Porous silicon (PSi) has been recognized as an advantageous material for use in optical biosensors due to its large internal surface area, ability to form multilayer optical structures, and compatibility with standard silicon lithographic techniques. We demonstrate an order of magnitude improvement in small molecule detection sensitivity for on-chip PSi ring resonators and photonic crystal nanobeams compared to the same structures fabricated on silicon-on-insulator wafers. Moreover, we demonstrate that PSi optical structures can be exploited for mobile diagnostics by using a smartphone with no additional functional accessories to detect color changes in the PSi that result from molecule capture.
High Q/V (quality factor/mode volume) platforms enable simultaneous localization of light in space and time and have enabled enhanced performance metrics in applications such as optical signal processing, photovoltaics, optical sensing and optical trapping. Slotted photonic crystal nanobeams (SPCNs) are one type of high Q/V structure that support mechanical modes in addition to high Q optical modes, opening the door to favorable optomechanical properties. In this work, in-plane excitation of fundamental resonance modes in SPCNs with high optical quality factor and high values of optomechanical coupling strength is investigated towards the realization of a monolithic configuration that is compatible with photonic integrated chips. In-line and side- coupled excitation configurations are studied. Simulations suggest that the number of optical modes supported in the SPCNs and the transmission intensity of light in these modes depend strongly on coupling configuration. For high Q SPCNs, in-line coupling suppresses the fundamental optical mode. Side-coupling supports excitation of the fundamental optical mode, but suppresses even order modes in the cavity.
Bulk thermal emittance sources possess incoherent, isotropic, and broadband radiation spectra that vary from
material to material. However, these radiation spectra can be drastically altered by modifying the geometry of
the structures. In particular, several approaches have been proposed to achieve narrowband, highly directional
thermal emittance based on photonic crystals, gratings, textured metal surfaces, metamaterials, and shock waves
propagating through a crystal. Here we present optimized aperiodic structures for use as narrowband, highly
directional thermal infrared emitters for both TE and TM polarizations. One-dimensional layered structures
without texturing are preferable to more complex two- and three-dimensional structures because of the relative
ease and low cost of fabrication. These aperiodic multilayer structures designed with alternating layers of silicon
and silica on top of a semi-infinite tungsten substrate exhibit extremely high emittance peaked around the
wavelength at which the structures are optimized. Structures were designed by a genetic optimization algorithm
coupled to a transfer matrix code which computed thermal emittance. First, we investigate the properties of the
genetic-algorithm optimized aperiodic structures and compare them to a previously proposed resonant cavity
design. Second, we investigate a structure optimized to operate at the Wien wavelength corresponding to a
near-maximum operating temperature for the materials used in the aperiodic structure. Finally, we present a
structure that exhibits nearly monochromatic and highly directional emittance for both TE and TM polarizations
at the frequency of one of the molecular resonances of carbon monoxide (CO); hence, the design is suitable for
a detector of CO via absorption spectroscopy.
We explore an approach to enhance the efficiency of solar cells using photonic nanostructures for solar ther-mophotovoltaics. Our focus is on designing photonic nanostructures that can provide broadband absorption in a narrow angular range for solar thermophotovoltaic systems which do not employ sunlight concentration. We consider structures consisting of an aperiodic multilayer stack of alternating layers of silicon and silica on top of a thick tungsten layer. The layer thicknesses are optimized to maximize the angular selectivity in the absorp-tivity for both TE and TM polarizations. Using such an approach, we design structures with highly directional absorptivity for both polarizations.