Start-Bit Detection and Gate-Pulse Generation Using Phase-Modulated Preamble for Asynchronous Packet Processing

Start-bit detection and a single gate pulse generation scheme scalable to high-speed operation for asynchronous packet processing have been achieved. It is based on phase-modulated two-bit preamble for a coder and one-bit-delayed detection combined with a balanced photodetector as exclusive or (xor) function for a decoder. By using pi/2 phase-shifted first-bit and a pi/2 phase-shifted one-bit delay line, a single gate pulse can be generated with high speed, regardless of packet period. We have successfully achieved the single gate-pulse generation with bit rate of 10.72 Gb/s and various packet periods from 12.8 to 120 ns. Amplitude of the gate pulse was almost constant with fluctuation of plusmn5%. Suppression ratio of a gate pulse could be improved up to 9.5 dB via nonlinear absorption characteristics of an electroabsorption modulator. Autonomous gating operation for an optical digital-to-analog converter was also verified for two-bit operation