The use of an optical local oscillator for coherent detection with a photodiode can significantly reduce the responsivity of the detector because of saturation effects. Consequently, local-oscillator shot-noise-limited operation of the detector may not be possible. This effect is analyzed and formulations are developed for the optimum optical local-oscillator power level and the resultant maximum possible signal-to-noise ratio in terms of parameters derived from the photodiode current versus the optical power response curve. An effective heterodyne responsivity that can be used as a part of the specifications when one is procuring photodiodes for use in coherent detection systems is defined.
© 1995 Optical Society of America
Original Manuscript: September 20, 1993
Revised Manuscript: August 8, 1994
Published: February 20, 1995
J. Fred Holmes and Badih J. Rask, "Optimum optical local-oscillator power levels for coherent detection with photodiodes," Appl. Opt. 34, 927-933 (1995)