JPH0593934A - Harmonic generator - Google Patents

Abstract

(57) [Abstract] [Purpose] To efficiently dissipate the heat generated by the resonating fundamental wave to the outside, reduce the temperature rise and uneven temperature distribution of the resonator, and perform temperature adjustment with a fast response speed. [Structure] A fundamental wave 17 incident on a resonator 15 propagates in a nonlinear optical material along a crystal axis a, and a spherical mirror 19
Is reflected at a point B of the spherical mirror 20 facing the point A, is directed to a point C of the plane mirror 21, is reflected at a point C of the plane mirror 21 and returns to a point A of the spherical mirror 19, is reflected at a point A, and is again crystal axis. The light propagates along a and overlaps with the original light to form a traveling wave type triangular ring resonance. In this resonance path, the distance between the optical path propagating along the crystal axis a that contributes to wavelength conversion and the surface 22 facing the plane mirror 21 is 1/3 or less of the distance between the plane mirror 21 and the surface 22. ing.

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 light source such as a semiconductor laser into a harmonic in a monolithic resonator containing a non-linear optical material.

[0002]

2. Description of the Related Art In recent years, various devices have been proposed for obtaining a second harmonic wave or a third harmonic wave whose wavelength is converted 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 reflecting film is provided on the end face of a non-linear optical material, and a monolithic resonator that resonates inside the reflecting film and a plurality of mirrors are arranged to form the resonator. An external resonator in which a non-linear optical material is arranged is known. Recently, in order to downsize the device and improve the conversion efficiency to higher harmonics, the mainstream is shifting from the external resonator type to the monolithic type that resonates the fundamental wave inside the nonlinear optical material. I am doing it.

FIG. 2 shows, as an example of a conventional harmonic generator, a second harmonic generator using a monolithic resonator.

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. Nonlinear optical material 5
In the figure, the left and right two surfaces 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 is formed on this surface. In addition, the surface on the right side in the figure is the exit surface of the second harmonic wave 7, and the surface on which the second harmonic wave 7 is highly reflected,
On the other hand, a spherical mirror 9 having high transmission is formed. Further, the lower surface of the non-linear optical material 5 in the figure shows the fundamental wave 6 and the second wave.
A plane mirror 10 that totally reflects all the higher harmonic waves 7 is formed.

In the above-mentioned structure, the fundamental wave 6 having a wavelength of 860 nm emitted from the LD 2 is collimated by the collimator lens 3, passes through the mode matching lens 4, and passes from the point A of the spherical mirror 8 of the nonlinear optical material 5. Incident. 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 material 5. The fundamental wave 6 is reflected in a ring shape at points A, B, and C in the ring resonator composed of the two 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 430n.
It is converted into the second harmonic wave 7 of m and emitted from point B of the spherical mirror 9. The nonlinear optical material 5 is temperature-controlled by a Peltier element or the like in order to meet the phase matching condition and stabilize the conversion efficiency to the harmonic. By using such a harmonic generator, the fundamental wave can be efficiently converted into a harmonic.

[0008]

However, in the above-mentioned conventional second harmonic generator, when the fundamental wave resonates while the second harmonic is generated, heat is generated due to scattering and absorption by the nonlinear optical material itself. The temperature rise of the non-linear optical material and the non-uniformity of the temperature distribution occur. Due to the thermal expansion and the change in the refractive index due to this temperature rise, the optical path length of the resonator changes.
It was sometimes impossible to maintain a stable resonance state. Moreover, it was not possible to obtain highly efficient phase matching due to the non-uniform temperature distribution.

Therefore, the object of the present invention is to suppress the change in the temperature of the resonator and the non-uniformity of the temperature distribution caused by the heat generation due to the resonance of the fundamental wave, thereby suppressing the change in the resonant optical path length and at the same time, the non-linear optical It is an object of the present invention to provide a harmonic generation device that enables phase matching over the material length and that can generate a harmonic output with high efficiency and high stability.

[0010]

In order to achieve the above object, the harmonic generator of the present invention is a nonlinear device which internally causes a fundamental wave to ring-resonate in a triangular shape by three reflecting surfaces of two curved surfaces and one flat surface facing each other. In a harmonic generation device including a monolithic resonator including an optical material, a distance between an optical path that contributes to wavelength conversion among resonance modes in the nonlinear optical material and a surface facing the reflecting surface formed of the one plane is The distance is 1/3 or less of the distance between the reflecting surface formed of the one flat surface of the nonlinear optical material and the surface facing the reflecting surface.

[0011]

In the harmonic generator of the present invention, the distance between the optical path of the resonance mode of the nonlinear optical material that contributes to wavelength conversion and the surface facing the reflecting surface formed of one plane is the one plane of the nonlinear optical material. Since it is 1/3 or less of the distance between the reflecting surface and the surface facing the reflecting surface, heat generated by the resonating fundamental wave is easily released to the outside from the surface facing the reflecting surface consisting of one plane, and the nonlinear optical The temperature rise of the material is small. In addition, since the distance between the temperature adjusting element such as a Peltier element placed adjacent to the surface facing the reflecting surface formed of one plane and the portion of the resonant optical path that contributes to wavelength conversion is smaller than that in the conventional case, It becomes possible to perform temperature adjustment with a fast response speed.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment in which the present invention is applied to a second harmonic generation device. The present invention is not limited to the second harmonic generation device, and can be applied to the third harmonic generation device and the like. The second harmonic generation device 11 is configured by sequentially arranging an LD 12, which is a light source of a fundamental wave, a collimator lens 13, a mode matching lens 14, a monolithic resonator 15, and a Peltier element 16.

In this embodiment, the LD 12 has a wavelength of 860 nm,
Basic wave with little astigmatism in single longitudinal / single transverse mode 17
The one that emits is used. As the light source, it is also possible to use laser oscillation light from a solid-state laser medium such as YAG or YLF excited by an LD. The collimator lens 13 receives the fundamental wave 1 emitted from the LD 12.
7 is a parallel beam, and the mode matching lens 14
Serves to match the incident mode with the resonance mode in the monolithic resonator 15 by focusing the beam.

In this embodiment, the monolithic resonator 15 uses KNbO ₃ crystal as the nonlinear optical material. One end face of the monolithic resonator 15 located on the incident side of the fundamental wave 17 is formed in a spherical shape,
A reflective film that reflects 93% of the fundamental wave 17 is vapor-deposited on this surface to form a spherical mirror 19. Also, the second harmonic 1
The other end face of the resonator 15 located on the emission side of 8 is also formed in a spherical shape, and the face wave 17 reflects 99.9% of the second harmonic wave 18 on this face. A spherical mirror 20 is formed by depositing a reflective film that transmits 90%. Further, the lower surface of the nonlinear optical material in the figure is a plane mirror 21 which is cut into a plane along the crystal axis a and totally reflects both the fundamental wave 17 and the second harmonic wave 18.

The nonlinear optical material forming the monolithic resonator 15 is a block having a length of 7.0 mm in the crystal axis a direction and a spherical radius of curvature of 5.0 mm. This second
When the fundamental wave 17 having a wavelength of 860 nm is emitted from the LD 12 using the harmonic generator 11, the fundamental wave 17 is collimated by the collimator lens 13 and then focused by the mode matching lens 14 to form a spherical mirror 19.
The light enters from the point A into the monolithic resonator 15.

The fundamental wave 17 incident on the resonator 15 propagates in the nonlinear optical material along the crystal axis a, is reflected at the point B of the spherical mirror 20 facing the spherical mirror 19, and is reflected at the point of the plane mirror 21. Toward C, the light is reflected at the point C of the plane mirror 21 and returns to the point A of the spherical mirror 19, 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. Is done. Thus, the fundamental wave 17 resonates along the triangular ring resonance path in the monolithic resonator 15 and is amplified. In this resonance path, the distance between the optical path propagating along the crystal axis a that contributes to wavelength conversion and the surface 22 facing the plane mirror 21 is 1/3 or less of the distance between the plane mirror 21 and the surface 22. ing.

When the fundamental wave 17 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 18 having a wavelength of 430 nm. The second harmonic wave 18 is emitted from the spherical mirror 20. Therefore, when the harmonic generating device 11 of the present invention is used as a light source for information detection to construct an information reading device for an optical recording medium, not only a device with high recording density can be obtained, but also the device can be downsized. It can also be realized.

[0018]

As described above, according to the present invention,
The distance between the optical path of the nonlinear optical material that contributes to wavelength conversion and the surface of the nonlinear optical material that faces the reflecting surface of one plane is the distance between the reflecting surface of the one plane and the surface that faces the reflecting surface. Since it is 1/3 or less of the above, heat generated by the resonating fundamental wave is easily released to the outside from the surface facing the reflecting surface composed of the one plane, and the temperature rise of the resonator and the uneven temperature distribution are reduced. It

Further, as compared with the prior art, the distance between a temperature adjusting element such as a Peltier element, which is placed adjacent to the surface facing the reflecting surface consisting of the one plane, and a portion of the resonance path that contributes to wavelength conversion. Is small, it is possible to perform temperature adjustment with a fast response speed, and it is possible to generate harmonics with high efficiency and high stability.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of a second harmonic generation device of the present invention.

FIG. 2 is a side view showing an example of a conventional second harmonic generator.

[Explanation of symbols]

 11 Second Harmonic Generator 12 LD 13 Collimating Lens 14 Mode Matching Lens 15 Monolithic Resonator 16 Peltier Element 17 Fundamental Wave 18 Second Harmonic Wave 19 Spherical Mirror 20 Spherical Mirror 21 Plane Mirror

Claims (1)

[Claims] 1. A harmonic generator comprising a monolithic resonator including a non-linear optical material in which a fundamental wave is triangularly ring-resonated inside by three reflecting surfaces of two curved surfaces and one flat surface facing each other. Of the resonance modes in the material, the distance between the optical path that contributes to wavelength conversion and the surface facing the reflecting surface consisting of the one plane is 1
1 / the distance between the reflecting surface consisting of a plane and the surface facing it
A harmonic generation device characterized by being 3 or less.