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A Novel Method of Biosensing Using a Temperature Invariant Microring Resonator
[Thesis]. Manchester, UK: The University of Manchester; 2016.
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Abstract
In this thesis, simulations of two novel features of a serially cascaded micro-ring resonatorare presented. The thesis firstly describes the simulation of a novel, silicon on insulator(SOI) method to determine the refractive index change of a covering analyte by theextraction of the refractive index change information in the time domain. Secondly a novelarrangement of the serially cascaded micro-rings has the effect of producing a null insteadof a peak in the Vernier enhanced resonant spectrum. The null feature, as well as theenhanced sensitivity of the sensor, allows the sensor to be used as an intensityinterrogating device. The development of these applications using ring resonator physicsis achievable, out-of-lab, by the application of photonic software.Finite difference time domain (FDTD), beam propagation method (BPM), finite element(FE) and eigenmode expansion (EME) methods were all used in the simulateddevelopment of the sensor. As a result of the dual ring resonator arrangement, thetemporal output undergoes a wavelength (or frequency) shift from the micrometre (orTeraHertz) to the centimeter (or GigaHertz) range of frequencies. This allows therefractive index information to become available for transmission in the cm wavelengthrange over a standard wireless network. The latter could be realized by integration of aphoto-detector and antenna into the final design. The sensor output is invariant to anystructural or temperature changes applied to both rings.Two sensors based on the same design, but having different fabrication methods, aresimulated. Models of the rib and ridge structures are realized by using optical simulationsoftware. The data obtained from these simulations are then used to plot the ring resonatoroutputs in MATLAB. The design can be applied for either bulk (homogeneous) or surfacesensing. Only homogeneous sensing, in the form of a uniform refractive index coverchange, is simulated in this thesis. The spectral sensitivity of the rib based design, withoutVernier enhancement, is 87.65nmRIU-1, while the spectral sensitivity of the ridgewaveguide, without Vernier enhancement, is 422nmRIU-1. The Vernier enhanced spectralsensitivity of the rib design is 6415nmRIU-1 and the limit of detection is 12.47x10-6 RIU.The temporal sensitivity of the ridge is 1.9418μsec RIU-1. The rib temporal sensitivity wasnot calculated but it is expected to be ~ five times less sensitive than the non Vernierenhanced ridge design.Titanium Nitride (TiN) heaters were also included over the coupling regions of the dualring resonators. The effect of the heaters on the dual ring resonant wavelength and on thesingle ring spectral shift were also simulated using a multi-physics utility of the appliedFEM and BPM software. With the heater at 1.28μm above the resonator couplingwaveguides, a single ring spectral shift of 717pm was exhibited by this simulation. For theheater positioned at 250nm above the coupling waveguides, a single ring spectral shift of2.89nm was exhibited.Finally the fabricated designs, which are based on the models of the simulation data, werecharacterized and the results compared to the predicted outputs generated by the models ofthe Temperature Invariant Modulated Output Sensor (TIMOS).