JPS62126684A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a high-quality, super-high-speed, optical modulating signal of 10GHz or more without wavelength fluctuation, by providing a pair of light modulating parts, which are constituted by materials or multilayer films, where one or both of light reflectivity or light absorbance are changed with the change in electric fields are current density, and electrodes, which are independent of current injecting electrodes, at both end surfaces of an active layer. CONSTITUTION:One or both of light reflectivity and light absorbance of materials or multilayer films 5a and 5b are changed with the change in electric field or current density. A pair of light modulating parts is formed by the films 5a and 5b and electrodes 7a and 7b, which are independent of current injecting electrodes 2a and 2b, are provided neighboring both end surfaces of an active layer 1 in the light propagating direction of a lightguide forming active layer 1. For example, on a substrate 3, a clad layer 4b, the active layer 1 and a clad layer 4a are formed. The current injecting electrodes 2a and 2b are provided on the upper and lower surfaces. On both end surfaces, the dielectric thin films 5a and 5b having a large electrooptical effects, transparent electrodes 6a and 6b, parts 8a and 8b having a large current density and the electrodes 7a and 7b are further provided. Thus a pair of the modulating parts is formed. A modulating signal is applied to one of the light modulating parts, and a signal, which is electrically inverted from said modulating signal, is applied to the other light modulating part. Thus modulation is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser capable of ultra-high-speed modulation and used in a large-capacity optical communication system.

Conventional technology Modulation of semiconductor laser optical output by injection current, page 2,
In other words, direct current modulation does not require an external modulator other than a semiconductor laser and can easily obtain an optical intensity modulation signal, so it has become the mainstream modulation method in optical communication systems. This direct current modulation uses changes in the laser oscillation state due to changes in the current density in the active layer to extract optical modulation signals (Hiroo Yonezu, "Optical Communication Device Engineering", February 1, 1982
5 Engineering Book P163).

Problems to be Solved by the Invention However, since laser direct current modulation uses changes in the laser oscillation state, the modulation limit related to the combination of optical density and current density in the laser oscillation state is 10 GHz to 20 GHz.
exists in z. Further, during modulation operation, the semiconductor laser constantly oscillates its oscillation state in an unstable manner, and many problems arise due to this. Particularly, near the natural oscillation related to the coupling of optical density and current density, that is, the relaxation oscillation frequency, chirping of the multi-longitudinal mode 9 oscillation wavelength, fluctuations in light intensity due to relaxation oscillation, etc. become noticeable. Even if the modulation characteristics can be improved by devising the laser structure, it is impossible to completely overcome the problems in direct current modulation. SUMMARY OF THE INVENTION Therefore, the present invention provides a semiconductor laser that has no wavelength fluctuation and can easily obtain a high-quality optical ultrahigh-speed modulation signal of 10 GHz or more.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention is characterized in that a pair of optical modulation sections are provided on both end faces of the semiconductor laser active layer. The light modulation section is composed of a material or a multilayer film whose light reflectance and/or light absorption change depending on changes in electric field or current density, and an electrode independent of the semiconductor laser current injection electrode.

The semiconductor laser is modulated by applying a modulation signal to one of a pair of optical modulation units and simultaneously applying a signal that is an electrical inversion of the modulation signal to the other optical modulation unit.

Operation The modulation operation of the semiconductor laser having the above configuration is as follows. First, a current higher than a threshold value is injected into the active layer of a semiconductor laser to cause laser oscillation. Next, by applying a modulation signal to one of the pair of modulation sections and simultaneously applying an electrically inverted modulation signal to the other modulation section, the laser light emitted from both end faces of the semiconductor laser according to the present invention is modulated. be done.

However, in this case, the changes in the light reflectance or light absorption of the pair of modulation sections are in opposite directions, so that the modulated optical signals emitted from both end faces are in a complementary relationship. Therefore, there is no fluctuation in optical density within the semiconductor laser according to the present invention, and 11-dimensional optical modulation in a stable oscillation state is achieved.

Embodiment Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings. FIG. 1 is a sectional view of a semiconductor laser according to an embodiment of the present invention. 1 is a semiconductor laser active layer, 2a, 2b
3 is a current injection electrode, 3 is a substrate, and 4a and 4b are cladding layers. 5a and 6b are dielectric thin films with a large electro-optic effect, and 6a and 6b are transparent electrodes. 7a,
An electrode 7b is in contact with the dielectric thin films 5a and esb via portions sa and sb with increased charge density. 58
~8a and 5b~8b form a pair of modulation sections.

FIG. 2 is a schematic diagram of a semiconductor laser light modulation method according to an embodiment of the present invention. 9 is a semiconductor laser according to the present invention shown in FIG. 10a is a modulation signal applied to the modulation section shown in FIGS. 5a to 8a, and 10b is a
A is a signal that is electrically inverted and applied to the modulation sections 5b to 8b. Modulation part electrode 6a-7a interval, e
The electric field applied between b and 7b changes the refractive index of 58 and 5b due to the electro-optic effect. When no electric field is applied as shown in FIG. 2B, the intensity of the optical output from both end faces of the semiconductor laser 9 is the same. However, by applying a pair of modulation signals as shown in A or C, the refractive index of the pair of modulation sections changes in opposite directions, making it possible to increase the reflectance of one side of the left and right end faces of the semiconductor laser and decrease the reflectance of the other. . Therefore,
The light intensities of the emitted lights 11a and 11b at the left and right end faces change complementarily, and optical modulation is realized. At this time, there is no large fluctuation in the optical density within the semiconductor laser active layer, and the laser remains in a stable oscillation state, making it possible to realize ultrahigh-speed optical modulation.

Effects of the Invention As described above, according to the present invention, ultrahigh-speed optical modulation of a semiconductor laser can be easily realized, and it is extremely useful in large-capacity optical communication systems and the like.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a semiconductor laser according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the operation of the semiconductor laser. 1... Active layer, csa, 5b... Dielectric material with large electro-optic effect, 6a, eb... Transparent electrode, 7a. 7b... Electrode, 5a to 8a, 5b to 8b...
...Pair of modulation sections, 9...Semiconductor laser, 1
0 a...Modulation signal, 1ob...10
Modulation signals 11a, 11b, which are electrically inverted a.
...Light output.

Claims (2)

[Claims] (1) A substance or multilayer film that changes one or both of light reflectance and light absorption with changes in electric field or current density;
A semiconductor laser having a pair of optical modulation sections each including an electrode independent of a current injection electrode, adjacent to both end surfaces of the active layer in the light propagation direction of an optical waveguide constituting the active layer. (2) A modulation signal is applied to one of the pair of optical modulation units, and at the same time, a signal obtained by electrically inverting the modulation signal is applied to the other optical modulation unit.
Semiconductor laser described in section.