Optical Manipulation and Sensing with Silicon Photonics
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CitationLin, Shiyun. 2013. Optical Manipulation and Sensing with Silicon Photonics. Doctoral dissertation, Harvard University.
AbstractOptical trapping enables the non-contact manipulation of micro and nanoparticles with extremely high precision. Recent research on integrated optical trapping using the evanescent fields of photonic devices has opened up new opportunities for the manipulation of nano- and microparticles in lab-on-a-chip devices. Considerable interest has emerged for the use of optical microcavities as “sensors-on-a-chip”, due to the possibility for the label-free detection of nanoparticles and molecules with high sensitivity. This dissertation focuses on the demonstration of an on-chip optical manipulation system with multiple functionalities, including trapping, buffering, sorting, and sensing. We demonstrate the optically trapping of polystyrene particles with diameters from 110 nm to 5.6 \(\mu m\) using silicon microrings and photonic crystal cavities. By integrating multiple microrings with different resonant wavelengths, we show that tuning the laser wavelength to the resonance wavelengths of different rings enables trapped particles to be transferred back and forth between the rings in a controllable manner. We term this functionality “buffering”. We furthermore demonstrate an integrated microparticle passive sorting system based on the near-field optical forces exerted by a 3-dB optical power splitter that consists of a slot waveguide and a conventional channel waveguide. In related work, we demonstrate an ultra-compact polarization splitter design leveraging the giant birefringence of silicon-on-insulator slot waveguides to achieve a high extinction ratio over the entire C band. We demonstrate trapping-assisted particle sensing, using the shift in the microcavity resonance induced by the trapped particle. We show that this permits the sensing of proteins via a binding assay approach, in which the presence of green fluorescent protein causes the particles to bind. By detecting the size distribution of particles clusters using the microcavity, we quantitatively detect the GFP concentration. In a complementary approach, we demonstrate a reusable and reconfigurable surface-enhanced Raman scattering (SERS) sensing platform. We use a photonic crystal cavity to trap silver nanoparticles in a controllable manner, and measure SERS from molecules on their surfaces. We anticipate that the on-chip sensing approaches we introduce could lead to various applications in nanotechnology and the environmental and life sciences.
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