Q-Factor-Based Level Design for Photonic ATM Switches∗

A photonic ATM switch based on wavelengthdivision multiplexing will include several lossy passive devices, erbium-doped fiber amplifiers, and semiconductor optical amplifiers (SOAs) in a cascade configuration for fast switching of ns order. Its level diagram, which is very different from those of optical transmission links, has not been adequately studied. This paper investigates the concept of basing the level design of the photonic asynchronous-transfer-mode (ATM) switch we are developing on its Q-factor. First, we derive formulation of the Q-factor in a single PD and a dual-PD in a Manchester-encoded signal, which has several merits in packet switching and that we believe will become popular in photonic packet switches. Using this formula, we show an example of the level-diagram design including the Q factor calculation in an optical combiner and distributor section without SOA in our photonic ATM switch. Next, we showed experimentally that the pattern effect in SOAs can be suppressed by using a Manchester-encoded signal. Finally, we confirm that the allowable minimum level diagram in the switch can be based on a simple Q calculation and easy measurement of a bit error rate (BER) in a back-to-back configuration when using a Manchesterencoded signal. These results show that basing the level design of photonic ATM switches on the Q factor is feasible when using a Manchester signals. This approach can be applied to various types of photonic packet switches. key words: Q factor, S/N, ATM, SOA