JPH0389574A - 2nd harmonic generator - Google Patents

Abstract

PURPOSE:To improve second harmonic generating efficiency by providing an external resonator for a crystal or a waveguide in hybrid or monolithic manner and causing resonance with primary coherent light. CONSTITUTION:Output light from a semiconductor laser 1 is collimated and transmitted through a half-mirror with transmittance of 5%, and a ring-type resonator is constructed from mirrors 2, 3, 4, 5. After the mirror 4, the laser light beam is led to a waveguide path 7 by a lens 6. Thus, the guided light radiates second harmonic wave to the substrate 8 side as a Cerenkov beam 9. On the other hand, the transmitted guided light is converged by a lens 10 and guided again to the waveguide path 7 via the mirrors 5, 2, 3, 5 to radiate the Cerenkov beam 9. Described process is repeated many times to enhance second harmonic radiation of the semiconductor laser so that second harmonic light output larger than several times the case of single bus can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improving the efficiency of a second harmonic generator.

[Conventional technology]

Conventionally, as a short wavelength light source for optical information processing, there is a method in which a waveguide formed on a nonlinear optical crystal is irradiated with laser light from a semiconductor laser to generate the second harmonic. Technical Digest, page 198
(CLEO' 87°Technical Diges
tp, 198) and will be studied.

In this method, as shown in FIG. 2, secondary light having a wavelength half that of the primary light is emitted into the substrate as a Cerenkov effect. This method has the excellent feature that it is relatively easy to achieve phase matching between the first and second order light in the generation of second harmonics, and it is small in size. It is also seen as a promising short-wavelength light source for optical information processing devices such as optical disks.

[Problem to be solved by the invention]

However, the above conventional example has a conversion efficiency of 1 to 2 at most.
%, and its optical output level is still not at a sufficient level to actually use it as a light source for an optical information processing device.

In the first place, it is well known that the conversion efficiency η of the second harmonic is given by η under the condition that phase matching is established. Here.

P is the power level of the first order light, A is the spot size area of the first order light, n is the refractive index, Q is the interaction length, and dsa is the component of the tensor giving the nonlinear optical constant. Therefore,
In the conventional method, it is not possible to achieve a value higher than the efficiency determined by each of the above factors, and the actual situation is that the optical output necessary for optical recording cannot be obtained.

The present invention aims to solve the above-mentioned problem of low efficiency, and provides a short wavelength coherent light source that generates a second water high frequency wave with even higher efficiency.

[Means to solve the problem]

In order to achieve the above object, in the present invention, the crystal itself that generates the second harmonic has an external resonator structure.
The light was made to go back and forth many times. Such external resonator configurations include a structure in which a nonlinear optical crystal is installed between mutually facing external resonator mirrors, a structure in which a Fabry-Perot etalon is formed on the end face of a waveguide on a nonlinear optical crystal, and A suitable structure is one in which distributed feedback type diffraction grating resonators are provided on the top and bottom or left and right sides of the waveguide.

[Effect]

According to the configuration of the present invention, it is possible to increase the interaction length in the equation giving the efficiency, and it is possible to improve the conversion efficiency. Of course, it is possible to increase the interaction length by increasing the length of the crystal white, but the effective interaction length is always the phase matching between the primary light and the secondary light. 1. It is difficult to create long crystals using normal crystal growth techniques, and it is also disadvantageous because it leads to high costs.

If you think about it, this method of increasing the interaction length using an external resonator is equivalent to increasing the internal output of the primary light within the external resonator, which also determines the conversion efficiency. The output P of the first-order light, which is one of the important factors, is increased to increase the conversion efficiency η to the second-order harmonic.

〔Example〕

A first embodiment of the present invention will be described below with reference to FIG.

The output light from the semiconductor laser 1 is collimated and transmitted through a half mirror 2 with a transmittance of 5%.
．． 5 constitutes a ring resonator. The beam passing through the mirror 4 is guided by a lens 6 to a waveguide 7, and the thus guided light emits a second harmonic as a Cerenkov beam 9 toward the substrate 8 side. On the other hand, the transmitted waveguide light is condensed by the lens 10 and mirrors 5.2 and 3.
By repeating the process of 0 or more in which the laser beam is guided again through the waveguide 7 through the laser diode 4 and radiates the Chenkov beam 9, the twice-high frequency of the semiconductor laser is enhanced, compared to the case of a single pass. It is possible to obtain a second harmonic optical output that is several times higher.

FIG. 3 shows a second embodiment of the invention.

A beam from semiconductor laser 1 is guided to waveguide 7 via lens system 11 . The waveguide 7 is formed on a secondary non-IIA type optical crystal such as a lithium niobate crystal, or on an organic crystal substrate 8.

Moreover, the input end face 12 and the output end face 13 of the waveguide are arranged to mutually constitute an etalon of a fiber bellows, and constitute a resonator for primary light. Therefore, the first-order light travels back and forth within the etalon and generates Cerenkov-type second-order harmonics 9 each time, so it is possible to obtain a larger optical output than in the case of a single pass.

FIG. 4 shows a third embodiment in which a distributed feedback resonator is constructed in place of the Fabry-Perot etalon.

A diffraction grating 14 is provided below or above the waveguide 7,
By using an external resonator for the first-order light, the output of the second-order harmonic 9 can also be increased.

In the embodiments described above, the increased optical output spreads as collimated parallel light in a plane perpendicular to the waveguide plane and as diffracted light determined by the width of the waveguide in a plane parallel to this. That is, it is emitted as a conical beam. Therefore, the beam cannot be focused in this state.

In the embodiment shown in FIG. 5, the tip 15 of the substrate 8 is processed into a semi-conical shape, and the second harmonic is extracted so as to be parallel to the optical axis.

Furthermore, it is also important in this method to achieve longitudinal mode matching between the external resonator and the semiconductor laser light. For this purpose, mode matching with the external resonator can always be achieved by controlling the temperature of the semiconductor laser or controlling the injection current. Alternatively, it is also possible to adopt a method of controlling the resonator spacing for external resonators.

This can be done, for example, by attaching a piezo element to the mirror for control, or by using the electrostrictive properties of the lithium oxide crystal itself to control the resonator length.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to improve the second harmonic generation efficiency of a semiconductor laser, which has been insufficient until now, and
m high-output short-wavelength light sources are now possible, which can be used for optical disk recording, laser beam printers, color printers, etc.
It is expected that it will have a wide range of applications.

[Brief explanation of drawings]

1, 3, and 4 are side views of the second harmonic generation device according to the embodiment of the present invention, FIG. 2 is a surface measurement diagram of the conventional device, and FIG.
The figure is a perspective view of a second harmonic generator according to another embodiment of the present invention. l... Semiconductor laser, 2, 3, 4.5... Mirror 7
... Waveguide, 8 ... Nonlinear optical crystal substrate, 9-mount Thierenkov beam, 12.13 ... Resonance mirror (monolithic), 14 ... Diffraction grating, 15 ... Semi-conical substrate . Vice 1 yo tea 2 figure t/- figure

Claims (1)

[Claims] 1. A means for guiding the first-order coherent light into a crystal having nonlinear optical characteristics or a waveguide created on the crystal, and the first-order coherent light is guided by the crystal or the waveguide. In a device that generates twice as high frequency,
The second harmonic is characterized in that the efficiency of second harmonic generation is improved by providing a hybrid or monolithic external resonator in the crystal or the waveguide and resonating the first coherent light. wave generator.