Abstract: The present invention provides photodiodes exhibiting photoconductive gain. It is shown that photodiodes may exhibit photoconductive gain under certain conditions, and traditional photoconductive gain theory has been extended to describe these cases. Particularly, there is introduced the basic principles of photoconductive gain in p-i-n diodes, and there is described several approaches to designing photodiodes with photoconductive gain. In one approach, photogenerated carrier delay is used to obtain photoconductive gain in a photodiode. Delay structures inserted into the intrinsic region preferentially impede the flow of one of the carriers relative to the other to obtain the gain. Another method of obtaining photoconductive gain in a photodiode is to increase the rate at which electron-hole pairs are generated in the p-region or n-region, so as to decrease the times &tgr;p or &tgr;n.

Abstract: Devices for measuring one or more properties of a light signal is disclosed. More particularly the invention relates to devices for wavelength and power demodulation based on the use of quantum well electroabsorption photodiodes. In one aspect the invention provides and power and wavelength demodulation system based on a quantum well electroabsorption (QWEA) filtering detector. The input optical signal passes through an optical beam splitter with part of the signal input into a filtering detector which is a multiple quantum well electroabsorption (MQW EA) photodiode having a tunable bandgap and the other part into a reference detector. The input light signal is impinged on the QW diode perpendicular to the plane of the quantum wells. The output of filtering detector is amplified by an amplifier and the output of the reference detector is input into another amplifier. The output from reference detector amplifier serves as a measurement of the power of the input optical signal.

Abstract: Light intensity detecting circuits using reverse biased photodiodes are disclosed. Two photodiodes are fabricated with essentially the same structure in close enough proximity to each other on a single semiconductor substrate so that they both experience the same environment. In one scheme the cathode of the first photodiode is common with the anode of the second photodiode and an inverting terminal of an operational amplifier with negative feedback. A negative voltage is applied to the anode of the first photodiode and a positive voltage of the same magnitude is applied to the cathode of the second photodiode. The output of the operational amplifier is proportional to the incident light provided the intensity on each photodiode are proportional to each other. In another circuit one of either the anodes or cathodes of each diode is common and the other is input into the inverting terminal of a separate operational amplifier.