THESIS
2013
xviii, 137 pages : illustrations ; 30 cm
Abstract
Lab-on-a-chip (LOC) devices are portable, easy-to-use and low-cost for refractive index
sensing and bioparticle sorting in tiny volume samples. Optofluidics combining integrated
photonics and microfluidics is a promising technology for LOC due to its features of
miniaturization, high sensitivity and mass production. In this thesis, we propose and
demonstrate silicon photonic device-based refractive index sensors and optical tweezers
arrays as building blocks for optofluidics.
On the refractive index sensor front, we propose coupled-resonator optical waveguide
(CROW)-based sensors for refractive index sensing using spatial domain detection. The
conventional optical sensors are typically based on resonance wavelength shift detection in
spectral domain. The measurements rely on bu...[
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Lab-on-a-chip (LOC) devices are portable, easy-to-use and low-cost for refractive index
sensing and bioparticle sorting in tiny volume samples. Optofluidics combining integrated
photonics and microfluidics is a promising technology for LOC due to its features of
miniaturization, high sensitivity and mass production. In this thesis, we propose and
demonstrate silicon photonic device-based refractive index sensors and optical tweezers
arrays as building blocks for optofluidics.
On the refractive index sensor front, we propose coupled-resonator optical waveguide
(CROW)-based sensors for refractive index sensing using spatial domain detection. The
conventional optical sensors are typically based on resonance wavelength shift detection in
spectral domain. The measurements rely on bulky and expensive equipment
(wavelength-tunable laser or spectrometer) which are not suitable for LOC applications.
The CROW sensors exhibit broadband transmissions with split modes corresponding to the
eigen states. In the spatial domain, the internal field distributions along the CROW show
distinguished patterns at different eigen states. Therefore, the refractive index change could be detected spatially by pattern recognitions at fixed probe wavelength. We fabricate
racetrack microring cavity CROW sensors in silicon-on-insulator (SOI) substrates. The light
scattering from each cavity is captured by an infrared camera and integrated as a pixel to
represent the internal field spatial distribution of the CROW. By identifying the pixelized
spatial patterns through the fourier transform algorithm, we demonstrate an 8-element CROW
sensor with a detection limit of 0.0082 RIU corresponding to 5% mass concentration change
of NaCl solutions. We also demonstrate proof-of-concept sensing experiment using
gaplessly coupled microdisk CROW on silicon nitride-on-silica substrates.
On the optical tweezers array front, we invent Silicon-on-insulator Multimode-interference
(MMI) waveguide-based ARrayed optical Tweezers (SMART) technique for
two-dimensional microparticle trapping and manipulation. The two-dimensional optical
tweezers or optical lattices are significant tools for trapping multiple particles simultaneously
and sorting particles by size or refractive index differences. The optical lattice generation
techniques (acousto-optic deflectors and holographic optical tweezers) usually require
electro-optical devices and sophisticated optics which cannot be integrated into a LOC system.
We utilize the self-imaging phenomena in the MMI waveguide to generate optical lattices.
We demonstrate arrayed trapping of 1μm- and 2.2μm-sized polystyrene particles in a
microfluidic cell with static fluidic. We simulate the multiple physical processes involved in
the SMART technique including optical force, thermal-induced flow and fluidic force using
the finite-element method. We demonstrate moving, splitting and combining of clusters of
microparticles by shaping the optical tweezers array. We also demonstrate 2.2μm
polystyrene particle fractionation in optical lattices generated by the SMART technique
assisted by a controllable microfluidic flow with a speed from ~2 μm/s to ~100 μm/s. We
demonstrate particle guiding along the optical lattice direction with up to ~12° relative to the
flow direction, particle blocking in a linear optical lattice and particle accelerations from ~20
μm/s (flow velocity) to ~60 μm/s in a non-uniform optical lattice.
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