A Broadband Optical Ring Resonator for Absorption and Refractive Index Detection
Oates, Thomas Christopher
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Optical ring resonators have been studied in recent years as chemical sensors. Conventionally, these devices are operated by means of tracking a single resonance wavelength through use of a finely tunable laser source. This wavelength will shift as a result of changing resonator conditions, such as a refractive index (RI) shift resulting from sample analyte activity. In this work, an alternative approach to the conventional ring resonator methods is presented. This approach utilizes a `broadband' (relative to a monochromatic laser) light source such as a light emitting diode. Results are presented for both absorption and RI detection. While the demonstrated absorbance enhancement for surface-active analytes is theoretically anticipated, the observed RI sensitivity exceeds expectations. Due to multiple optical mechanisms that are simultaneously affected by an RI shift, detection limits on the order of 10<super>-6</super> RIU (refractive index units) are presented using Fourier-transform based extraction of interference components from output spectra. Additional device characterizations are performed for a number of variables, including wall thickness, fabrication method, detector resolution, and dynamic range. Through study of these new methods, certain advantages become clear. While one is the ability to take absorbance and RI measurements with the same device, perhaps the most significant advantage is the compatibility these methods have with lower quality resonators, such as those which could be mass-produced. With these aspects in mind, potential absorption and RI based applications are probed further. Low-cost and/or portable devices are proposed, as well as improvements on classical analytical methods and biosensing applications.
- Chemistry