PAM Transmission System with a DAC and ADC

A packaged Silicon Photonic Traveling Wave Mach-Zehnder modulator operating at 1310 nm is presented and studied. The modulator is a series push-pull device and requires a bias applied to the common n-doped region. Effects of varying the bias voltage on the modulator’s Vπ, bandwidth, and on chip-insertion loss are studied, and its impact on transmission performance are experimentally investigated for PAM-4 and PAM-8 formats at a throughput of 112 Gb/s, over varying distances of 0, 2, 10 and 20 km. Residual chromatic dispersion is shown to have no impact on performance up to 20 km.

The PAM RF driving waveform is generated by an 8-bit digital-to-analog converter, while direct detection is done with a PIN+TIA followed by an 8-bit analog-to-digital converter. This IM/DD system utilizes digital signal processing with transmitter spectral compensation and receiver residual equalization. The performance impact for a varying number of transmitter pre-compensation taps and receiver equalization taps is studied, which has a direct impact on the transceiver’s power consumption. Using PAM-4, a BER below the FEC limit is obtained for either combinations of (transmitter, receiver) tap lengths: (19,19), (7,27), or (35,7), allowing flexibility in power consumption distribution.