Range Of Incident Directions Research Articles

Metasurface-enhanced transparency

We consider the problem of light transmission from a high refractive index medium into a low index environment. While total internal reflection severely limits such transmission in systems with smooth interfaces, diffractive metasurfaces may help out-couple light that enters an interface at blazing angles. We demonstrate that the profile of the structured interface can be numerically optimized to target a particular emission pattern. Our study suggests that while metasurfaces can help to out-couple light from a range of incident directions, there exists a universal limit for total transmission efficiency that depends only on the dielectric properties of the two materials and is independent of the profile and the composition of the metasurface coupler.

Negative result of multi-frequency topological derivative based imaging in limited-aperture inverse scattering problem

A negative result of topological derivative based imaging of thin, rectangular shaped inhomogeneity with the least range of incident directions was obtained. Using the obtained result, we add a condition for the application of topological derivatives to the limited-aperture inverse scattering problem.

Polarization-independent narrow bandpass filter and narrow transmission-angle filter based on photonic heterostructures composed of single-negative materials

We propose a photonic heterostructure consisting of two substructures composed of single-negative materials. Calculating the transmission spectra, we find that only the electromagnetic wave within a narrow bandpass and a narrow range of incident directions can be transmitted through this structure. Such structure can be used as a polarization-independent frequency filter integrated with a direction filter.

Mechanically coupled ears for directional hearing in the parasitoid fly Ormia ochracea.

An analysis is presented of the mechanical response to a sound field of the ears of the parasitoid fly Ormia ochracea. This animal shows a remarkable ability to detect the direction of an incident sound stimulus even though its acoustic sensory organs are in very close proximity to each other. This close proximity causes the arrival times of the sound pressures at the two ears to be less than 1 to 2 microseconds depending on the direction of propagation of the sound wave. The small differences in these two pressures must be processed by the animal in order to determine the incident direction of the sound. In this fly, the ears are so close together that they are actually joined by a cuticular structure which couples their motion mechanically and subsequently magnifies interaural differences. The use of a cuticular structure as a means to couple the ears to achieve directional sensitivity is novel and has not been reported in previous studies of directional hearing. An analytical model of the mechanical response of the ear to a sound stimulus is proposed which supports the claim that mechanical interaural coupling is the key to this animal's ability to localize sound sources. Predicted results for sound fields having a range of incident directions are presented and are found to agree very well with measurements.

Conjugate generation and beam steering by nearly degenerate four-wave mixing in waveguide arrays

We analyze the frequency-shifted conjugate beam generated by nearly degenerate four-wave mixing in an array of single-mode waveguides. We show that if the array sufficiently samples the signal beam, a high-quality conjugate will be generated when the pump beams are counterpropagating. The ability of a waveguide mode to couple to incoming beams over a range of incident directions relaxes the strict phase-matching requirement present in bulkmedia four-wave mixing. A shift in the propagation direction of one of the pump beams changes the propagation direction of the generated beam while maintaining the spatial phase coherence.