JPS5892289A - Variable wavelength semicondutor laser - Google Patents

Abstract

PURPOSE:To vary the oscillating wavelength in a broad range, by forming a comb shaped electrode ultrasonic wave oscillator (IDT) on a light confining layer so that the pitches of the oscillator are different depending on positions, thereby making the oscillating frequency vary. CONSTITUTION:When an electric field of a frequency (f) is applied to an IDT10, an SAW is generated and proparated in the light emitting direction along a p type GaAs layer 3. Single mode vertical oscillation can be generated by the SAW. Laser light having a wavelength lambda shown by an expressionIis obtained, where LAMBDA is the wavelength of the SAW. When the frequency (f) of the applied electric field is varied, DELTAlambda is obtained by an expression II, where V is the propagating speed of the SAW. When the oscillating frequency of the IDT10 is varied by DELTAf, the oscillating wavelength can be varied by DELTAlambda. The pitches between the electrodes are different. With the frequencies f1-fn corresponding to the different wavelengths LAMBDA1-LAMBDAn of the SAW as the center, each frequency can be varied by DELTAf. The corresponding oscillating wavelength can be varied by DELTAlambda with lambda1-lambdan as the centers.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tunable wavelength semiconductor laser whose laser oscillation wavelength can be changed arbitrarily.

Conventionally, GaAs-Ga semiconductor lasers have been developed as single-longitudinal mode oscillation semiconductor lasers developed for long-distance optical transmission.
□-xAl! xA! Double heterostructure DFB (Dis
Tributed fee4back) laser diodes are known. This laser diode has a corrugation with a constant period of 1 μm or less formed on an optical confinement layer, and the oscillation wavelength λ is λ-2n A / m *** (11
n; refractive index of the active layer m; determined by the relationship of order of Black diffraction, and has the advantage that longitudinal mode operation of single wavelength oscillation is stably performed at this oscillation wavelength λ. However, the period of corrugation formation is usually 1 μm.
Since it is small (less than m), it is necessary to use an electron beam exposure method or an erographic method, and after forming corrugations using these methods on an optical confinement layer such as a GaAs active layer, Ga knee x Al! The need to grow the xAs layer poses a problem of thermal damage, and the manufacturing process is complicated. Moreover, while the oscillation wavelength is determined by the corrugation period and is stable, it cannot be made variable, which poses the problem of closing the possibility of application to branch multiplex communication, which is a method of multiplex communication.

An object of the present invention is to provide a tunable wavelength semiconductor laser that is easy to manufacture, capable of stable single-longitudinal mode oscillation, and whose oscillation wavelength can be varied over a wide range.

The tunable wavelength semiconductor laser according to the present invention is provided with a comb-shaped electrode ultrasonic vibrator that generates surface acoustic waves on an optical confinement layer, and the pitch of the comb-shaped electrodes differs depending on the location. It is characterized by changing the laser oscillation wavelength by changing the frequency.

Therefore, manufacturing is easy because it is only necessary to form a comb-shaped ultrasonic transducer on the optical confinement layer of a normal laser diode, and the laser oscillation wavelength can be adjusted by changing the vibration frequency of the comb-shaped electrode ultrasonic transducer. It can also be effectively applied to wavelength division multiplexing communications. In the case of comb-shaped electrodes with the same pitch, even if the frequency of the applied electric field is changed, the wavelength of the oscillated surface acoustic wave is determined by the pitch of the comb-shaped electrodes, and the frequency cannot be changed over a wide band. However, in this invention, since the pitch of the comb-shaped electrodes differs depending on the location, there are multiple types of electrode pitches, and it is possible to generate surface acoustic waves with wavelengths corresponding to each pitch, allowing the laser oscillation wavelength to be extended over a wide range. variable over the period.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a first embodiment in which the invention is applied to a double heterostructure laser diode. As shown in this figure,
Double heterostructure laser diode 01) is n-G
aAs single crystal substrate (1) n-Ga□-xAl! using two-liquid phase epitaxy technology! xA8 layer (2), p-G
a, As layer (3), p-Ga1-xAl! Grow the xA8 layer (4) and the p-GaAs layer (5),
Electrodes (6) and (7) are provided on both sides. When a forward current is passed through this diode (Il+), when this current exceeds the threshold value, the p-GaAs layer (3) becomes an active layer that confines carriers and light, and the laser beam (A) is activated.
is emitted.

This double heterostructure laser diode-1'ill+
A part of the p −
The GaAs layer (3) is exposed and an insulating film (8) is formed on this layer (3), and a comb-shaped electrode ultrasonic wave element (101 (hereinafter referred to as T) is formed on this insulating film (8). A digital transducer) will be established.This IDToo)
The pitch of the electrode generates surface acoustic waves (SA
They are formed in a sequential manner in the propagation direction of the wave (referred to as W).

In the configuration shown in Fig. 1, when an electric field of frequency f is applied to T (10), a SAW is generated and the p-GaA
The light propagates along the s-layer (3) in the light emission direction.

This SAW produces an effect similar to corrugation in conventional DFB laser diodes, and can produce single-longitudinal mode oscillation. That is, if the wavelength of the SAW is A, a laser beam with a wavelength λ shown in equation (1) can be obtained. Then, when the frequency f of the applied electric field of T(101 is changed and the SAW wavelength Δ is changed by ΔA,
From equation (1), Δλ=2nΔA/m...(2) If the SAW propagation speed is ■, then V=fA, so substituting equation (3) into equation (2), we get Than
By changing the oscillation frequency of T (101 by △f), the laser oscillation wavelength can be changed by △λ.

The pitch between the electrodes of TQ(l) is different as mentioned above, and corresponds to the different wavelengths A1 to An of the SAW. Therefore, the wavelength of the SAW generated from T f+01 is can be changed by ΔA around It becomes possible to change each pitch by Δf around fn. Therefore, by appropriately setting the pitches A1 to An, the variable frequency bandwidth F can be made more T(
F
= n・△f. This situation is shown in FIG. This allows the laser beam corresponding to frequencies f1 to fn to
If the oscillation wavelengths of the diodes (11) are λ1 to λn, respectively, it becomes possible to change the laser oscillation wavelength by △λ, which is expressed by the equation (4), centering on λ1 to λn, respectively, so that n・△λ A semiconductor laser whose oscillation wavelength can be varied over a wide range can be obtained.

FIG. 3 shows a second embodiment. Here, T+20+ is constructed by arranging electrodes (20a) to (200) with different pitches in a direction perpendicular to the laser beam emission direction. In this case, the wavelength λl differs depending on the emission position of the laser beam.
~λn (n = 3 in this embodiment) laser light can be obtained, and the configuration of the scanner can be simplified.

FIG. 4 shows a third embodiment. The T piece has three types of arc-shaped electrodes (30a) to (30a) with different pitches.
3, Oc), and each of these circular arcs is connected to each other. Since the SAW generated from such an arc-shaped electrode tends to converge, the emitted laser light is prevented from spreading.

FIG. 5 shows a fourth embodiment, in which T
+40) is composed of arc-shaped electrodes whose pitch changes continuously. In this case, the wavelength of the emitted laser light varies depending on the emitting position, and the laser light converges on one point. Therefore, optical coupling to an optical fiber or the like becomes easy.

Needless to say, the present invention is applicable not only to DFB laser diodes but also to TG (integrated dual waveguide) laser diodes and other semiconductor lasers.
Further, the present invention can be applied to semiconductors other than GaAs as long as they have piezoelectricity to propagate the SAW.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the first embodiment of the present invention, FIG. 2 is a diagram showing the spread of the oscillation frequency bandwidth, and FIGS. FIG. 1 is a schematic configuration diagram showing third and fourth embodiments. (31@@e GaAs layer (light confinement layer'), 10
1'(2 [[1t401... comb-shaped electrode ultrasonic vibrator, +Ill... semiconductor laser 0 Patent applicant: Tateishi Electric Co., Ltd. CF

Claims (1)

[Claims] Variable wavelength live conductor laser.