Chalcogenide glass materials for integrated infrared photonics

Abstract

Chalcogenide glasses (ChGs) are amorphous compounds containing the chalcogen elements (S, Se, Te) and exhibit wide infrared transparency windows. They are easy to synthesize in bulk and thin film forms and their compositional flexibility allows tuning of optical properties such as refractive index making them ideal for infrared photonics. We have studied the material attenuation in ChGs that arises due to the presence of impurities in the raw materials and established UV photolithography-based process flows that enable fabrication of chalcogenide glass waveguides and microresonators for near- and mid-IR wavelength ranges. Waveguides and optical resonators are key microphotonic elements for many on-chip applications such as telecommunications and chemical sensing. In this thesis, we show that scattering losses dominate in our ChG microphotonic devices while material attenuation from impurities is low. We demonstrate resonators coated with nanoporous polymers to improve their selectivity against target analytes for sensing applications. We exploit the photosensitivity of As2S3 glass to build silicon-based tunable photonic devices that offer post-fabrication tuning to optimize performance. Resonators also serve as a test platform for studying the effects of radiation on silicon and chalcogenide materials systems. Further, we propose new mid-IR microphotonic device designs using ChG materials and the challenges associated with measuring mid-IR devices along with solutions to address them. We employ input-to-output offsets, standard tapered waveguides, and a fiber collimator to improve mid-IR measurements and demonstrate transparent ChG waveguides with losses as low as 2.5 dB/cm. Finally, we propose a novel design that integrates PbTe detectors with ChG waveguides for on-chip mid-IR detection. Our simulations show that the use of a low-index spacer layer leads to a well-distributed field along the width of the detector due to a reduction in the effective index of the structure. We develop a fabrication process for waveguide-integrated detector designs and fabricate prototype structures that exhibit attenuation at telecom and mid-IR wavelengths. Such an integrated sensor design will enable the creation and deployment of low-cost remote sensor arrays with small footprints, and ultimately lead to "lab-on-a-chip" structures.