Petermann-factor sensitivity limit near an exceptional point in a Brillouin ring laser gyroscope
Exceptional points are singularities of open systems, and among their many remarkable properties, they provide a way to enhance the responsivity of sensors. Here we show that the improved responsivity of a laser gyroscope caused by operation near an exceptional point is precisely compensated by increasing laser noise. The noise, of fundamental origin, is enhanced because the laser mode spectrum loses the oft-assumed property of orthogonality. This occurs as system eigenvectors coalesce near the exceptional point and a bi-orthogonal analysis confirms experimental observations. While the results do not preclude other possible advantages of the exceptional-point-enhanced responsivity, they do show that the fundamental sensitivity limit of the gyroscope is not improved through this form of operation. Besides being important to the physics of microcavities and non-Hermitian photonics, these results help clarify fundamental sensitivity limits in a specific class of exceptional-point sensor.
Additional Information© 2020 The Author(s). This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Received 06 November 2019; Accepted 28 February 2020; Published 31 March 2020. This work was supported by the Defense Advanced Research Projects Agency (DARPA) under PRIGM:AIMS program through SPAWAR (grant no. N66001-16-1-4046) and the Kavli Nanoscience Institute. Data availability: The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. Author Contributions: H.W., Y-H.L., and K.V. conceived the idea. H.W. derived the theory with feedback from Y-H.L., Z.Y., and K.V. Y-H.L. designed and perform the experiments with Z.Y. and H.W. Z.Y. analysed the data with Y-H.L. and H.W. M-G.S. fabricated the devices. All authors participated in writing the paper. K.V. supervised the research. The authors declare no competing interests.
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