ABSTRACT: For too long the functionality of optical devices and systems has been severely
restricted by the very limited range of refractive indices at the disposal of designers. These
limitations become especially constricting in the currently most active areas of optics –
integrated photonics, photonic crystals, metamaterials and metasurfaces. A simple increase of
the value of refractive index by 50% can result in disproportionally large improvement in
performance (i.e. smaller size, less cross-talk, higher resolution, and so on, depending on
application) With that in mind, I explore what are the fundamental limits that limit the scope
of refractive indices as a function of wavelength, explain why higher index materials have not
yet materialized and point out a few tentative directions for the search of these elusive
materials, be they natural or artificial.
In the second part of the talk, I investigate a closely related issue: changing refractive index to
achieve effective modulation. There exist many methods of index modulation, starting with
Pockels and Kerr electro-optic effects, acousto-optic and opto-mechanical effect, optical
nonlinearities, thermal, carrier injection/depletion, etc. In my talk I will try to provide a
comprehensive analysis that will show that independent of the modulation technique, one
must supply and maintain (but not necessarily dissipate) anywhere between few times 10 3
and 105 J/cm3 of energy in order to achieve relative index change on the order of 50-100% (with
energy requirements increasing in sync with the increase of operating frequency). The general
conclusion is that unless radically new material systems are developed, the improvement of
the performance of existing modulation techniques will have evolutionary rather than
revolutionary character with no order of magnitude improvement in sight. I will try to argue
for using collective effects and fast phase transitions to achieve future breakthroughs

BIO: Dr. Jacob Khurgin is a Professor in the Department of Electrical and Computer Engineering
at Johns Hopkins University, specializing in optics, electronics, condensed matter physics, and
telecommunications. He completed his PhD in Electro-Physics from New York University in
1987 and joined Johns Hopkins in 1988.