Decision-Directed Costas Loop Stable Homodyne Detection for 10-Gb/s BPSK Signal Transmission

This letter demonstrates decision-directed Costas loop stable homodyne detection for 10-Gb/s binary phase shift keying signal fiber-transmission of over 100 km utilizing frequency-stabilized several kilohertz spectral linewidth external cavity laser diodes (E-LDs). We design a phase-locked loop circuit that adopts an injection-current controlled E-LD as its local oscillator; its low phase error allows it to achieve the standard deviation of 1.9°. Owing to this phase-lock performance and the highly coherent light source, the receiver sensitivity approaches within 6 dB of the shot noise limit and the phase-locked loop recovers the optical carrier stably even if the waveform is distorted by the chromatic dispersion of 880 ps/nm after fiber transmission.