Patent
1990-04-04
1991-07-30
Gonzalez, Frank
350 9613, 357 22, G02B 610
Patent
active
050354795
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for optical signal processing.
It is an object of the present invention to provide a device for optical signal processing, with which the magnitude of a flow of light or a lightbeam in semiconductor can be influenced in a simple way.
2. Description of the Background Art
Known devices for optical signal processing make use of the non-linear effect; the disadvantages thereof are the requirement of a rather high level of power or slowness. Fabry-Perot resonators or resonators using superlattices are required for this purpose; these are difficult to integrate.
Further there is known a device showing distributed feedback transistor operation, in which a lattice is employed. This device is also based on non-linear effect.
Further the following prior art is known: Journal of Lightwave Technology, vol. LT-5, No. 9, September 1987, IEEE, J. H. Abeles et al.: "Novel single quantum well optoelectronic devices based on exciton bleaching", pages 1296-1300; Electronics Letters, Vol. 22, No. 18, Aug. 28, 1986, S. H. Lin et al.: "GaAs PIN electro-optic travelling-wave modulator at 1.3 .mu.m", pages 934-935; Applied Physics Letters, vol. 48, No. 19, May 12, 1986, American Institute of Physics, A. Alping et al.: "Highly efficient waveguide phase modulator for integrated optoelectronics, pages 1243-1245; EP-A-0209190; Applied Physics Letters, vol. 50, No. 15, Apr. 13, 1987, T. Hiroshima: "Electric field induced refractive index changes in GaAs-Al.sub.x Ga.sub.1-x As quantum wells", pages 968-870; EP-A-0233011; Journal of Lightwave Technology, vol. LT-5, No. 10, October 1987, R. G. Walker: "High-speed electrooptic modulation in GaAs/GaAlAs waveguide devices", pages 1444- 1453.
A further object of the present invention is to provide a device with which switching rates in the order of picoseconds or subpicoseconds can be achieved.
SUMMARY OF THE INVENTION
The foregoing and other objectives are achieved by the present invention of a device for optical signal processing comprising a substrate, a waveguide of doped semiconductor material on top of the substrate, the waveguide having a refractive index which is not greater than the refractive index of the substrate, and with a junction region between the waveguide and the substrate. A gate for receiving an electric potential with respect to the substrate is positioned on top of the waveguide.
The materials chosen for the substrate and the waveguide are selected such that there is a discontinuity between their conducting bands, causing electrons in the waveguide to migrate to the substrate, thereby creating a two-dimensional gas of electrons having a very high mobility in the junction region. When light is passed through the waveguide in a direction parallel to the substrate, the passage of the light can be controlled by selectively applying a voltage to the gate which causes the electron gas to be depleted in the junction region. The frequency of the light is preferably lower than the plasma frequency of the electron gas.
BRIEF DESCRIPTION OF THE DRAWINGS
Further characteristics, details and advantages of the present invention will be clear in view of the following description of preferred embodiments of the device according to the present invention, illustrated by means of a drawing, in which show:
FIG. 1 a diagramatic sectional view of the structure of a first embodiment;
FIG. 2 a diagram of the bands of the structure from FIG. 1;
FIG. 3 a diagram of the structure according to a second preferred embodiment;
FIG. 4 a graph in which the absorption and reflection coefficients are plotted relative to the densitiy of carriers for the TE mode of the structure from FIG. 3;
FIG. 5 a graph similar to FIG. 4 for the TM mode of the structure from FIG. 3;
FIG. 6 a diagramatic sectional view of a third preferred embodiment of the device according to the present invention;
FIG. 7 a perspective view of the embodiment from FIG. 6;
FIG. 8 a graph in which absorption and reflection coefficients a
REFERENCES:
patent: 4211488 (1980-07-01), Kleinknecht
patent: 4721983 (1988-01-01), Frazier
patent: 4784451 (1988-11-01), Nakamura et al.
Gonzalez Frank
Interuniversitair Micro-Elektronica Centrum vzw
Shaw, Jr. Philip M.
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