Abstract
Microlasers in near-degenerate supermodes lay the cornerstone for studies of non-Hermitian physics, novel light sources, and advanced sensors. Recent experiments of the stimulated scattering in supermode microcavities reported beating phenomena, interpreted as dual-mode lasing, which, however, contradicts their single-mode nature due to the clamped pump field. Here, we investigate the supermode Raman laser in a whispering-gallery microcavity and demonstrate experimentally its single-mode lasing behavior with a side-mode suppression ratio (SMSR) up to 37 dB, despite the emergence of near-degenerate supermodes by the backscattering between counterpropagating waves. Moreover, the beating signal is recognized as the transient interference during the switching process between the two supermode lasers. Self-injection is exploited to manipulate the lasing supermodes, where the SMSR is further improved by 15 dB and the laser linewidth is below 100 Hz.
Highlights
Microlasers in near-degenerate supermodes have drawn much attention in the past decades, promoting various advances such as spontaneous symmetry breaking [1, 2], exceptional points [3,4,5,6], precise measurement [7,8,9,10,11], and novel light sources [12,13,14,15,16]
Single microcavities supporting high-Q whispering-gallery modes (WGMs) [17,18,19] are found as a natural platform for studying supermodes, which are formed by the coupling between degenerate counterpropagating waves [20,21,22]
Given that the energy splitting of supermodes is sensitive to the external perturbation [31, 32], the stimulated scattering, such as Raman or Brillouin lasers in supermode microcavities, has shown unique merit for nanoparticle detection [8, 9], an exceptional-point-enhanced optical gyroscope [11, 33], and an Earth rotation reader [34], featuring a beat note corresponding to the splitting
Summary
Pei-Ji Zhanga,b,1, Qing-Xin Jia, , Qi-Tao Caoa,, Heming Wanga, , Wenjing Liua,b , Qihuang Gonga,b,c,d, and Yun-Feng Xiaoa,b,c,d,2. Recent experiments of the stimulated scattering in supermode microcavities reported beating phenomena, interpreted as dual-mode lasing, which, contradicts their single-mode nature due to the clamped pump field. We investigate the supermode Raman laser in a whispering-gallery microcavity and demonstrate experimentally its single-mode lasing behavior with a side-mode suppression ratio (SMSR) up to 37 dB, despite the emergence of near-degenerate supermodes by the backscattering between counterpropagating waves. Supermode lasers in WGM microcavities have been demonstrated with intrinsic gain materials [3, 7, 12,13,14], and nonlinear optical effects, e.g., stimulated scattering [2, 8, 9, 11].
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