DAC-Less 32-GBd PDM-256-QAM Using Low-Power InP IQ Segmented MZM

We demonstrate DAC-less generation and transmission of 256-quadrature amplitude modulation signals at a symbol rate of 32 GBd using an indium phosphide segmented Mach-Zehnder modulator with 15 active sections and dedicated BiCMOS driver arrays. The linear quantization characteristic of the segmented modulator with 4-bit resolution allows the generation of spectrally efficient modulation formats without any transmitter side signal processing. The chip power consumption of 1.64 W translates into the record-low energy per bit of 6.4 pJ/b. Back-to-back performance is evaluated and two different low-density parity check codes enable error-free transmission over 80 and 120 km with a net data rate of 320 and 240 Gb/s, respectively.