Low-phase-noise clock recovery from NRZ signal and simultaneous NRZ-to-RZ format conversion

We propose and demonstrate an improved optoelectronic oscillator based on a dual-parallel Mach-Zehnder modulator for simultaneous low-duty-cycle and low-phase-noise clock recovery from NRZ signal and wavelength-preserved NRZ-to-RZ format conversion. A 25-GHz optical clock with a 25% duty cycle and a 22.5-dB extinction ratio is successfully extracted from the incident 25-Gb/s NRZ signal. Benefiting from the intrinsic property of the optoelectronic oscillator, an electrical clock with a 174-fs root-mean-square timing jitter (100 Hz-10 MHz) is also achieved. Simultaneously, error-free wavelength-preserved NRZ-to-RZ format conversion with a {-}{\rm 2}{\hbox{-}}{\rm dB} power penalty at a bit error rate of 10^-9 is demonstrated.