JPH0743761A - Second harmonic generator - Google Patents

Abstract

(57) [Summary] [Purpose] Even when incorporated into a system such as a laser disk, stable harmonic output is obtained without being affected by thermal effects in the system. [Structure] In a harmonic generator 21 having a monolithic resonator 5, a fiber coupling lens 12 and an optical fiber 13 are arranged on the high-long-wavelength optical axis on the exit side of the second harmonic 7 of the resonator 5.

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 monolithic 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 in which the fundamental wave is resonated inside the nonlinear optical material in order to downsize the device and improve the conversion efficiency to higher harmonics. is there.

FIG. 2 shows a second harmonic generator using a monolithic resonator as an example of a conventional harmonic generator. This second harmonic generation device 1 includes a semiconductor laser (hereinafter abbreviated as “LD”) 2, a collimating lens 3, a mode matching lens 4, and a monolithic resonator 5 made of a nonlinear optical material such as KNbO ₃ crystal. It is configured. LD2 has a wavelength of 860n, for example.
The fundamental wave 6 of m is emitted. Two surfaces of the monolithic resonator 5 facing each other in the left and right in the figure are polished into a spherical shape and provided with predetermined optical films. That is, the surface on the left side of the figure is
It forms an incident surface of the fundamental wave 6 and a spherical mirror 8 provided with an optical film that partially transmits the fundamental wave 6. The surface on the right side of the drawing is the exit surface of the second harmonic wave 7,
A spherical mirror 9 provided with an optical film that is highly reflective and highly transmissive to the second harmonic 7. Further, the lower surface of the monolithic resonator 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 figure, 11a is a Peltier element that controls the temperature of the LD 2, and 11b is a Peltier element that controls the temperature of the monolithic resonator 5.

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, passes through the mode matching lens 4, and passes through the spherical mirror 8 of the monolithic resonator 5 at point A. Incident from. At this time, the fundamental wave 6 is incident at a specific angle with respect to the crystal axis a so that the fundamental wave 6 incident on the point A travels parallel to the crystal axis a of the monolithic resonator 5. The incident fundamental wave 6 is reflected in a ring shape at points A, B, and C in the resonator constituted by the two spherical mirrors 8 and 9 and the plane mirror 10 to be multiplied.

Thus, the multiplied fundamental wave 6 propagates through the monolithic resonator 5 in the crystal axis a direction, and when the phase matching condition is satisfied, a part of the fundamental wave 6 has a wavelength of 430 nm of c-axis linearly polarized light. Converted to the second harmonic 7. Then, a part of the fundamental wave 6 is scattered by impurities or the like inside the crystal and becomes return light having a reverse path. When this return light enters the LD 2, the frequency of the LD light is drawn to the resonance frequency of the resonator 5 and locked to the resonance frequency of the resonator 5 with a certain region. This locked frequency range is called the rocking range, and the amount of light returned from the resonator 5 is 40 dB.
At this time, the rocking range is about 3.5 GHz.

By maintaining the frequency of the LD light within such a rocking range, a stable second harmonic output can be obtained.

[0008]

However, although both the resonator 5 and the LD 2 are temperature controlled, in reality,
When the environmental temperature changes, the resonator temperature and LD temperature change,
As a result, the locking range and the LD frequency are shifted, and finally the LD frequency deviates from the locking range, and the second harmonic light is stopped. Therefore, when the second harmonic generation device is incorporated into a laser disk system or a laser printer system, there is a problem that stable operation becomes difficult due to thermal influence from other parts in the system.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and includes a light source for generating a fundamental wave, a coupling optical system, and a resonator including a nonlinear optical material. The second harmonic generation device is characterized in that an optical fiber is provided on the second harmonic emission side of the resonator in the second harmonic generation device. In the present invention, a monolithic type resonator is optimally applied as a resonator in the present invention, and therefore a monolithic type resonator will be described below as an example, but a discrete type resonator can of course be used.

[0010]

EXAMPLES The present invention will be described below with reference to examples. It should be noted that substantially the same parts as those of the apparatus of FIG. 2 described as the conventional example are denoted by the same reference numerals, and the description thereof will be omitted. FIG. 1 is a schematic configuration diagram of a second harmonic generation device 21 which is an embodiment of the present invention. As compared with the conventional example of FIG. 2, a fiber coupling lens 12 and an optical fiber 13 are further provided on the second harmonic emission side of the monolithic resonator 5.
And are arranged on the optical axis of the second harmonic wave 7. As the fiber coupling lens 12, a spherical lens, a SELFOC lens (manufactured by Nippon Sheet Glass Co., Ltd., a product name), a convex lens, an aspherical lens, and a combination lens thereof can be used.
As the optical fiber 13, a constant polarization optical fiber (core diameter 3 to 5 μm, length 2 m) having a small propagation loss is suitable.

[0011]

In the present invention, the fiber coupling lens 12 functions so as to efficiently couple the second harmonic emission light 7 of the monolithic resonator 5 to the optical fiber 13. The second harmonic light 7 guided into the optical fiber 13 is emitted from the other end of the fiber with almost no propagation loss. In the present invention, since the optical fiber 13 is used, the light source can be freely arranged, and the degree of freedom in designing the entire system such as a laser disk and a laser printer is increased. In particular, the second harmonic generation device 21 is vulnerable to temperature changes (heat), so that the arrangement for thermal isolation can be facilitated through the optical fiber 13, which contributes to stable operation of the light source and the entire system.

[0012]

According to the present invention, since the light source can be freely arranged in the system by incorporating the optical fiber, it is possible to easily avoid the influence of heat generation and vibration from the system. Have. In addition, by incorporating the optical fiber, the accuracy of the light emitting point position, which is important in the optical pickup, is improved, the manufacturing yield of the optical system of the optical pickup is improved, and the cost of the device is reduced.

[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 generation device.

[Explanation of symbols]

 1, 21: Harmonic generation device 2: Semiconductor laser (LD) 3: Collimating lens 4: Mode matching lens 5: Monolithic resonator 6: Fundamental wave 7: Second harmonic wave 8, 9: Spherical mirror 10: Plane mirror 11a, 11b: Peltier element 12: Fiber coupling lens 13: Optical fiber

Claims (1)

[Claims] 1. A second harmonic generation device including a light source for generating a fundamental wave, a coupling optical system, and a resonator including a nonlinear optical material, wherein an optical fiber is provided on the second harmonic emission side of the resonator. A second harmonic generation device characterized in that