JPS5994486A - Semiconductor laser device and driving method therefor - Google Patents

Abstract

PURPOSE:To enable to vary the oscillating wavelength with one element by altering the period of diffraction lattice in one direction in a distributed feedback type structure and providing a plurality of electrodes in the altering direction. CONSTITUTION:In a semiconductor laser, 7-1-7-10 are positive electrodes, broken lines indicate the direction of grooves of diffraction grating 5 in the crystal. The period of the grating is constant in y direction and continuously variable in x direction. The light output is cleaved in the crystal at one end of the electrode, and produced therefrom. In such a structure, when the adjacent two positive electrodes are simultaneously driven by the currents at the suitable rate, an oscillation can be obtained at the intermediate value of the wavelengths corresponding to the respective electrodes. Further, a plurality of positive electrodes which are not adjacent are simultaneously driven to simultaneously obtain the oscillating wavelengths corresponding to the electrodes. In this manner, one element can readily produce an oscillation with arbitrary wavelength in the gain spectrum of the active substance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure of a semiconductor radar and a method of driving the same.

In a conventional Frebri-Perot semiconductor radar with two parallel arm-opening planes as reflectors, there are many closely spaced resonant modes, and therefore there are usually many close wavelengths in the gain spectrum of the active material. oscillate at the same time. The wavelength and intensity of these oscillation lines vary irregularly depending on the excitation conditions and temperature of the active part, the manufacturing conditions of the device, and the like. Therefore, with this type of semiconductor laser, it is difficult to obtain an oscillation output consisting of an arbitrary wavelength.

On the other hand, in a distributed feedback semiconductor laser, an example of which is shown in FIG. 1, a diffraction grating 5 formed along the active portion 4 constitutes an optical resonator, and the resonant wavelength λ is λ=2A.
n g/m. Here, A is the period of the diffraction grating, ng is the effective refractive index for propagating light, and m is an integer and the order of diffraction. Therefore, by selecting the period A of the diffraction grating, it is possible to obtain oscillation at any wavelength within the gain spectrum of the active material. However, it is difficult to completely change the oscillation wavelength using - distributed feedback radars.

An object of the present invention is to eliminate these drawbacks of conventional semiconductor radars and provide a semiconductor radar whose oscillation wavelength can be varied.

In order to achieve the above object, the semiconductor laser of the present invention has a distributed feedback structure, the period of the diffraction grating is changed in one direction, and a plurality of electrodes are provided along the direction of this change. By driving the electrode at the position of period i1H, λ1
= 2 AI' ng/m wavelength oscillation is obtained.

The present invention will be explained in detail below using examples.

Embodiment FIG. 2 is a top view of a semiconductor radar with variable oscillation wavelength according to the present invention. The cross section is similar to that in FIG.

7-1.7-2. ......7-10 is the positive electrode, and point #! 9 indicates the direction of the grooves of the diffraction grating 5 in the crystal.

The period of the grating is constant in the X direction and continuously changes in the X direction. The light output is extracted from a crystal that opens at one end of the electrode.

To create such a structure, first the n-type layer a
N-type Ga1-X was deposited on the substrate 2 by continuous liquid phase growth.
An A7XAS (x″:0.3) layer 3 and a p-type QaAs active layer 4 are grown. Next, a photoresistor is applied to this surface, and the period is set to 2 using the interference of laser light.
A lattice-like interference fringe that continuously changes between 423A and 2456A is exposed. Here, the period was selected so as to obtain second-order diffraction (m=2) within the gain spectrum of GaAs. To obtain such interference fringes, He-
Parallel light rays 10 of a Cd laser were diverged in the X direction using a cylindrical lens, and made to interfere with each other in an arrangement as shown in FIG.

Here, 11 is a cylindrical lens, 12 is a semi-transparent mirror, 1:I is a total reflection mirror, and 14 is a sample coated with photoresist.

The interference fringes obtained by the above optical system have a constant period in the X direction, as shown in FIG. 4, and this period changes continuously in the X direction. The sample was exposed to a lattice interference pattern within the dotted line 15 in the figure. Using the photoresist grating obtained by developing this as a mask, the surface of the p+ type GaAs active layer 4 is chemically etched to form a diffraction grating 5 with a depth of about 0.12 μm, and the photoresist is removed. On top of this, p-type oa, -x AtxAs, (o in x,
3) Grow layer 6. Here, as added impurities, Sn was used for the n-type layer and Ge was used for the p-type layer. The thicknesses of layers 3, 4.6 are 2μ, 0.5μ and 10μ, respectively. After crystal growth, 7yu-Q e − is applied to the entire surface of the n-type GaAs substrate 2.
Ni was vapor-deposited to form a negative electrode 1. p-type -G al
-x Atx A s layer 6 has (:' r -A II
20μ x 409μ 10
strip-shaped positive electrodes 7-1.7-2. ......, 7-
10 was formed. In order to extract light output to the outside, a crystal was opened at one end of the positive electrode and bonded to the stem.

When the above semiconductor laser device is operated in pulses at room temperature,
7-1.7-2. Oscillation was obtained at a threshold current density of 3 to 4 KA/cm2 for each electrode of 7-10. FIG. 5 shows the relationship between the driven electrodes and the obtained oscillation wavelength. The width of the oscillation line was approximately 0.3A.

Laser wavelengths other than those mentioned above could be obtained by the following two methods.

By simultaneously driving two adjacent positive electrodes with an appropriate ratio of current, we were able to obtain oscillation at an intermediate value of the wavelengths corresponding to each electrode. In this case, the electrodes other than those driven were short-circuited to the negative electrode in order to concentrate the current distribution between the two positive electrodes. As another method, since ng changes with temperature, it was possible to continuously change the oscillation wavelength by changing the temperature of the element. In this case, the oscillation wavelength changed to a longer wavelength as the temperature rose at a temperature change rate ti 0.8 A/deg.

Further, in the semiconductor laser of the present invention, it is possible to simultaneously drive a plurality of non-adjacent positive electrodes, and to obtain a variable oscillation wavelength corresponding to these electrodes.

As explained above, the semiconductor laser of the present invention, in which distributed feedback lasers with diffraction gratings of different periods are integrated on one substrate, can easily oscillate at any wavelength within the gain spectrum of the active material with a single element. The effect is remarkable in that it is possible to

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional distributed feedback semiconductor laser;
The figure is a top view of a semiconductor laser in an embodiment of the present invention. In Fig. 1.2, 1... negative electrode, 2... n-type GaAs substrate, 3...
n-type G ar -x A L x A s layer (0.
3), 4 ・I) type GaAs active layer, 5...period approximately 0
．． Diffraction grating of 24μ, depth of about 0.12μ, 6... p-type G a l-X A l x A s layer (0.3 in X)
, 7 and 7-1.7 to 2...7-10...
Positive electrode, 8... Open plane, 9... Represents the direction of the grooves of the diffraction grating. FIG. 3 shows the arrangement of an optical system for exposing lattice interference fringes in an embodiment of the present invention. In Fig. 3, a parallel beam of wavelength 3250A from a 10 He-Cd laser,
11...Cylindrical lens, 12...Semi-transparent mirror, 13...
- Total reflection mirror, 14...This is a sample coated with photoresist. FIG. 4 shows lattice-like interference fringes obtained with the optical system arrangement shown in FIG. The area indicated by the dotted line 15 was used for exposing the sample. FIG. 5 shows the oscillation wavelength at room temperature of the semiconductor laser in the embodiment of the present invention. The horizontal axis is the driven figure 1, figure 2, figure 3, and figure 4.

Claims (1)

[Claims] 1. In a distributed feedback radar device formed on a single substrate and having a diffraction grating inside the device, the diffraction grating has at least two desired regions with different periods, and the two A semiconductor radar device characterized by having electrode layers separated from each other in a shape that corresponds to a desired area and extends in the traveling direction of radar light. 2. In a distributed feedback radar device formed on a single substrate and having a diffraction grating inside the device, the diffraction grating has at least two desired regions having different periods, and the diffraction grating has at least two desired regions corresponding to the two desired regions; A method for driving a semiconductor radar device, characterized in that it has electrode layers separated from each other in a shape extending in the traveling direction of Rade light, and causes adjacent active regions to simultaneously oscillate via the electrode layers to obtain a predetermined oscillation wavelength. .