JP2001284718A - External cavity laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam with a narrow wavelength width stably with a simple low-cost configuration. SOLUTION: The external resonance type laser includes a laser oscillator for casting a laser beam with a prescribed wavelength and an external resonator for resonating the laser beam cast from the laser oscillator. A photopolymer volume hologram is provided in the resonator. The laser beam cast from the oscillator is diffracted by the photopolymer volume hologram and cast as an incident beam into an optical system in the resonator. Then, the laser beam with a prescribed wavelength is transmitted selectively through the photopolymer volume hologram and cast outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a laser, and more particularly to a laser having a dispersion optical element formed of a volume hologram in an optical resonator.

[0002]

2. Description of the Related Art An external resonance type semiconductor laser that feeds back emitted light using an external resonator can narrow the line width of emitted light, and can also use Distribution Feed Back L.
aser (DFB), Distributed Bragg Reflector Laser (DBR)
It is easy to increase the output as compared with a semiconductor laser such as this. Further, the wavelength can be changed by means such as rotating a mirror or a diffraction grating. Taking advantage of these features, it can be used for many applications such as wavelength multiplexing optical communication, wavelength conversion using nonlinear optical effects, laser cooling, frequency standard, spectroscopic measurement for environment and process management, and interferometer. Such an external cavity semiconductor laser is now commercially available.

FIG. 12 shows a typical configuration example of a resonator.
Littman type (Michael G. Littman and Ha
rold Metcalf, ”Spectrally narrow pulsed dye laser
without beam expander ”, Applied Optics. 17.2224.1
978, Michael G. Littman, ”Single-mode operation of
grating-incident pulsed dye laser ”, Optics Lette
rs.3.38.1978, KCHervey and CJMyatt, ”External
-cavity diode laserusing a grazing-incident diffra
ction grating ”, Optics Letters.16.910.1991) and Figure 1
Littrow type as shown in FIG. In the Littrow type,
The blazed shape of the blazed diffraction grating 18 has a specific order (usually the first order) of incident light and diffracted light for a specific wavelength.
Are designed so that their optical paths match exactly. Then, the laser light is oscillated from the laser oscillator 2,
Is converted into parallel light by the blazed diffraction grating 1
The diffracted light diffracted by 8 returns to the laser cavity,
A nested external resonator is formed outside the internal resonator. As a result, the wavelength of the light that returns due to the dispersion of the grating is selected, and only a specific wavelength is received and amplified. In the case of Littman type,
Similarly, wavelength selectivity works. In the case of the Littman type, by changing the angle of the external mirror 4,
Since the wavelength that is fed back to the internal resonator can be controlled, a tunable laser can be realized.

[0004]

When an external resonance type laser is put to practical use, it is necessary to stabilize the output and the wavelength. For this purpose, the oscillation wavelength of the external resonator and the oscillation wavelength of the internal resonator are required. Need to match.
As a method for controlling this, for example, an electric control method using a liquid crystal cell (J. Struck: meier et al, “Electr
onically tunableexternal-cavity laser diode ”, Opti
cs Letters. 24.1573.1999), a control method using feedback (Japanese Patent Laid-Open No. 7-30180), a control method using a micromachine (Japanese Patent Laid-Open No. 11-307879,
Japanese Patent Application Laid-Open No. Hei 10-209552) has been proposed. In order to facilitate the adjustment, a method using a confocal optical system (BE Bernacki et al, “Alignmen-insens
itive technique for widebandtuening of an unmodifi
ed semiconductor laser ”, Optics Letters.13.725.19
88, JP-A-11-503877), a method of stabilizing the frequency using reflected light selected by the resonance of a resonator (B. Dahmani et al, “Frequency stabiizati”).
on of semiconductor lasers by resonant optical fee
dback ”, Optics Letters.12.876.1987), a method of accurately positioning a mirror by rotating it around a specific position (US Pat. No. 5,319,668), and oscillation using the dispersion of a diffraction grating. The method of selecting a wavelength is not limited to a semiconductor laser, and is often used for gas lasers such as Co ₂ and Ar ions, excimer lasers, dye lasers, and tunable solid-state lasers such as Ti: Saphire. Diffraction efficiency of more than 90% as a blazed grating is difficult to manufacture and expensive, and the above-described method requires some control and complicates the configuration of the external resonator. There is a problem that becomes.

Further, a recently developed display using an active driving grating by a micromachine, that is, a grating light valve (hereinafter referred to as a GLV) displays a clearer and brighter image than a conventional spatial modulator without a seam. It has attracted attention because of its excellent features such as being able to be manufactured at low cost using micromachine technology and being capable of high-speed operation. But,
In such a display, it is essential to stabilize the wavelength width of the laser beam used. Considering the three primary colors of light, that is, red, green, and blue, the visual characteristics of the human eye are particularly sensitive to red. For example, when comparing red light having a wavelength of 630 nm and red light having a wavelength of 650 nm, the visibility of red light having a wavelength of 650 nm is about 2.5 times that of red light having a wavelength of 630 nm. That is, when viewing red light with a wavelength of 650 nm, the user feels 2.5 times brighter than when viewing red light with a wavelength of 630 nm of the same light amount. Therefore, in order to express a desired color, a laser beam that has as small a wavelength variation as possible with respect to temperature and the like and that has a small wavelength difference between laser solids is required.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a laser capable of stably supplying a laser beam having a narrow wavelength width with a simple and inexpensive configuration. With the goal.

[0007]

An external resonance type semiconductor laser according to the present invention comprises a laser oscillator for emitting laser light of a predetermined wavelength, and an external resonator for resonating the laser light emitted from the laser oscillator. An external resonance type laser having a photopolymer volume hologram in a resonator, and the photopolymer volume hologram is diffracted by selectively resonating a laser beam emitted from a laser oscillator, so that a laser beam having a predetermined wavelength is obtained. It is characterized by selectively causing laser oscillation of light.

The external resonance type semiconductor laser according to the present invention comprises:
Since the photopolymer volume hologram is provided in the external resonator, the wavelength selectivity of the external resonator is improved. This allows
Since only the wavelength closer to the desired wavelength oscillates selectively, the wavelength width of the laser light emitted from the external resonance type laser is narrow. Further, a laser beam having a desired wavelength can be efficiently extracted due to the high diffraction efficiency of the photopolymer volume hologram.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a detailed description will be given based on specific embodiments. It should be noted that the present invention is not limited to the following description, and can be appropriately changed without departing from the gist of the present invention.

FIG. 1 shows a first embodiment to which the present invention is applied, and is an example of an external resonance type semiconductor laser using a reflection type photopolymer volume hologram 1. The external resonance type semiconductor laser according to the first embodiment includes a laser oscillator 2 that oscillates a laser beam having a predetermined wavelength, and a laser beam oscillated by the laser oscillator 2 converted into parallel light to form a reflection-type photopolymer volume hologram 1. A collimator lens 3 to be incident and a reflective photopolymer volume hologram 1 as a dispersive optical element
And a mirror 4.

In the external cavity semiconductor laser according to the first embodiment,
The reflection type photopolymer volume hologram 1 and the mirror 4 constitute an external resonator. That is, the laser beam oscillated from the laser oscillator 2 is converted into parallel light by the collimator lens 3 and enters the reflection type photopolymer volume hologram 1. Then, the light is diffracted in a predetermined direction in the reflection type photopolymer volume hologram 1, further reflected by the mirror 4, and returns to the reflection type photopolymer volume hologram 1 again.
As for the laser beam incident on the reflection type photopolymer volume hologram 1, only the laser beam of a predetermined wavelength returns to the laser oscillator 2 due to its wavelength selectivity, and the laser beams of other wavelengths are emitted in a predetermined direction as emitted light. To be emitted.

The above-mentioned external resonance type semiconductor laser is characterized in that a reflection type photopolymer volume hologram 1 is used as a dispersion optical element in an external resonator instead of a blazed diffraction grating which is usually used. Volume holograms have much higher wavelength selectivity and angle selectivity than ordinary diffraction gratings. Thousands /
It has an excellent spatial frequency of mm. By using a photopolymer volume hologram instead of the blazed diffraction grating, the performance of the external resonance type semiconductor laser can be improved.

First, the wavelength selectivity can be increased and the wavelength width can be narrowed. That is, the coherence length of the laser beam oscillated from the external cavity semiconductor laser can be increased. Photopolymer volume holograms can easily achieve higher spatial frequencies and higher diffraction efficiencies compared to blazed diffraction gratings commonly used for external resonators because they record the interference fringes of two rays in the recording medium. It is possible. Therefore, the wavelength selectivity of the external resonator can be improved as compared with the case where a blazed diffraction grating is used.

As described above, by increasing the wavelength selectivity of the external resonator, the wavelength width of the emitted laser beam can be narrowed. That is, since laser oscillation of a wavelength other than the desired wavelength can be suppressed, only a laser beam closer to the desired wavelength can be oscillated.

Although the volume selectivity of the volume hologram itself is much wider than the wavelength selectivity of the Littman type external resonator itself, the volume type hologram itself also has a wavelength selectivity higher than that of a commonly used interference filter. It contributes to improving selectivity. Since the volume hologram has high diffraction efficiency, the finesse of the external resonator can be made higher than usual, so that this effect is further enhanced.

This makes it possible to further narrow the wavelength width of the laser beam. Then, by stabilizing the wavelength width of the laser beam to a specific wavelength, the luminous characteristics of the laser beam can be improved, and the light source can function as a display light source with good luminous characteristics.

Further, in order to make maximum use of the wavelength selectivity of the volume hologram, it is sufficient that the object light and the reference light are incident so as to face each other. When the wavelength selectivity of the volume hologram is utilized to the maximum, for example, an on-axis volume hologram external resonance type semiconductor laser 5 including a laser oscillator, a collimator lens, and a volume hologram as shown in FIG. 2 can be configured. An external resonator can be configured only with a volume hologram, simplifying the configuration of the external resonator.
It is possible to reduce the size.

Second, since the angle mode selectivity of the volume hologram also causes the selectivity of the transverse mode,
The transverse mode can be stabilized. For example, when a plane wave is used for recording a volume hologram, only a plane wave component of incident light is diffracted during reproduction. Therefore, even when a higher-order mode in which the wavefront is not a plane wave occurs, almost no diffracted light is generated, resulting in a loss in the external resonator. As a result, what is fed back to the internal resonator is a plane wave component, the transverse mode is selected, and the transverse mode of the laser beam can be stabilized.

In a normal application, a TEM
It is desirable to use the fundamental mode of 00, but if a special beam shape is required, it is not necessary to limit to the plane wave.

In recent years, it has been proposed to generate a desired beam pattern by inserting a diffractive optical element into a resonator. A similar effect can be realized by a volume hologram. In the case of a volume hologram, more excellent beam pattern control is possible because of high diffraction efficiency. In other words, by using a volume hologram, it is possible to produce a laser beam having a uniform intensity distribution within a beam called a top hat, correct astigmatism of a semiconductor laser, and change the vertical and horizontal divergence angles of a semiconductor laser to form a perfect circular beam. Can be realized. Such a special beam profile can be produced by recording such that the phase, diffraction efficiency, absorption, and the like of the volume hologram change spatially.

In the present invention, a photopolymer volume hologram is used as the volume hologram. The volume hologram includes a crystal-type volume hologram formed of a crystal such as lithium niobate. In the present invention, a photopolymer volume hologram made of a photopolymer is used. Since a photopolymer volume hologram can be formed in a free shape as compared with a crystal-type volume hologram, the degree of freedom of the shape of the volume hologram is greatly expanded, and various applications as described later become possible. Also,
In the case of a crystal-type volume hologram, the interference fringes formed in the volume hologram disappear after repeated reproduction, but in the case of a photopolymer volume hologram, the hologram does not change with time and has excellent aging characteristics. The reliability as an optical element can be improved.

The volume holograms can be classified into a reflection volume hologram 1 and a transmission volume hologram 6. In the present invention, any volume hologram can be used.

With the above-described effects, the external resonance type semiconductor laser of the first embodiment can supply a laser beam having a desired wavelength with a narrow wavelength width and a stable transverse mode.

FIG. 3 shows a second embodiment to which the present invention is applied, which is an example of an external resonance type semiconductor laser using a transmission type photopolymer volume hologram 6. As shown in FIG. The external resonance type semiconductor laser according to the second embodiment converts a laser beam oscillated by a laser beam having a predetermined wavelength into a parallel beam and causes the laser beam oscillated by the laser oscillator 2 to enter a transmission type volume hologram 6. It comprises a collimator lens 3, a transmission type photopolymer volume hologram 6, and a mirror 4.

In the external resonance type semiconductor laser of the second embodiment,
An external resonator is constituted by the transmission type photopolymer volume hologram 6 and the mirror 4. That is, the laser beam oscillated from the laser oscillator 2 is converted into parallel light by the collimator lens 3 and enters the transmission type photopolymer volume hologram 6. Then, the light is diffracted in a predetermined direction by the transmission type volume hologram 6, further reflected by the mirror 4 and returns to the transmission type photopolymer volume hologram 6 again. As for the laser beam incident on the transmission type photopolymer volume hologram 6, only the laser beam of a predetermined wavelength returns to the laser oscillator 2 due to its wavelength selectivity, and the laser beams of other wavelengths are emitted in a predetermined direction as emitted light. To be emitted.

With the above configuration, in the external cavity semiconductor laser of the second embodiment, as in the first embodiment,
A laser beam having a desired wavelength with a narrow wavelength width and stable transverse mode can be supplied.

Here, the diffraction efficiency of the reflection type volume hologram shows a gradual change at the center angle or near the center wavelength with respect to the angle phase mismatch or the wavelength phase mismatch. Thereby, the reflection type volume hologram has an advantage that the wavelength selectivity is high and the angle tolerance can be relatively wide. On the other hand, the diffraction efficiency of the volume hologram shows a steep change as compared with the reflection type volume hologram. Thereby, the reflection volume hologram has advantages that the angle selectivity is high and the wavelength tolerance can be relatively wide. Therefore, in consideration of the characteristics of the change with respect to the angular phase mismatch or the wavelength phase mismatch, it is also possible to appropriately select a volume hologram and a volume hologram according to the purpose and utilize these characteristics.

In the Littman resonator described above, the mirror 4 is usually used at one end of the external resonator.
This may be replaced with a corner cube 7. FIG.
Is a third embodiment of the present invention, in which the mirror 4 is replaced by a corner cube 7 in the first embodiment.

The external resonance type semiconductor laser of the third embodiment is a laser oscillator 2 for oscillating a laser beam of a predetermined wavelength.
A collimator lens 3 that converts a laser beam oscillated by a laser oscillator 2 into parallel light and makes it incident on a reflective photopolymer volume hologram 1, a reflective photopolymer volume hologram 1, and a corner cube 7. Is done.

In the external cavity semiconductor laser of the third embodiment,
The reflection type photopolymer volume hologram 1 and the corner cube 7 constitute an external resonator. That is, the laser beam oscillated from the laser oscillator 2 is
Is converted into parallel light, and enters the reflection type photopolymer volume hologram 1. Then, the light is diffracted in a predetermined direction by the reflection type photopolymer volume hologram 1, further reflected by the corner cube 7, and returns to the reflection type photopolymer volume hologram 1 again. The laser beam incident on the reflection type photopolymer volume hologram 1 has only a predetermined wavelength due to its wavelength selectivity.
Returning, laser beams of other wavelengths are emitted in a predetermined direction as emitted light.

Here, since the corner cube 7 accurately reflects the incident light in the incident direction, alignment can be made unnecessary. Especially when used as a wavelength variable laser, the oscillation wavelength can be changed only by rotating the volume hologram, so that adjustment and a movable mechanism can be simplified, which is effective.

With the above configuration, the external resonance type semiconductor laser of the third embodiment supplies a laser beam of a desired wavelength with a narrow wavelength width and stable transverse mode, as in the first embodiment. be able to.

By processing the shape of the volume hologram, it is also possible to make these components monolithic. That is, when only a laser beam of a specific wavelength is used, reflection at the end surface of the reflective photopolymer volume hologram 1 can be used instead of the mirror 4 of the first embodiment. FIG. 5 shows a fourth embodiment to which the present invention is applied. In the first embodiment, the end surface of the reflection type photopolymer volume hologram 1 on the mirror 4 side is mirror-finished to form a reflection surface 8. This is an example of replacing

The external resonance type semiconductor laser of the fourth embodiment has a laser oscillator 2 for oscillating a laser beam of a predetermined wavelength.
And a collimator lens 4 for converting a laser beam oscillated by a laser oscillator 2 into parallel light to be incident on a reflection type photopolymer volume hologram 1 and a reflection type photopolymer volume hologram 1.

Here, in the external resonance type semiconductor laser of the fourth embodiment, in the reflection type photopolymer volume hologram 1, the end face in the direction in which the diffracted light of the laser beam from the laser oscillator 2 travels, that is, in the first embodiment, the mirror 4 The mirror surface is applied to the end surface in the direction in which is disposed as the reflection surface 8. Thereby, the laser beam diffracted in the reflection type photopolymer volume hologram 1 is reflected on the reflection surface 8 and returns to the hologram again. Therefore, Example 4
In the external resonance type semiconductor laser, an external resonator is constituted only by the reflection type photopolymer volume hologram 1. That is, the laser beam oscillated from the laser oscillator 2 is converted into parallel light by the collimator lens 4 and enters the reflection type photopolymer volume hologram 1. Then, the light is diffracted in a predetermined direction in the reflection-type photopolymer volume hologram 1, is further reflected on the reflection surface 8, and returns to interference fringes again. Then, only the laser beam of a predetermined wavelength returns to the laser oscillator 2 due to the wavelength selectivity, and laser beams of other wavelengths are emitted in a predetermined direction as emitted light.

With the above configuration, the external resonance type semiconductor laser of the fourth embodiment supplies a laser beam having a desired wavelength with a narrow wavelength width and stable transverse mode, as in the first embodiment. be able to. And Example 4
Since the external resonator is composed only of the reflection type photopolymer volume hologram 1, the configuration of the device can be simplified and downsized, and the cost can be reduced.

FIG. 6 shows a fifth embodiment to which the present invention is applied. In the first embodiment, the end surface of the reflection type photopolymer volume hologram 1 on the mirror 4 side is processed into a corner cube shape, and the mirror 4 is formed. This is an example of replacing

The external resonance type semiconductor laser of the fifth embodiment is a laser oscillator 2 for oscillating a laser beam of a predetermined wavelength.
And a collimator lens 4 for converting a laser beam oscillated by a laser oscillator 2 into parallel light to be incident on a reflection type photopolymer volume hologram 1 and a reflection type photopolymer volume hologram 1.

Here, in the external resonance type semiconductor laser of the fifth embodiment, in the reflection type photopolymer volume hologram 1, the end face in the direction in which the diffracted light of the laser beam from the laser oscillator 2 travels, that is, in the first embodiment, the mirror 4 Are processed into a corner cube shape to form a reflection surface 9. Thereby, the laser beam diffracted in the reflection type photopolymer volume hologram 1 is reflected on the reflection surface 9 and returns to the hologram again. Therefore, in the external resonance type semiconductor laser of the fourth embodiment, the external resonator is constituted only by the reflection type photopolymer volume hologram 1. That is, the laser beam oscillated from the laser oscillator 2 is converted into parallel light by the collimator lens 3 and enters the reflection type photopolymer volume hologram 1. Then, the light is diffracted in a predetermined direction in the reflection type photopolymer volume hologram 1, further reflected on the reflection surface 9, and returns to the hologram again. Then, only the laser beam of a predetermined wavelength returns to the laser oscillator 2 due to the wavelength selectivity, and laser beams of other wavelengths are emitted in a predetermined direction as emitted light.

With the above configuration, the external resonance type semiconductor laser of the fifth embodiment supplies a laser beam of a desired wavelength having a narrow wavelength width and a stable transverse mode, as in the first embodiment. be able to. And Example 5
Since the external resonator is composed only of the reflection type photopolymer volume hologram 1, the configuration of the device can be simplified and downsized, and the cost can be reduced.

In the case of such a configuration, the wavelength tunable operation can be performed by rotating the reflection type photopolymer volume hologram 1 in a predetermined direction.

Further, by forming the volume hologram in the collimator lens, the volume hologram and the collimator lens can be integrated.

FIG. 7 shows a sixth embodiment to which the present invention is applied, in which a volume hologram is formed in the shape of a collimator lens. The external cavity semiconductor laser of the sixth embodiment is
A laser oscillator 2 for oscillating a laser beam of a predetermined wavelength;
And a photopolymer volume hologram formed in a collimator lens shape.

Here, in the external resonance type semiconductor laser of the sixth embodiment, by forming the photopolymer volume hologram in the shape of a collimator lens, a state where the collimator lens and the reflection type photopolymer volume hologram are integrated is created. I have. Therefore, in the external resonance type semiconductor laser of the sixth embodiment, the external resonator is constituted only by the photopolymer volume hologram 1 in structure.

That is, when the laser beam oscillated from the laser oscillator 2 is incident on the photopolymer volume hologram 1 formed in the shape of a collimator lens, only the laser beam of a predetermined wavelength is emitted due to the wavelength selectivity of the photopolymer volume hologram. It is returned to the laser oscillator 2 and resonates.

With the above configuration, the external resonance type semiconductor laser of the sixth embodiment supplies a laser beam having a desired wavelength with a narrow wavelength width and stable transverse mode, as in the first embodiment. be able to. And Example 6
Since the external resonator is composed of only the photopolymer volume hologram 1, the configuration of the device can be simplified and reduced in size, and the cost can be reduced. Is possible.

Further, the volume hologram is formed by a laser oscillator 2
The volume hologram can be integrated with the laser oscillator 2 by using it for the window 10 of the package.

FIG. 8 shows a seventh embodiment to which the present invention is applied, in which a reflection type photopolymer volume hologram 1 is used for a window 10 of a semiconductor laser package and is integrated with a laser oscillator 2. In the external resonance type semiconductor laser of the seventh embodiment, the window 10 of the package of the laser oscillator 2 is constituted by the reflection type photopolymer volume hologram 1. Therefore, in the external resonance type semiconductor laser according to the seventh embodiment, the laser oscillator 2 has a configuration also serving as an external resonator.

That is, in the laser oscillator 2, the laser beam oscillated from the laser light emitting element 12 formed on the Peltier element 11 is applied to the reflection type photopolymer volume hologram 1 formed in the window 10 of the package of the laser oscillator 2. Only the laser beam of the predetermined wavelength returns to the laser oscillator 2 due to the wavelength selectivity.

Incidentally, in the above-described external resonance type semiconductor laser, there is a problem that the resonator length changes with time in practical use. When the optical path length changes due to the effects of vibration, temperature change, convection of air, etc., the resonator length changes and output fluctuation occurs. However, with respect to these problems, there are optical devices such as a mirror that removes vibration, shields the entire resonator, mounts a semiconductor laser on a Peltier element to control the temperature, controls the injection current of the semiconductor laser, and operates a mirror. This can be solved by various methods such as mounting the unit on an actuator such as a piezo element or a voice coil motor and controlling the position with a feedback signal from output light.

In a volume hologram, when recording a hologram, as shown in FIG. 9, a laser beam having a wavelength λ ₁ oscillated from, for example, a laser oscillator is applied to a reference beam 14 having a predetermined wavefront by a beam splitter 13. It is separated into object light 15. And each mirror 4
Then, the light is reflected and incident on the photopolymer volume hologram 16 for recording. At this time, the recording reference light wavefront 17 and the recording object light wavefront 18 are in the state shown in FIG.

Then, at the time of reproduction, as shown in FIG. 10, a laser beam of wavelength λ ₂ oscillated from the laser oscillator 2 is reflected by the mirror 4 and made incident on the photopolymer volume hologram. At this time, the reproduction reference light wavefront 19 and the reproduction object light wavefront 20 are in the state shown in FIG.

However, it is not necessary that the wavelength of the laser beam used is the same at the time of recording and at the time of reproduction. That is, the recording reference light wavefront 17 and the reproduction reference light wavefront 19 need not coincide with each other, and the recording object light wavefront 18 and the reproduction object light wavefront 20 do not need to match. However, even in this case, it is desirable that both the reference beam during reproduction and the object beam during reproduction are plane waves from the Bragg phase matching condition during reproduction.

In a photopolymer volume hologram, the wavelength of a laser beam used for recording and reproducing interference fringes is different, and when it is desired to generate a wavefront 22 other than a plane wave during reproduction, the recording is performed including this correction. It is necessary to design the optical system at the time including the correction optical system 21. Here, as the correction optical system 21, a hologram, an aspherical optical element, an optical system having an aberration such as an eccentric optical system, a spatial modulator such as a diffractive optical element or a liquid crystal panel to generate an arbitrary wavefront, Etc. can be used. By arranging these correction optical systems 21 between the mirror 4 on the side of the reference beam 14 and the photopolymer volume hologram 16 as shown in FIG. 11, for example, a hologram capable of generating a desired wavefront at the time of reproduction is recorded. can do.

The case where the semiconductor laser is used as the laser medium has been described above. This is because semiconductor lasers are considered to be the most practical because they are solid, small, stable, and can be manufactured at low cost by mass production. However, the present invention is not limited to a semiconductor laser, and a feedback optical system in a resonator such as a gas laser such as Co ₂ and Ar ions, an excimer laser, a dye laser, and a wavelength-tunable solid-state laser such as Ti: Saphire. The same effect can be obtained by applying the method described above. Therefore, the present invention can provide excellent effects even when combined with these lasers.

As described above, according to the present invention, a laser such as an external cavity semiconductor laser having a narrow wavelength width and a stable transverse mode can be realized at a low cost with a simple configuration. Using the lateral mode selectivity, the beam profile of the output light can be controlled. By using a hologram to correct astigmatism and control the divergence angle of a semiconductor laser, the number of optical components can be reduced, and the system can be made smaller and less expensive. Can be provided.

The present invention is not limited to a laser display, but includes a hologram wavelength multiplexing recording, an information recording device such as an optical disk and a hologram memory, a wavelength multiplexing optical communication, a wavelength conversion using a nonlinear optical effect, a laser cooling. , Frequency standard, spectroscopic measurement for environment and process management, interferometer and so on.

[0058]

Since the external cavity semiconductor laser according to the present invention has a photopolymer volume hologram in the external cavity, the wavelength selectivity of the external cavity can be improved. As a result, it is possible to selectively oscillate only the wavelength closer to the desired wavelength, and to narrow the wavelength width of the laser light emitted from the external resonance type laser.

Since the photopolymer volume hologram has a high diffraction efficiency, it is possible to efficiently oscillate a laser beam having a desired wavelength.

Then, the photopolymer volume hologram is
Since there is no change with time, laser light can be taken out stably.

Therefore, according to the present invention, it is possible to provide a laser capable of stably supplying a laser beam having a narrow wavelength width with a simple and inexpensive configuration.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an external resonance type semiconductor laser using a reflection type photopolymer volume hologram according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of an on-axis volume hologram external resonance type semiconductor laser including a laser oscillator, a collimator lens, and a volume hologram.

FIG. 3 is a view showing a second embodiment to which the present invention is applied, illustrating a configuration of an external resonance type semiconductor laser using a transmission type photopolymer volume hologram;

FIG. 4 is a diagram illustrating a third embodiment to which the present invention is applied, illustrating a configuration of an external resonance type semiconductor laser in which a mirror is replaced with a corner cube in the first embodiment.

FIG. 5 shows a fourth embodiment to which the present invention is applied. In the first embodiment, an external resonance type semiconductor laser in which mirror processing is performed on an end surface on the mirror side of a reflection type photopolymer volume hologram and the mirror is replaced with a mirror. FIG. 3 is a diagram illustrating the configuration of FIG.

FIG. 6 shows a fifth embodiment to which the present invention is applied. In the first embodiment, an external resonance type semiconductor laser in which a mirror-side end surface of a reflection type volume hologram is processed into a corner cube shape and replaced with a mirror. FIG. 3 is a diagram illustrating the configuration of FIG.

FIG. 7 is a view illustrating a configuration of an external resonance semiconductor laser in which a volume hologram is formed in a collimator lens according to a sixth embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration of an external resonance type semiconductor laser integrated with a laser oscillator using a volume hologram as a window of a semiconductor laser package according to a seventh embodiment of the present invention.

9 is a diagram illustrating a state of recording interference fringes photopolymer volume hologram with a laser beam having a wavelength lambda _1.

FIG. 10 is a diagram illustrating a state in which a photopolymer volume hologram is reproduced using a laser beam having a wavelength of λ ₂ .

FIG. 11 is a diagram illustrating a state in which a correction optical system is arranged between a mirror on the reference light side and a photopolymer volume hologram to record interference fringes.

FIG. 12 is a diagram illustrating a configuration of a Littman resonator.

FIG. 13 is a diagram illustrating a configuration of a Littrow resonator.

[Explanation of symbols]

1 reflection type photopolymer volume hologram, 2 laser oscillator, 3 collimator lens, 4 mirror, 6 transmission type photopolymer volume hologram, 7 corner cube,
8 reflective surface, 9 reflective surface, 11 Peltier element, 12
Laser light emitting element, 13 beam splitter, 14 reference light, 15 object light, 16 photopolymer volume hologram,
17 Reference wave front at recording, 18 Object wave front at recording, 1
9 Reference light wavefront during reproduction, 20 Object light wavefront during reproduction, 21
Correction optical system, 22 Wavefront other than plane wave

Claims (9)

[Claims] 1. An external resonance type laser comprising: a laser oscillator that emits a laser beam of a predetermined wavelength; and an external resonator that resonates the laser beam emitted from the laser oscillator. The photopolymer volume hologram includes a polymer volume hologram, and the laser beam emitted from the laser oscillator is diffracted and made incident on an optical system in the resonator, and selectively transmits a laser beam having a predetermined wavelength. An external resonance type laser that emits light to the outside. 2. The external resonance type laser according to claim 1, wherein said photopolymer volume hologram is a reflection type photopolymer volume hologram. 3. The external resonance type laser according to claim 1, wherein said photopolymer volume hologram is a transmission type photopolymer volume hologram. 4. The external resonance type laser according to claim 1, wherein said laser oscillator is a semiconductor laser oscillator. 5. The external cavity laser according to claim 1, wherein the optical system in the resonator is a corner cube. 6. The external resonance type laser according to claim 1, wherein the optical system in the resonator is a reflection surface formed on the photopolymer volume hologram. 7. The external resonance type laser according to claim 1, wherein the optical system in the resonator is a reflection surface of the photopolymer volume hologram formed in a corner cube shape. 8. The external resonance type laser according to claim 1, wherein said photopolymer volume hologram is formed in a collimator lens shape. 9. The external resonance type laser according to claim 1, wherein the photopolymer volume hologram is disposed at a tip of a laser beam emitting portion for emitting a laser beam in the laser oscillator.