Chip-Scale, Optical-Frequency-Stabilized PLL for DSP-Free, Low-Power Coherent QAM in the DCI

We demonstrate a DSP-free 16-QAM/50GBd link based on independent transmit and LO frequency-stabilized ultra-narrow-linewidth SBS lasers, with ∼40Hz integral linewidths and 7×10
⁻¹⁴
fractional frequency stability. The low-BW optical-frequency-stabilized-PLL with 3×10
⁻⁴
rad
²
phase error operates within 1% of DSP and self-homodyne.