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PT-symmetry-breaking gyroscopes

Tuesday October 8, 2019
2:00 pm


 Presenter:  Dr. David Smith
NASA
 Series:  OSE Seminars
 Abstract:  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.
 Location:  Room 103, Center for High Tech Materials

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