JPH06347848A - Second harmonic generation device - Google Patents

Abstract

(57) [Summary] [Object] To realize a second harmonic generation device having stable wavelength controllability by constructing an external resonator with only a diffraction grating and a semiconductor laser in the second harmonic generation device. [Structure] The light from the semiconductor laser 1 is separated by a beam splitter 2, one of them is guided to a second harmonic element 4, and the other is composed of a diffraction grating 5 and an external resonator composed of the semiconductor laser 1 to select a wavelength. To do. The light emitted from the semiconductor laser 1 is made into a parallel beam by the lens 7 and is incident on the diffraction grating 5 arranged in the Littrow arrangement from the beam splitter 2 which reflects and separates 30% or more. The primary reflected light of the diffraction grating 5 returns to the semiconductor laser 1 through the same optical path. The angle of the diffraction grating 5 is adjusted so that the fundamental wavelength matches the phase matching wavelength corresponding to the period of the polarization inversion grating 12, and the second harmonic wave 6
To occur.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a second harmonic generation device using a laser as a fundamental wave light source.

[0002]

2. Description of the Related Art In a second harmonic generating device disclosed in Japanese Patent Laid-Open No. 4-107536, a diffraction grating is used as a means for selecting a fundamental wave of a semiconductor laser in order to satisfy a phase matching condition of a second harmonic generating element. The second harmonic generation element is arranged between the semiconductor laser and the semiconductor laser. This conventional example is shown in FIG.
The TE mode light emitted from the semiconductor laser 1 is converted into the TM mode by the half-wave plate 3 using one end face of the semiconductor laser 1 as the low reflection surface 11, and the polarization inversion region 12 by the quasi phase matching method is used. Is coupled to the waveguide type second harmonic generation element 4, and the emitted light is made into a parallel beam by the lens 9 and is incident on the diffraction grating 5. By returning the reflected light from the diffraction grating 5 to the semiconductor laser 1 through the waveguide 13 of the second harmonic generation element, the oscillation wavelength can be changed by the rotation angle θ of the diffraction grating 5 and the phase matching condition of the second harmonic generation element can be obtained. Selectively control the wavelength to satisfy The second harmonic generation element by the quasi-phase matching method is described in Electronics, Letters No. 25.
Vol. 731-732, a LiNbO ₃ substrate is provided with a polarization inversion layer 12 in which the direction of spontaneous polarization is inverted at an equal pitch and an optical waveguide 13 formed by a proton exchange method.

[0003]

In the above prior art, since the waveguide type second harmonic generating element is arranged between the diffraction grating for selecting the oscillation wavelength and the low reflection end face of the semiconductor laser, the optical waveguide is Since the coupling loss of 2 is doubled in a round trip, the amount of light reflected back from the diffraction grating to the semiconductor laser is insufficient, and there is a problem that the oscillation wavelength of the semiconductor laser cannot be controlled stably.

[0004]

As means for solving the above-mentioned problems of the prior art, the second harmonic generating element is not arranged between the semiconductor laser and the diffraction grating, and wavelength selection by the diffraction grating is performed by the semiconductor laser. By using an external resonator, the light from the semiconductor laser is separated by a beam splitter, one is guided to the second harmonic element, and the other is configured as an external resonator with a diffraction grating and a semiconductor laser, thereby changing the wavelength. select. Further, the beam splitter is a polarization beam splitter, and TE, T emitted from the semiconductor laser
The wavelength of the semiconductor laser is selected by separating the light of M mode by the polarization beam splitter, returning one of the light by the second harmonic element and the other light by the diffraction grating.

[0005]

In the second harmonic generation device, in order to reduce the coupling loss to the waveguide type second harmonic generation element, only the diffraction grating and the semiconductor laser are used without passing through the second harmonic generation element. By forming the resonator, it is possible to realize a second harmonic generation device having a semiconductor laser having a stable wavelength controllability as a fundamental wave.

[0006]

EXAMPLE FIG. 1 shows an example of the present invention. The light from the semiconductor laser 1 is separated by a beam splitter 2, one of which is a second harmonic element 4 and the other is a diffraction grating 5 and an external resonator formed of the semiconductor laser 1 to select a wavelength. Semiconductor laser has a low reflection surface with a front reflectance of 2% or less 1
The other one has a highly reflective surface 10 that reflects 90% or more. The light emitted from the semiconductor laser 1 is made into a parallel beam by the lens 7 and is incident on the diffraction grating 5 arranged in the Littrow arrangement from the beam splitter 2 which reflects and separates 30% or more.
The primary reflected light of the diffraction grating 5 returns to the semiconductor laser 1 through the same optical path. At this time, the oscillation wavelength is selected according to the angle θ of the diffraction grating 5. On the other hand, the light transmitted through the beam splitter 2 has its polarization direction TE-controlled by the half-wave plate 3.
Mode is converted to TM mode and is guided to the optical waveguide 13 of the waveguide type second harmonic generation element 4. The second harmonic wave 6 is generated by adjusting the angle of the diffraction grating 5 so that the wavelength of the fundamental wave matches the phase matching wavelength corresponding to the period of the polarization inversion grating 12. 4 shows another embodiment of the invention of FIG. Depending on the ratio of the separated lights of the beam splitter used in the embodiment of FIG. 1, there is a case where 10% or more of the reflected return light necessary for wavelength control cannot be obtained. Therefore, when the beam splitter is the polarization beam splitter 33 and only the TM mode 31 of the polarization mode emitted from the semiconductor laser 1 is reflected by the diffraction grating 5, the TM mode is almost reflected by the semiconductor laser 1. Therefore, good wavelength control can be performed. The TE mode 32 transmitted through the polarization beam splitter is converted into a TM mode by the half-wave plate 3 and the second harmonic wave 6 is generated by the second harmonic wave generating element.

[0007]

By constructing an external resonator with a beam splitter or a polarization beam splitter using only a diffraction grating and a semiconductor laser, a second harmonic wave generator having stable wavelength controllability can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram illustrating an embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating a conventional technique.

FIG. 3 is a configuration diagram illustrating an embodiment of the present invention.

[Explanation of symbols]

1 semiconductor laser, 2 beam splitter, 3 1 /
2 wavelength plate, 4 second harmonic generation element, 5 diffraction grating,
6 second harmonic, 7 lens, 8 lens, 9 lens, 10 high reflection film, 11 low reflection film, 12 polarization inversion grating, 13 optical waveguide, 31 TM mode, 32 T
E-mode, 33 polarization beam splitter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenchi Ito 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Stock company Hitachi Central Research Laboratory (72) Inventor Takumi Mita 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Hitachi, Ltd. Central Research Laboratory (72) Inventor, Kazutomi Kawamoto, 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Stock Company Hitachi Central Research Laboratory

Claims (3)

[Claims] 1. A second harmonic generation device using a semiconductor laser as a fundamental wave, comprising optical means for constituting an external resonator for causing laser oscillation with respect to a semiconductor laser having at least one end face having a low reflection end face. A second harmonic generation device characterized by selecting a fundamental wave having an oscillation wavelength that satisfies the phase matching condition of the second harmonic generation element. 2. The second harmonic generation device according to claim 1, wherein a diffraction grating and a beam splitter are arranged as optical means constituting the external resonator. 3. The second harmonic generation device according to claim 2, wherein a polarization beam splitter is used as the beam splitter.