Effect of Chirped Dispersion and Modal Partition Noise on Multimode VCSEL Encoded With NRZ-OOK and PAM-4 Formats

Chirp-dispersion and data transmission analyses of the multimode vertical-cavity surface-emitting laser (MM-VCSEL) with a 7.5-μm oxide-confined aperture and a root-mean-square spectral linewidth of 1 nm is performed for intra-data-center application. For directly modulating the non-return-to-zero on-off keying (NRZ-OOK) and the 4-level pulse amplitude modulation (PAM-4) data streams, an optimized bias current of 17 mA and a data amplitude of 800 mV are selected to provide the MM-VCSEL with an output optical power of 6.1 mW and a transverse mode number of 17. Such an optimized operation enables the MM-VCSEL with a differential resistance of 45.3 Ω to approach the impedance matching by driving the circuit such that the -3-dB bandwidth can be achieved to 23.8 GHz. The relative intensity noise and mode-partition-noise of the MM-VCSEL are analyzed to perform the optimized NRZ-OOK/PAM4 data encoding. By utilizing the pre-emphasis technique to compensate for the intensity and phase variation, the encoded NRZ-OOK and PAM-4 can be respectively promoted to 61 Gbit/s and 96 Gbit/s in the back-to-back (BtB) case. After passing through the 100-m OM5 multi-mode-fiber (MMF) link to suffer the severe modal dispersion, the data rate would respectively degrade to 45 Gbit/s (or 4.5 Gbit·km/s) and 70 Gbit/s (or 7 Gbit·km/s) for OOK and PAM-4 transmission.