Optical waveguides – Temporal optical modulation within an optical waveguide – Electro-optic
Reexamination Certificate
2001-08-23
2003-06-03
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Temporal optical modulation within an optical waveguide
Electro-optic
C385S016000, C385S040000
Reexamination Certificate
active
06574381
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to replacements for electronic switches, and more particularly to semiconductor devices for switching, amplifying, and modulating beams of light.
2. Description of Related Art
One obvious way to switch a beam of light on and off is to interrupt it with a shutter. Mirrors can be used too with the advantage of being able to redirect the beam of light elsewhere. In fiber-optic devices, moving mirrors, lenses, and other optics principles have been developed. But these mechanical methods of switching light are relatively slow, and not well-suited to high-speed switchboard and router use.
Broadband Internet communication is now being made possible by fiberoptics backbones and distribution cables that are being installed all over the world. Each fiber can carry an incredible amount of information in a single beam of laser light. Fast and effective ways are needed to be able to switch these communications channels as fast as they are able to carry data from point-to-point.
One of the present inventors, Carl E. Watterson, reported on experiments with a miniature gallium arsenide (GaAs) integrated optical switch. Such switch provided power amplification from a few milliwatts input to a one watt output according to combinations of digital signals applied to its electrodes. This GaAs optical switch integrated a curved tapered waveguide section and a segmented heatsink.
Tapered semiconductor laser amplifiers are capable of outputting powers in excess of one watt. Single-mode preamplifiers and tapered power-amplifiers have been integrated together in prior art monolithic devices for high-quality and high-power beams. The single-mode preamplifier is used to provide a proper Gaussian-shaped input to the tapered section. The one described by Watterson was a single-angle facet curved ridge preamplifier, wherein the input ridge waveguide was slanted from the crystalline cleavage plane to reduce the effective reflectivity. For a 5° angle, a three micrometer mode width, and a carrier light at 0.83 &mgr;m, the effective modal reflectivity was under 10
−6
.
A prior art device reported by Watterson included an integrated circuit device with a preamplifier section and a power amplifier section. The preamplifier section had three stages each with a pair of independent control electrodes. The power amplifier had another pair of independent electrodes. Each such controlled part exhibited a “contrast ratio” between the light that was passed in the “on” state and that which was passed in the “off” state. In light lock applications, as few as one stage in the off condition has to completely block light passage through the switch to maintain the locked condition.
Sol P. Dijaili, et al., describe a Cross-Talk Free, Low-Noise Optical Amplifier in U.S. Pat. No. 5,436,759, issued Jul. 25, 1995. Crosstalk is a major problem in semiconductor optical amplifiers (SOA), and Dijaili describes carrier lifetimes as being at fault. A tapered amplifier is mentioned as a prior art attempt at a solution that increases output saturation power. So a segmented transverse lasing field is proposed to reduce crosstalk. A clamping action of the laser gain reduces crosstalk by gain saturation.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical switch.
Another object of the present invention is to provide an integrated semiconductor device that combines the functions of an optical switch and an optical amplifier.
Another object of the present invention is to provide an optical switch with modulation capabilities.
Briefly, an integrated optical switch/amplifier embodiment of the present invention comprises a semiconductor waveguide with an input end-face and an output end-face. The waveguide is disposed on a substrate and separated from it by an I-region. A laser cavity is fabricated transverse to the semiconductor waveguide and supports a bleed laser during operation. A pair of switching electrodes with one placed on top of the semiconductor waveguide and another placed beneath the substrate provide for a selective injection of electron carriers from a top length of the semiconductor waveguide and from the substrate through the I-region. Thus, an optical signal presented at the input end-face is either blocked or amplified-through according to the relative polarity of voltages applied to the pair of switching electrodes.
An advantage of the present invention is that an optical switch is provided that is rugged and suitable for use in optical signal networks and routing.
Another advantage of the present invention is that an optical switch is provided that is economical to build.
Another advantage of the present invention is that an optical switch is provided that can modulate optical signals.
The above and still further objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description of specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5436759 (1995-07-01), Dijaili et al.
patent: 5454058 (1995-09-01), Mace et al.
patent: 5710847 (1998-01-01), Takano et al.
patent: 6181843 (2001-01-01), Lee et al.
Egor Alekseev, et al., “77GHz High-Isolation Coplanar Transmit-Receive Switch Using InGaAs/InP PIN Diodes”, ©1995-99 Univ. of Michigan, published at http://www.eecs.umich.edu/dp-group/PIN/gaasic98/.
S. S. Saini, et al., “A 2x2 Crosspoint Switch Fabricated On The Passive Active Resonant Coupler (PARC) Platform”, IEEE Photonics Technology Letters, vol. 13, No. 3, Mar. 2001, 1041-1135/01©2001 IEEE.
C. E. Watterson, “Advanced Electro-Optic Surety Devices”, Federal Manufacturing & Technologies, Allied Signal, KCP-613-6144, Jan. 1999.
Hendrix James
Koo Jackson
Stoddard Robert
Yu Conrad
Main Richard B.
Palmer Phan T. H.
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