Multifunctional mid-infrared photonic switch using a MEMS-based tunable waveguide coupler.

We demonstrate a multifunctional photonic switch on silicon-on-insulator platform operating at the mid-infrared wavelength range (3.85-4.05 µm) using suspended waveguides with sub-wavelength cladding and a micro-electro-mechanical systems (MEMS) tunable waveguide coupler. Leveraging the flip-chip bonding technology, a top wafer acting as the electrode is assembled above the silicon-on-insular wafer to enable the electrostatic actuation. Experimental characterizations for the functions of the proposed device include (1) an optical attenuator with 25 dB depth using DC voltage actuation, (2) a 1×2 optical switch with response time of 8.9 µs and -3dB bandwidth up to 127 kHz using AC voltage actuation, and (3) an on-chip integrated light chopper with the comparable performance of a commercial rotating disc light chopper.

Integration of MEMS IR detectors with MIR waveguides for sensing applications.

Waveguides have been utilized for label-free and miniaturized mid-infrared gas sensors that operate on the evanescent field absorption principle. For integrated systems, photodetectors based on the photocarrier generation principle are previously integrated with waveguides. However, due to the thermal excitation of carriers at room temperature, they suffer from large dark currents and noise in the long-wavelength region. In this paper, we introduce the integration of a MEMS-based broadband infrared thermopile sensor with mid-infrared waveguides via flip-chip bonding technology and demonstrate a proof-of-concept gas (N2O) sensor working at 3.9 µm. A photonic device with input and output grating couplers designed at 3.72 µm was fabricated on a silicon-on-insulator (SOI) platform and integrated with a bare thermopile chip on its output side via flip-chip bonding in order to realize an integrated photonic platform for a myriad range of sensing applications. A responsivity of 69 mV/W was measured at 3.72 µm for an 11 mm waveguide. A second device designed at 3.9 µm has a 1800 ppm resolution for N2O sensing.

Development of a Highly Sensitive Humidity Sensor Based on a Piezoelectric Micromachined Ultrasonic Transducer Array Functionalized with Graphene Oxide Thin Film.

A novel relative humidity sensor that is based on a linear piezoelectric micromachined ultrasonic transducer (pMUT) array was proposed and microfabricated for high sensitivity, fast response, and good stability. The humidity-sensitive graphene oxide (GO) film was deposited on the pMUT array with a facile drop-casting method and characterized by scanning electron microscope (SEM), atomic force microscope (AFM), and Fourier transform infrared spectrum (FTIR). With the humidity level ranging from 10% to 90% RH, the sensor exhibited a high sensitivity of 719 Hz/% RH and an extremely high relative sensitivity of 271.1 ppm/% RH. The humidity-sensing results also showed good short-term repeatability and long-term stability, fast response and recovery, and low hysteresis. Moreover, the temperature coefficient of frequency (TCF) of the present humidity sensor was investigated and it could be easily compensated owing to the pMUT array structure design. This work confirmed that the GO functionalized pMUT is an excellent candidate in humidity detection and it may enable many potential applications, such as ultrasensitive mass detection and simultaneous detection of multiple parameters.