All-optical clock extraction from 40-Gbit/s NRZ data using cascaded long-period fiber grating
All-optical clock extraction from a 40-Gbit/s NRZ input signal is demonstrated using a cascaded long-period fiber grating (CLPG) and a mode-locked fiber ring laser. The CLPG has a MachZehnder configuration with two arms along the core and cladding regions. Using the difference in propagation delay between two arms, the non-return-to-zero (NRZ) signal is converted to the pseudo-return-to-zero (PRZ) signal. To obtain repetitive pulses as a clock signal from the PRZ signal, a ring laser with a semiconductor optical amplifier (SOA) is used. Subsequently, the measured carrier-to-noise ratio (CNR) of the PRZ and clock signals are enhanced up to 30dB and 31dB, respectively, compared to that of the original NRZ signal. Also, the clock signal centered at 40GHz has a low timing jitter of  40Gbit/s due to its small time delay between the core and cladding regions.
all-optical clock extraction cascaded long-period fiber grating (clpg) mode-locked fiber ring laser pseudo-return-to-zero (prz) optical data processing nrz-to-prz converter clock component