JPS63121829A - Harmonic generating device - Google Patents

Abstract

PURPOSE:To use a small-sized, low-output semiconductor laser, etc., and the exciting light of continuous oscillation and to obtain high conversion efficiency by using a resonator and a nonlinear optical material. CONSTITUTION:Nonlinear optical crystal 1, mirrors 2 and 3 which constitute the resonator, and an optical waveguide 4 are united. The length L of the nonlinear optical crystal 1 is so designed that incident laser beam 5 generates a standing wave in the optical waveguide and nonlinear optical crystal 1. A mirror M12 constituting an optical resonator has a >=99.8% reflection factor to laser beam 5 and a >=99.8% reflection factor at a frequency 6 twice as high as that of the laser beam, but a mirror [M2]3 has >=99% transmissivity to the frequency 6 twice as high as that of the laser beam. Consequently, beam from the semiconductor laser is used as the exciting light to obtain >=30% high conversion efficiency to a 2nd harmonic.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a harmonic generator, and more particularly to a harmonic generator comprising a semiconductor laser, a resonator, and a nonlinear optical material.

2. Description of the Related Art When a nonlinear optical crystal is irradiated with laser light, harmonics whose optical frequency is an integral multiple of the fundamental wave are obtained due to the nonlinear optical effect. Among these waves, those with twice the frequency of the fundamental wave are called second harmonics. Since the conversion efficiency from a fundamental wave to a harmonic wave increases in proportion to the intensity of incident light, a method is generally adopted in which a pulse wave is used to increase the light intensity and improve the conversion efficiency.

Problems to be Solved by the Invention However, when a semiconductor laser is used as excitation light, the output is low at 10 to 30 mW, and it is a continuous wave, so when a nonlinear optical material is irradiated with semiconductor laser light as excitation light, harmonics are generated. The drawback was that the conversion efficiency was extremely low.

The present invention was made in view of the above-mentioned circumstances, and its purpose is to provide a harmonic generation device with high conversion efficiency using compact, low-output, continuous wave pumping light such as a semiconductor laser. .

Means for Solving the Problems The present invention, which was made to solve the above problems, utilizes the fact that harmonic conversion efficiency increases in proportion to the intensity of incident light to convert nonlinear optical materials into optical resonators. In order to further increase the harmonic generation efficiency, temperature, electric field, and magnetic field are controlled externally to achieve more complete phase matching and high efficiency harmonic generation. It is a wave generator.

By inserting a material with a large operational nonlinear optical coefficient and low optical loss into an optical resonator, and satisfying the conditions for oscillation with phase matching, the input fundamental wave will be converted into harmonics with high efficiency. .

Embodiment Hereinafter, a harmonic generator according to an embodiment of the present invention will be described with reference to the drawings.

[Embodiment 1] FIG. 1 shows a configuration diagram of a harmonic generator according to the present invention. In the figure, 1 indicates a nonlinear optical crystal. Although not shown in the figure, both end faces of this crystal are coated with an antireflection film against the incident laser beam 5.

This embodiment shows a harmonic generation device in which a nonlinear optical crystal 1, a mirror 2.3 constituting a resonator, and an optical waveguide 4 are integrated. In the figure, L indicates the length of the nonlinear optical crystal 1, and this length is designed so that the incident laser beam 5 forms a standing wave within the optical waveguide and the nonlinear optical crystal 1. The mirror (Ml) 2 that constitutes the optical resonator has a reflectance of 99.8% or more for laser light (fundamental wave), and has a frequency (second harmonic) twice that of the laser light (fundamental wave). Mirror (MZ) 3 has a reflectance of 99.8% or more for laser light (fundamental wave), but it has a reflectance of 99.8% or more for laser light (fundamental wave). (fundamental wave) twice the frequency (second harmonic) 6, 98%
It has a transmittance of more than

Here, BazNaNbsO is used as the nonlinear optical crystal 1.
+s crystal is used, and the optical waveguide 4 is designed to be formed along the crystallographic a-axis by utilizing the nonlinear coefficient d3□. Further, the temperature of this nonlinear optical crystal 1 is controlled to keep it at a phase matching temperature.

In the harmonic generator having the above structure, the laser beam (fundamental wave) 5 is introduced into the optical waveguide 4 while being adjusted so that the laser beam 5 enters the optical waveguide 4 most accurately. The laser light (fundamental wave) 5 that entered the optical waveguide is a mirror (MZ)
3, travels backwards in the optical waveguide, and is reflected by the mirror (Ml
) 2 and forms a standing wave within the optical waveguide 4. On the other hand, the second harmonic 6 generated within the leading waveguide 4 (partly within the nonlinear optical crystal 1) is transmitted through the mirror (MZ) 3 and radiated to the outside as the second harmonic 6. The conversion efficiency (η) of the above harmonic generator from the laser beam (fundamental wave) 5 to the second harmonic 6 is as high as 30% or more when using a semiconductor laser with an output of 20 mW and a wavelength of 0.78 μm. Obtained. Brewster boards may be used if necessary.

[Embodiment 2] FIG. 2 shows a configuration diagram of a harmonic generator according to the present invention. In the figure, 7 is a nonlinear optical thin film (the substrate forming the thin film is not shown), 8 is a leading waveguide, 9 is an electrode for applying an electric field to the nonlinear optical thin film 7, 10 is a transducer for generating ultrasonic waves, 1 ) is a sound absorbing material, 12 is a temperature control oven,
Reference numeral 13 indicates a semiconductor laser, and reference numeral 4 indicates an active layer of the semiconductor laser, which also serves as a waveguide for laser light.
guided by. 16 is a mirror [M2
], this has a reflectance of 99.8% or more for the laser beam (fundamental wave) (ν) 17, and is generated when the laser beam 17 passes through the optical guide 8 or the nonlinear optical thin film 7. It has a transmittance of 98% or more for harmonics (2ν)18. 15 is a mirror [:MZ) 16 together with a mirror [M1] which forms a resonator, and the laser beam (ν) 17
and harmonic (2ν) 18, both have reflectances of 99.8% or more. Reference numeral 19 denotes a filter adopted as necessary, which selectively transmits only the harmonic (2ν) 18. The electrode 9, ultrasonic transducer 10, temperature control oven, etc. are phase matched (refractive index matched) of the nonlinear optical thin film 7 and the optical waveguide 8 as necessary to improve conversion efficiency from fundamental waves to harmonics. used for the purpose of improving

By optimizing the above conditions, a high conversion efficiency of 15% or more from the fundamental wave to harmonics has been achieved.

[Embodiment 3] FIG. 3 shows a configuration diagram of a harmonic generator according to the present invention. In the figure, 20 is a nonlinear optical crystal, 21 is a leading waveguide, 22 is a semiconductor laser, 23 is an active layer (waveguide) of the semiconductor laser, and 24 is a nonlinear optical crystal 20 and a semiconductor laser 22
At this junction surface, the optical waveguide 21 of the nonlinear optical crystal and the waveguide 23 of the semiconductor laser are joined in a positional relationship that maximizes the coupling efficiency. 25 is a mirror CM+) which is a laser beam ν) 27 and harmonics (2ν
)28 both have a reflectance of 99.8% or more. 2
6 is a mirror [M2] which has a reflectance of 99.8% or more for laser light (ν) 27, but harmonics (2ν)
)28, it shows a transmittance of 98% or more. As a semiconductor laser, output power 15 mW, wavelength λ-0, using 78 μm, stable second harmonic λ-0, 6 mW in continuous oscillation.
39 μm was obtained. Here, KNb is used as a nonlinear optical crystal.
O3 was adopted. When using the light within the waveguide with higher efficiency, the mirrors 25 and 26 of the resonator are replaced with gratings.

Effects of the Invention The present invention is based on a structure that combines an optical resonator, a nonlinear optical material, and a semiconductor laser, and is configured so that temperature control, electric field control, and ultrasonic waves are applied to this for the purpose of facilitating phase matching. . As a result, it has become possible to obtain a high conversion efficiency of 30% or more from a semiconductor laser (λ-0.78 μm) to the second harmonic (λ-0.39 μm) using excitation light, which was previously thought to be extremely difficult. done.

λ-0.4μ, which was thought to be difficult with semiconductor lasers
It was possible to easily obtain a laser beam of m.

As for applications, for example, if applied to optical recording, it becomes possible to increase the density four times at once, and furthermore, the range of applications is wide, such as application to submicron photolithography processes.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 are configuration diagrams showing the implementation state of the harmonic generator of the present invention. 1...Nonlinear optical crystal, 2...Mirror [M,] 3...Mirror (MZ), 4...
... Optical waveguide, 5 ... Laser light, 6 ...
...Second harmonic.

Claims (10)

[Claims] (1) A harmonic generation device characterized by using a resonator and a nonlinear optical material. (2) The harmonic generation device according to claim (1), characterized in that a resonator and a nonlinear optical material are integrated. (3) The harmonic generation device according to claim 1 or 2, which is a combination of a semiconductor laser, a resonator, and a nonlinear optical material. (4) A harmonic generation device according to any one of claims (1), (2), and (3), characterized in that an optical waveguide is formed in a nonlinear optical material. (5) Claims (1), (2), or (3) characterized in that an electric field is applied to a nonlinear optical material.
The harmonic generator according to any one of paragraphs. (6) Claims (1), (2), or (3) characterized in that the temperature of the nonlinear optical material is controlled.
The harmonic generator according to any one of paragraphs. (7) Claims (1), (2), or (3) characterized in that a magnetic field is applied to a nonlinear optical material.
The harmonic generator according to any one of paragraphs. (8) The harmonic generation device according to any one of claims (1), (2), and (3), characterized in that a thin film-like material is used as the nonlinear optical material. (9) Claims (1), (2), or (3) characterized in that a sound wave is applied to a nonlinear optical material.
The harmonic generator according to any one of paragraphs. (10) A harmonic generation device according to any one of claims (1), (2), and (3), characterized in that the mirror of the resonator is a grating.