JPH03274784A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser device, having a narrow spectral line and variable in wavelength within a gain range, by employing duel-laser structure in which one laser is furnished with means for feeding a specific wavelength within the gain range back to an active layer. CONSTITUTION:A dual-resonator laser 1 has a nonreflective film 2 on one end, and it is coupled through an object lens 3 to an external refractive grating 4. The light from the laser is fed back to an active layer 5 to provide single- mode oscillation with a narrow spectral line of selected wavelength. The angle of the reflective grating 4 is varied by a rotating mechanism 6 to vary the feedback wavelength so that the wavelength can be varied within the range of gain of semiconductor lasers 1a and 1b. The wavelength can be continuously varied by controlling currents to semiconductor lasers 1a and 1b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device that is tunable in wavelength and has a narrow spectral linewidth.

[Prior Art] One method of changing the wavelength of a semiconductor laser is to use a diffraction grating or the like to feed back light of a specific wavelength from a light emitting section, as shown in FIG. By injecting a current between the top electrode and the bottom electrode, photons generated in the active layer are guided along the active layer, one photon is reflected from the cleavage plane and returns to the active layer, and the other photon is lost. The photons transmitted through the reflective film are collected by a convex lens, selectively reflected by a diffraction grating, returned to the active layer, and undergo multiple reflections by the cleavage plane and the diffraction grating, causing oscillation. The oscillated light is emitted from the cleavage plane. Note that the diffraction grating is controlled by a rotation mechanism so that only desired wavelengths can be selectively reflected. Specifically, the diffraction grating is rotated to control the incident angle of the light relative to the normal line of the diffraction grating, which changes the wavelength of the feedback light and introduces a strong wavelength dependence to the resonator loss, thereby changing the oscillation wavelength. can be done.

Note that in this method, if the non-reflection film has ideal characteristics, oscillation will occur in all of the resonator modes determined by the optical distance between the cleavage surface and the diffraction grating.

[Problem to be solved by the invention]

However, in the conventional technology, the characteristics of the anti-reflection film are insufficient, which may cause a region in the wavelength tunable band that cannot be adjusted, such as a mode jump, to continuously change the oscillation wavelength. It was adjusted by changing the temperature.

Furthermore, selecting a specific oscillation mode by micro-movement of the diffraction grating lacks reproducibility.

The present invention has been made in view of these circumstances, and an object of the present invention is to provide a semiconductor laser device whose oscillation wavelength can be freely adjusted within a gain band and which has a narrow spectral linewidth.

[Means for Solving the Problems] In order to solve the above problems, in the semiconductor laser device of the present invention, ■ a composite resonator is formed from two or more semiconductor lasers at the bottom, and ■ light emitted from the composite resonator is The structure is such that only a predetermined wavelength is selected and fed back.

Furthermore, in the present invention, C3
(Cleaved Coupled Cavity) An element called a laser is used. This C3 laser is described in the Applied Physics Letter
48(18), 5 May 1986PP1190~
1192J and rApplied Physics Le
tter 42(8), 15 April 1983
As shown in the structure and principle of PP650-652J, the active layers of two semiconductor lasers that are located very close to each other are optically strongly coupled. Therefore, although it operates as a so-called composite cavity laser, unlike a normal laser, the oscillation wavelength can be electrically changed by controlling the currents injected into the two semiconductor lasers.

A feature of the present invention is that one of the two component semiconductor lasers has a structure that includes means for returning light of a specific wavelength within the gain band of the semiconductor laser into the active layer.

[Effect]

According to the semiconductor laser device configured in this way, in the structure of the above-mentioned document, laser oscillation and electrical control of the oscillation wavelength can only be performed near the peak of the gain, but in the present invention, the gain can be controlled by selective wavelength feedback. Electrical control of oscillation and oscillation wavelength over a very wide range of the spectrum becomes possible.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows the configuration of a first embodiment of a semiconductor laser device of the present invention. In this example, a DH (Double
(Heterostructure) A C3 laser is used in which the lasers are arranged with a slight gap. Furthermore, a diffraction grating and its rotation mechanism are used as means for returning light of a specific wavelength into the active layer of the semiconductor laser.

Specifically, if a non-reflection film 2 is formed on one side of this composite cavity laser 1, and the light is returned to the active layer 5 by coupling it with an external diffraction grating 4 using an objective lens 3, the selected Single-mode oscillation with a narrow spectral linewidth can be obtained with light at a given wavelength. When the angle of the diffraction grating 4 is changed by the rotation mechanism 6, the feedback wavelength changes, so that the wavelength can be changed within the gain bands of the semiconductor lasers 1a and 1b. At this time, by adjusting the current to each part of the semiconductor laser 1a and the semiconductor laser 1b, the selectable wavelengths can be changed continuously. One embodiment is shown in FIG. This is a composite cavity laser 1 whose bottom is formed by two semiconductor lasers la and 1b, and an electrode 7 on the top surface of the semiconductor laser 1a on the laser beam emission side.
The injection current If・50m injected between the electrode 8 and the lower surface electrode 8
A screen showing the measurement of the oscillation wavelength when the current injected between the electrode 9 on the top surface of the semiconductor laser 1b on the diffraction grating side and the electrode 10 on the bottom surface was varied from Ir=40mA to Ir・10mA while keeping constant A. It is. According to this, the oscillation wavelength is 1
．． 0.0 from 280325μm to 1.279975μm.
It can be seen that there is a change of 00035 μm.

(Second Embodiment) FIG. 3 shows the configuration of a second embodiment of the semiconductor laser device of the present invention. As in the first embodiment, anti-reflection films 2.11 are formed on both end faces, a diffraction grating 4 is coupled to one end face via an objective lens 3, and a half mirror is coupled to the other end face via an objective lens 12. Combine 13. At this time, they are installed so that the distances L1 and L2 to the external mirrors are approximately equal. By setting these distances approximately equal, the phase relationship can be adjusted and adjacent compound resonance modes can be brought out of the gain band, thereby maximizing the single mode property (side mode suppression ratio) of the oscillation spectrum. be able to.

(Third Embodiment) FIG. 4 is a configuration diagram showing a third embodiment of the semiconductor laser device of the present invention. As a substitute for the diffraction grating 5 of the first embodiment, a bandpass filter 14, a fiber 15, a fiber 16, and a total reflection mirror 17 added to the fiber 16
This is what was used. In this case, by varying the characteristics of the bandpass filter 14, the range (
(1,237 μm to 1.321 μm).

Further, by adjusting the coupling distance L3 between the anti-reflection film 2 and the fiber 15 and changing the coupling mode with the fiber 15, the single mode property (side mode suppression ratio) of the oscillation spectrum can be maximized. In other words, it is sufficient to use means for adjusting the intensity of the light that returns to the composite resonator laser 1. Specifically, in addition to the means for adjusting the distance L3 mentioned above, (1) adjusting the distance M to maximize the coupling mode with the fiber 15;
Adjust L3, fiber 15 and bandpass filter 14
There is a means for adjusting the intensity of light by providing an optical attenuator between them, and a means for adjusting the intensity of light by using the fiber optic 5 as an optical amplifier.

In each of the above embodiments, an example of a C3 laser formed on an InP substrate was shown, but the structure and material are not limited to this. An element having a structure having two or more separated electrodes may also be used.

〔Effect of the invention〕

As explained above, the semiconductor laser device of the present invention includes a composite cavity laser composed of two or more semiconductor lasers, and a composite cavity laser that is optically coupled to the composite cavity laser and emits a specific wavelength within the gain band of the semiconductor laser. A means for returning light into the active layer of the semiconductor laser is provided. Therefore, it has a large oscillation wavelength tuning range in a single mode oscillation state with a large side mode suppression ratio, and the oscillation wavelength can be electrically controlled.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the first embodiment of the present invention, Fig. 2 is a diagram showing the measurement of the oscillation wavelength when the current is varied in the first embodiment of the present invention, and Fig. 3 is a diagram showing the oscillation wavelength of the first embodiment of the present invention. Fig. 4 is a block diagram showing the second embodiment of the present invention, Fig. 4 is a block diagram showing the third embodiment of the present invention, and Fig. 5 shows the oscillation wavelength when the filter characteristics of the third embodiment of the present invention are varied. 6 is a structural diagram of another composite resonator laser, and FIG. 7 is a diagram showing a configuration using a conventional composite resonator mode. 1... Compound cavity laser, la, lb... semiconductor laser, 2.11... Anti-reflection film, 3, 12. 4 . . . 5 . . . 6 . . . 7, 8° 13・ ・ 14. . . 15, 16. 17. . . . Objective lens, diffraction grating, active layer, rotation mechanism. 9.10... Electrode, half mirror, band pass filter, fiber, total reflection mirror

Claims (2)

[Claims] (1) A composite resonator laser composed of two or more semiconductor lasers, and an active layer of the semiconductor laser that is optically coupled to the composite resonator laser and transmits light of a specific wavelength within the gain band of the semiconductor laser to the active layer of the semiconductor laser. What is claimed is: 1. A semiconductor laser device characterized by comprising means for returning the laser beam to the interior of the semiconductor laser. (2) The semiconductor laser device according to claim 1, wherein the semiconductor laser device is constituted by a semiconductor laser composed of two or more electrodes whose injection current can be independently controlled.