Characteristics of a class of new opto-coupler amplifiers with positive feedback

This paper discusses a new method of optoelectronic amplification that utilizes an array of one or more series connected light emitters (LED´s or laser diodes) from which the light is collected by closely coupled PIN diode detectors with high quantum efficiency. Positive current feedback is applied to the opto-coupler in order to increase the current gain of the system. It is shown that the gain-bandwidth product of the system is proportional to the number of light emitters used. Current, voltage, and power gains of the opto-amplifier are derived and typical results shown. The system noise becomes very small if devices of high current transfer efficiency are used. Further, the noise figure is found to be independent of the positive feedback applied. For a given system, there is a minimum noise figure, and it is independent of the number of light emitters used in the array. With a transfer efficiency of 0.95, a single light emitter opto-amplifier can provide a current gain of 14.7 dB with a noise figure of about 1.5 dB