This thesis provides components for a minimally invasive mid-infrared light-delivery, sensing and detection system in silicon. Both Photonic Needles for deep-media light delivery and a CMOS-compatible waveguide-integrated detector at 3.7μm are explored in depth. Other integratable elements presented include ring resonators in the mid-infrared for gas absorption sensing and frequency comb generation, a MEMS weak electric field sensor, and wavelength sensitive gratings for directional coupling to/from the environment.
Chapter 1 provides a primer for mechanical, optical, and electrical concepts related to the work later presented in this text. The mechanical primer covers Euler bucking theory as well as an intuitive perspective on stiffness, elastic modulus, second moment of inertia, and beam bending. The optical primer covers Snell’s law, ring resonators, Fresnel equations, Fabry-Perot resonances and losses, distributed Bragg reflectors, Bragg gratings, and optical coupling losses. The electrical primer covers the Fourier transform of a pulse train, noise equivalent power, loss due to impedance mismatch, and RC limited bandwidth. In Chapter 2 we demonstrate a new platform for minimally invasive, light-delivery probes leveraging the maturing field of silicon photonics, enabling massively parallel fabrication of photonic structures. These Photonic Needles probes have sub-10μm cross-sectional dimensions, lengths greater than 3mm-- surpassing 1000 to 1 aspect ratio, and are released completely into air without a substrate below. We show the Photonic Needles to be mechanically robust when inserted into 2% agarose. The propagation loss of these waveguides is low-- on the order of 4dB/cm. In Chapter 3 we demonstrate a CMOS-compatible mid-infrared detector at wavelengths ranging from 3.36 to 3.74μm by exciting mid bandgap states in a sulfur-doped silicon waveguide with responsivities up to 30mA/W. We also measure a noise equivalent power (NEP) of 3e-10W/√Hz at 3.7μm wavelength and 30V reverse bias voltage. Chapter 4 presents other device elements that could also be integrated into this same silicon on insulator (SOI) platform for long wavelengths with preliminary and/or simulation results for each. These elements could be implemented as part of future projects. Chapter 5 provides veins of promising future research directly related to the work from Chapters 2 and 3.