Patent
1986-06-27
1988-01-05
Lee, John
350 9611, G02F 100
Patent
active
047172282
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to an optical coupler with optical amplification for cross and bar state switching of optical signals together with associated amplification. This kind of coupler may be used in such applications as telephony in the transmission of baseband signals and where the optical transmission medium (fibre) has a certain attenuation per unit length.
BACKGROUND
Optical couplers of, for example, the directional coupler type are already known. These couple an incoming optical signal to one of two outputs as shown, for example, in "Guided Wave Devices for Optical Communication", I.E.E.E. 1981, Vol. QE-17 number 6, pp 946-959. One of the problems with integrated optical directional couplers in lithium niobate (LiNbO.sub.3), semiconductors and other materials are the optical losses which allow circuits of only limited complexity to be realizable. Examples of losses in such integrated couplers are 0.5 dB/cm. in lithium niobate and 1 dB/cm. in semiconductors.
In different fibre optical systems, e.g. local networks, bus systems and so on, the minimum given power is a limiting factor in forming the system. To compensate for attenuation in the couplers or branches, an amplification function analogous with that in electronics must be built in. Such a function integrated with the optical coupling in the coupler would thus be of great value. A number of proposals relating solely to light or laser amplification have been reported in the literature, both with amplifiers of the wandering wave type and the Fabry-Pero type as shown, for example, in "Semi-conductor Optical Amplifiers" in I.E.E.E. Spectrum, May 1984 pp 22-33. Typical gain or amplification factors in such known amplifiers are 10-30 dB, for an input signal power of -30 dBm-20 dBm. The known amplifiers mentioned above are discrete amplifier elements.
SUMMARY OF INVENTION
It is an object of the invention to provide a coupler in which, apart from coupling optical signals, an amplification of such signals could also be obtained so that one and the same component effects both coupling and amplification, whereby attenuation of optical signals is avoided.
In achieving the above and other objects of the invention there is provided an optical directional coupler having the possibility of amplification and comprising first, second and third waveguides. The first waveguide serves for incoming light, the second waveguide serves for bar coupling of light from the first waveguide, and the third waveguide serves for cross coupling of light from the first waveguide. The waveguides are transparent for the wave length of the incoming light and have a predetermined characteristic refractive index in the coupling area.
The optical directional coupler further comprises wave guide sections constituting coupling elements for the above-noted waveguides as well as electrodes. In accordance with the invention, there is further provided a device for achieving optical amplification of light passing through the first and second waveguides in the bar coupling state of the directional coupler and optical amplification of the light passing through the first and the third waveguide in the cross coupling state of the directional coupler by feeding a current to the electrodes according to which coupling state is desired, at an alteration of both real and imaginary parts of the refractive index of the respective waveguide sections, an alteration of the imaginary part achieving a amplification and an alteration of the real part achieving an alteration of the state of the coupler for bar coupling or cross coupling of the incoming light.
Other objects, features and advantages of the invention will be found in the Detailed Description which follows hereinafter.
BRIEF DESCRIPTION OF DRAWINGS
The invention will next be described in detail with reference to the accompanying drawings, in which:
FIG. 1 schematically illustrates an optical coupler in accordance with the invention in a view from above,
FIG. 2 is a section through coupler along the line A--A in
REFERENCES:
patent: 4012113 (1977-03-01), Kogelnik et al.
patent: 4521069 (1985-06-01), Ikeda
J. C. Shelton et al., "Rib Waveguide Switches with MOS Electrooptic Control for Monolithic Integrated Optics in GaAs-Al.sub.x Ga.sub.1-x As", Applied Optics, vol. 17, No. 16, Aug. 1978, pp. 2548-2555.
Henry et al., "Spectral Dependence of the Change in Refractive Index Due to Carrier Injection in GaAs Lasers", J. Appl. Phys., vol. 52, No. 7, Jul. 1981, pp. 4457-4461.
Lee John
Menz Michael
Telefonaktiebolaget LM Ericsson
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