Enhancing Sensitivity at Higher-Order Exceptional Points

Active photonic molecule lasers that are non-uniformly pumped could provide a way to generate high sensitivity exceptional points in a systematic way. A research team at the University of Central Florida’s College of Optics & Photonics (CREOL) has demonstrated this concept. The team generated second order exceptional points using a coupled binary photonic molecule under parity-time symmetric conditions and extended this concept to higher-order exceptional points. The researchers generated a higher-order exceptional point by coupling three micro-rings made from a semiconductor laser materal. The third-order exceptional point has an even higher, cube-root (rather than square-root) dependence on perturbations.

To achieve higher-order exception point sensitivity, the team fabricated a device consisting of three coupled, InGaAs ring resonators, each planted on top of a 150-nm-thick gold platform that served as a microheating element. They then pumped the system with 1064-nm light, dynamically shaping the beam and tweaking the microheaters until the system reached a third-order exceptional point.

Parity–time-symmetric coupled cavity systems that support exceptional points.The CREOL team used three coupled ring resonators, atop gold heating elements, to create a third-order exceptional point. Courtesy of University of Central Florida.

To experimentally verify this enhanced sensitivity response, the team simulated sensor perturbations by making tiny adjustments to the microheaters. They found that the frequency shift scaled according to the cube root of the perturbation — an indication that the system did attain a third-order exceptional point. Using this scheme, the team could record more than an order of magnitude enhancement in sensitivity.

According to the researchers, their results “may pave the way toward a new class of on-chip ultrasensitive sensing systems.” Professor Mercedeh Khajavikhan and the team are planning to use this sensitivity enhancement to develop a new generation of integrated ring laser gyroscopes that can be used in a variety of applications from drones to driverless cars to game controllers.

The research was published in Nature (doi:10.1038/nature23280).