Programmable Photonics integrated circuits 

     One advantage of the integrated photonics is the ability to realized a large-scale photonics integrated circuits. In our research, we focus on developing photonics integrated circuits which can be programed dynamically and accurately. The applications include quantum photonics and neuromorphic photonics. 

Silicon Nitride Waveguides for Reconfigurable Quantum Photonics

Ultra-thin Si-padded Si3N4 Waveguides for Low-loss Photonics

We proposed an ultra-thin Si-padded Si3N4 waveguide consisting of a very thin Si slab underneath a Si3N4 strip, separated by a SiO2 layer. The Si slab and the Si3N4 strip form a hybrid waveguide mode, where the mode field is both confined in these two structures. The measured waveguide propagation loss is 0.055 dB/cm and the bending loss is 0.09 dB per 900 bend, depending on the bending radius. Because part of the waveguide mode is distributed in the Si slab, this waveguide structure is potential for implementing low-loss and high-speed photonic integrated circuits.

Programmable N-by-N Photonic Integrated Circuits

In general, most optical quantum computations can be defined through an M×M unitary operation. Furthermore, any unitary operation can be implemented using a reconfigurable beam-splitter waveguide circuit with a triangular or rectangular topology. The reconfigurable network operates through tunable Mach-Zehnder interferometers (MZIs), with the principle involving tunable phase shifters deployed on waveguides. By adjusting the phase shifters of each MZI, any unitary linear operation can be accomplished.

Non-invasive Optoelectronic Probes for Monitoring Tunable 2-by-2 Mach-Zehnder Interferometers in Programmable Si Photonic Integrated Circuits

We present an integrated non-invasive optoelectronic probe for real-time monitoring the phase condition of a Si tunable 2×2 Mach-Zehnder-interferometer (MZI) beam splitter applied for a programmable photonic integrated circuit. This optoelectronic probe, made by an AC-coupled Wheatstone-bridge circuit, can detect the splitting ratio of the MZI beam splitter without affecting the light propagating in the device. The MZI is also integrated with current-controlled thermo-optic phase shifters for finely tuning the waveguide phase. Therefore, the phase condition of the MZI beam splitter can be observed and tuned by investigating the variable splitting ratio with respect to the driving current. A π-phase shift and measurement are accomplished. This optoelectronic optical probe can be monolithically integrated into an MZI-based programmable photonic integrated circuit for phase error pre-calibration and phase management. 

Reference: Bo-Xian Ke, Kai-Hong Lo, Da-Wei Tsai, and Ming-Chang M. Lee, “Non-invasively Monitoring Tunable 2-by-2 Mach-Zehnder Interferometers in Programmable Si Photonic Integrated Circuits”, IEEE Journal of Lightwave Technology, Vol.42, No.19, pp. 6857 - 6862, 1 Oct. 2024