JPH03148191A - Variable wavelength semiconductor laser - Google Patents

Abstract

PURPOSE:To enable wavelength variation of good reproducibility at a fast speed by providing a diffraction grating or a prism, a wavelength control part which consists of a transmission factor variable element which can change transmission factor electrically, and a reflectance variable element which can change reflectance. CONSTITUTION:Light of a wavelength corresponding to wavelength of lambdaa to lambdac, for example is diffracted to different directions by a diffraction grating 3 having dispersion characteristics of wavelength from a semiconductor gain medium 1 which produces gain through current injection; and is injected to transmission factor variable elements 4a to 4c whose transmission factors can be electrically changed respectively. At this time, if the transmission factor variable element 4a alone has high transmission factor and others has low one, light of wavelength lambdaa alone is selectively reflected by a recessed mirror 5. As a semiconductor laser resonator, it has high reflectance to a wavelength lambdaa alone and oscillates at the wavelength lambdaa. Then, if the transmission factor variable element 4b alone is put in a state of high transmission factor, an oscillation wavelength is switched to lambdab. Thereby, a wavelength can be changed with good reproducibility at a fast speed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The invention of Part B relates to a wavelength tunable semiconductor laser whose wavelength can be electrically changed at high speed.

[Conventional technology]

FIG. 5 shows, for example, Matthews (M, R, Mat
thews etal, Electronics Le
tters, Vol, 21. No, 3. pp, 113-
115, 1985) et al. is a schematic diagram showing a conventional wavelength tunable semiconductor (1) laser. In this figure, 1 is a semiconductor gain medium using a semiconductor laser, 2 is a lens, 3 is a diffraction grating, and 6 is a cleavage plane of the semiconductor laser coated with an anti-reflection coating.

Next, the operation will be explained.

The diffraction grating 3 has wavelength dispersion characteristics and can return only light of a specific wavelength, for example (λ,), to the semiconductor gain medium 1. When this wavelength λ1 is within the wavelength range in which the semiconductor gain medium 1 has a gain, and the gain exceeds the loss of the laser resonator B, laser oscillation starts at the wavelength λ.

By mechanically rotating this diffraction grating 3, the oscillation wavelength of the external cavity semiconductor laser can be changed.

[Problem to be solved by the invention]

Since the conventional wavelength tunable semiconductor laser is configured as described above, it is necessary to mechanically rotate the diffraction grating 3.
There were problems such as slow operation and poor reproducibility due to backlash and the like.

(2) The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a wavelength tunable semiconductor laser that can change the wavelength at high speed and with good reproducibility.

[Means to solve the problem]

A wavelength tunable semiconductor laser according to the present invention includes a semiconductor gain medium that generates gain by current injection, at least one diffraction grating or prism having wavelength dispersion characteristics from the semiconductor gain medium, and a transmittance that can be electrically changed. Transmittance Variable Element 2 A wavelength control section comprising a reflectance variable element capable of changing the reflectance.

[Effect]

In this invention, the wavelength control section is composed of a diffraction grating and an element that can electrically change the reflectance or transmittance, and thereby controls the oscillation wavelength by feeding back only a specific wavelength.

〔Example〕

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

(3) FIG. 1 is a configuration diagram showing an embodiment of the wavelength tunable semiconductor laser of the present invention. In this figure, 1 is a semiconductor gain medium, 2 is a lens, 3 is a diffraction grating, and 4 is, for example, a thickness of 1
GaAs well layer about 0 nm thick and AlG about 5 nm thick
A multi-quantum well structure in which a pair of 10 or more aAs barrier layers is sandwiched between p-type and n-type electrodes to electrically change the transmittance, like a multi-quantum well structure that can be reverse biased. transmittance variable element, 5
is a reflecting mirror that reflects the light diffracted by the diffraction grating 3,
For example, a concave mirror is used. 6 is the semiconductor gain medium 1
This is a cleavage surface of a semiconductor laser coated with an anti-reflection coating.

Next, this operation will be explained using FIG.

In FIG. 2, here, for example, the wavelength λ. λb.

λ0 (lights with corresponding wavelengths are diffracted in different directions by the diffraction grating 3, and transmitted through variable transmittance elements 4a.

4b and 4c. At this time, if only the variable transmittance element 4a has high transmittance, and the variable transmittance element 4b
, 4c, only the light of wavelength λ is selectively reflected by the concave (4) mirror 5.

Therefore, the semiconductor laser resonator has a high reflectance only for the wavelength λ1 and oscillates at this wavelength. Next, if only the variable transmittance element 4b is set to have a high transmittance, the oscillation wavelength becomes λb(ζ).

Note that in the above embodiment, a multi-quantum well structure is used as the variable transmittance element 4, but a liquid crystal may be used instead.

Further, although the above embodiment uses one diffraction grating 3, two diffraction gratings 3 may be used as shown in FIG. In this case, there is an advantage that the plane mirror 7 can be used as a reflecting mirror because the optical path only moves in parallel even if the wavelengths are different.

Further, in the above embodiment, the semiconductor laser cleavage plane 6 is coated with an anti-reflection coating, but it is possible to set the reflectance to an arbitrary value.

Further, in the above embodiment, a total reflection type concave mirror is used as the concave mirror 5, but a semi-transmission type concave mirror may be used (5). In this case, the angle of the emitted light will be electrically controlled. Furthermore, in FIG. 3, if the plane mirror 7 is of a semi-transmissive type, only the position of the emitted light can be electrically controlled without changing the angle of the emitted light.

Further, as shown in FIG. 4, even if the diffraction grating 3 is placed on the side opposite to the wavelength control section, the output angle can be controlled in the same way.

Further, in the above embodiment, the diffraction grating 3 is used as having wavelength dispersion, but the same effect can be obtained by using a prism.

〔Effect of the invention〕

As explained above, the present invention includes a semiconductor gain medium that generates gain by current injection, at least one diffraction grating or prism that has wavelength dispersion characteristics from the semiconductor gain medium, and that can electrically change transmittance. Variable Transmittance Element 2 A wavelength control section consisting of a variable reflectance element that can change the reflectance allows the device to be made smaller, and
It is possible to tune the wavelength at high speed and with good reproducibility, and a spectrum (6) with a narrow linewidth can be obtained. Furthermore, it becomes possible to electrically control the emission angle or position of the beam.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a wavelength tunable semiconductor laser according to an embodiment of the invention of B, Fig. 2 is an enlarged view of the wavelength selection section of the invention, and Fig. 3 is another embodiment of the invention. FIG. 4 is a schematic diagram of another embodiment of the present invention having beam deflection characteristics. FIG. 5 is a schematic diagram of a conventional wavelength tunable semiconductor laser. FIG. In the figure, 1 is a semiconductor gain medium, 2 is a lens, 3 is a diffraction grating, 4 is a transmittance variable element, 5 is a concave mirror, 6 is a semiconductor laser cleavage plane, and 7 is a plane mirror, λ1°λb, λ. is the wavelength. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A semiconductor gain medium that generates gain by current injection, a diffraction grating or prism that wavelength-disperses the laser light from this semiconductor gain medium, and a diffraction grating or prism that wavelength-disperses laser light from this semiconductor gain medium. A wavelength tunable semiconductor laser comprising: a wavelength control unit that selectively causes the wavelength to be incident on the semiconductor gain medium.