Parity-Time (PT) Symmetric Photonics
Abstract
Parity-Time (PT) Symmetric PhotonicsRefractive index, gain, and loss play a pivotal role in light propagation. Modulating the refractiveindex as a means to mold light transport dates back to antiquity when rock crystals like the~Loupe of Sargon~ were used to produce fire by focusing sun rays. Since then, index craftinghas reached such a level of perfection that artificial structures as diverse as optical fibers,photonic crystals, and meta-materials became possible (1-3). Optical amplification or gain wasrealized much later, followed by the discovery of the laser, and has enabled numerousapplications in many areas of science and technology. Gain is a valuable commodity, which istypically used to mitigate losses, to boost the level of a signal or to produce coherent lightsources. However, this is not the case for attenuation. Loss, unlike the other two processes, isstill perceived to be a foe, an undesirable attribute that should be avoided or compensated at allcosts. It is perhaps for this particular reason that the simultaneous use of index, gain, and loss asa viable route to achieve new optical behavior has been generally overlooked.At a first glance, deliberately intermixing amplification with absorption may appearcounterintuitive and to some extent pointless. Lately however, it was realized that engaging allthese three elements in a parity-time (PT) symmetric fashion can lead to photonic structures withcustomized properties and functionalities previously thought to be unattainable (4-8). In general,PT symmetry demands that gain and loss are balanced in an antisymmetric manner, while therefractive index profile is evenly distributed. What makes this particular arrangement stand outamong other non-conservative configurations is that it provides a strategy to manage one of themost intriguing attributes of non-Hermitian systems: their exceptional points (9,10). Exceptionalpoints (EPs) represent important features in parameter space, where degenerate eigenvalues andtheir corresponding eigenstates simultaneously coalesce. The presence of EPs marks theboundary of phase transitions beyond which the eigenvalues abruptly enter the complex domain.Interestingly, in a PT symmetric configuration, this can be achieved while maintaining globalcontrol over its eigenvalue spectrum.The objective of this proposal is to utilize the physics and peculiarities of parity-time-symmetricexceptional points (EPs) in order to develop alternative strategies in designing new photonicdevices that complement and/or improve existing integrated photonic systems. In particular, ourefforts will be directed towards three areas associated with chip-scale photonics where currentapproaches are still in need of a solution: (i) parity-time-symmetric lasers with customizedcharacteristics, (ii) the role of nonlinearities on PT phase transitions, (iii) PT photonic moleculesfor extreme sensing applications. Within the context of lasers, we plan to study, for the first time,the frequency response of PT symmetric lasers as well as their linewidth behavior around anexceptional point. We will also investigate the exciting possibility of controlling the spectral andspatial emission characteristics of random lasers by employing tactics similar to those previouslydeveloped by our group for mode management in PT lasing systems (11-13). In addition, we willexplore the prospect of PT symmetry as a means to further confine the mode in plasmonic lasercavities. In the past few years, our group has developed a semiconductor (InP-based) platformthat can be effectively used to implement a variety of PT-symmetric settings. Understanding therole of nonlinearities in PT systems (that are ubiquitous in semiconductor active media) isimportant not only in evaluating the performance of high power PT lasers, but also for buildingnew classes of PT-assisted all-dielectric optical isolators and circulators.2Finally, it should be noted that non-conservative arrangements are of fundamental interest
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141612640
Entities
People
- Mercedeh Khajavikhan
Organizations
- Office of Naval Research
- United States Navy
- University of Central Florida Board of Trustees