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A compact silicon nitride grating coupler with flexible bandwidth was demonstrated taking advantage of a basic grating integrated with a serially connected multistage multimode interference (MMI) filter. The spectral response could be tailored by varying the order of the MMI filter, without affecting the basic grating structure. The dependence of the spectral response of the proposed device on the order of the MMI stage was thoroughly investigated. As regards the fabricated grating coupler with a four-stage MMI filter, the observed spectral bandwidth was efficiently altered from 53 to 21 nm in the ?1550 nm spectral band.

An interrogation scheme based on optical power monitoring was proposed and implemented to demonstrate a compact photonic temperature sensor, which incorporates a tunable silicon resonator with a heating electrode, a single-wavelength light source, and a photodetector. The temperature is basically determined by tracking the notch of the resonator, which is displaced by the thermal effects. By utilizing the proposed interrogation scheme, which did not require any complex spectral scanning, the ambient temperature was successfully estimated with a resolution of better than 0.1 °C over the range of 20 to 50 °C, and the electrical power consumption was ~600 mW.