The information rate (IR) of a digital coherent transceiver is constrained by the inherent practical signal-to-noise ratio (SNR) limit. Coded modulation, which is the combination of multi-level modulation and forward error correction, aims to maximize the IR within this SNR envelope. While probabilistic constellation shaping has enhanced this methodology by providing an increase in IR over conventionally employed square quadrature amplitude modulation (QAM) formats, it is the ability to eloquently tune the per wavelength IR by varying the symbol probabilities that has gained this scheme significant traction within optical communications in recent years. As commercial line cards continue their evolution towards 100 GBd and to modulation formats beyond 64QAM, we discuss the merits of probabilistic shaping for high symbol rate digital coherent transceivers in the presence of a practical SNR limit.
We report on InP-based high power modified uni-traveling carrier (MUTC) photodiodes heterogeneously integrated on silicon on diamond (SOD) waveguides. Typical dark currents of MUTC photodiodes on SOD waveguides are 20 nA at - 5 V bias voltage. A 50-μm long photodiode has an internal responsivity of 1.07 A/W at 1550 nm wavelength. The bandwidths of photodiodes with active areas of 14×25 μm2, 14×50 μm2, 14×100 μm2 and 14×150 μm2 are 22 GHz, 16 GHz, 10 GHz and 7 GHz, respectively. The maximum output RF powers of 14×100 μm2 photodiodes are 13 dBm, 14.4 dBm and 15.3 dBm at 10 GHz, respectively. The maximum DC dissipated power is 0.67 W. To our knowledge, this is the first demonstration of III-V photodiodes integrated on SOD waveguides.
Recently, microwave photonic techniques have emerged to address the challenges that microwave systems face under high-frequency or wideband conditions. To a large extent, the performance of microwave photonic systems depends on the performance of individual optoelectronics devices, such as high power photodiodes. Here, we report a fullypackaged photodetector module based on InGaAs/InP modified uni-traveling carrier (MUTC) photodiode. The modules demonstrated a 3-dB bandwidth up to 50GHz and a record-high output power of 14.0 dBm at 50GHz.