Structured FBG filters for 10-Gb/s DPSK signal demodulation in single ended applications

Differential phase-shift keying (DPSK) demodulations operated by a structured fiber Bragg grating (FBG) filter and by a Mach–Zehnder delay interferometer (MZDI) in a single-ended configuration are compared. Experimental measurements at 10 Gb/s demonstrate that a specially designed FBG outperforms an integrated-optic MZDI of ∼4 dB and ∼3.5 dB in back-to-back and after 25-km propagation, respectively. Both demodulators show low polarization sensitivity and signal frequency detuning dependence, but only MZDI operating point requires a thermal control. FBG filter proves an interesting solution for DPSK demodulation in low-cost applications and, moreover, can be designed to match colorless requirements of wave division multiplexed passive optical network (WDM-PON) applications.

Research highlights
► A Fiber Bragg Grating (FBG) is employed as a DPSK demodulator at 10 Gb/s.
► The FBG mimics the reflectance of Mach–Zehnder delay interferometer.
► BER comparison with single-ended MZDI is made also after 25-km propagation.
► FBG demonstrate low-polarization sensitivity similar to actively-stabilized MZDI.
► FBG-based DPSK detectors are suitable for low-cost colorless WDM-PON ONUs.