<p><a>The quick, reliable, and sensitive detection of bacterial contamination is desired in areas such as counter bioterrorism, medicine, and food/water safety as pathogens such as<i> E. coli</i> can cause harmful effects with the presence of just a few cells. However, standard high sensitivity techniques require laboratories and trained technicians, requiring significant time and expense. More desirable would be a sensitive point-of-care device that could detect an array of pathogens without sample pre-treatment, or a continuous monitoring device operating without the need for frequent operator intervention.<br> <br> Optical microring resonators in silicon photonic platforms are particularly promising as scalable, multiplexed refractive index sensors for an integrated biosensing array. However, no systematic effort has been made to optimize the sensitivity of microrings for the detection of relatively large discrete analytes such as bacteria, which differs from the commonly considered cases of fluid or molecular sensitivity. This work demonstrates the feasibility of using high finesse microrings to detect whole bacterial cells with single cell resolution over a full range of potential analyte-to-sensor binding scenarios. Sensitivity parameters describing the case of discrete analyte detection are derived and used to guide computational optimization of microrings and their constituent waveguides, after considering a range of parameters such as waveguide dimension, material, modal polarization, and ring radius. The sensitivity of the optimized 2.5 µm radius silicon TM O-band ring is experimentally demonstrated with photoresist cellular simulants. A multiplexed optimized ring array is then shown to detect <i>E. Coli</i> cells in an experimental proof of concept.</a></p>

Silicon photonics as a one of the most promising photonic integration technologies has attracted many attentions in recent years. The major feature of this technology is its compatibility with complementary metal-oxide semiconductor (CMOS) processes which makes it possible to integrate optical and electronic devices in a same chip and reduce the cost significantly. Another reason of using silicon photonics is the high index contrast between the silicon core and silicon dioxide cladding which ensures the high density integration of photonic devices on a single chip. Monolithic integration with electronic and optical circuits makes silicon photonics technology suitable for numerous applications. One example is microwave photonics (MWP). MWP is an area that studies the interaction between microwave and optical signal for the generation, processing, control and distribution of microwave signals by means of photonics. Silicon photonics offers a reduction in footprint, losses, packaging cost and power dissipation in MWP systems. This research in this thesis is focused on the design and fabrication of the silicon photonic devices for MWP signal processing and generation. Four MWP systems based on silicon photonic devices are proposed and experimentally demonstrated. 1) A single pass-band frequency-tunable MWP filter based on phase-modulation to intensity-modulation conversion in an optically pumped silicon-on-insulator (SOI) microring resonator (MRR) is designed and experimentally demonstrated. In the proposed filter, a phase-modulated optical signal is filtered by the SOI MRR, to have one first-order sideband suppressed by the MRR notch. The phase-modulated optical signal is converted to an intensity-modulated single-sideband (SSB) signal and detected at a photodetector (PD). The entire operation is equivalent to a single pass-band filter. The frequency tunability is achieved by tuning the resonance wavelength of the MRR, which is realized by optically pumping the MRR. A single pass-band MWP filter with a tunable center frequency from 16 to 23 GHz is experimentally demonstrated. 2) A broadband optically tunable MWP phase shifter with a tunable phase shift using three cascaded SOI MRRs that are optically pumped is designed and experimentally demonstrated. A microwave signal to be phase shifted is applied to an optical single-sideband (OSSB) modulator to generate an optical carrier and an optical sideband. The phase shift is introduced to the optical carrier by placing the optical carrier within the bandwidth of one resonance of the three cascaded MRRs. The experimental results show that by optically pumping the cascaded MRRs, a broadband MWP phase shifter with a bandwidth of 7 GHz with a tunable phase shift covering the entire 360o phase shift range is achieved. 3) A multi tap MWP filter with positive and negative coefficients using a silicon ring resonator modulator (RRM) is proposed and experimentally demonstrated. The RRM is designed and fabricated to operate based on the carrier depletion effect. The positive and negative coefficients are obtained by using opposite slopes of the modulation transmission response of the RRM. Two filter responses with two and three taps are experimentally demonstrated, showing the proof-of-principle for frequencies up to 18 GHz. 4) An approach to generate microwave signal based on enhanced four wave mixing (FWM) in an active silicon waveguide (SiWG) is studied. This SiWG is designed and fabricated, and the use of the active SiWG for MWP frequency multiplication to generate a frequency-sextupled millimeter-wave signal is experimentally demonstrated. Thanks to a reverse-biased p-n junction across the SiWG, the conversion efficiency of the FWM is improved, which leads to the improvement of the microwave frequency multiplication efficiency.

<p>  </p> <p>A harmonic oscillator is a ubiquitous tool in various disciplines of engineering and physics for sensing and energy transduction. The degrees of freedom, low noise oscillation, and efficient input-output coupling are important metrics when designing sensors and transducers using such oscillators. The ultimate examples of such oscillators are quantum mechanical oscillators coherently transducing information or energy. Atoms are oscillators whose degrees of freedom can be controlled and probed coherently by means of light. Elegant techniques developed during the last few decades have enabled us to use atoms, for example, to build exquisite quantum sensors such as clocks with the precision of <1 second error over the lifetime of the universe, to store and transduce information of various forms and also to develop quantum processors. Similar to atoms, mechanical oscillators can also be controlled ultimately to their single vibrational quanta and be used for similar sensing and transduction applications.</p> <p><br></p> <p>In this thesis, we explore both atomic and mechanical systems and develop a toolbox to build an effective atom-light interface and light-oscillator interface for controlling such atomic and mechanical oscillators and use them in sensing and storage applications. Primarily, we study two disparate platforms: 1) rare-earth ions in solids integrated into photonic chips as a compact and heterogeneous platform and 2) nanoscopic and macroscopic oscillators interfaced with light and magnetic field to isolate them from environmental noise. </p> <p><br></p> <p>Rare earth (RE) ions in crystals have been identified as robust optical centers and promising candidates for quantum communication and transduction applications. Lithium niobate (LN), a novel crystalline host of RE ions, is considered as a viable material for photonic system integration because of its electro-optic and integration capability. This thesis first experimentally reports the activation and characterization of LN crystals implanted with Yb and Er ions and describes their scalable integration with a silicon photonic chip with waveguide and resonator structures. The evanescent coupling of light emitted from Er ions with optical modes of waveguide and microcavity and modified photoluminescence (PL) of Er ions from the integrated on-chip Er:LN-Si-SiN photonic device with quality factor of 104 have been observed at room temperature. This integrated platform can ultimately enable developing quantum memory and provide a path to integrate more photonic components on a single chip for applications in quantum communication and transduction.</p> <p><br></p> <p>Optomechanical systems are also considered as candidates for light storage and sensing. In this thesis, we also present results of the theoretical study of coherent light storage in an array of nanomechanical resonators. The majority of the thesis is focusing on an optomechanical sensing experiment based on levitation. An oscillator well isolated from environmental noise can be used to sense force, inertia, torque, and magnetic field with high sensitivity as the interaction with these quantities can change the amplitude or frequency of the oscillator’s vibration, which can be accurately measured by light. It has been proposed that such levitated macroscopic objects could be used as quantum sensors and transducers at their quantum ground states. They are also proposed as a platform to test fundamental physics such as detecting gravitational waves, observing macroscopic quantum entanglement, verifying the spontaneous collapse models, and searching for dark matter.</p> <p><br></p> <p>In particular, we consider superconducting levitation of macroscopic objects in vacuum whose positions are measured by light. We build an optomechanical platform based on a levitated small high reflective (HR)-coated mirror above a superconductor disk. We use this levitated mirror at ambient conditions to detect the magnetic field with a sensitivity on the order of <em>pT/sqrt(Hz).</em> Moreover, the levitated mirror is used as the end mirror of a Fabry–Pérot cavity to create an optical resonance that could be used to study coherent radiation pressure forces. The platform provides a sensitive tool to measure the various forces exerted on the mirror and it offers the possibility of the coherent optical trapping of macroscopic objects and precision gravity sensing. Moreover, we study the nonlinear dissipation and mode coupling of a levitated HR-coated magnetic mirror above a superconducting disk in vacuum conditions. We observe that by exciting one vibrational mode of the mirror, the vibrational noise of another mode can be significantly suppressed by a factor of 60. We attribute this unique noise suppression mechanism to the mode coupling and nonlinear dissipation caused by the driven magnetic inhomogeneity of the levitated object. Such a suppression mechanism can enable cooling certain modes independent of their detection and position in the spectrum, which may be promising for precision sensing applications.</p>