On-Chip Monitoring Phase Conditions of Tunable Mach-Zehnder Interferometers via Integrated Microelectromechanical-System Optical Probes

Integrated microelectromechanical-system (MEMS) optical probes were developed to dynamically monitor the waveguide power of tunable Mach-Zehnder interferometers (MZIs) for phase error calibration in programmable photonic integrated circuits. These optical probes, consisting of movable waveguides actuated by MEMS cantilever beams, can selectively tap waveguides within the circuit. The tapped waveguide power is emitted through a grating coupler on the probe and evaluated by analyzing the pixel intensity of the light-spot image captured by an IR camera. By extracting the relationship of the waveguide power varying with the driving current of the phase shifter, the initial phase condition of the MZI can be determined with an accuracy of 4.7 degrees. The MEMS optical probe is 45 mu m wide and 60 mu m long with an actuation distance of 300 nm. Since the optical probe can be dynamically switched between the coupled and decoupled states, it does not disturb the operation of photonic circuits. Therefore, this approach is ideal for phase calibration without interfering with the overall functionality of the photonic circuits.