Photoparametric amplifier

This paper compares the spot signal-to-noise ratio of a semiconductor microwave p-n junction photodiode operated as, 1) a simple reverse-biased photodiode, and 2) a photodiode with integral parametric amplification. The gain and noise properties of the photoparametric diode are expressed in terms of the gain and noise of a hypothetical amplifier coupled to the simple (nonparametric) photodiode. For the simple photodiode, the signal-to-noise ratio is an increasing function of the Q of the diode at the signal frequency. For a suitably designed high-Q photodiode, operation as a nondegenerate photoparametric diode, with properly chosen idler and pump frequencies, can yield noise figures for the equivalent hypothetical amplifier as low as a few tenths of a decibel. One advantage of operation as a photoparametric amplifier is that a circulator is not needed. Another is that it is not necessary to pump the diode hard to get gain. There are also certain advantages in broadbanding.