A $Q$ -Factor Enhanced Optoelectronic Oscillator for 40-Gbit/s Pulsed RZ-OOK Transmission

By using a Mach-Zehnder intensity modulator (MZM)-based Q-factor enhanced 40-GHz optoelectronic oscillator (OEO) loop, a self-starting pulsed encoder is demonstrated to generate 40-Gbit/s return-to-zero on-off-keying (RZ-OOK) data-stream. By nonlinearly driving the MZM with an OEO circuitry via a proper setting on the intra-loop delay, both the RF and optical output of the OEO at 40 GHz can be extracted to deliver the clock with a Q-factor of up to 2×10⁸, and trigger the synthesizer-free 40-Gbit/s RZ-OOK data-stream. The maximal output power and the carrier-to-noise ratio of the RF output from the OEO are 20 dBm and 62 dB, respectively. Moreover, the single side-band phase noise is suppressed to -120 dBc/Hz at 100-kHz offset frequency by lengthening the single-mode fiber in the OEO loop up to 900 m. In addition, the pulsed RZ carrier with a pulsewidth of 10.5 ps provides a jitter as low as 120 fs and an on/off extinction ratio of 7.7 dB, which is particularly suitable for the RZ-OOK transmission at 40 Gbit/s. The back-to-back transmitted synthesizer-free 40-Gbit/s RZ-OOK data with a pattern length of 2²³-1 reveals a receiving power sensitivity of -15.2 dBm at the requested bit error rate of 10^-9.