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Parity–time symmetry and variable optical isolation in active–passive-coupled microresonators

Nature Photonics volume 8, pages 524–529 (2014)Cite this article

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Abstract

Compound-photonic structures with gain and loss1 provide a powerful platform for testing various theoretical proposals on non-Hermitian parity–time-symmetric quantum mechanics2,3,4,5 and initiate new possibilities for shaping optical beams and pulses beyond conservative structures. Such structures can be designed as optical analogues of complex parity–time-symmetric potentials with real spectra. However, the beam dynamics can exhibit unique features distinct from conservative systems due to non-trivial wave interference and phase-transition effects. Here, we experimentally realize parity–time-symmetric optics on a chip at the 1,550 nm wavelength in two directly coupled high-Q silica-microtoroid resonators with balanced effective gain and loss. With this composite system, we further implement switchable optical isolation with a non-reciprocal isolation ratio from −8 dB to +8 dB, by breaking time-reversal symmetry with gain-saturated nonlinearity in a large parameter-tunable space. Of importance, our scheme opens a door towards synthesizing novel microscale photonic structures for potential applications in optical isolators, on-chip light control and optical communications.

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Figure 1: On-chip WGM silica microtoroid resonators with gain and loss for PT symmetry and optical isolation.
Figure 2: Transmission spectra in PT symmetry.
Figure 3: Supersensitive optical isolation performance of the system.
Figure 4: Optical isolation performance of the device versus separation distance between toroid 2 and fibre 2.

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Acknowledgements

This research was supported by the National Basic Research Program of China (nos. 2012CB921804 and 2011CBA00205), the National Natural Science Foundation of China (nos. 11104137 and 11321063), the Natural Science Foundation of Jiangsu Province, China (BK2011554) and the Specialized Research Fund for the Doctoral Program of Higher Education (20110091120015). J.M.W. and L.J. acknowledge funding support from a DARPA QUINESS grant, the Alfred P. Sloan Foundation and the David and Lucile Packard Foundation. The authors thank Huibo Fan and Yang Ding for the preparation of the erbium-doped silica sol–gel film.

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Authors and Affiliations

  1. National Laboratory of Solid State Microstructures and College of Engineering and Applied Sciences, Nanjing University, Nanjing, 210093, China

    Long Chang, Xiaoshun Jiang, Shiyue Hua, Chao Yang, Guanyu Li, Guanzhong Wang & Min Xiao

  2. Synergetic Innovation Center in Quantum Information and Quantum Physics, Nanjing University, Nanjing, 210093, China

    Long Chang, Xiaoshun Jiang, Shiyue Hua, Chao Yang, Guanyu Li, Guanzhong Wang & Min Xiao

  3. Department of Applied Physics, Yale University, New Haven, 06511, Connecticut, USA

    Jianming Wen & Liang Jiang

  4. Department of Physics, University of Arkansas, Fayetteville, 72701, Arkansas, USA

    Min Xiao

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Contributions

X.J., J.W., L.J. and M.X. conceived the idea. X.J. and M.X. supervised the experiment with contributions from L.C., S.H., C.Y., G.L. and G.W. All authors contributed to the discussions about the project, analysis of experimental data and writing of the manuscript.

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Correspondence to Xiaoshun Jiang, Jianming Wen or Min Xiao.

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Chang, L., Jiang, X., Hua, S. et al. Parity–time symmetry and variable optical isolation in active–passive-coupled microresonators. Nature Photon 8, 524–529 (2014). https://doi.org/10.1038/nphoton.2014.133

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