JP2001102681A - Laser light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a laser light source, having a smooth intensity distribution characteristic with reduced influence of the speckled pattern unique to the laser and provide an light source having a high degree of design flexibility for displays. SOLUTION: An injection current I to a semiconductor laser 101 is switched on and off at a high speed to make the speckle pattern smoothly distributed not visible, thereby decreasing its influence. Since by only controlling the injection current I decreases the influence of the speckled pattern position on the semiconductor laser 101, the influence restricting its layout can be decreased to improve the degree of design flexibility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser light source, and more particularly to a laser light source device suitable for a display such as a projection.

[0002]

2. Description of the Related Art Blue-emitting semiconductor lasers, which have been difficult to manufacture due to short wavelengths, have been announced, and it has been hoped that the display light source will be constituted by red, green and blue light-emitting lasers. I have.

[0003] Semiconductor lasers have the features of being able to convert electric power into light with high efficiency, and having high color purity because they emit light within a narrow wavelength band. Therefore, it is considered that a display having low power consumption and a wide color reproduction range can be manufactured.

However, since a semiconductor laser emits coherent light whose phases are aligned both temporally and spatially,
When the output laser light is transmitted or diffused, it interferes with each other, resulting in a pattern in which light and dark spots are randomly studded, a so-called speckle pattern. The speckle pattern has a large difference in lightness and darkness, and when observed at a fixed position, the pattern looks fixed, so that the observation quality of the display is significantly impaired.

[0005] As a known technique for removing the speckle pattern, there is Japanese Patent Application Laid-Open No. H11-64789. In this technique, a speckle pattern is superimposed and averaged by providing a fly-eye or the like that rotates about the optical axis between a laser and a spatial modulation element, thereby reducing the speckle pattern.

[0006] However, there is a problem that it takes a large scale to rotate the optical axis. Further, there is a problem that a conventional display light source such as a projection has a small degree of freedom in arrangement due to optical restrictions.

[0007]

As described above, when a laser is used as a display light source, it is necessary to take measures to reduce the influence of the speckle pattern. Conventionally, this measure requires a large-scale device. In addition, there is a problem that the degree of freedom of arrangement as a display light source is small.

An object of the present invention is to provide a laser light source having a smooth intensity distribution characteristic in which the influence of a speckle pattern peculiar to a laser is reduced, and to provide a display light source having a large degree of freedom in design.

[0009]

In order to solve the above-mentioned problems, a laser light source device according to the present invention comprises a semiconductor laser as a semiconductor light emitting means having a laser resonator structure, and an optical fiber means for transmitting emitted light. Optical waveguide means for optically coupling the output end of the semiconductor laser and the input end of the optical fiber means, and the parameters of the laser light source so that the output light distribution from the output end of the optical fiber means becomes smooth. And a parameter control means for controlling.

[0010] An edge emitting semiconductor light emitting means having one end face as a reflection face and the other end face as a non-reflection coated face, an optical fiber means for transmitting light emitted by the light emission means, An optical waveguide means for optically coupling a light emitting means and an input end of the optical fiber means; a light reflecting means for forming an optical resonance structure by repeating reflection between a reflecting surface of the light emitting means; and an output of the optical fiber means Parameter control means for controlling the parameters of the laser light source so that the output light distribution from the end becomes smooth.

According to each of the above-described means, the influence of the speckle pattern can be reduced by controlling the parameters of the laser light source to smooth the output distribution of the laser light. Further, by extracting the laser output from the optical fiber, the degree of freedom in design is improved.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram for explaining a first embodiment of the present invention. Here, red, green,
The light source configuration for one color of the blue light source is shown, and the configuration for three colors is omitted.

In FIG. 1, a semiconductor laser 101 is supplied from a control power supply 104 capable of controlling output current.
Laser oscillation is caused by injecting a current equal to or greater than the threshold value of 01, and a laser beam is output from the end face 101a. In the semiconductor laser 101, light is confined in the active layer 101b, and the laser is emitted from the end face 101c of the active layer 101b. The end surfaces 101a and 101d are reflection surfaces, respectively, and have a structure in which the laser light emitted from the semiconductor laser 101 resonates.

The output laser light enters the optical waveguide 103. The side of the core portion 103a of the optical waveguide 103 facing the semiconductor laser 101 is substantially equal to the cross section of the active layer 101b of the semiconductor laser 101, and the side of the core section 103a facing the optical fiber 102 matches the cross section of the core 102a of the optical fiber 102. The core portion 1 of the optical waveguide 103 is formed as follows.
The outer periphery of 03a is surrounded by a clad 103b having a smaller refractive index than the core. Therefore, the light is
Are confined in the core portion 103a and the cladding portion 103b, and the spot size is converted and propagated to the optical fiber 102.

In the optical fiber 102, of the incident light, the core diameter d, the core portion 102a and the clad portion 102b
Only the propagating mode given by the relative refractive index difference (specific refractive index difference) Δ propagates to the output end of the optical fiber 102 without loss.

The light radiated from the output end of the optical fiber 102 has a light intensity distribution according to a propagable mode.
It is used as a display light source through an optical system (not shown).

A control power supply 104 for supplying power to the semiconductor laser 101 is a power supply capable of variably controlling the injection current I at high speed. Here, general characteristics of the injection current I of the semiconductor laser 101 versus the optical output P are shown in FIG. The current value at the point where the light output P starts to increase sharply with the increase of the injection current I is called the threshold current Ith. As shown in FIG. 2, the control power supply 104 has a variable control range from a small current that does not cause laser oscillation to a maximum Imax including the threshold current Ith.

FIG. 3 shows an example of the current control of the control power supply 104. The injection current I is controlled in a rectangular waveform having a cycle tp and an amplitude Imax. This cycle tp is set to a short cycle so that the observer does not feel flicker. For example, the image update cycle to the subsequent spatial modulation element (not shown) is t
It may be set to be an integral multiple of p, or the cycle tp may be set to be much shorter than the video update cycle so as to eliminate the relationship with the video update cycle.

The current waveform is not limited to a rectangular wave. Further, the duty is not limited to 50%. The control of the waveform and the duty may also be performed, and it may also be used as a means for adjusting the intensity ratio and the luminance of red / green / blue.

By controlling the injection current I as described above, the semiconductor laser 101 is pulse-driven, exhibits a transient response, and the speckle pattern changes according to the change of the injection current I. As described above, in the pulse driving with the period tp, the light and dark generated in the fixed speckle pattern are averaged in the speckle pattern that fluctuates at a high speed, and a good light source that is not visually perceived as flicker by the observer. Becomes

FIG. 4 is a configuration diagram for explaining a second embodiment of the present invention. An edge semiconductor light emitting device 201 having a structure similar to that of a super luminescent diode (SLD) emits light when a current is injected from a power supply 204, and outputs light from the edge 201a. In the semiconductor light emitting device 201, light is applied to the active layer 201b.
The waveguide structure is confined in the waveguide. FIG.
Although there is a stimulated emission gain in a structure similar to that of the semiconductor laser 101, there is no feedback due to end face reflection.
The semiconductor light emitting element 201 alone does not oscillate. That is, the end surface 201d of the semiconductor light emitting element 201 on the side from which light is not extracted is a reflective surface, and the end surface 201a on the side from which light is extracted is a non-reflective coating.

Light output from the semiconductor light emitting element 201 is input to the optical waveguide 203. The side of the core portion 203a of the optical waveguide 203 facing the semiconductor light emitting element 201 is substantially equal to the cross section of the active layer 201b of the semiconductor light emitting element 201, and the side facing the optical fiber 202 is the optical fiber 202.
Is formed so as to coincide with the cross section of the core 202a,
The outer periphery of the core 203 a of the optical waveguide 203 is
It is surrounded by a cladding 203b having a smaller refractive index than 3a. Therefore, the light is confined in the core portion 203a and the clad portion 203b of the optical waveguide 203, the spot size is changed, and the light propagates to the optical fiber 202.

In the optical fiber 202, of the incident light, only a propagating mode given by the core diameter d, the relative refractive index difference Δ and the like propagates in the optical fiber 202 without loss. On the output end side of the optical fiber 202, a grating 202b for the used wavelength is provided, and reflects most of the propagated light. The reflected light is transmitted through the optical fiber 2
02 through the optical waveguide 203 and the semiconductor light emitting element 2
Propagate to 01. Since the semiconductor light emitting element 201 has a sufficient stimulated emission gain, it is optically amplified and
3. Repetition of reflection, propagation, and amplification to the optical fiber 202 leads to laser oscillation.

Therefore, in the case of this embodiment, the portion between the reflection end face 201d of the semiconductor light emitting element 201 and the optical fiber grating section 202b has a laser resonator structure. The light radiated from the output end of the optical fiber 202 without being reflected by the optical fiber grating section 202b has a light intensity distribution according to a propagating mode of the optical fiber 202, and is used as a display light source through an optical system (not shown). Is done.

The optical waveguide 203 includes a medium portion exhibiting an electro-optic effect such as the Pockels effect in which the refractive index changes according to the applied electric field E. An electrode pair 203c1 and 203c2 are provided in this medium portion.
The oscillation electric field E is generated between the modulation power sources 205 and 203c2.
Is given.

The time change of the oscillating electric field E is repeated at a cycle tp as shown in FIG. Therefore, the period tp
In the electro-optic effect medium in the electric field application region, the refractive index oscillates, and the phase of light propagating in response to the oscillation also oscillates. The period tp is set to be short so that at least the flicker is not visually perceived.

By controlling the vibration of the applied electric field in this way, the speckle pattern fluctuates according to the vibration of the applied electric field. Brightness and darkness generated by the fixed speckle pattern are changed to a speckle pattern that fluctuates at high speed and averaged, and a good light source that is not perceived as flicker by an observer.

In this embodiment, the configuration has an optical phase shifter including the electrode pairs 203c1 and 203c2 and the modulation power supply 205 at the position of the optical waveguide 203. But,
If the light propagation characteristics of the optical waveguide 203 or the distribution of light input / output to / from the optical waveguide 203 itself is changed, the effect can be obtained. It may be arranged on the side.

Next, referring to the configuration diagram of FIG.
This embodiment will be described, and the same components as those of the second embodiment will be denoted by the same reference numerals. That is, the light emitted from the semiconductor light emitting element 201 enters the optical waveguide 303. Core part 303 of optical waveguide 303
The end face 201a side of the semiconductor light emitting element 201 facing a
The side of the semiconductor light emitting element 201 which is substantially equal to the cross section of the active layer 201b and faces the optical fiber 302 is the optical fiber 30.
It is formed so as to coincide with the cross section of the second core portion 302a. The outer periphery of the core 302a of the optical waveguide 303 is surrounded by a clad 302b having a smaller refractive index than the core 302a. Accordingly, light is transmitted to the core 30 of the optical waveguide 303.
1 a and the cladding 302 b, the spot size is changed, and the light is transmitted to the optical fiber 302.

The optical fiber 302 is a multimode optical fiber, and there are modes that can propagate without being cut off even in higher-order modes other than the fundamental mode. Only light corresponding to the propagable mode propagates without loss, and most of the light is reflected by the fiber grating section 302b. As in the second embodiment, the reflection end face 201 of the semiconductor light emitting element 201
The portion from a to the optical fiber grating portion 302b has a laser resonator structure and oscillates laser.

The multi-mode optical fiber 302 is provided with a piezoelectric actuator 305 for applying a stress to a part of the fiber, and is driven by a control voltage from a control power supply 306. The fiber 302 is a piezoelectric actuator 30
When a stress is applied from No. 5, the structure is slightly deformed and becomes a perturbed structure.

Therefore, in the ideal situation without stress, each propagation mode can independently propagate independently, whereas in the perturbed structure, the interaction in which the power is converted into the power of another mode or receives the power from the other mode together with the propagation. Happens.
This is called mode coupling.

In this embodiment, the time change of the stress applied to the fiber 302 by the piezoelectric actuator 305 is as shown in FIG. Since the applied stress changes with time, the coupling coefficient of mode coupling also changes with time. That is, since the power ratio of the plurality of oscillating modes changes with time, the state of interference changes and the speckle pattern also changes with time.

Since the time change cycle tp of the stress is at least short enough not to be visually perceived as flicker, the lightness and darkness conventionally caused by the fixed speckle pattern are as follows.
In this embodiment, the speckle pattern changes at a high speed. Therefore, the intensity distribution is smoothly averaged, resulting in a good display light source.

Although a means for applying pressure has been described using a piezoelectric actuator, an element for applying pressure electromagnetically may be used. The present invention is not limited to the above embodiment. For example, in the embodiment of FIG. 1, the semiconductor laser 101,
Although the description has been given using the optical fiber 102 as the optical fiber means, an edge-emitting semiconductor light emitting device 201 having a structure similar to that of a super luminescent diode (SLD)
The configuration shown in FIG. 8 using the optical fiber 202 having the fiber grating section 202b changes the resonance parameter and obtains the same effect.

In the second embodiment shown in FIG. 4, an edge emitting semiconductor element 201 as a semiconductor light emitting means and an optical fiber 20 having a fiber grating portion 202b are provided.
Although the description has been made with reference to FIG. 2, the configuration shown in FIG. 9 using the semiconductor laser 101 and the optical fiber 102 changes the propagation parameter, and achieves the same effect.

In the embodiment shown in FIG. 6, the semiconductor light emitting means is described using the edge emitting semiconductor element 201 and the multimode optical fiber 302 having the fiber grating portion 302b. With the configuration shown in FIG. 10 using the optical fiber 402, the propagation parameter changes, and the same effect can be obtained.

The reflection end face 201d of the edge emitting type semiconductor element 201 is formed by a non-reflection coding face and an optical waveguide.
The reflection end face may be formed by an optical fiber having a fiber grating. That is, the configuration may be the same as that of the non-reflective coating surface 201a on the output side, the optical waveguide 203, and the optical fiber 202 having the fiber grating.

Further, a plurality of the above laser light sources are prepared,
By making the fiber output side close or inputting to an optical fiber coupler to form a set of light sources, the respective resonance parameter control means can be combined and controlled to increase the output and further reduce the speckle pattern. The resonance parameter control means may be combined, and the speckle pattern can be further reduced.

Further, in each of the embodiments, the optical waveguide is used for the optical coupling between the semiconductor light emitting means and the optical fiber means.
A lens optical system may be used. Since the optical fiber is arranged on the output side, the degree of freedom in light source arrangement is improved by bending and drawing the optical fiber, for example, by placing the semiconductor light emitting means that generates heat in a position with good heat dissipation.

[0041]

As described above, according to the laser light source device of the present invention, the light source having a smooth distribution can be obtained by visual averaging by changing the speckle pattern at high speed. it can. Further, since the optical fiber is provided on the output side, a light source having a high degree of freedom in optical arrangement can be obtained by bending the optical fiber.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for describing an example of characteristics of an injection current versus an optical output of a semiconductor laser.

FIG. 3 is an explanatory diagram for describing an example of injection current control of a control power supply in FIG. 1;

FIG. 4 is a configuration diagram for explaining a second embodiment of the present invention.

FIG. 5 is an explanatory diagram for explaining an example of an oscillating electric field between an electrode pair by the modulation power supply in FIG. 4;

FIG. 6 is a configuration diagram for explaining a third embodiment of the present invention.

FIG. 7 is an explanatory diagram for describing an example of a temporal change in stress caused by the piezoelectric actuator of FIG. 6;

FIG. 8 is a configuration diagram for explaining a modification of the embodiment of FIG. 1;

FIG. 9 is a configuration diagram for describing a modification of the embodiment in FIG. 4;

FIG. 10 is a configuration diagram for explaining a modification of the embodiment of FIG. 6;

[Explanation of symbols]

101: semiconductor laser, 102, 202: optical fiber,
103, 203, 303 ... optical waveguide, 104, 306 ...
Control power supply, 101a, 101d, 201a, 201d ...
End face, 101b, 201b ... active layer, 202a, 302
a: Fiber grating section, 203c1, 203c
2 ... electrode pair, 204 ... power supply, 205 ... modulation power supply, 30
2,402: Multi-mode optical fiber, 305: Piezoelectric actuator.

Claims (5)

[Claims] A semiconductor laser as a semiconductor light emitting means having a laser resonator structure; an optical fiber means for transmitting light emitted from the semiconductor laser; an output end of the semiconductor laser and an input end of the optical fiber means And a parameter control means for controlling parameters of the laser light source so that an output light distribution from an output end of the optical fiber means becomes smooth. Laser light source device. 2. An edge emitting semiconductor light emitting means having one end face as a reflection face and the other end face as a non-reflection coated face, an optical fiber means for transmitting light emitted by said light emission means, Optical waveguide means for optically coupling the light emitting means and the input end of the optical fiber means, light reflecting means,
In a laser light source that forms a laser resonance structure by repeating reflection between the reflection surface of the light emitting means and the light reflecting means, the output light distribution from the output end of the optical fiber means becomes smooth, A laser light source device comprising: parameter control means for controlling parameters. 3. The laser light source device according to claim 1, wherein said parameter control means is an injection current control means capable of changing an injection current amount to a semiconductor light emitting means at a high speed. 4. The laser light source device according to claim 1, wherein said parameter control means is an optical phase shifter capable of changing a phase of a propagating light at a high speed. 5. A laser according to claim 1, wherein said parameter control means is a pressure control means capable of applying a pressure to said optical fiber means to rapidly change an inter-mode coupling amount. Light source device.