Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1997-03-14
1998-11-10
Le, Que
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
250205, 327515, 330 59, H01J 4014
Patent
active
058347631
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to optoelectronic coupling and more particularly to a photon coupled circuit for applications including low noise optocoupling, optical interconnects, current amplifiers, light amplifiers and optical bistable devices. As used herein, the term "photon coupled circuit" refers to a configuration of optoelectronic devices which are photonically and electronically coupled.
BACKGROUND ART
Many prior art devices achieve a current amplification by the use of active electronic circuits. Such devices are not able to offer a low noise operation and in particular are often limited by the shot noise in the system. Australian patent 648682 describes a means of generating multiple noise-correlated lightwave beams in order to suppress shot noise in optical measurement systems.
DISCLOSURE OF INVENTION
It is an object of this invention to provide a sub-shot noise photon coupled amplifier circuit through quantum noise suppression and to provide increased gain or increased bandwidth to the circuit through the application of AC feedback.
Accordingly, in one aspect this invention consists in a sub-shot noise, optoelectronic amplifier circuit comprising a high quantum efficiency semiconductor light emitter; means to provide signal input current and bias current to said light emitter, the light output of said light emitter being controlled by the current flowing therein; a high quantum efficiency semiconductor light detector optically coupled with low photon losses to said light emitter to provide an overall quantum transfer efficiency in excess of 0.5; means to provide a bias voltage to said light detector, the current flowing in said light detector being controlled by the light received from said light emitter and used to provide an output signal; means to isolate a portion of the alternating current flowing in said detector and to feed this portion of the alternating current back to reinforce or oppose the signal current flowing in the light emitter.
In one form of the invention the feedback is positive to reinforce the signal current flowing in a light emitter and thus to provide increased AC current gain exceeding unity. In another form of the invention the feedback is negative in order to oppose signal current flowing in the light emitter and thus to provide increased bandwidth. As used herein, the term quantum transfer efficiency refers to the efficiency of the transfer of the current modulating the light emitter into current flowing in the light detector. It is therefore equal to the open loop current gain of the circuit.
In one form of the invention the light emitter comprises an array of high quantum efficiency laser diodes or light emitting diodes which are driven by a signal current from a high impedance source.
In one form of the invention using an array of high quantum efficiency semiconductor light emitting or laser diode junctions, the product of the number of elements in the array and the value of the quantum transfer efficiency between each element and the light detector is much greater than 1. In this case the quantum partition noise introduced in the coupling between the light emitting array and the detecting system is negligible and negative feedback may be applied to widen the bandwidth of the system.
In another form of the invention, employing a single light emitter the quantum transfer efficiency preferably exceeds 0.75 and ideally is as close to unity as possible.
Preferably, the light detector comprises a back biassed PIN photo diode operating in photoconductive mode.
The high quantum transfer efficiency between the light emitter and the light detector is preferably achieved by low loss photon coupling through close physical positioning as for example, in an optoelectronic integrated circuit (OEIC) together with selection of high quantum efficiency light emitters and light detectors. Low loss photon coupling can also involve the use of an optical waveguide or a low loss light pipe.
In one form of the invention the current in the light emitter is preferably mo
REFERENCES:
patent: 4876442 (1989-10-01), Fukushima
Cheung Wood Nang
Edwards Paul Julian
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