Receiver sensitivity of type-I 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 the RZ signal composed of strong and weak pulses, which represent marks and spaces, respectively (hereinafter referred to as Type I). Using our derived expressions, we show that the receiver sensitivity of a Type-I RZ signal is independent of the duty cycle if the system performance is limited by signal-dependent noise. Otherwise, there exists an optimum duty cycle for receiver sensitivity. We also quantitatively discuss the varying impact of finite ER on the receiver sensitivity for different duty cycles. We present the experimental results supporting our theoretical analysis.