Receiver sensitivity of type-II return-to-zero signals having finite extinction ratios

In this two-part paper, we develop expressions describing the receiver sensitivity of return-to-zero (RZ) signals having finite extinction ratios (ERs) and arbitrary duty cycles. Between the two known ways of modeling RZ signals, this work focuses on RZ pulses riding on a constant pedestal of optical power (hereinafter referred to as Type II). We find out that the sensitivity of a receiver limited by signal-dependent noise degrades as the duty cycle decreases. By contrast, an optimum duty cycle for the receiver sensitivity exists if signal-independent noise limits the receiver performance. As the duty cycle approaches 0, we discover that the signal-dependent noise dominates the signal-independent noise, regardless of the receiver used. We present the experimental results supporting our theoretical analysis.