JP4862960B2 - Wavelength conversion laser device and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a watt-class and high-efficient wavelength converting laser device. <P>SOLUTION: The wavelength converting laser device includes: an active layer emitting laser beams; an optical resonator oscillating the laser beams; and a wavelength converter which is arranged inside the optical resonator and wave-converts the laser beams into higher harmonics and which controls the laser beams and the vertical-lateral mode of the higher harmonics and has a slab-shaped optical waveguide structure for expanding horizontally the beam diameters of the laser beams and the higher harmonics. The wavelength converter has a periodic polarization reversal structure the shape of which is approximately in parallel with the wavefront of the laser beams. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a laser device, and more particularly to a wavelength conversion technique for shortening the wavelength of laser light.

  In recent years, for example, green and blue visible light lasers have been researched and developed as light sources in the field of optical information processing and the like. As a kind of visible light laser, a wavelength conversion laser device that applies a wavelength conversion technique to shorten the wavelength of near-infrared laser light is known.

  In general, in a wavelength conversion laser device, a wavelength converter made of a nonlinear optical material is installed inside or outside an optical resonator of a semiconductor laser or a solid-state laser, and a laser beam (fundamental wave) generated by the optical resonator is applied to the nonlinear optical material. By propagating, the second harmonic wave that has been wavelength-converted to a half wavelength (double frequency) with respect to the fundamental wave is output.

  An example of such a wavelength conversion laser device is disclosed in Japanese Patent Publication No. 63-121829 (Patent Document 1). In particular, in the wavelength conversion laser device disclosed in the third embodiment and FIG. 3, a semiconductor laser and a wavelength converter are joined, and a reflector is integrally formed on one end face thereof to constitute an optical resonator. Even when using small, low-power, continuous-wave excitation light such as a semiconductor laser, high light conversion efficiency can be obtained by inserting a wavelength converter into the optical resonator to increase the light intensity. It is.

JP-A-63-121829

  However, such a conventional wavelength conversion laser device is composed of a semiconductor laser and a wavelength converter, and a narrow stripe semiconductor laser having a small light emitting area can provide a high-power laser beam (fundamental wave) of the watt class. Therefore, there is a limit to increasing the output of the wavelength conversion laser device. On the other hand, in a broad area type semiconductor laser having a large light emitting area and high output in the watt class, the horizontal mode (horizontal transverse mode) in the horizontal direction with respect to the active layer is not mode-controlled, and the multi-laterality with low beam quality Oscillates in mode. When such a broad area type semiconductor laser is used, a laser beam (fundamental wave) having a low beam quality has insufficient coupling efficiency or angular phase matching with the wavelength converter, and a highly efficient wavelength conversion laser device is not available. There is a problem that it cannot be obtained.

  As described above, the conventional wavelength conversion laser device has a problem in that it cannot obtain a watt-class high output and high efficiency.

  The object of the present invention is to solve the above-mentioned problems of the conventional wavelength conversion laser device.

  A wavelength conversion laser device according to the present invention includes an active layer that emits laser light, an optical resonator that oscillates the laser light, and a wavelength that is disposed in the optical resonator and wavelength-converts the laser light into a harmonic. A wavelength converter having a slab-shaped optical waveguide structure for controlling a vertical transverse mode of the laser beam and the harmonic wave and expanding a beam diameter of the laser beam and the harmonic wave in a horizontal direction; The wavelength converter has a periodically poled structure whose shape is substantially parallel to the wavefront of the laser beam.

  As described above, in this wavelength conversion laser device, the wavelength converter has an optical waveguide structure for expanding the beam diameter in the horizontal direction, so that the laser beam (basic) that propagates between the active layer and the wavelength converter can be obtained. Wave) coupling loss can be reduced, and the wavelength conversion in the wavelength converter can be made highly efficient. Furthermore, the laser beam (fundamental wave) and harmonic power density are reduced by expanding the beam diameter in the horizontal direction in the wavelength converter, thereby reducing heat generation due to light absorption and increasing the heat radiation area to prevent temperature rise. be able to. For this reason, the shift of the phase matching wavelength due to the temperature rise is reduced, which also makes it possible to increase the efficiency of wavelength conversion in the wavelength converter. In addition, since the periodically poled structure is formed substantially parallel to the wavefront of the laser beam (fundamental wave) for adjusting the angle phase matching, the angle phase matching is sufficient and highly efficient wavelength conversion can be obtained.

(A) is a vertical direction sectional view showing the configuration of the wavelength conversion laser device according to Embodiment 1 of the present invention, (b) is a horizontal direction sectional view showing the configuration of the wavelength conversion laser device according to Embodiment 1 of the present invention, (A) is a vertical direction sectional view showing the configuration of the wavelength conversion laser device according to Embodiment 1 of the present invention, (b) is a horizontal direction sectional view showing the configuration of the wavelength conversion laser device according to Embodiment 1 of the present invention, (A) is a vertical direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 2 of the present invention, (b) is a horizontal direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 2 of the present invention, (A) is a vertical direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 3 of the present invention; (b) is a horizontal direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 3 of the present invention; (A) is a vertical direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 3 of the present invention; (b) is a horizontal direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 3 of the present invention; (A) is a vertical direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 4 of the present invention; (b) is a horizontal direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 4 of the present invention; (A) is a vertical direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 5 of the present invention, (b) is a horizontal direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 5 of the present invention, (A) is a vertical direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 5 of the present invention, (b) is a horizontal direction sectional view showing a configuration of a wavelength conversion laser device according to Embodiment 5 of the present invention, (A) is a vertical direction sectional view showing the configuration of a wavelength conversion laser device according to Embodiment 6 of the present invention; (b) is a horizontal direction sectional view showing the configuration of the wavelength conversion laser device according to Embodiment 6 of the present invention; (A) is a vertical direction sectional view showing the configuration of a wavelength conversion laser device according to Embodiment 6 of the present invention; (b) is a horizontal direction sectional view showing the configuration of the wavelength conversion laser device according to Embodiment 6 of the present invention; (A) is a vertical direction sectional view showing the configuration of a wavelength conversion laser device according to Embodiment 6 of the present invention; (b) is a horizontal direction sectional view showing the configuration of the wavelength conversion laser device according to Embodiment 6 of the present invention; (A) is a vertical direction sectional view showing the configuration of a wavelength conversion laser device according to Embodiment 6 of the present invention; (b) is a horizontal direction sectional view showing the configuration of the wavelength conversion laser device according to Embodiment 6 of the present invention; (A) is a vertical sectional view showing the configuration of a wavelength conversion laser device according to a seventh embodiment of the present invention; (b) is a horizontal sectional view showing the configuration of a wavelength conversion laser device according to a seventh embodiment of the present invention; (A) is a vertical sectional view showing the configuration of a wavelength conversion laser device according to a seventh embodiment of the present invention; (b) is a horizontal sectional view showing the configuration of a wavelength conversion laser device according to a seventh embodiment of the present invention; (A) is a vertical sectional view showing the configuration of a wavelength conversion laser device according to an eighth embodiment of the present invention; (b) is a horizontal sectional view showing the configuration of the wavelength conversion laser device according to an eighth embodiment of the present invention; It is.

Embodiment 1 FIG.
The wavelength conversion laser device according to the first embodiment of the present invention includes a semiconductor laser and a wavelength converter disposed in the optical resonator. Laser light (fundamental wave) laser-oscillated by the optical resonator is wavelength-converted to a harmonic by the wavelength converter and output. The vertical transverse mode of the laser beam (fundamental wave) and the harmonic is controlled by the optical waveguide structure, and the horizontal transverse mode of the laser beam (fundamental wave) is controlled by the optical resonator.

  1 and 2 are configuration diagrams showing a wavelength conversion laser device according to Embodiment 1 of the present invention. The cross-sectional structure of the wavelength conversion laser device is illustrated in the (a) vertical direction and (b) horizontal direction with respect to the active layer of the semiconductor laser.

  In FIG. 1, an active layer 1a made of, for example, an InGaAs compound semiconductor mixed crystal is formed in a semiconductor laser 1. The active layer 1a has a layer thickness of about 1 μm and constitutes a slab optical waveguide that controls the vertical transverse mode of laser light (fundamental wave). A pn junction is formed at the boundary surface of the active layer 1a. The active layer width is 200 μm, which is a so-called “broad area type”, and has a high output characteristic of an output of 5 W or more. The length of the semiconductor laser 1 in the longitudinal direction of the optical resonator is 4 mm, and the semiconductor laser 1 has a gain band of about 3 nm with a wavelength of 946 nm as the center. The wavelength converter 2 is made of, for example, an MgO: LiNbO3 crystal having a periodically poled structure, and the crystal axis in the z-axis direction coincides with the horizontal direction of the active layer 1a. The wavelength converter 2 has a wide slab optical waveguide 2a having a thickness similar to that of the active layer 1a of the semiconductor laser 1, and the vertical transverse mode of laser light (fundamental wave) and harmonics is controlled. . The length of the wavelength converter in the longitudinal direction of the optical resonator is 10 mm, and the periodic polarization reversal structure shown in the form of stripes in the figure has a polarization reversal period of 4.6 μm in the vertical axis direction. The active layer 1a of the semiconductor laser 1 and the slab optical waveguide 2a of the wavelength converter 2 are joined at the end face. Reference numeral 3 denotes a first reflector, and reference numeral 4 denotes a second reflector. These constitute an optical resonator of a semiconductor laser, and a wavelength converter 2 is disposed in the optical resonator. The first reflector 3 is a coating film that is integrally formed on one end face of the semiconductor laser 1 and totally reflects almost at a wavelength of 946 nm. The second reflector 4 is integrally formed with the wavelength converter 2 and is almost totally reflected for the wavelength 946 nm and has a high transmittance for the wavelength 473 nm (hereinafter referred to as “reflected Bragg grating reflector”). Abbreviated as a grating). The second reflector 4 has a radius of curvature of 180 mm in the horizontal direction in order to control the horizontal transverse mode of the semiconductor laser 1. Furthermore, the first reflector 3 and the second reflector 4 have a reflection spectrum with a wavelength width of about 0.02 nm centered on the wavelength 946 nm for selection of the oscillation wavelength. 5 schematically represents a horizontal section of the fundamental wave beam reciprocating in the optical resonator.

Next, the operation will be described.
When a forward current is passed from the electrode (not shown) to the semiconductor laser 1, electrons and holes are injected into the active layer 1a, and the electrons and holes recombine to emit light. The 1st reflector 3 and the 2nd reflector 4 are arrange | positioned facing, and an optical resonator is comprised. Here, when the injection current is increased to form an inversion distribution, stimulated emission occurs, and the laser beam having a wavelength of 946 nm is amplified corresponding to the reflection spectra in the first reflector 3 and the second reflector 4. . An optical resonator loss, such as an absorption loss in the semiconductor laser 1, a transmission loss in the first reflector 3 and the second reflector 4, and a loss due to wavelength conversion or scattering in the wavelength converter, is represented by an amplification gain of laser light. If it exceeds, laser oscillation will occur.

  At this time, in the semiconductor laser 1, the vertical transverse mode of the laser beam (fundamental wave) is controlled by the active layer 1a. In the wavelength converter 2, the vertical transverse mode of laser light (fundamental wave) and harmonics is controlled by the slab optical waveguide 2a. On the other hand, the horizontal and transverse modes of laser light (fundamental wave) and harmonics are not controlled by the active layer 1a or the slab optical waveguide 2a. The horizontal transverse mode of the laser light (fundamental wave) is controlled by the first reflector 3 and the second reflector 4 having a radius of curvature of 180 mm. Here, the spatial mode of the optical resonator is defined by the active layer width and the radius of curvature of the second reflector 4, and laser light (fundamental wave) having a horizontal transverse mode with a low optical resonator loss causes laser oscillation. The wavefront of the laser beam (fundamental wave) in the second reflector 4 is substantially parallel to the reflecting surface.

  Here, the broad area type semiconductor laser 1 has high output characteristics, and the beam diameter is expanded in the horizontal direction to reduce the power density of the laser beam (fundamental wave). Therefore, higher harmonics can be output. Both the semiconductor laser 1 and the wavelength converter 2 have an optical waveguide structure, the waveguide mode of the optical waveguide formed by the semiconductor laser 1 and the wavelength converter 2 is matched in the vertical direction, and a pair of reflectors are used in the horizontal direction. It is possible to reduce the coupling loss of laser light (fundamental wave) propagating between the semiconductor laser 1 and the wavelength converter 2 as a spatial mode formed by an optical resonator, and to improve the efficiency of wavelength conversion in the wavelength converter 2. is there.

  In particular, since the wavelength converter 2 has the slab optical waveguide 2a, the beam diameter is expanded in the horizontal direction in the wavelength converter 2 to reduce the power density of laser light (fundamental wave) and harmonics. In addition, heat generation due to light absorption is reduced and the heat radiation area is widened to prevent an increase. For this reason, the shift of the phase matching wavelength due to the temperature rise is reduced, and this also makes it possible to increase the efficiency of wavelength conversion in the wavelength converter 2.

  Further, the wavelength converter 2 has a periodic polarization inversion structure, and the propagating harmonics are quasi-phase matched so that the wavelength conversion in the wavelength converter 2 can be made highly efficient.

By the way, since the refractive index of the nonlinear optical material has wavelength dispersion, the fundamental wave and the second harmonic have different phase velocities, and the second harmonic generated at each point propagates with a phase shift between the respective harmonics. Propagating beyond the coherent length lc, which is the distance at which the phase difference becomes π, decreases the intensity of the synthesized harmonics, and repeats increasing and decreasing with the period of the coherent length. Therefore, in the periodic polarization reversal structure, the sign of the nonlinear optical constant of the nonlinear optical material, that is, the direction of spontaneous polarization of the ferroelectric material is reversed at a period of coherent length. Here, assuming that the wavelength of the fundamental wave is λ1, the wavelength of the second harmonic is λ2, the refractive index for the fundamental wave of the nonlinear optical material is n1, and the refractive index for the second harmonic wave is n2, the fundamental wave vector k1 = (2πn1 / λ1) and second harmonic wave vector k2 = (2πn2 / λ2), phase mismatch amount Δk = 2k1-k2, and the coherent length lc is expressed by the following Equation 1.
lc = π / △ k = λ1 / 4 / (n1 − n2) (1)

The phase of the second harmonic is inverted with such a period of the coherent length, resulting in a quasi-phase matching that compensates for the phase of the synthesized harmonic, and the intensity increases additively to efficiently generate the second harmonic. be able to.

  In the periodic polarization reversal structure, a periodic pattern electrode is formed on the substrate surface of the nonlinear optical material, and the polarization is reversed by applying a high voltage exceeding the holding electric field of the ferroelectric material by applying an electric field. Therefore, it is manufactured at intervals of a coherent length on the order of microns.

  When a LiNbO3 crystal having a large nonlinear optical constant is used as the nonlinear optical material, highly efficient wavelength conversion is realized by d33 which is the maximum component of the nonlinear optical constant in the quasi phase matching. However, since LiNbO3 crystals are susceptible to optical damage, the power density of the fundamental wave is limited and there is a limit to increasing the output. When MgO: LiNbO3 crystal doped with MgO is used, resistance against optical damage is increased, and high output can be achieved.

  Also, since the laser beam (fundamental wave) reciprocating in the optical resonator is polarized in the horizontal direction, the nonlinear optical constant of the MgO: LiNbO3 crystal is maximum with respect to the polarization direction of the laser beam (fundamental wave). It is possible to increase the efficiency of wavelength conversion in the wavelength converter 2 by matching the crystal axes in the z-axis direction.

  The longitudinal mode interval of the laser beam (fundamental wave) depends on the length of the optical resonator and is sufficiently small at 0.013 nm. As the oscillation wavelength of the laser light (fundamental wave), a longitudinal mode near the wavelength of 946 nm is selected within the wavelength width of the reflection spectrum of the first reflector 3 and the second reflector 4. In order to select the longitudinal mode, the second reflector 4 is composed of a grating, and the phase matching wavelength of the wavelength converter 2 and the oscillation wavelength of the laser beam (fundamental wave) are made to coincide with each other to thereby increase the amount of harmonic phase mismatch. It is possible to reduce the wavelength conversion in the wavelength converter 2 and increase the efficiency. Here, since the longitudinal mode interval is sufficiently small, the oscillation wavelength of the laser beam (fundamental wave) can be controlled sufficiently close to the phase matching wavelength.

  Since the first reflector 3 and the second reflector 4 are integrally formed with the optical waveguides of the semiconductor laser 1 and the wavelength converter 2, the optical waveguide is formed by the first reflector 3 and the second reflector 3. It is possible to reduce the diffraction loss of the laser beam (fundamental wave) reflected back and forth within the optical resonator and to increase the output of harmonics by the laser beam (fundamental wave) oscillated at a higher output.

  Here, the laser light (fundamental wave) is not output to the outside of the optical resonator by the total reflection of the first reflector 3 and the second reflector 4, but is confined inside the optical resonator, and the second reflection. Only harmonics that have been wavelength-converted due to the high transmittance of the device 4 are output to the outside. Since the wavelength converter 2 is disposed inside the optical resonator in which high-power laser light (fundamental wave) is confined, harmonics that have been wavelength-converted with high efficiency are emitted with high output.

  As described above, the wavelength converter 2 converts the laser beam (fundamental wave) having a wavelength of 946 nm with high efficiency and emits a harmonic having a wavelength of 473 nm with a high output of 3 W.

  Further, as shown in FIG. 2, the coating film and the grating may be interchanged in the first reflector 3 and the second reflector 4. In FIG. 2, the first reflector 3 is formed integrally with the semiconductor laser 1, and is a grating that totally reflects the wavelength 946 nm. The second reflector 4 is formed integrally with the end face of the wavelength converter 2. It is a coating film that substantially totally reflects at a wavelength of 946 nm and has a high transmittance at a wavelength of 473 nm. The coating film as the second reflector 4 is formed on the curved end face of the wavelength converter 2 and has a curvature radius of 180 mm in the horizontal direction in order to control the horizontal transverse mode of the laser beam (fundamental wave). Have. Furthermore, the coating film of the first reflector 3 and the grating of the second reflector 4 have a reflection spectrum with a wavelength width of about 0.02 nm centered on a wavelength of 946 nm for selecting the longitudinal mode of the laser beam (fundamental wave). Have. In the configuration shown in FIG. 2 as well, the same effect as in the case of FIG. 1 can be obtained.

  As described above, in the wavelength conversion laser device according to the first embodiment of the present invention, the horizontal lateral mode is controlled by the optical resonator in the broad area type semiconductor laser having a large emission area and high output in the watt class. Therefore, it oscillates in the transverse mode with high beam quality. As a result, laser light (fundamental wave) with high output of watt class and high beam quality has sufficient coupling efficiency with the wavelength converter, and highly efficient wavelength conversion can be obtained. There is an effect that a highly efficient wavelength conversion laser device can be realized.

Embodiment 2. FIG.
The wavelength conversion laser device according to the second embodiment of the present invention has substantially the same configuration and operation as the wavelength conversion laser device according to the first embodiment, but the embodiment differs with respect to the optical resonator.

  FIG. 3 is a block diagram showing a wavelength conversion laser device according to Embodiment 2 of the present invention. The cross-sectional structure of the wavelength conversion laser device is illustrated in the (a) vertical direction and (b) horizontal direction with respect to the active layer of the semiconductor laser. Moreover, in the figure, the same code | symbol shows the same or an equivalent part.

  In FIG. 3, the first reflector 3 is integrally formed with the semiconductor laser 1, and is a nearly totally reflecting grating with respect to a wavelength of 946 nm, and the second reflector 4 is integrally formed on one end face of the wavelength converter 2. The coating film is almost totally reflected at a wavelength of 946 nm and has a high transmittance at a wavelength of 473 nm. The grating of the first reflector 3 has a radius of curvature of 170 mm in the horizontal direction in order to control the horizontal mode in the horizontal direction.

  As in the first embodiment, the vertical transverse mode of the laser beam (fundamental wave) is controlled by the optical waveguide structure of the semiconductor laser 1 and the wavelength converter 2. On the other hand, the horizontal transverse mode is controlled by the first reflector 3 and the second reflector 4 having a radius of curvature of 170 mm. Here, the spatial mode of the optical resonator is defined by the active layer width and the radius of curvature of the first reflector 3, and laser light (fundamental wave) having a horizontal transverse mode with a low optical resonator loss oscillates. The wavefront of the laser beam (fundamental wave) in one reflector 3 is substantially parallel to the reflecting surface.

Further, although not shown, the first reflector 3 may be configured as a coating film having a curvature radius of 170 mm, and the second reflector 4 may be configured as a grating.
The operation of the wavelength conversion laser device according to the second embodiment as described above is the same as that according to the first embodiment, and the same effect can be obtained.

Embodiment 3 FIG.
The wavelength conversion laser device according to the third embodiment of the present invention has substantially the same configuration and operation as those of the wavelength conversion laser devices of the first and second embodiments, but is an angle phase matching adjusting means in the wavelength converter. Is provided.

  4 and 5 are configuration diagrams showing a wavelength conversion laser device according to Embodiment 3 of the present invention. The cross-sectional structure of the wavelength conversion laser device is illustrated in the (a) vertical direction and (b) horizontal direction with respect to the active layer of the semiconductor laser. Moreover, in the figure, the same code | symbol shows the same or an equivalent part.

  In FIG. 4, as an embodiment different from FIG. 1, the semiconductor laser 1 is a wide area type having an active layer width of 100 μm and high output characteristics. The grating of the second reflector 4 has a radius of curvature of 16 mm in the horizontal direction in order to control the horizontal transverse mode. Furthermore, the periodic polarization reversal structure of the wavelength converter 2 has a polarization reversal period of about 4.6 μm, but has a curved surface shape that is substantially parallel to the wavefront of the laser beam (fundamental wave) in the horizontal direction to adjust the angle phase matching. Is formed.

  By the way, the problem of angular phase matching is that when the fundamental wave is propagated to the wavelength converter by phase matching of the harmonics, the allowable amount of propagation angle is limited, and the fundamental wave with good beam quality with small beam expansion. Laser light is required. For example, in the planar periodic domain-inverted structure as shown in FIG. 1 in the first embodiment, the polarization of the fundamental wave beam spreads in a curved shape in the horizontal direction and the propagation angle is different by δ between the central portion and the peripheral portion of the beam. The inversion period Λ changes to Λ / cos δ, and the wavelength conversion efficiency decreases at the periphery of the beam.

  Here, in the wavelength converter 2 according to Embodiment 3 shown in FIG. 4, the beam of the laser light (fundamental wave) spreads in the horizontal direction and is tilted by a maximum of 0.1 deg. However, since the periodic polarization reversal structure is formed in a curved surface shape that is substantially parallel to the wavefront of the laser beam (fundamental wave) in the horizontal direction, the polarization reversal period substantially matches the beam expansion of the fundamental wave, and the harmonics. Is sufficiently quasi-phase matched, and the wavelength conversion in the wavelength converter can be made highly efficient.

  As shown in FIG. 5, as an embodiment different from FIG. 3, the semiconductor laser 1 is a wide area type having an active layer width of 120 μm and high output characteristics. The grating of the second reflector 4 has a radius of curvature of 14 mm in the horizontal direction in order to control the horizontal mode in the horizontal direction. Furthermore, the periodic polarization reversal structure of the wavelength converter 2 has a polarization reversal period of about 4.6 μm, but has a curved surface shape that is substantially parallel to the wavefront of the laser beam (fundamental wave) in the horizontal direction to adjust the angle phase matching. Is formed. In the wavelength converter 2, the laser beam (fundamental wave) is spread in the horizontal direction and tilted by a maximum of 0.06 deg. However, in the configuration of FIG. 5 as well, the same operation and effect as in the case of FIG. 4 can be obtained.

  As described above, in the wavelength conversion laser device according to Embodiment 3 of the present invention, the periodically poled structure is formed in a curved surface shape substantially parallel to the wavefront of the laser beam (fundamental wave) for adjusting the angle phase matching. Therefore, the angle phase matching becomes sufficient, and there is an effect of obtaining highly efficient wavelength conversion.

Embodiment 4 FIG.
The wavelength conversion laser device according to the fourth embodiment of the present invention has substantially the same configuration and operation as the wavelength conversion laser device of the third embodiment, but includes an optical waveguide element in which a reflector of an optical resonator is formed. It is.

  FIG. 6 is a block diagram showing a wavelength conversion laser device according to Embodiment 4 of the present invention. The cross-sectional structure of the wavelength conversion laser device is illustrated in the (a) vertical direction and (b) horizontal direction with respect to the active layer of the semiconductor laser. Moreover, in the figure, the same code | symbol shows the same or an equivalent part.

  In FIG. 6, reference numeral 6 denotes an optical waveguide device, which includes a slab optical waveguide 6 a having substantially the same thickness as the slab optical waveguide 2 a of the wavelength converter 2. The wavelength converter 6 has a length of 5 mm, and the second reflector 4 is a grating formed integrally with the optical waveguide element, and has a radius of curvature of 130 mm in the horizontal direction.

The operation of the wavelength conversion laser device according to the fourth embodiment as described above is the same as that according to the third embodiment, and the same effect is obtained. In addition, since the second reflector 4 is formed as an independent optical waveguide element so that the second reflector 4 with a different design can be selected or exchanged, the design flexibility in the wavelength conversion laser device is high. There is an effect.
Further, although not shown, the first reflector 3 may be configured as a grating integrally formed with an optical waveguide element including a slab optical waveguide having the same thickness as that of the active layer 1a of the semiconductor laser 1. The same effects as those described above can be obtained.

Embodiment 5 FIG.
The wavelength conversion laser device according to the fifth embodiment of the present invention has substantially the same configuration and operation as the wavelength conversion laser device of the third embodiment, but a reflection that reflects harmonics between the semiconductor laser and the wavelength converter. It is equipped with a vessel.

  7 and 8 are configuration diagrams showing a wavelength conversion laser device according to Embodiment 5 of the present invention. The cross-sectional structure of the wavelength conversion laser device is illustrated in the (a) vertical direction and (b) horizontal direction with respect to the active layer of the semiconductor laser. Moreover, in the figure, the same code | symbol shows the same or an equivalent part.

  In FIG. 7, reference numeral 7 denotes a third reflector, which is a coating film that is formed between the semiconductor laser 1 and the wavelength converter 2 and substantially totally reflects at a wavelength of 473 nm. In FIG. 8, the third reflector 7 is a grating that is formed on the optical path element 6 disposed between the semiconductor laser 1 and the wavelength converter 2 and substantially totally reflects the wavelength 473 nm.

  In the configuration in which the wavelength converter 2 is arranged in the optical resonator, the laser light (fundamental wave) propagates from the wavelength converter 2 in the direction of the semiconductor laser 1 because the laser light (fundamental wave) reciprocates in the optical resonator. Is also converted into a harmonic by the wavelength converter 2. Therefore, the harmonics propagating from the wavelength converter in the direction of the semiconductor laser are turned back by the third reflector 7 and emitted from the second reflector, so that it is possible to further increase the output of the harmonics. Furthermore, the incidence of harmonics on the semiconductor laser 1 is blocked by the third reflector 7 to prevent temperature rise and optical damage caused by the harmonics being absorbed by the active layer 1a of the semiconductor laser 1. Is possible.

Embodiment 6 FIG.
The wavelength conversion laser device according to the sixth embodiment of the present invention has substantially the same configuration and operation as the wavelength conversion laser device of the fifth embodiment, but a vertical transverse mode conversion means is provided between the semiconductor laser and the wavelength converter. It is to be prepared.

  9, FIG. 10, FIG. 11 and FIG. 12 are configuration diagrams showing a wavelength conversion laser device according to Embodiment 6 of the present invention. The cross-sectional structure of the wavelength conversion laser device is illustrated in the (a) vertical direction and (b) horizontal direction with respect to the active layer of the semiconductor laser. Moreover, in the figure, the same code | symbol shows the same or an equivalent part.

  In FIG. 9, the thicknesses of the slab optical waveguides of the semiconductor laser 1 and the wavelength converter 2 are different, 8 is a transverse mode conversion means, and the thickness of the slab optical waveguide formed in the optical waveguide element gradually increases. It has changed. In FIG. 10, as the transverse mode conversion means 8, a cylindrical lens having a curved surface only in the vertical direction is provided. In FIG. 11, the lateral mode conversion means 8 includes a graded index type lens having a refractive index distribution that gradually decreases in the vertical direction. In FIG. 12, as the transverse mode conversion means 8, the thickness of the active layer 1a of the semiconductor laser 1 is gradually changed.

  When the thickness and refractive index distribution of the slab optical waveguides of the semiconductor laser 1 and the wavelength converter 2 are different, the mode mismatch between the vertical transverse mode of the laser light in the semiconductor laser 1 and the vertical transverse mode of the laser light in the wavelength converter 2 Occurs. Therefore, the transverse mode conversion means 8 adjusts the beam diameter, the divergence angle, and the wavefront of the laser light (fundamental wave) incident on the slab optical waveguides of the semiconductor laser 1 and the wavelength converter 2 to adjust the semiconductor laser 1 and the wavelength converter. It is possible to reduce the coupling loss of the laser light (fundamental wave) propagating between the two and increase the wavelength conversion in the wavelength converter.

Embodiment 7 FIG.
The wavelength conversion laser device according to the seventh embodiment of the present invention has substantially the same configuration and operation as the wavelength conversion laser device of the fifth embodiment, but includes a semiconductor laser and temperature control means for the wavelength converter. .

  13 and 14 are configuration diagrams showing a wavelength conversion laser device according to Embodiment 7 of the present invention. The cross-sectional structure of the wavelength conversion laser device is illustrated in the (a) vertical direction and (b) horizontal direction with respect to the active layer of the semiconductor laser. Moreover, in the figure, the same code | symbol shows the same or an equivalent part.

  In FIG. 13, 9 is a temperature control means, which is a Peltier element (thermoelectric element) that is installed in contact with the wavelength converter 2 and changes the temperature of the wavelength converter 2 and keeps it constant.

  When the temperature control means 9 changes the temperature of the wavelength converter 2, the phase matching wavelength shifts due to the change in refractive index and thermal expansion. On the other hand, the temperature of the second reflector 4 integrally formed with the wavelength converter 2 also changes, and the reflection spectrum shifts in wavelength due to a change in refractive index and thermal expansion in the grating. Then, the oscillation wavelength of the laser light (fundamental wave) depending on the reflection spectrum is shifted in wavelength. Here, since the wavelength shift ratio with respect to the temperature change in the phase matching wavelength and the oscillation wavelength is different, it is possible to adjust the phase matching wavelength and the oscillation wavelength so as to substantially match with the temperature control of the wavelength converter 2. By such adjustment, the amount of harmonic phase mismatch can be reduced, and the wavelength conversion in the wavelength converter 2 can be made highly efficient. Although the longitudinal mode of the laser beam (fundamental wave) is discrete, the longitudinal mode interval in this embodiment is sufficiently small, so that the oscillation wavelength can be adjusted so as to substantially match the phase matching wavelength. is there.

  Further, in FIG. 14, the temperature control means 9 is a Peltier element (thermoelectric element) that is installed in contact with the semiconductor laser 1, the wavelength converter 2, and the optical waveguide element 6, and changes these temperatures and keeps them constant.

  According to the configuration shown in FIG. 14, even when the ambient temperature fluctuates, the temperature control means 9 keeps the temperatures of the semiconductor laser 1, the wavelength converter 2, and the optical waveguide element 6 constant, so that these refractive indexes can be maintained. It is possible to stabilize the high output and high efficiency characteristics of the wavelength conversion laser device by suppressing the change and thermal expansion.

  By the way, if the wavelength shift ratio with respect to the temperature change in the phase matching wavelength and the oscillation wavelength is set to be approximately equal, the wavelength conversion efficiency can be kept substantially constant without temperature control. For this reason, in the configuration shown in FIG. 14, it is possible to appropriately select the material of the optical waveguide element 6 so that the influence of the refractive index change and the thermal expansion due to the temperature change in each element can be offset. is there. As a result, even when the ambient temperature fluctuates, the phase mismatch amount of the harmonics is reduced by matching the two phase matching wavelengths of the wavelength converter and the oscillation wavelength of the laser light (fundamental wave) without temperature control. The wavelength conversion in the wavelength converter 2 can be made highly efficient.

Embodiment 8 FIG.
The wavelength conversion laser device according to the eighth embodiment of the present invention includes a semiconductor laser and a wavelength converter arranged outside the optical resonator. Laser light (fundamental wave) laser-oscillated by the optical resonator is wavelength-converted to a harmonic by the wavelength converter and output. The vertical transverse mode of the laser beam (fundamental wave) and the harmonic is controlled by the optical waveguide structure, and the horizontal transverse mode of the laser beam (fundamental wave) is controlled by the optical resonator.

  FIG. 15 is a block diagram showing a wavelength conversion laser device according to Embodiment 8 of the present invention. The cross-sectional structure of the wavelength conversion laser device is illustrated in the (a) vertical direction and (b) horizontal direction with respect to the active layer of the semiconductor laser. Moreover, in the figure, the same code | symbol shows the same or an equivalent part.

  In FIG. 15, the first reflector 3 is integrally formed on one end face of the semiconductor laser 1, and a coating film that almost totally reflects the wavelength 946 nm, and the second reflector 4 is integrally formed on the semiconductor laser 1. A grating that partially reflects the wavelength of 946 nm. The grating of the second reflector 4 has a radius of curvature in the horizontal direction in order to control the horizontal mode in the horizontal direction. The wavelength converter 2 is disposed outside the optical resonator in contact with one end face of the semiconductor laser 1.

Next, the operation will be described.
As in the first embodiment, laser oscillation occurs when the laser resonator amplification gain exceeds the optical resonator loss including absorption in the semiconductor laser 1 and transmission loss in the first reflector 3 and the second reflector 4. It reaches.

  At this time, in the semiconductor laser 1, the vertical transverse mode of the laser beam (fundamental wave) is controlled by the active layer 1a. In the wavelength converter 2, the vertical transverse mode of laser light (fundamental wave) and harmonics is controlled by the slab optical waveguide 2a. On the other hand, the horizontal and transverse modes of laser light (fundamental wave) and harmonics are not controlled by the active layer 1a or the slab optical waveguide 2a. The horizontal and transverse mode of the laser beam (fundamental wave) is controlled by the first reflector 3 and the second reflector 4 having a radius of curvature. Here, the spatial mode of the optical resonator is defined by the radius of curvature of the second reflector 4, and laser light (fundamental wave) having a horizontal transverse mode with low optical resonator loss oscillates, and the second reflector. The wavefront of the laser beam (fundamental wave) at 4 is substantially parallel to the reflecting surface.

  Here, the broad area type semiconductor laser 1 has high output characteristics, and the beam diameter is expanded in the horizontal direction to reduce the power density of the laser beam (fundamental wave). Therefore, higher harmonics can be output. Both the semiconductor laser 1 and the wavelength converter 2 have an optical waveguide structure. The waveguide mode of the optical waveguide formed by the semiconductor laser 1 and the wavelength converter 2 is matched in the vertical direction, and a pair of reflections in the horizontal direction. As a spatial mode formed by an optical resonator, a coupling loss of laser light (fundamental wave) propagating between the semiconductor laser 1 and the wavelength converter 2 is reduced, and the wavelength conversion in the wavelength converter 2 is made highly efficient. Is possible.

  The laser beam (fundamental wave) reciprocating in the optical resonator is polarized in the horizontal direction. For this reason, the crystal axis in the z-axis direction where the nonlinear optical constant of the wavelength converter 2 is the maximum coincides with the polarization direction of the laser light (fundamental wave), and the wavelength conversion in the wavelength converter 2 is made highly efficient. Is possible. Further, the wavelength converter 2 has a periodic polarization inversion structure, and the propagating harmonics are quasi-phase matched so that the wavelength conversion in the wavelength converter 2 can be made highly efficient. Furthermore, the periodically poled structure is formed in the horizontal direction along the light propagation direction and substantially parallel to the wavefront of the laser beam (fundamental wave), and the angle phase matching is sufficient, and the wavelength conversion in the wavelength converter 2 is highly efficient. It is possible to

  The longitudinal mode interval of the laser beam (fundamental wave) depends on the length of the optical resonator and is 0.13 nm. As the oscillation wavelength of the laser light (fundamental wave), a longitudinal mode near the wavelength of 946 nm is selected within the wavelength width of the reflection spectrum of the first reflector 3 and the second reflector 4. In order to select the longitudinal mode, the second reflector 4 is composed of a grating, and the phase matching wavelength of the wavelength converter 2 and the oscillation wavelength of the laser beam (fundamental wave) are made to coincide with each other to thereby increase the amount of harmonic phase mismatch. It is possible to reduce the wavelength conversion in the wavelength converter 2 and increase the efficiency.

Embodiment 9 FIG.
An image display apparatus according to Embodiment 9 of the present invention uses the wavelength conversion laser apparatus of Embodiments 1 to 8 as a light source for generating an image.

  In the image display device of the present invention, the laser light from the high-intensity light source is modulated by the light modulation means and projected to generate an image on the screen. Here, for example, a wavelength conversion laser device that outputs 3 W at a wavelength of 473 nm is used as a blue light source among the three primary colors, and a wavelength conversion laser device that outputs 2 W at a wavelength of 532 nm is used as a green light source. A semiconductor laser device is used as a red light source among the three primary colors.

  Further, a liquid crystal or a digital reflection element DMD (Digital Micromirror Device) is used as the light modulation means. In a liquid crystal display device using liquid crystal as the light modulation means, a liquid crystal material is sandwiched between glass substrates, etc., and an external electric field is applied to change the optical properties of the element caused by changes in the molecular arrangement of the liquid crystal. Use it to generate images. In a micromirror image display device using DMD as a light modulation means, micromirrors manufactured by MEMS (Micro Electro Mechanical Systems) technology are two-dimensionally arranged, and each mirror is shaken to be turned ON / OFF. To generate an image.

  When a wavelength conversion laser device is used as a light source for generating an image, there are advantages such as monochromaticity and high brightness of laser light compared to a conventional lamp device. It is possible to improve. Further, the wavelength conversion laser device has advantages such as high efficiency and long life compared with the conventional lamp device, and energy saving and long life can be achieved in the image display device.

Claims (17)

An active layer that emits laser light;
An optical resonator for oscillating the laser beam;
A wavelength converter that is disposed in the optical resonator and converts the wavelength of the laser beam into a harmonic wave, and controls a vertical transverse mode of the laser beam and the harmonic wave, and the laser beam and the harmonic beam. A wavelength converter having a slab-shaped optical waveguide structure for expanding the diameter in the horizontal direction;
With
2. The wavelength conversion laser device according to claim 1, wherein the wavelength converter has a periodically poled structure whose shape is substantially parallel to the wavefront of the laser beam.   The wavelength conversion laser device according to claim 1, wherein a shape of the periodic polarization reversal structure in a horizontal direction is a curved surface shape. The optical resonator includes a pair of opposing reflectors having reflecting surfaces shaped such that the optical resonator loss for the required horizontal transverse mode of the laser light is lower than the optical resonator loss for other horizontal transverse modes. Configured,
2. The wavelength conversion laser device according to claim 1, wherein a shape of a reflection surface of the pair of opposing reflectors is substantially parallel to a wavefront of the laser light.   The active layer and the wavelength converter align the waveguide mode of the laser light formed between the active layer and the optical waveguide structure of the wavelength converter in the vertical direction, and the pair of opposing reflections in the horizontal direction. 4. The laser light is arranged so as to propagate between the active layer and the optical waveguide structure of the wavelength converter as a spatial mode formed by the optical resonator composed of a resonator. 5. The wavelength conversion laser device described. The optical resonator includes a pair of opposing reflectors having reflecting surfaces shaped such that the optical resonator loss for the required horizontal transverse mode of the laser light is lower than the optical resonator loss for other horizontal transverse modes. Configured,
The one of the pair of opposing reflectors is a coating film integrally formed on one end face having a convex curved shape outside the optical resonator in the wavelength converter. The wavelength conversion laser device described.   2. The wavelength according to claim 1, wherein the active layer constitutes a slab-shaped optical waveguide structure for controlling a vertical transverse mode of the laser light and expanding a beam diameter of the laser light in a horizontal direction. Conversion laser device. 2. The wavelength conversion laser device according to claim 1, wherein the wavelength converter is made of an MgO: LiNbO ₃ crystal in which a Z-axis crystal axis substantially coincides with a polarization direction of the laser light.   The wavelength conversion laser device according to claim 1, wherein the active layer, the optical resonator, and the wavelength converter are integrated.   The wavelength conversion laser device according to claim 1, further comprising a reflector as a coating film that reflects the harmonics between the active layer and the wavelength converter.   2. The wavelength conversion according to claim 1, further comprising a transverse mode conversion means for reducing mode mismatch between a vertical transverse mode of laser light in the active layer and a vertical transverse mode of laser light in the wavelength converter. Laser device.   2. The wavelength conversion laser device according to claim 1, further comprising temperature control means for controlling the temperature of the active layer and the temperature of the wavelength converter.   The wavelength shift ratio with respect to the temperature change in the oscillation wavelength of the laser light emitted from the active layer and the wavelength shift ratio with respect to the temperature change in the phase matching wavelength of the laser light of the wavelength converter substantially coincide with each other. The wavelength conversion laser device according to claim 1. The wavelength conversion laser device according to any one of claims 1 to 12,
An image display device used as a light source for generating an image.   The image display device according to claim 13, wherein the light source for generating the image is a green light source of three primary colors.   The image display device according to claim 13, wherein the light source for generating the image is a blue light source of three primary colors.   The image display device according to claim 13, wherein liquid crystal is used as light modulation means for generating an image.   14. The image display device according to claim 13, wherein a digital reflection element is used as the light modulation means for generating an image.

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