Optical waveguides using a visible transparent nitride were developed to perform fluorescence measurement on a chip. Through finite difference time domain (FDTD) design, the exciting green light was guided by the micron-scale ridge waveguide, while its evanescent wave was expanded outside the waveguide surface and capable to efficiently excite the fluorescent molecules that were approaching the waveguide facets. Since the waveguide was centimeters long, it has a longer fluorescence excitation path comparing to traditional samples prepared for microscopy measurements. As result, the waveguide device can excite stronger fluorescent signals. In addition, the nitride waveguide was prepared by the complementary metal–oxide–semiconductor (CMOS) process thus enabling high volume manufacturing and reducing the cost of the device fabrication.
The AlN waveguide was then integrated with a microfluidic devices to experimentally demonstrate real-time fluorescence detection. Solution samples with different dye concentrations were sequentially injected into the microfluidic chamber. By recording the emission signals, we showed that the fluorescent signals were consistently amplified as the dye concentrations increased. In addition, real-time fluorescence detection with a response time less than seconds was achieved. The developed waveguide based fluorescence measurement provides a new miniaturized platform for low cost and highly accurate point-of-care application.
Tunable photonic circuits were demonstrated by using ferroelectrics that had large electro-optic effect. The photonic circuits were fabricated by complementary metal–oxide–semiconductor (CMOS) technology thus enabling their integration with the present microelectronics for high speed signal modulation. From the scanning electron microscopy and energy-dispersive X-ray spectroscopy, we showed the photonic devices, including the optical waveguides, had sharp waveguide edges and interfaces. A sharp fundamental waveguide mode was observed over a broad spectral range. Tunability using Pockels effect were experimental results. Our device paves the way for ultra broadband integrated photonics critical for optical computing.
In-situ gas analysis was demonstrated using a mid-infrared (mid-IR) microcavity. Optical apertures were made of ultrathin silicate membranes using the complementary metal-oxide-semiconductor (CMOS) process. Fourier transform infrared spectroscopy (FTIR) shows that the silicate membrane is transparent in the range 2.5 - 6.0 μm, overlapping with gas absorption lines and therefore enables gas detection applications. CH4, CO2, and N2O were selected as analytes due to their strong absorption bands corresponding to functional group stretching: C-H, C-O, and O-N, respectively. A short response time of subsecond and high accuracy of gas identification were achieved. The chip-scale mid-IR sensor is a new platform for an in-situ, remote, and embedded gas monitoring system.