By J. Koscinski
The key system design parameters for analog fiber optic systems are their noise and distortion specifications. Both the optical transmitter and optical receiver have the potential to significantly limit the link's noise and distortion performance. A thorough system analysis first requires establishing the individual noise and distortion parameters for the laser transmitter and optical receiver, and secondly, examining the complete link's (noise and distortion) performance over the required range of optical loss budgets.
Noise performance of an RF optical link may be limited by either the transmitter (laser noise) or the optical receiver noise depending on the optical loss budget. Additionally, there are several independent noise sources contributing to the optical receiver noise. These are referred to as the "quantum" and "circuit" noise. Distortion is introduced primarily in the optical source (laser). However, when high optical powers are delivered into the optical receiver, the receiver may also generate significant distortion. The focus of this paper will be to 1) quantify these noise and distortion parameters for the laser transmitter and optical receiver; and then, 2) apply these system performance parameters by analyzing an optical link over a range of optical loss budgets.