JPH06138508A - Harmonic generator - Google Patents

Abstract

(57) [Abstract] [Purpose] To increase the tolerance for polishing accuracy of nonlinear optical materials and improve the yield of resonator fabrication. [Structure] Fundamental wave 18 emitted from semiconductor laser 13
The collimating lens 14 and the mode matching lens 1
The light is incident on the non-linear optical material 16 through 5, and the spherical mirror 20 of the non-linear optical material 16 and the total reflection plane mirror 22
And a separate reflection mirror 17 to resonate, and the harmonic wave 19 is extracted from the reflection mirror 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a harmonic generator for converting a fundamental wave emitted from a laser light source into a harmonic using a discrete resonator having a non-linear optical material.

[0002]

2. Description of the Related Art In recent years, various devices have been proposed for obtaining a wavelength-converted second harmonic or third harmonic by passing a fundamental wave emitted from a semiconductor laser or the like through a nonlinear optical material. In these devices, a nonlinear optical material is arranged in a resonator composed of a plurality of reflecting surfaces, and a fundamental wave is confined in the resonator to be amplified so that harmonics are efficiently generated.

As a resonator, a monolithic resonator having a reflecting film provided on the end face of a non-linear optical material for causing resonance therein, and a resonator having a plurality of mirrors arranged therein are constructed. A discrete resonator in which a non-linear optical material is arranged is known. Recently, the mainstream is shifting from discrete type to monolithic type that resonates the fundamental wave inside the nonlinear optical material in order to miniaturize the device and improve the conversion efficiency to harmonics. is there.

FIG. 3 shows a second harmonic generation device using a monolithic resonator as an example of a conventional harmonic generation device.

This second harmonic generator 1 is composed of a semiconductor laser (hereinafter referred to as LD) 2, a collimating lens 3, a mode matching lens 4, and a nonlinear optical material 5 made of KNbO ₃ crystal or the like. The LD 2 emits the fundamental wave 6 having a wavelength of 860 nm, for example. In the non-linear optical material 5, the two surfaces facing each other in the figure are polished into a spherical shape. Of these, the surface on the left side of the drawing is the incident surface of the fundamental wave 6, and a spherical mirror 8 that partially transmits the fundamental wave 6 and reflects the second harmonic wave 7 is formed on this surface.
The surface on the right side of the drawing is an exit surface for the second harmonic wave 7, and a spherical mirror 9 that reflects the fundamental wave 6 and transmits the second harmonic wave 7 is formed on this surface. Further, the lower surface of the nonlinear optical material 5 in the figure forms a plane mirror 10 that totally reflects both the fundamental wave 6 and the second harmonic wave 7.

In the above structure, the fundamental wave 6 having a wavelength of 860 nm emitted from the LD 2 is collimated by the collimator lens 3 and condensed by the mode matching lens 4, and the non-linear optical material 5 is applied from the point A of the spherical mirror 8. Incident on. At this time, the fundamental wave 6 is incident at a specific angle θ with respect to the crystal axis a so that the fundamental wave 6 incident on the point A travels in parallel with the crystal axis a of the nonlinear optical material 5. The fundamental wave 6 is reflected in a ring shape at points A, B, and C in the ring resonator formed by the spherical mirrors 8 and 9 and the plane mirror 10 to be amplified.

When the fundamental wave 6 passes through the nonlinear optical material 5 in the direction of the crystal axis a, a part of the fundamental wave 6 has a wavelength of 43.
It is converted into the second harmonic wave 7 of 0 nm and emitted from the point B of the spherical mirror 9. In order to meet the phase matching condition and stabilize the conversion efficiency to harmonics, the nonlinear optical material 5
Is temperature controlled by the Peltier element 11 and the like. By using such a monolithic resonator, the fundamental wave can be efficiently converted into a harmonic wave.

[0008]

However, in the conventional harmonic generator 1 using the monolithic resonator,
In some cases, the resonance state may not be obtained due to the polishing accuracy of the nonlinear optical material 5 at the time of manufacturing the resonator. Further, even when resonating, there is a problem that the resonance axis and the crystal orientation axis may deviate from each other, resulting in a significant decrease in the second harmonic output.

Therefore, an object of the present invention is to enable the crystal axis and the resonance state to be independently adjusted, thereby preventing the non-resonance state and the deviation between the resonance axis and the crystal orientation axis from occurring, and increasing the harmonic output efficiency. It is to improve the yield of resonator production by reducing the influence of the polishing accuracy of the nonlinear optical material on the harmonic output, as well as generating it frequently.

[0010]

In order to solve the above problems, the present invention provides a light source for generating a fundamental wave, a coupling optical system,
A harmonic generation device including a discrete resonator having a non-linear optical material, wherein the discrete resonator is composed of two parts, and at least one of the parts is the non-linear optical material. And

In a preferred embodiment of the present invention, the discrete resonator comprises one nonlinear optical material arranged on the incident side of the fundamental wave and one reflecting mirror arranged on the emitting side of the harmonic. Composed.

In a further preferred aspect of the present invention, a traveling-wave resonator composed of a non-linear optical material having a spherical mirror and a total reflection plane mirror and a reflecting mirror is used as the discrete resonator.

In still another preferred aspect of the present invention, a standing wave type resonator composed of a non-linear optical material having a plane mirror and a reflecting mirror is used as the discrete type resonator.

[0014]

In the present invention, since the resonator is composed of two parts, the adjustment of the crystal axis by the nonlinear optical material and the adjustment of the resonance state by the reflection mirror can be performed independently. Therefore, not only the non-resonance state and the deviation between the resonance axis and the crystal orientation axis are reduced, it is possible to efficiently generate the harmonic output, but also the polishing accuracy of the nonlinear optical material at the time of manufacturing the resonator. It is possible to improve the yield of the resonator fabrication by reducing the influence of the on the harmonic output.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment in which the present invention is applied to a second harmonic generator. The present invention is the second
The present invention is not limited to the harmonic generator, but can be applied to a third harmonic generator and the like.

In this second harmonic generator 12, an LD 13 as a laser light source, a collimating lens 14, a mode matching lens 15, a nonlinear optical material 16 having a convex mirror and a total reflection surface, and a reflecting mirror 17 are sequentially arranged. It is configured.

The LD 13 in this embodiment has a wavelength of 86.
A 0 nm, single vertical, single horizontal mode that emits a fundamental wave 18 with little astigmatism is used. As the light source, light emitted from a solid-state laser medium such as YAG or YLF excited by an LD can be used. The collimator lens 14 converts the fundamental wave 18 emitted from the LD 13 into a parallel beam, and the mode matching lens 15
Serves to match (mode match) the resonance mode of the ring resonator constituted by the nonlinear optical material 16 and the reflection mirror 17 with the incident beam by narrowing the beam.

KNbO ₃ crystal is used for the nonlinear optical material 16, and its length in the direction of the crystal axis a is 4.5 mm. The end face located on the incident side of the fundamental wave 18 is formed in a spherical shape with a radius of curvature of 5.0 mm, and a reflective film that reflects 93% of the fundamental wave 18 is vapor-deposited on this face to form a spherical mirror 20. . Further, in this nonlinear optical material 16, the end face 24 located on the emission side of the second harmonic wave 19 is formed in a flat shape, and the fundamental wave 18 and the second harmonic wave 19 are both 99.5% on this surface. An antireflection film that transmits the light is applied. Further, the lower surface of the nonlinear optical material 16 in the figure is cut into a plane along the crystal axis a and polished to obtain the fundamental wave 1
Plane mirror 22 that totally reflects both the 8th and second harmonics 19
There is.

Optical quartz glass is used for the reflection mirror 17. On the concave surface 21 of the reflection mirror 17, a reflection film that reflects 99.9% of the fundamental wave 18 and 90% of the second harmonic wave 19 is vapor-deposited.

Using this second harmonic generator 12, LD
When the fundamental wave 18 having a wavelength of 860 nm is emitted from 13, the fundamental wave 18 is collimated into a parallel beam by the collimator lens 14 and then condensed by the mode matching lens 15 to obtain a part of the resonator from point A of the spherical mirror 20. Is incident on the nonlinear optical material 16.

The fundamental wave 18 that has entered the resonator propagates in the nonlinear optical material 16 along the crystal axis a, is completely transmitted through the end face 24, is then reflected at the point B of the reflection mirror 17, and is again end face 24. To the point C of the plane mirror 22,
The light is totally reflected at the point C of the plane mirror 22, returns to the point A of the spherical mirror 20, is reflected at the point A, propagates again along the crystal axis a, and overlaps with the original light to cause traveling wave type resonance. . In this way, the fundamental wave 18 resonates and is amplified by taking a triangular ring-shaped resonance path in the resonator constituted by the nonlinear optical material 16 and the reflection mirror 17.

When the fundamental wave 18 amplified in this way propagates through the nonlinear optical material 16 in the direction of the crystal axis a, a part thereof is converted into a second harmonic wave 19 having a wavelength of 430 nm. This second harmonic wave 19 is emitted from the reflection mirror 17. The nonlinear optical material 16 is made of the Peltier element 23 in order to meet the phase matching condition and stabilize the conversion efficiency to the harmonic.
The temperature is controlled by the above.

In the case of the traveling wave type resonator in this embodiment, since the resonator is composed of two parts, first, the nonlinear optical material 16 is adjusted so that the fundamental wave 18 follows the a-axis to generate harmonics. After increasing the efficiency, it is possible to adjust the reflection mirror 17 so that the resonance state is optimal, and it is possible to generate a highly efficient and stable harmonic wave.

FIG. 2 shows another embodiment in which the present invention is applied to the second harmonic generator. The present invention is not limited to the second harmonic generation device, but can be applied to the third harmonic generation device and the like. Further, in this embodiment, substantially the same parts as those of the device shown in the embodiment of FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

This embodiment basically has the same structure as the device of the embodiment shown in FIG. 1, but the nonlinear optical material 116 on both end planes and the reflection mirror 17 make the standing wave. The difference is that it constitutes a type resonator.

Nonlinear optical material 116 in this embodiment
Is made of KNbO ₃ crystal, and its length in the crystal axis a direction is 5.0 mm. The end face located on the incident side of the fundamental wave 18 is formed in a flat shape, and the surface of the fundamental wave 1 is formed on this end face.
A reflective film that reflects 93% of 8 is vapor-deposited to form a flat mirror 12.
It is set to 0. Further, the end face 124 located in the emitting direction of the second harmonic 19 is also formed in a flat shape, and an antireflection film that allows the fundamental wave 18 and the second harmonic 19 to pass through 99.5% or more is formed on this face. It has been subjected.

Using this second harmonic generator 112, L
When the fundamental wave 18 having a wavelength of 860 nm is emitted from D13,
The fundamental wave 18 is made into a parallel beam by the collimator lens 14, is condensed by the mode matching lens 15, and enters the nonlinear optical material 116 which is a part of the resonator from the point A of the plane mirror 120.

The fundamental wave 18 that has entered the resonator propagates in the nonlinear optical material 116 along the crystal axis a, and the end face 12
4, after being completely transmitted, is reflected at a point B of the reflection mirror 17,
The light is completely transmitted through the end face 124 again, returns to the point A of the plane mirror 120, is reflected at the point A, and propagates again along the crystal axis a,
Standing wave type resonance is made by overlapping with the original light. In this way, the fundamental wave 18 resonates along the linear resonance path in the resonator constituted by the nonlinear optical material 116 and the reflection mirror 17, and is amplified.

When the fundamental wave 18 amplified in this way propagates through the nonlinear optical material in the direction of the crystal axis a, a part thereof is converted into the second harmonic wave 19 having a wavelength of 430 nm. This second harmonic wave 19 is emitted from the reflection mirror 17. In addition,
In order to meet the phase matching condition and stabilize the conversion efficiency into harmonics, the nonlinear optical material 116 is used for the Peltier element 23.
The temperature is controlled by the above.

Also in the case of the standing wave type resonator in this embodiment, the resonator is composed of two parts. First, the nonlinear optical material 116 is adjusted so that the fundamental wave 18 follows the a-axis, and the higher harmonic wave is generated. After increasing the generation efficiency, it is possible to adjust the reflection mirror 17 so that the resonance state is optimal, and it is possible to generate a highly efficient and stable harmonic wave.

[0031]

As described above, according to the present invention,
By using a discrete resonator composed of two parts using at least one nonlinear optical material,
It is possible to adjust the resonance state and the deviation between the resonance axis and the crystal axis, and it is possible to efficiently generate the harmonic output. Further, since the resonator length can be easily changed by PZT or the like, the stabilization can be improved by controlling the resonance frequency. Further, the processing accuracy of the nonlinear optical material can be relaxed, and the alignment of the resonator can be facilitated, so that the product yield and the productivity can be improved.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment in which the present invention is applied to a second harmonic generation device.

FIG. 2 is a side view showing another embodiment in which the present invention is applied to a second harmonic generation device.

FIG. 3 is a side view showing an example of a conventional second harmonic generator.

[Explanation of symbols]

 12: Harmonic generator 13: Semiconductor laser 14: Collimating lens 15: Mode matching lens 16: Non-linear optical material 17: Reflecting mirror 18: Fundamental wave 19: Second harmonic 20: Spherical mirror 21: Spherical mirror 22: Plane mirror 23: Peltier element 112: Harmonic generator 116: Non-linear optical material

Claims (2)

[Claims] 1. A harmonic generation device comprising a light source for generating a fundamental wave, a coupling optical system, and a discrete resonator having a nonlinear optical material, wherein the discrete resonator is composed of two parts. A harmonic generator characterized in that at least one of the parts is the non-linear optical material. 2. The discrete resonator comprises one non-linear optical material arranged on the incident side of the fundamental wave and one reflecting mirror arranged on the emergent side of the harmonic. The harmonic generator according to Item 1.