Special OSE Seminar by Dr. Dave D. Smith on PT-symmetry-breaking gyroscopes
Posted: October 7, 2019
Date: Tuesday, October 8, 2019
Time: 2:00 PM to 3:15 PM
Location: CHTM, Room 103
Map to CHTM:
ADA Accommodations are available.
Dr. Dave D. Smith
N.A.S.A, Marshall Space Flight Center
One of the hot topics to emerge in optical physics over the last decade is the use of singularities to dramatically boost the sensitivity of optical cavities to changes in optical path length (OPL). In particular, the sensitivity diverges when the anomalous dispersion of a medium placed inside the cavity reaches a critical value, or when a second resonator is coupled to the first and the system eigenvalues coalesce at the exceptional point (EP) (these two singularities are, it turns out, equivalent). The increased sensitivity has been proposed as a means for enhancing the precision of active- and passive-cavity optical gyroscopes and was directly observed for the first time in experiments at NASA with passive cavities containing Rb87 atomic vapor. Materials with anomalous dispersion are now being pursued as a means of enhancing the sensitivity of active laser cavities, but these systems are difficult to miniaturize, are subject to variations owing to the atomic absorption, and only work at the discrete wavelengths of the material transitions that create the dispersion. Recently, EPs have been observed in coupled-resonator (CR) lasers that possess parity-time (PT)-symmetry, which are promising because they can be microfabricated and work at any (lasing) wavelength. We have found, however, that PT-symmetric gyros require undamped power oscillations to work as originally envisioned (with the beat frequency measured from a single output direction), which can make them susceptible to Kerr effect, and limit their operating range. We will discuss how PT-symmetry breaking can eliminate these power oscillations and enable enhancements to be obtained farther from the EP. We refer to the process by which this occurs as lasing without gain, a phenomenon analogous to lasing without inversion, where oscillation can occur even when there is no net gain (in the bare-state or uncoupled-resonator basis). Finally, we show that gain saturation can dramatically increase the size of the sensitivity enhancement in CR systems.
David D. Smith is a physicist at the NASA Marshall Space Flight Center in the Optics and Imaging Branch, in the Space Systems Department, and is co-located at the Research Development and Engineering Center of the U.S. Army Aviation and Missile Command on the Redstone Arsenal. Dr. Smith also teaches classes in optical physics part-time at the University of Alabama in Huntsville. He has served as Project Scientist on a variety of NASA spaceflight experiments, Assistant Mission Scientist for USMP-4, and Project Manager for the Fast Light Optical Gyroscopes Project. Dr. Smith was born in Rochester, New York, received a B.S. in Optics from the University of Rochester, and a Ph.D. in Physics from the University of Alabama in Huntsville. He has been a Visiting Professor at the University of New Mexico, the University of Rochester, and Oklahoma State University as a NASA Administrator’s Fellow, as well as serving as a Fulbright Scholar at the University of Chile in Santiago. Dr. Smith is a fellow of the Optical Society of America.