Ultralow-loss silica resonators and waveguides on a silicon chip

Abstract

Compared to fiber optic systems, on-chip optical devices provide reasonable optical performance and mechanical stability in a smaller footprint and at a lower cost. Such devices, including resonators and waveguides, have been applied in diverse areas of scientific research, including quantum information, nonlinear optics, cavity optomechanics, telecommunications, biodetection, rotation sensing, high stability microwave oscillators, and all-optical signal processing. As performance demands on these applications increase, resonators and waveguides with ultralow propagation loss become critical. In this thesis, we first demonstrate a new resonator with a record Q factor of 875 million for on-chip devices. The fabrication of our device avoids the requirement for a specialized processing step, which in microtoroid resonators has made it difficult to control their size and achieve millimeter- and centimeter-scale diameters. Attaining these sizes is important in applications such as microcombs. The resonators not only set a new benchmark for the Q factor on a chip, but also provide, for the first time, full compatibility of this important device class with conventional semiconductor processing. Meanwhile, we demonstrate a monolithic waveguide as long as 27 m (39 m optical path length), and featuring broadband loss rate values of (0.08 ± 0.01) dB/m measured over 7 m by optical backscattering. Resonator measurements show a further reduction of loss to 0.037 dB/m, close to that of optical fibers when first considered a viable technology. Scaling this waveguide to integrated spans exceeding 250 m and attenuation rates below 0.01 dB/m is discussed. This chip-based waveguide and resonator improve shock resistance, and afford the possibility of integration for system-on-a chip functionality. We finally demonstrate a highly sensitive nanoparticle and virus detection method by using a thermal-stabilized reference interferometer in conjunction with an ultrahigh-Q microcavity. Sensitivity is sufficient to resolve shifts caused by binding of individual nanobeads in solution down to a record radius of 12.5 nm, a size approaching that of single protein molecules. A histogram of wavelength shift versus nanoparticle radius shows that particle size can be inferred from shift maxima.