JPH01157586A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To establish a stable external resonator with a high coupling efficiency by providing an external mirror which is made by coating a reflecting film on the back of a micro-Fresnel lens, and displacing the Fresnel lens with respect to a semiconductor laser using a piezoelectric element. CONSTITUTION:The back of a lens member 2 is flattened, and a reflecting film 22 such as gold or silver is formed by vaporization on the flattened part and adjusted in its reflectivity to r=1, for example. The back of the lens member 2 is fixed to a piezoelectric element 3 using a resin adhesive, and is made variable in its position on the optical axis of an emitted laser beam from a semiconductor laser 1 by means of the piezoelectric element. The emitted laser beam from the semiconductor laser 1 is collimated by the Fresnel lens 21, and reflected by the reflecting film 22 coated on the back of the flat plate micro- Fresnel lens 21, and thereby fed back in the opposite direction on the same optical axis of the emitted laser beam to the semiconductor laser 1.

Description

[Detailed Description of the Invention] Summary of the Invention A micro Fresnel lens, which has a strong wavelength dependence and a property in which a change in the wavelength of incident light appears as a change in focal length, is coated with a reflective film on the back surface and used as an external mirror. By displacing this Fresnel lens with respect to the semiconductor laser using a piezoelectric element, the external resonator length is changed. This makes it possible to realize a semiconductor laser device with wavelength tunability and wavelength stability.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device which has a variable wavelength and whose wavelength is stabilized by having an external resonator.

Conventionally, tunable wavelengths of semiconductor lasers have been obtained by changing the injection current or temperature.

Since there is a drawback that mode hops occur, the use of an external resonator is being considered. For example, Haka Mizuta [Wideband frequency modulation operation method of semiconductor laser] IEICE Technical Report 0QE
8B-67 (198B>), an external mirror is placed opposite the semiconductor laser.

There are some devices in which the distance between the semiconductor laser and the external mirror (external resonator length) is changed using a piezo probe, and this distance change is combined with a change in the injection current level to obtain a continuously variable wavelength. In addition, similar configurations using a diffraction grating instead of an external mirror are available, such as Haka Iwasaki "Broadband frequency control of external cavity type semiconductor laser" IEICE Technical Report 0QE83-120 (
, 1983).

However, in the configuration of such a conventional semiconductor laser device, the emitted light from the semiconductor laser diverges, and this divergent light is reflected by the external mirror, resulting in a decrease in the optical coupling rate and the connection between the semiconductor laser and the external mirror. There was a drawback that the amount of reflected light varied depending on the distance between the mirror and the mirror.

Summary of the Invention Object of the Invention The object of the present invention is to provide a semiconductor laser device whose wavelength is variable by changing an external mirror, with a stable external resonator having high coupling efficiency.

Structure and Effects of the Invention A semiconductor laser device according to the present invention includes a semiconductor laser,
A lens member provided with a micro φ Fresnel lens on one side for collimating the emitted light of the semiconductor laser and a reflective film formed on the other side for reflecting the collimated light, and a lens member that is displaced with respect to the semiconductor laser. The invention is characterized in that it is equipped with a displacement device for causing

According to this invention, the emitted light of the semiconductor laser is
After being collimated by the Fresnel lens, it is reflected by the reflective film and returned, so the coupling efficiency between the semiconductor laser and the reflective film is high and the coupling state is stable. Since the micro Fresnel lens as a collimating lens and the reflective film as an external mirror are integrated as a lens member, even if the lens member is displaced, there is no distance variation between them. Furthermore, Fresnel lenses have high wavelength selectivity and have the characteristic that the focal length changes depending on the wavelength, so one oscillation wavelength can be defined by changing the distance between the semiconductor laser and the Fresnel lens using a displacement device, and it can be used over a wide range. The wavelength can be varied stably.

Description of examples Embodiments of the invention will be described with reference to the drawings.

The block 4, which acts as a heat sink for the semiconductor laser 1 and also serves as a support shrine, is, for example, a copper block, and its entire surface is plated with gold. A piezoelectric element 3 to which a semiconductor laser 1° and a lens member 2 are attached is fixed to this block 4. The semiconductor laser 1 is fixed to the block 4 using, for example, indium solder, and the piezoelectric element 3 is fixed to the block 4 using a resin adhesive.

A lens member 2 is arranged on one emission surface side of the semiconductor laser 1 . A flat micro Fresnel lens 21 is provided on the surface of the lens member 2 on the semiconductor laser 1 side. A Fresnel lens has a concentric concave and convex pattern,
The lens function (condensing light, collimating, etc.) is performed by utilizing Fresnel diffraction of light due to this concavo-convex pattern. There are various types of concavo-convex patterns of Fresnel lenses, such as a step-like pattern and a blazed pattern. The micro Fresnel medium lens 21 may be formed integrally with the lens member 2, or may be formed separately to form the Fresnel lens 21.
may be adhered to the lens member 2. For example, the Fresnel lens 21 and the lens member 2 are made of synthetic resin P.
It is made of MMA, and the thickness of the lens member 2 is t.
For example, t −4 mm, refractive index n L = 1.49
It is. The flat micro Fresnel lens 21 has a focal length from the output surface of the semiconductor laser 1 on the Fresnel lens side.

For example, it is located at f = 1 ml11.

The back surface of the lens member 2 is flat, and a reflective film 22 made of, for example, gold or silver is deposited thereon, and the reflectance is adjusted to, for example, rζ1. The lens member 2 is fixed to the piezoelectric element 3 on the back surface using a resin adhesive, and the position of the emitted light of the semiconductor laser 1 on the optical axis is made variable by the piezoelectric element.

Laser light emitted from the other emission surface of the semiconductor laser 1 passes through the window 4a of the block 4 and is emitted to the outside. window 4a
An optical system (which may include a Fresnel lens) may be placed nearby to collimate the output light.

The light emitted from the semiconductor laser 1 toward the Fresnel lens 21 is turned into parallel light by the Fresnel lens 21. This parallel light is reflected by the flat micro Fresnel plate and the reflective film 22 on the back surface of the lens 21, and is returned to the semiconductor laser 1 along the same path as the emitted light in the opposite direction. Therefore, between the semiconductor laser 1 and the reflective film 22, there is an equivalent resonator length L−1.
+1.49X4-6, Ha+I+1 external resonator is formed.

In this way, since the emitted light with a certain divergence angle is converted into parallel light, reflected, and returned, the feedback rate of the emitted light (
(coupling efficiency) can be increased, and waste of emitted light can be reduced.

In addition, the flat micro Fresnel lens has a feature that it has one focal length for the oscillation wavelength of the semiconductor laser.

There is a relationship f−df=−λ·dλ, and there is a characteristic that the focal length of the flat micro Fresnel medium lens changes with respect to the oscillation wavelength of the semiconductor laser. In other words, it has the characteristic of maintaining wavelength for a certain focal length. On the other hand.

- When the external cavity length is elongated, the oscillation wavelength of the semiconductor laser tends to become shorter, and as the wavelength of the incident light becomes shorter, the focal length of the flat micro Fresnel ◆ lens also becomes longer. Therefore, when the lens member 2 is displaced in the direction away from the semiconductor laser 1 by the piezoelectric element 3, the external resonator length becomes longer.

The oscillation wavelength becomes shorter, which causes the Fresnel lens 2
Since the focal length of the lens 1 becomes longer, the laser beam having a shorter wavelength can be properly collimated by the Fresnel lens 21. When the lens member 2 is displaced in a direction closer to the semiconductor laser 1, the oscillation wavelength becomes longer, and the light of this longer wavelength is also collimated by the Fresnel medium lens 21 having a shorter focal length.

In this way, wavelength tuning and wavelength stabilization can be performed simultaneously. If necessary, changing the current injected into the semiconductor laser 1 or changing the temperature may be used in order to change the wavelength.

In this embodiment, a semiconductor laser 1. Lens member 2
And since the piezoelectric element 3 is integrated into the block 4,
Miniaturization is possible by not causing axis misalignment and by reducing the actual dimensions of the composite resonator.

[Brief explanation of the drawing]

−7= The drawings are cross-sectional views showing embodiments of the invention. 1... Semiconductor laser. 2... Lens member. 3...Piezoelectric element. 21...Micro Fresnel lens. 22... Reflective film. that's all

Claims (1)

[Claims] A semiconductor laser, a lens member provided with a micro Fresnel lens on one side for collimating the emitted light of the semiconductor laser, and a reflective film formed on the other side for reflecting the collimated light, and the lens member facing the semiconductor laser. What is claimed is: 1. A semiconductor laser device comprising: a displacement device for displacing a semiconductor laser;