Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1993-05-25
1994-04-19
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
2502141, H01J 4114
Patent
active
053047940
ABSTRACT:
The present invention utilizes the internal photovoltaic effect of a GaAs SFET to mix an RF modulated optical signal with a microwave signal. As those skilled in the art will readily recognize, a GaAs MESFET generically comprises an n layer of GaAs (channel) deposited on semi-insulating GaAs (substrate). Source, gate and drain electrodes are then formed on the channel with the gate acting as a Schottky barrier. In this standard MESFET, the difference in doping between the channel and substrate produces a potential barrier. It has been found that when the device is illuminated, the potential barrier is reduced in the region between the source and the gate and drain and the gate. This reduced potential barrier allows more drain current to flow from the device. It has been found that this drain current photoresponse is highly non-linear with respect the gate voltage applied to the device and therefore, it may be used to mix RF modulated optical signals with microwave signals. Accordingly, the present invention uses this effect to mix an optical signal directly or indirectly delivered to the MESFET with an RF signal so as to produce an IF signal.
REFERENCES:
patent: 4546249 (1985-10-01), Whitehouse et al.
patent: 5157357 (1992-10-01), Katoh
Malone Steven A.
Paolella Arthur C.
Anderson William H.
Nelms David C.
Shami K.
The United States of America as represented by the Secretary of
Zelenka Michael
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