Analytical characterization of SOA-based optical pulse delay discriminator

Semiconductor optical amplifier (SOA)-based optical timing extraction and clock-recovery schemes offer compact size, low operating power, and added possibility for integration into an all-optical circuitry. In this paper, we analyze a device that could measure the relative delay between counterpropagating pulses incident on an SOA. Unlike previous designs based on differential photodiodes, our optical pulse delay discriminator (OPDD) uses the voltage difference between two contacts on the SOA. We therefore eliminate the two photodiodes and two optical couplers, making integration far easier. After giving a qualitative description of the operation of the proposed design, we carry out a comprehensive analytical analysis of the operation of the device performance. At each stage, we demonstrate the accuracy of the derived approximate formulas. An analytical expression for the transient response of OPDD shows it to be exponential with a time constant set by the carrier-recovery lifetime. We show that it is possible to reliably measure the incident delay between counterpropagating, periodic pulse trains by measuring the mean value (or low-pass-filtered value) of the induced voltage difference. Our analysis shows the OPDD has excellent linearity.