RESUMEN
Optical phased arrays (OPAs) with phase-monitoring and phase-control capabilities are necessary for robust and accurate beamforming applications. This paper demonstrates an on-chip integrated phase calibration system where compact phase interrogator structures and readout photodiodes are implemented within the OPA architecture. This enables phase-error correction for high-fidelity beam-steering with linear complexity calibration. A 32-channel OPA with 2.5-µm pitch is fabricated in an Si-SiN photonic stack. The readout is done with silicon photon-assisted tunneling detectors (PATDs) for sub-bandgap light detection with no-process change. After the model-based calibration procedure, the beam emitted by the OPA exhibits a sidelobe suppression ratio (SLSR) of -11â dB and a beam divergence of 0.97° × 0.58° at 1.55-µm input wavelength. Wavelength-dependent calibration and tuning are also performed, allowing full 2D beam steering and arbitrary pattern generation with a low complexity algorithm.
RESUMEN
An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium phosphide based photonic integrated circuit and commercial off-the-shelf electronic components. As an input reference, a stable microresonator-based optical frequency comb with a 50-dB span of 25 nm (~3 THz) around 1550 nm, having a spacing of ~26 GHz, was used. A widely-tunable on-chip sampled-grating distributed-Bragg-reflector laser is offset locked across multiple comb lines. An arbitrary frequency synthesis between the comb lines is demonstrated by tuning the RF offset source, and better than 100Hz tuning resolution with ± 5 Hz accuracy is obtained. Frequency switching of the on-chip laser to a point more than two dozen comb lines away (~5.6 nm) and simultaneous locking to the corresponding nearest comb line is also achieved in a time ~200 ns. A low residual phase noise of the optical phase-locking system is successfully achieved, as experimentally verified by the value of -80 dBc/Hz at an offset of as low as 200 Hz.
RESUMEN
Germanium-on-silicon thermo-optic phase shifters are demonstrated in the 5 µm wavelength range. Basic phase shifters require 700 mW of power for a 2π phase shift. The required power is brought down to 80 mW by complete undercut using focused ion beam. Finally an efficient thermo-optic phase shifter is demonstrated on the germanium on SOI platform. A tuning power (for a 2π phase shift) of 105 mW is achieved for a Ge-on-SOI structure which is lowered to 16 mW for a free standing phase shifter.