Low noise amplifiers for optical heterodyne receivers

This paper presents the results of a theoretical study of low noise amplification techniques for wide bandwidth optical and infrared heterodyne receivers; noise figures of 1.5 dB or less over a bandpass of 10 MHz to 1.5 GHz are the goal. Data for the state-of-the-art transistor amplifiers is presented showing that the best obtainable noise figure is 1.5 dB. Other methods of obtaining the low noise figure are presented with emphasis on wide bandwidth parametric and photoparametric amplifiers. Low noise is easily obtainable with these devices but wide bandwidths are hard to obtain, thus the design criteria for wide bandwidth operation are discussed. Theoretical data is presented showing gain as a function of diode capacitance, resistance, signal frequency and idler frequency. Finally, the feasibility of these devices for use in a heterodyne receiver is discussed.