JPH10133243A - Light wavelength converting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely lock an oscillation wavelengh of a semiconductor laser to a wavelength phase matching with a period of a domain inversion part in a device wavelength converting a laser beam outgoing from the semiconductor laser by a light wavelength converting element of an optical waveguide type having a periodic domain inversion structure. SOLUTION: After the laser beam 11 as a basic wave outgoing from the light wavelength converting element 15 in a divergent light state without wavelength converted is made parallel light by a collimate lens 20, it is diffracted by a grating 22. Further, the diffracted laser beam 11 is converged by a condenser lens 23 constituting a confocal optical system with the collimate lens 20. Then, the laser beam 11 is reflected by a line mirror 24 that the width of the converged position of the laser beam 11 in the shifted direction due to a difference of a diffraction angle in the grating 22 is formed sufficiently thinly to be fed back to the semiconductor laser 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type optical wavelength converter for converting a fundamental wave into a second harmonic or the like, and more particularly, to an optical waveguide using a ferroelectric crystal substrate as an optical waveguide substrate. The present invention relates to an apparatus for converting the wavelength of a laser beam emitted from a semiconductor laser using an optical wavelength conversion element formed with a periodic domain inversion structure.

[0002]

2. Description of the Related Art A method of wavelength-converting a fundamental wave into a second harmonic using an optical wavelength conversion element provided with a region in which spontaneous polarization (domain) of a ferroelectric material having a nonlinear optical effect is periodically inverted. Has already been proposed by Bleombergen et al. (See Phys. Rev., vol. 127, No. 6, 1918 (1962)).
In this method, the period ド メ イ ン of the domain inversion unit is given by: Λc = 2π / {β (2ω) -2β (ω)} where β (2ω) is the propagation constant of the second harmonic and β (ω) is the propagation of the fundamental wave. By setting so as to be an integral multiple of the coherent length Λc given by the constant, the fundamental wave and the second harmonic can be phase-matched (so-called quasi-phase matching).

[0003] For example, as disclosed in Japanese Patent Application Laid-Open No. 6-699582, an optical waveguide type optical wavelength conversion element which has an optical waveguide made of a nonlinear optical material and converts the wavelength of a fundamental wave guided therethrough. Attempts have been made to form a periodic domain inversion structure as described above to achieve efficient phase matching.

Meanwhile, the optical waveguide type optical wavelength conversion element having the above-mentioned periodic domain inversion structure is often used for wavelength conversion of a laser beam emitted from a semiconductor laser. In this case, if the oscillation wavelength of the semiconductor laser does not coincide with the wavelength that matches the phase Λ of the domain inversion section, the wavelength conversion efficiency becomes extremely low,
It is difficult to obtain a practical short-wavelength light source.

In view of such circumstances, conventionally, for example, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 6-69582, a laser beam emitted without wavelength conversion from an optical wavelength conversion element is subjected to a grating (diffraction grating). ), The light is fed back to a semiconductor laser via an optical wavelength conversion element, and the oscillation wavelength of the semiconductor laser is locked at a desired value by utilizing the wavelength dispersion of the grating.

FIG. 8 shows a side view of an example of such a configuration. In the figure, 1 is a semiconductor laser that emits a laser beam 2 as a fundamental wave, 3 is an incident optical system, 4 is an optical waveguide type optical wavelength conversion element having a channel optical waveguide 4a and a periodic domain inversion structure 4b, and 5 is an optical waveguide A collimator lens for collimating the laser beam 2 and the second harmonic 6 emitted from the laser beam 4a.
A dichroic mirror separating the laser beam from the laser beam; and a grating for reflecting and diffracting the laser beam.

The locking of the oscillation wavelength in this configuration will be described with reference to FIG. The grating 8 diffracts the laser beam 2 at a different diffraction angle for each wavelength. Therefore, when the laser beam 2 is converged by the collimator lens 5 after being reflected and diffracted by the grating 8, the converging position is dispersed in the direction of the arrow α in the figure for each wavelength. Therefore, if the grating 8 is rotated about an axis extending in the γ direction so that only the laser beam 2 of a desired wavelength returns to the optical waveguide 4a, the laser beam 2 of that wavelength is fed back to the semiconductor laser 1 and the oscillation wavelength Is locked to that wavelength.

[0008]

The configuration in which the oscillation wavelength of the semiconductor laser is locked by using the bulk grating has the advantage that the oscillation wavelength can be adjusted by changing the angle of the grating, but it has a disadvantage in adjusting the optical axis. If the inclination of the grating is not precisely adjusted, the diffracted light cannot return to the optical waveguide of the optical wavelength conversion element.

In other words, referring to FIG. 9, the grating 8 is fixed after rotating the center of the axis extending in the γ direction and adjusting the lock wavelength. In this fixing, for example, the axis extending in the α direction is fixed. It may rotate slightly as the center. Then, the laser beam 2 follows the optical path indicated by the broken line in the figure and shifts in the width direction of the optical waveguide 4a, and cannot return to the optical waveguide 4a.

[0010] The problems described above make it difficult to make adjustments during assembly of the optical wavelength conversion device, and when the device is used, a slight displacement of the grating makes the oscillation unstable or stops the oscillation. The problem of doing so occurs.

[0011] The present invention has been made in view of the above circumstances, and a laser beam emitted from a semiconductor laser is provided.
In an apparatus for wavelength conversion by an optical waveguide type optical wavelength conversion element having a periodic domain inversion structure, an oscillation wavelength of a semiconductor laser is accurately locked to a wavelength that is phase-matched with a period of a domain inversion unit, and adjustment during assembly is performed. An object of the present invention is to facilitate the operation and stably oscillate the semiconductor laser.

[0012]

A first optical wavelength conversion device according to the present invention comprises, as described above, an optical waveguide type optical wavelength conversion device having a periodic domain inversion structure, and an optical wavelength conversion device as a fundamental wave. In a light wavelength conversion device comprising a semiconductor laser emitting an incident laser beam, a collimator lens for collimating a laser beam emitted in a divergent light state from an optical waveguide of an optical wavelength conversion element, and a collimator lens for collimating the laser beam. A grating that diffracts the laser beam converted into light at different diffraction angles for each wavelength, and a condensing unit that forms a confocal optical system with the collimator lens and converges the laser beam that has passed through the grating. The diffraction angle, wherein the laser beam is reflected at a convergence position by the condensing means and fed back to the semiconductor laser. It is characterized in that a mirror displacement direction of the width of the convergence position due to the difference is sufficiently narrow form is provided.

In the above configuration, if an optical system is provided for branching a wavelength-converted wave from a laser beam emitted from an optical wavelength conversion element, the wavelength-converted wave can be branched and extracted from a system for locking an oscillation wavelength. it can.

A second optical wavelength conversion device according to the present invention comprises an optical waveguide type optical wavelength conversion device having a periodic domain inversion structure as described above, and a laser beam incident on the optical wavelength conversion device as a fundamental wave. In a light wavelength conversion device comprising a semiconductor laser emitting a laser beam, the laser beam emitted from the semiconductor laser in a divergent light state and before entering the light wavelength conversion element is made into a parallel light by a collimator lens, It is provided with the same grating, condensing means and mirror as in the first optical wavelength conversion device.

In the above configuration, if an optical system is provided for branching a laser beam as a fundamental wave emitted from the semiconductor laser into a beam incident on the optical wavelength conversion element and a beam incident on the grating, the oscillation wavelength can be increased. The fundamental wave can be easily branched from the system for locking and wavelength-converted.

A third optical wavelength conversion device according to the present invention comprises an optical waveguide type optical wavelength conversion element having a periodic domain inversion structure as described above, and a laser beam incident on this optical wavelength conversion element as a fundamental wave. In the optical wavelength conversion device comprising a semiconductor laser emitting light, a laser beam in a divergent light state emitted from the semiconductor laser as backward emission light not directed to the optical wavelength conversion element is collimated by a collimator lens. And the same grating, focusing means and mirror as in the first and second optical wavelength converters.

In the present invention, a line mirror extending long in a direction substantially orthogonal to the direction of deviation of the convergence position of the laser beam, which is the fundamental wave, due to the difference in the diffraction angle at the grating is preferably used as the mirror. .

In the present invention, preferably, a condensing grating is used as the grating.
Thereby, the grating also serves as the light collecting means.

[0019]

In the optical wavelength conversion device according to the present invention, the laser beam is reflected by a mirror in which the width of the convergence position of the laser beam in the direction of deviation due to the difference in the diffraction angle at the grating is sufficiently small. Since the feedback is made to the semiconductor laser, only the laser beam diffracted at a predetermined diffraction angle (that is, a laser beam having a predetermined wavelength) can be fed back to the semiconductor laser by changing the position of the mirror in the shift direction. In this way, if only a laser beam of a predetermined wavelength is fed back to the semiconductor laser, the semiconductor laser oscillates at this wavelength, so that the oscillation wavelength is selected and locked to a desired wavelength that is phase-matched with the cycle of the domain inversion unit. be able to.

In the first optical wavelength conversion device of the present invention, the condensing means for converging the laser beam as described above converts the laser beam emitted in a divergent light state from the optical waveguide of the optical wavelength conversion element into a parallel light beam. Laser beam converged by the collimator lens by following the optical path returning to the semiconductor laser side because the mirror is slightly rotated from the normal state. Even if it does, it will always return to the emission point from the optical waveguide of the optical wavelength conversion element.

As described above, in the first optical wavelength conversion device of the present invention, even if the mirror is slightly tilted from the normal state during adjustment or use of the device, the laser beam (basic wave) selected by the mirror and the grating is used. ) Is always fed back to the semiconductor laser via the optical wavelength conversion element, so that the semiconductor laser oscillates stably. If the inclination of the mirror can be tolerated as described above, the adjustment work at the time of assembling the optical wavelength conversion device becomes easy.

The wavelength conversion element emits a wavelength-converted wave together with the laser beam whose wavelength has not been converted.
Therefore, as described above, if an optical system that splits a wavelength-converted wave from a laser beam emitted from an optical wavelength conversion element is provided, the wavelength-converted wave can be separated from a feedback laser beam and guided to a utilization unit. .

On the other hand, in the second and third optical wavelength converters according to the present invention, the condensing means for converging the laser beam as described above includes a laser beam emitted from the semiconductor laser (that is, from its optical waveguide) in a divergent light state. Since a confocal optical system is formed with a collimator lens that collimates the beam, the laser beam converged by the collimator lens along the optical path returning to the semiconductor laser side is slightly shifted from the normal state by the mirror. Even when the semiconductor laser is rotated, it always returns to the emission point of the semiconductor laser from the optical waveguide.

As described above, in the second and third optical wavelength converters of the present invention, even if the mirror is slightly tilted from the normal state during adjustment or use of the device, the laser beam (wavelength selected by the mirror and the grating) is selected. Fundamental wave)
Is always fed back to the semiconductor laser, and the semiconductor laser oscillates stably. If the inclination of the mirror can be tolerated as described above, the adjustment work at the time of assembling the optical wavelength conversion device becomes easy.

In the second optical wavelength converter of the present invention, the laser beam emitted from the semiconductor laser needs to be incident on the optical wavelength conversion element for wavelength conversion.
Therefore, if an optical system is provided for branching a laser beam emitted from a semiconductor laser into one that enters a light wavelength conversion element and one that enters a grating, the laser beam emitted from the semiconductor laser is guided to the light wavelength conversion element. be able to.

In each of the optical wavelength converters of the present invention, the adjustment of the oscillation wavelength of the semiconductor laser is performed not by rotating the mirror but by moving the mirror linearly. Becomes

Further, particularly when a line mirror extending long in a direction substantially perpendicular to the direction of deviation of the convergence position due to the difference in the diffraction angle of the laser beam in the grating is used, the mirror position adjustment in this direction is performed by adjusting the length of the mirror. It is only necessary to bring the convergence position of the laser beam within the range, so that this position adjustment is very easy.

On the other hand, when a light-gathering grating is used as the grating, and the grating also serves as a light-gathering means, it is not necessary to separately provide a general lens or the like as the light-gathering means, so that the apparatus can be made compact and the cost can be reduced. Is realized.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an optical wavelength conversion device according to a first embodiment of the present invention. As shown in the figure, the optical wavelength conversion device includes a semiconductor laser (laser diode) 10 and a collimator lens for collimating a laser beam 11 emitted from the semiconductor laser 10 in a divergent light state.
12, a condensing lens 13 for converging the collimated laser beam 11, a polarization controlling λ / 2 plate 14 disposed between these lenses 12 and 13, and an optical wavelength conversion element 15. Have.

The optical wavelength conversion element 15 has a spontaneous polarization direction parallel to the z-axis inverted on a substrate 16 of MgO-LN (LiNOb ₃ doped with MgO) crystal, which is a ferroelectric substance having a nonlinear optical effect. A periodic domain inversion structure 17 in which the formed domain inversion portions are periodically formed, and a channel optical waveguide 18 extending along the periodic domain inversion structure 17 are formed.

The MgO-LN crystal substrate 16 is made of, for example, MgO
Is 5 mol% doped. In addition, the periodic domain inversion structure 17 is formed such that the domain inversion portions are arranged in the x-axis direction of the substrate 16, and the period に 対 し て thereof is set to a wavelength around 980 nm in consideration of the wavelength dispersion of the refractive index of MgO-LN. 1
The thickness is set to 5.3 μm so that the next cycle will occur. Such a periodic domain inversion structure 17 is disclosed in, for example, Japanese Patent Laid-Open No. 6-242.
No. 478.

On the other hand, in the channel optical waveguide 18, after forming the periodic domain inversion structure 17, a metal mask pattern is formed on the + z plane of the substrate 16 by known photolithography and dry etching. It can be produced by a method of performing a proton exchange treatment by immersion, annealing after removing the mask, or the like. Then, both end faces 18 of this channel optical waveguide 18
When the a and b are edge-polished, the light wavelength conversion element 15 is completed.

As the semiconductor laser 10, for example, a laser that emits a laser beam 11 having a wavelength of about 980 nm is used. This laser beam 11 is applied to a collimator lens 12
After that, the polarization direction is adjusted in the z-axis direction of the channel optical waveguide 18 by the λ / 2 plate 14, and the light is condensed by the condenser lens 13, and the end face 18 a of the channel optical waveguide 18 is condensed.
Converges at Thereby, the laser beam 11 enters the channel optical waveguide 18 and guides it.

The laser beam 11 as a fundamental wave traveling in the waveguide mode is phase-matched (so-called quasi-phase matching) in the periodic domain inversion region in the channel optical waveguide 18 to obtain a second harmonic having a wavelength of about 490 nm. The wavelength is converted to 19. The second harmonic wave 19 also propagates in the channel optical waveguide 18 in the waveguide mode, and exits from the optical waveguide end face 18b.

From the end face 18b of the optical waveguide, the laser beam 11 whose wavelength has not been converted is also emitted in a diverging light state, and is collimated by the collimator lens 20. The collimated second harmonic 19 is reflected by the dichroic mirror 21 and guided to the use position. On the other hand, the laser beam 11 whose wavelength has not been converted passes through the dichroic mirror 21 and enters the grating 22, where it is reflected and diffracted. The reflected and diffracted laser beam 11 is condensed by a condenser lens 23 forming a confocal optical system together with the collimator lens 20, and converges on a line mirror 24.

As shown in FIG. 2, the line mirror 24 has a support 25 on which a thin film of, for example, Au (gold) is formed.
An AR (anti-reflection) coat 26 is applied leaving a sufficiently thin linear opening on the upper surface, and the Au portion exposed from this opening serves as a light reflecting portion. The line mirror 24 is disposed such that its extending direction matches the γ direction in FIG. The laser beam 11 reflected by the line mirror 24
Is fed back to the semiconductor laser 10 along an optical path opposite to the optical path up to that point.

Here, the grating 22 is a laser beam
11 is diffracted at a different diffraction angle for each wavelength. Therefore, when the laser beam 11 converges by the condenser lens 23 after being reflected and diffracted by the grating 22, the converging position is dispersed in the direction of the arrow A in the figure for each wavelength.

Since the line mirror 24 is sufficiently narrow in the direction of dispersion of the convergence position, the mirror 24 is slid to change its position in the direction of arrow A, thereby diffracting the light at a predetermined diffraction angle. Only the laser beam 11 (that is, of a predetermined wavelength) can be fed back to the semiconductor laser 10. Thus, if only the laser beam 11 having the predetermined wavelength is fed back to the semiconductor laser 10, the semiconductor laser 10 oscillates at this wavelength. So, line mirror
24 is appropriately slid linearly in the direction of arrow A to change the oscillation wavelength of the semiconductor laser 10 into the periodic domain inversion structure.
It can be selected and locked to a desired wavelength that is phase-matched with 17 periods.

Then, the laser beam 11 is applied to the line mirror 24.
The converging lens 23 that converges above constitutes a confocal optical system with the collimator lens 20, so that the laser beam 11 converged by the collimator lens 20 following the optical path returning to the semiconductor laser 10 side, Even if the mirror 24 is slightly rotated from the normal state as shown by the arrow B in FIG. 1 or around an axis extending in the direction of the arrow A, the mirror 24 must be rotated from the channel optical waveguide 18 of the optical wavelength conversion element 15 without fail. It returns to the emission point. An example of the optical path of the laser beam 11 when the mirror 24 rotates is shown by a broken line in FIG.

As described above, in the present apparatus, even when the line mirror 24 is slightly tilted from the normal state during adjustment or use of the apparatus, the laser beam 11 whose wavelength has been selected by the mirror 24 and the grating 22 must be an optical wavelength conversion element. The signal is fed back to the semiconductor laser 10 via 15, and the semiconductor laser 10 oscillates stably. If the inclination of the mirror 24 can be tolerated as described above, the adjustment work at the time of assembling the optical wavelength conversion device becomes easy.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that, in FIG. 3, the same elements as those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description thereof will be omitted (hereinafter, referred to as
Similar).

In the optical wavelength conversion device shown in FIG. 3, a reflective light-gathering grating 30 forming a confocal optical system with a collimator lens 20 is used instead of the grating 22 in the device shown in FIG. . The light-gathering grating 30 is a grating having a bend and a chirp period as shown in a front view in FIG. 4, and the laser beam 11 reflected and diffracted there is condensed and converged. And
The laser beam 11 thus converged is reflected by the line mirror 24 and fed back to the semiconductor laser 10.

When the above-described condensing grating 30 is used, the condensing lens 23 can be omitted as compared with the apparatus shown in FIG. 1, so that the apparatus can be made compact and the cost can be reduced.

Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, instead of the light-gathering grating 30 used in the apparatus shown in FIG. 3, a transmission-type light-grating 40 constituting a confocal optical system with the collimator lens 20 is used. I have.
This condensing grating 40 is also a grating having a bend and a chirp period, and the laser beam 11 diffracted there is converged and converged. The laser beam 11 thus converged is reflected by the line mirror 24 and fed back to the semiconductor laser 10.

Next, a fourth embodiment of the present invention will be described with reference to FIG. In the optical wavelength conversion device shown in FIG. 6, the laser beam 11 emitted from the semiconductor laser 10 in a diverging light state and then collimated by the collimator lens 12 is split by the beam splitter 50. That is, the laser beam 11 transmitted through the beam splitter 50 is guided to the optical wavelength conversion element 15 in the same manner as in the apparatus of FIG. On the other hand, the laser beam 11 reflected by the beam splitter 50 enters the grating 22, where it is reflected and diffracted. The reflected and diffracted laser beam 11 is condensed by a condenser lens 23 that forms a confocal optical system with the collimator lens 12, and converges on a line mirror 24.

The laser beam 11 reflected by the line mirror 24
Is fed back to the semiconductor laser 10 along an optical path opposite to the optical path up to that point.

The grating 22 diffracts the laser beam 11 at a different diffraction angle for each wavelength. Therefore, when the laser beam 11 converges by the condenser lens 23 after being reflected and diffracted by the grating 22, the converging position is dispersed in the direction of the arrow A in the figure for each wavelength.

The line mirror 24 is formed sufficiently thin in the dispersion direction of the convergence position. Therefore, also in this case, by linearly sliding the line mirror 24 in the direction of arrow A, the oscillation wavelength of the semiconductor laser 10 is selected to a desired wavelength that is phase-matched with the period of the periodic domain inversion structure 17.
Can be locked.

Then, the laser beam 11 is applied to the line mirror 24.
The converging lens 23 that converges above constitutes a confocal optical system with the collimator lens 12, so that the laser beam 11 converged by the collimator lens 12 following the optical path returning to the semiconductor laser 10 side is: Even if the mirror 24 is slightly rotated from the normal state as shown by the arrow B in FIG. 6 or around an axis extending in the direction of the arrow A, the mirror 24 must be located at the emission point of the semiconductor laser 10 from the optical waveguide 10a. Come back.

As described above, in the present apparatus, even when the line mirror 24 is slightly tilted from the normal state during adjustment or use of the apparatus, the laser beam 11 whose wavelength has been selected by the mirror 24 and the grating 22 must be applied to the semiconductor laser 10 without fail. The feedback is made, and the semiconductor laser 10 oscillates stably. If the inclination of the mirror 24 can be tolerated as described above, the adjustment work at the time of assembling the optical wavelength conversion device becomes easy.

Next, with reference to FIG. 7, a fifth embodiment of the present invention will be described in which the oscillation wavelength of the semiconductor laser 10 is selected and locked using the backward emission light. In the optical wavelength conversion device of FIG. 7, a laser beam 11 R (rearward emission light) emitted in a divergent light state backward from the semiconductor laser 10, that is, on the opposite side to the optical wavelength conversion element 15, is collimated by a collimator lens 60. It is lightened. The parallel laser beam 11R enters the grating 61, where it is reflected and diffracted. The reflected and diffracted laser beam 11R is
The light is condensed by the converging lens 62 that forms a confocal optical system together with the collimator lens 60, and converges on the line mirror 24.

The converged laser beam 11R is reflected by the line mirror 24, follows an optical path opposite to the optical path up to that, and is fed back to the optical waveguide 10a of the semiconductor laser 10 from the rear side. Therefore, also in this case, the line mirror
By sliding 24 linearly in the direction of arrow A,
The oscillation wavelength of the semiconductor laser 10 can be selected and locked to a desired wavelength that is phase-matched with the period of the periodic domain inversion structure 17.

The condenser lens 62 is a collimator lens.
Since the confocal optical system is configured with 60, the semiconductor laser 10
The laser beam 11 converged by the collimator lens 60 following the optical path returning to the side is slightly moved around the axis extending from the normal state of the line mirror 24 as shown by the arrow B in FIG. Even if it turns to
This always returns to the emission point of the semiconductor laser 10 from the optical waveguide 10a.

As described above, in the present apparatus, even when the line mirror 24 is slightly tilted from the normal state during adjustment or use of the apparatus, the laser beam 11R whose wavelength has been selected by the mirror 24 and the grating 61 must be applied to the semiconductor laser 10. The feedback is made, and the semiconductor laser 10 oscillates stably.

In the embodiment described above, the semiconductor laser 10 is DC-driven. In this driving method, the semiconductor laser 10 itself operates in a low frequency region (below the MHz level).
, Light amount noise, that is, a change in light amount level was observed. This is due to the fact that the light amount level is not stabilized (of course, the wavelength is locked to the phase matching wavelength according to the present invention, so that there is no level fluctuation due to wavelength fluctuation). Conventionally, it has been known that a semiconductor laser should be driven at a high frequency in order to reduce such noise. Then, when the semiconductor laser 10 was driven at a high frequency at a frequency of 0.1 to 1 GHz, the fluctuation of the light amount level was 1% or less, and a more desirable result was obtained.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing an optical wavelength conversion device according to a first embodiment of the present invention.

FIG. 2 is a front view of a line mirror used in the optical wavelength conversion device of FIG.

FIG. 3 is a schematic side view showing an optical wavelength conversion device according to a second embodiment of the present invention.

FIG. 4 is a front view of a light-gathering grating used in the optical wavelength converter of FIG.

FIG. 5 is a schematic side view showing an optical wavelength conversion device according to a third embodiment of the present invention.

FIG. 6 is a schematic side view showing an optical wavelength conversion device according to a fourth embodiment of the present invention.

FIG. 7 is a schematic side view showing an optical wavelength conversion device according to a fifth embodiment of the present invention.

FIG. 8 is a schematic side view showing a conventional optical wavelength converter.

9 is a plan view showing a main part of the optical wavelength conversion device in FIG.

[Explanation of symbols]

 10 Semiconductor laser 11 Laser beam (fundamental wave) 11R Laser beam (backward emitting light) 12 Collimator lens 13 Condensing lens 14 λ / 2 plate 15 Optical wavelength conversion element 16 MgO-LN crystal substrate 17 Periodic domain inversion structure 18 Channel light guide Wave path 19 Second harmonic 20 Collimator lens 21 Dichroic mirror 22 Grating 23 Condensing lens 24 Line mirror 30 Reflective condensing grating 40 Transmissive condensing grating 50 Beam splitter 60 Collimator lens 61 Grating 62 Condensing lens

Claims (7)

[Claims] An optical waveguide is formed on a ferroelectric crystal substrate having a non-linear optical effect, and a domain inversion portion in which the direction of spontaneous polarization of the substrate is inverted is periodically formed in the optical waveguide. An optical wavelength conversion element that wavelength-converts a fundamental wave guided in the direction in which the domain inversion portions are arranged in the optical waveguide; a semiconductor laser that emits a laser beam incident on the optical wavelength conversion element as the fundamental wave; A collimator lens for collimating the laser beam emitted in a divergent light state from the optical waveguide of the conversion element; and diffracting the laser beam collimated by the collimator lens at different diffraction angles for each wavelength. A grating, and a confocal optical system with the collimator lens for converging the laser beam passing through the grating. A condensing means, and a mirror which reflects the laser beam at the converging position by the condensing means and feeds it back to the semiconductor laser, and a width of the converging position in the shift direction due to the difference in the diffraction angle is formed sufficiently narrow. An optical wavelength conversion device comprising: 2. The optical wavelength conversion device according to claim 1, further comprising an optical system that branches a wavelength converted wave from the laser beam emitted from the optical wavelength conversion element. 3. An optical waveguide is formed on a ferroelectric crystal substrate having a non-linear optical effect, and a domain inversion portion in which the direction of spontaneous polarization of the substrate is inverted is periodically formed on the optical waveguide. An optical wavelength conversion element for wavelength-converting a fundamental wave guided in the direction in which the domain inversion portions are arranged in the optical waveguide; a semiconductor laser for emitting a laser beam incident on the optical wavelength conversion element as the fundamental wave; A collimator lens for collimating the laser beam before it enters the optical wavelength conversion element after being emitted in a divergent light state from the laser beam; and A grating that diffracts the beam at an angle, and the collimator lens and confocal light that converge the laser beam that has passed through the grating. A condensing unit that forms a system; and a laser beam is reflected at the converging position by the converging unit and fed back to the semiconductor laser. Wavelength conversion device comprising a mirror that has been set. 4. An optical system for splitting the laser beam emitted from a semiconductor laser into one that enters the optical wavelength conversion element and one that enters the grating. An optical wavelength converter according to the above. 5. An optical waveguide is formed in a ferroelectric crystal substrate having a non-linear optical effect, and a domain inversion portion in which the direction of spontaneous polarization of the substrate is inverted is periodically formed in the optical waveguide. An optical wavelength conversion element for wavelength-converting a fundamental wave guided in the direction in which the domain inversion portions are arranged in the optical waveguide; a semiconductor laser for emitting a laser beam incident on the optical wavelength conversion element as the fundamental wave; A collimator lens for collimating a divergent laser beam emitted as backward emission light not traveling to the light wavelength conversion element, and converting the laser beam, which has been collimated by the collimator lens, for each wavelength A grating for diffracting the laser beam at different diffraction angles, and the collimator for converging the laser beam passing through the grating. Condensing means forming a confocal optical system with a lens; and reflecting the laser beam at the converging position by the condensing means and feeding it back to the semiconductor laser. The width of the converging position in the deviation direction due to the difference in the diffraction angle. An optical wavelength conversion device comprising a mirror formed sufficiently thin. 6. The optical wavelength conversion device according to claim 1, wherein the mirror is a line mirror that extends long in a direction substantially orthogonal to the direction of deviation of the convergence position of the laser beam. . 7. The optical wavelength conversion device according to claim 1, wherein a light-gathering grating is used as said grating, and said grating also functions as said light-gathering means.