JPH0158876B2 - - Google Patents

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, semiconductor lasers that perform single longitudinal mode oscillation were developed for long-distance optical transmission.
GaAs−Ga _1-x Al _x As double heterostructure DFB
(Distributed feedback) 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 depends on the period Λ of the corrugation. λ=2nΛ/m...(1) n; refractive index of the active layer m: Determined by the 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 formation of corrugations
Since the period is usually small, less than 1 μm, it is necessary to use electron beam exposure or holographic methods, and after forming corrugations on an optical confinement layer such as a GaAs active layer using these methods,
The disadvantage is that the Ga _1-x Al _x As layer needs to be grown, which causes 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 is a problem in that the application to wavelength division multiplexing communication, which is a method of multiplex communication, is closed.

An object of the present invention is to provide a tunable wavelength semiconductor laser that is easy to manufacture, is capable of stable single longitudinal mode oscillation, can vary the oscillation wavelength, and can reduce the spread of the laser beam. do.

In the tunable wavelength semiconductor laser according to the present invention, a comb-shaped electrode ultrasonic vibrator that generates a surface acoustic wave is provided on an optical confinement layer, and the comb-shaped electrode is formed in an arc shape to suppress the spread of the propagating surface acoustic wave.
It is characterized in that the laser oscillation wavelength is changed by changing the vibration frequency of the comb-shaped electrode ultrasonic vibrator.

Therefore, manufacturing is easy because it is only necessary to form a comb-shaped electrode ultrasonic vibrator on the optical confinement layer of a normal laser diode, and furthermore, by changing the vibration frequency of the comb-shaped electrode ultrasonic vibrator, Since the laser oscillation wavelength can be changed, it can also be effectively applied to wavelength multiplexing communications. In addition, since the comb-shaped electrodes are formed in an arc shape, the spread of the generated surface acoustic waves is suppressed, and as a result, the spread of the laser beam can be reduced, and the high-frequency power applied to the comb-shaped electrodes can be small. Since the confinement effect is also large, the laser oscillation efficiency becomes high.

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.
The dual heterostructure laser diode is n-
Using liquid phase epitaxy technology on a GaAs single crystal substrate 1, an n-Ga _1-x Al _x As layer 2, a p-GaAs layer 3, a p-
Grow Ga _1-x Al _x As layer 4 and P-GaAs 5,
Electrodes 6 and 7 are provided on both sides. When a forward current is passed through this diode, when this current exceeds a threshold value, the p-GaAs layer 3 becomes an active layer that carries and confines light, and emits laser light A.

A part of this double heterostructure laser diode is cut out using etching technology, and 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 transducer 10 (hereinafter referred to as IDT ((inter-digital transducer)) is provided on this insulating film 8. . This IDT10 is
It is formed in an arc shape to prevent the generated surface acoustic waves (hereinafter referred to as SAW) from spreading due to the diffraction effect and propagate uniformly.

In the configuration shown in FIG. 1, when an electric field of frequency f is applied to the IDT 10, SAW is generated and p-
The light propagates along the GaAs layer 3 in the light emission direction. This SAW produces an effect similar to corrugation in conventional DFB laser diodes, allowing single longitudinal mode oscillation to occur. That is, if the wavelength of the SAW is Λ, a laser beam with a wavelength λ shown in equation (1) can be obtained. Then, by changing the frequency f of the applied electric field of IDT10, the SAW wavelength Λ
When changing △Λ, from equation (1), △λ=2n△Λ/m...(2) If the SAW propagation speed is V, then V=fΛ Therefore, △f=△Λ×(−f ² /V) ...(3) Substituting equation (3) into equation (2), △λ=-2nV△f/f ² m ...(4) If the oscillation frequency of IDT10 is changed by △f, The laser oscillation wavelength can be changed by Δλ.

For example, in equation (4), m=1, V=3300
(m/s), n=3.37, f=20 (GHz), △f=2
(GHz), △λ=0.11 (μm), and if the oscillation frequency of IDT10 is 20 (GHz) and a laser beam with a wavelength of 1 μm is obtained, then the oscillation frequency of IDT10 is 2 (GHz). It can be seen that the wavelength of the laser beam can be changed by 1100 (Å) by changing it to .

Furthermore, since the IDT 10 is formed in an arc shape, it is possible to suppress the oscillation mode and the spread of the emitted laser light. FIG. 2a shows an IDT 11 formed in a straight line. This IDT11
Then, due to the diffraction effect, the generated SAW spreads and propagates by an angle θ expressed by the following equation, and as a result, the laser oscillation mode and the laser beam spread.

Θ∝Λ/D...(5) D: Cross width However, since the IDT 10 in this invention is formed in an arc shape, the SAW propagates in the direction of convergence, as shown in Figure 2b, and the angle Θ Even considering the spread, the waves propagate almost in parallel. As a result, the spread of the laser beam A is suppressed and the oscillation mode is stabilized. In addition, the light confinement effect increases, increasing laser oscillation efficiency.
The power of the high frequency electric field applied to the IDT 10 can also be reduced.

FIG. 3 shows a second embodiment, in which the invention is applied to an ITG (integrated dual waveguide) laser diode. In this figure, the ITG laser diode consists of an n-GaAs substrate 21, a Ga _1-x Al _x As layer 22 formed on this substrate 21,
24, 26, GaAs active layers 23, 25 and p-
GaAs layer 27, electrodes 28, 29, and insulating film 30
It is composed of. In this ITG laser diode, an arc-shaped IDT is formed on the surface of the insulating film 30 parallel to the GaAs active layer 23, which is the optical confinement layer.
10 are formed.

When a high frequency electric field is applied to this IDT10, SAW
is propagated onto the GaAs active layer 23, which is an optical confinement layer, and a function similar to corrugation in a DBF laser diode can be achieved. As described above, the laser oscillation wavelength can be changed by changing the frequency of the IDT 10, and the spread of the laser beam can be suppressed because the IDT 10 has an arc shape.

The tunable wavelength semiconductor laser obtained by the present invention can be effectively applied to wavelength division multiplexing communications. That is, as shown in FIG. 4, in response to a control signal from a central processing unit 41, laser light signals of different wavelengths are emitted from a tunable wavelength semiconductor laser 42 according to the present invention, and are transmitted through an optical fiber 43 to an optical demultiplexing device 44. send. Optical fibers 45 for each channel of 1, 2, . Since even one tunable wavelength semiconductor laser 42 according to the present invention can obtain laser light signals with different wavelengths depending on the control signal, it is possible to easily configure a wavelength division multiplexing communication system, and it can be applied to this system. This will give you a big effect. Furthermore, since the spread of the laser beam is suppressed, optical coupling to the optical fiber 43 is also facilitated.

This invention is applicable to the above-mentioned DFB laser diode and
Needless to say, the present invention can be applied to semiconductor lasers other than ITG laser diodes, and can also be applied to semiconductors other than GaAs-based semiconductors as long as they have piezoelectricity to propagate SAW.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a first embodiment of the invention;
FIG. 2 is a diagram showing the spread of surface acoustic waves, FIG. 3 is a perspective view showing a second embodiment, and FIG. 4 is a block diagram showing a wavelength division multiplexing communication device. 3, 23...GaAs layer (light confinement layer), 10
...Comb-shaped electrode ultrasonic transducer.

Claims (1)

[Claims] 1 A comb-shaped electrode ultrasonic transducer that generates surface acoustic waves is provided on the optical confinement layer, and the comb-shaped electrode is formed in an arc shape to suppress the spread of the propagating surface acoustic waves, and the vibration frequency of the comb-shaped electrode ultrasonic transducer is A tunable wavelength semiconductor laser whose laser oscillation wavelength changes depending on changes in the wavelength.