electrode 11, the third electrode 13, and the second electrode 12 increases, the force (the electrostatic force) by which the elastic plate 15 is attracted to the second electrode 12 side ) Increases, the deformation of the elastic plate 15 increases, and the displacement of the external mirror 4 also increases. Elastic plate 15
When the elastic plate 15 reaches a certain size, the elastic plate 15
7, the elastic plate 15 and the second electrode 12 are prevented from being electrically short-circuited.

To vibrate the elastic plate 15, the elastic plate 15
Utilizing the mechanical resonance frequency of That is, by making the frequency of the voltage applied between the first electrode 11 and the third electrode 13 and the second electrode 12 substantially coincide with the mechanical resonance frequency of the elastic plate 15,
5 vibrates autonomously. The resonance frequency of the elastic plate 15 can be obtained from the effective spring constant and the mass of the elastic plate 15. For example, when the material of the elastic plate 15 is polysilicon, 300 μm in length, 5 μm in width, and 10 μm in height, the resonance frequency is about 200 kHz. Therefore, if the frequency of the voltage applied between the first electrode 11, the third electrode 13, and the second electrode 12 is about 200 kHz, the external mirror 4 can be vibrated at a frequency of 200 kHz. Further, the vibration amplitude of the external mirror 4 can be adjusted by the magnitude of the applied voltage.

As described above, according to the present embodiment, the external mirror 4 can be vibrated at an arbitrary frequency and amplitude by appropriately changing the shape of the elastic plate 15.

FIGS. 7 and 8 are diagrams showing another specific configuration example of the vibrating means for vibrating the external mirror 4 of the semiconductor laser device described above. FIG. 7 is a plan view, and FIG. 8 is a perspective view. FIG. 7 and 8, a semiconductor laser 2 and first to third electrodes 21 to 21 are mounted on a mount base 1.
23, an elastic plate 25 having a mirror 4 formed at one end,
Two stoppers 27 are provided with the elastic plate 25 interposed therebetween.

The one end 25 a of the elastic plate 25 is bent, and the one end 25 a is arranged so as to be substantially parallel to the end face 2 a of the semiconductor laser 2. An external mirror 4 is formed on a surface of one end 25a of the elastic plate 25 on the semiconductor laser 2 side. The other end of the elastic plate 25 is connected to the second electrode 22.
And the elastic plate 25 is held by the second electrode 22.

The two stoppers 27 are arranged on both sides of the elastic plate 25 at a predetermined distance. The two stoppers 27 are moved by the elastic deformation of the elastic plate 25.
Is provided to prevent an electrical short circuit with the first and third electrodes 21 and 23.

In the semiconductor laser device having the above configuration, the first
When a voltage is applied between the first electrode 21 and the second electrode 22, an electrostatic force is generated between the elastic plate 25 and the first electrode 21. This causes the elastic plate 25 to bend because it is in a cantilever state. Therefore, when a voltage having a frequency substantially equal to the resonance frequency of the elastic plate 25 is applied between the first electrode 21 and the second electrode 22, the elastic plate 25 vibrates self-excitingly and the elastic plate 25 The external mirror 4 formed at one end 25a vibrates. Also in the case of the present embodiment, the resonance frequency of the elastic plate 15 can be obtained from the effective spring constant and the mass of the elastic plate 15. For example, the material of the elastic plate 25 is polysilicon, a length of 150 μm, a width of 5 μm, and a height of 1.
When it is set to 0 μm, the resonance frequency is about 200 kHz.

[0036]

According to the present invention, speckle noise can be greatly reduced, and for example, a semiconductor laser device suitable for a display device or various optical measuring devices can be obtained. According to the present invention, since the semiconductor laser and the external mirror are provided on the same base, assembly is easy,
A semiconductor laser device which can be downsized and has stable operation can be obtained. Further, the vibration frequency of the external mirror can be made very high. Further, since the external mirror is driven by the elastic plate and the electrode without using the ultrasonic transducer, the size of the semiconductor laser device can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a semiconductor laser device of the present invention.

FIG. 2 is a perspective view showing another embodiment of the semiconductor laser device according to the present invention.

FIG. 3 is a perspective view showing still another embodiment of the semiconductor laser device according to the present invention.

FIG. 4 is a view for explaining another example of a driving method of the external mirror 4 in still another embodiment of the semiconductor laser device according to the present invention.

FIG. 5 is a plan view illustrating a specific configuration example of a vibration unit that vibrates an external mirror of the semiconductor laser device according to the embodiment.

6 is a perspective view of the semiconductor laser device shown in FIG.

FIG. 7 is a plan view illustrating another specific configuration example of the vibration unit that vibrates the external mirror of the semiconductor laser device according to the embodiment.

8 is a perspective view of the semiconductor laser device shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Mount base, 2 ... Semiconductor laser, 4 ... External mirror, 11, 12, 13, ... Electrode, 15 ... Elastic plate, 17 ...
Stopper.

Claims (11)

[Claims] A semiconductor laser having two resonator end faces integrally formed on a base; and a semiconductor laser provided at a predetermined position on the base spaced a predetermined distance from one end face of the semiconductor laser. At least one external mirror having a reflection surface substantially parallel to one end face of the semiconductor laser, and a vibration means for vibrating the external mirror at a predetermined frequency in a direction substantially parallel to a cavity length direction of the semiconductor laser. Semiconductor laser device. 2. The semiconductor device according to claim 1, wherein said semiconductor laser is a wide stripe type semiconductor laser, and said plurality of external mirrors are arranged at one end face of said semiconductor laser at a predetermined distance. Laser device. 3. The semiconductor laser device according to claim 1, wherein a combination of two or more semiconductor lasers and an external mirror is provided on said base. 4. The semiconductor laser device according to claim 1, wherein the amplitude of the vibration by said vibration means is about half the wavelength of the laser. 5. The semiconductor laser device according to claim 1, wherein said oscillating means can set an oscillating frequency of an external mirror to 100 kHz or more. 6. The semiconductor laser device according to claim 1, wherein said vibration means is capable of changing a center position of vibration of an external mirror. 7. The semiconductor laser device according to claim 1, wherein said vibrating means has an elastic plate provided with said external mirror, and electrostatic means for causing said elastic plate to undergo elastic deformation of a predetermined period by an electrostatic force. 8. The electrostatic means has first and second electrodes for supporting both ends of the elastic plate, respectively, and a third electrode disposed near a central portion of the elastic plate. The semiconductor laser device according to claim 7, wherein the elastic plate is vibrated by applying a voltage having a predetermined frequency between the first and second electrodes and the third electrode. 9. The electrostatic means has a first electrode that supports one end of the elastic plate, and a second electrode that is disposed to face at least one surface of the elastic plate. The semiconductor laser device according to claim 7, wherein the elastic plate is vibrated by applying a voltage having a predetermined frequency between the first and second electrodes. 10. The semiconductor laser device according to claim 7, wherein said electrostatic means causes elastic deformation of a cycle substantially coincident with a resonance frequency of said elastic plate. 11. The semiconductor laser device according to claim 7, wherein said elastic plate is formed of polysilicon.