Jad Salman — Page 2

arXiv2018

Mid-infrared optics using dielectrics with refractive indices below unity

Conventional transparent materials at optical frequencies have refractive index values (n) greater than unity -- most commonly between about 1 and 4. This paper explores optical phenomena made possible by using materials with refractive indices less than unity. We focus primarily on fused silica (SiO2), a polar dielectric with strong phonon resonances in the mid infrared that result in a spectral region in which n < 1 with modest optical loss. Using this ubiquitous easy-to-deposit material, we demonstrate infrared-frequency external reflection, frustrated external reflection, and direct coupling to surface plasmon polaritons from free space. Our work suggests that materials with refractive indices below unity can bring significant new functionality to optical devices.

physics.optics↗

arXiv2018

Limiting optical diodes enabled by the phase transition of vanadium dioxide

A limiting optical diode is an asymmetric nonlinear device that is bidirectionally transparent at low power, but becomes opaque when illuminated by sufficiently intense light incident from a particular direction. We explore the use of a phase-transition material, vanadium dioxide (VO2), as an active element of limiting optical diodes. The VO2 phase transition can be triggered by optical absorption, resulting in a change in refractive index orders of magnitude larger than what can be achieved with conventional nonlinearities. As a result, a limiting optical diode based on incident-direction-dependent absorption in a VO2 layer can be very thin, and can function at low powers without field enhancement, resulting in broadband operation. We demonstrate a simple thin-film limiting optical diode comprising a transparent substrate, a VO2 film, and a semi-transparent metallic layer. For sufficiently high incident intensity, our proof-of-concept device realizes broadband asymmetric transmission across the near infrared, and is approximately ten times thinner than the free-space wavelength.

physics.app-ph↗