  Modern fiber-optic coherent communications employ advanced
spectrally-efficient modulation formats that require sophisticated narrow
linewidth local oscillators (LOs) and complex digital signal processing (DSP).
Here, we establish a novel approach to carrier recovery harnessing large-gain
stimulated Brillouin scattering (SBS) on a photonic chip for up to 116.82
Gbit/sec self-coherent optical signals, eliminating the need for a separate LO.
In contrast to SBS processing on-fiber, our solution provides phase and
polarization stability while the narrow SBS linewidth allows for a
record-breaking small guardband of ~265 MHz, resulting in higher
spectral-efficiency than benchmark self-coherent schemes. This approach reveals
comparable performance to state-of-the-art coherent optical receivers without
requiring advanced DSP. Our demonstration develops a low-noise and
frequency-preserving filter that synchronously regenerates a low-power
narrowband optical tone that could relax the requirements on very-high-order
modulation signaling and be useful in long-baseline interferometry for
precision optical timing or reconstructing a reference tone for quantum-state
measurements.
