Optimized Optical Filtering For 40 Gb/s/Channel Optical Differential Quadrature Phase Shift Key (DQPSK), In DWDM Systems For Acces Network

In recent years, several modulation formats have been suggested as alternatives to the commonly used non return-to-zero (NRZ) and return-to-zero (RZ). These include, carrier-suppressed RZ (CS-RZ) [i, ii ], duobinary [iii, iv], and optical differential quadrature phase shift key (DQPSK) . Due to its narrower spectra DQPSK is expected to provide improvements in terms of tolerance to chromatic dispersion (CD) and should allow increased spectral efficiency in dense wavelength division multiplexing (DWDM) systems. DQPSK modulation format is gradually becoming a research focus [i]. However, the relative performance of this modulation format strongly depends on the type of sys