Biography
Dr. Hairun Guo
Dr. Hairun Guo
Shanghai University, China
Title: Nanophotonic Optical Frequency Combs: From Microresonator Combs to Supercontinuum-based Spectroscopy
Abstract: 
Optical frequency combs provide equidistant laser frequencies, and have become a pivotal tool for time measurement and frequency metrology, including optical clocks, spectroscopy and low-noise microwave generation [1,2]. In 2007, a new method to generate optical frequency combs was discovered based on high-Qand nonlinear optical microresonators [3–6]. Microresonator frequency combs have since then been widely investigated.They enable combs with large bandwidth, high repetition rate, and high compactness, and have found advanced applications such as coherent communication [7], ultrafast ranging [8], fully integrated optical synthesizer [9], astro-comb, etc. In particular, they can be implemented on nanophotonic integrated platforms, e.g. the silicon nitride photonics that is CMOS compatible [10], and combines both high material nonlinearity with unprecedented ways that dispersion is lithographically controlled in integrated photonics. Remarkably, this has led to combs with octave-spanning bandwidth [11,12] and enables the self-referencing without external broadening regime [13]. On another direction of the development, the loss rate of the photonic integrated waveguides has been largely reduced, leading to record-high quality (Q) factor in silicon nitride microresonators, and combs that can be generated at diode’s power level [14]. Fundamentally, microresonator frequency combs correspond to temporal soliton pulses that are spontaneously formed in the resonator [5], and allow for rich soliton dynamics including the Raman effects [15], soliton induced Cherenkov radiation, soliton switching [16], breather solitons [17–19], and soliton spatial multiplexing [20]. In this presentation, the developments at EPFL will be reviewed, with respect to both fundamental physics and applications of microresonator frequency combs. In addition, we will review nanophotonic supercontinuum generation in silicon nitride waveguides, which benefits from the high-flexible nanophotonic dispersion engineering, and is alternative to mid-infrared frequency comb generation [21]. A supercontinuum-based mid-infrared spectroscopy will also be presented.

References:
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2. T. Udem, R. Holzwarth, and T. W. H"ansch, "Optical frequency metrology," Nature 416, 233–237 (2002).
3. P. Del’Haye, A. Schliesser, O. Arcizet, T. Wilken, R. Holzwarth, and T. J. Kippenberg, "Optical frequency comb generation from a monolithic microresonator," Nature 450, 1–4 (2007).
4. T. J. Kippenberg, R. Holzwarth, and S. A. Diddams, "Microresonator-Based Optical Frequency Combs," Science 332, 555–559 (2011).
5. T. Herr, V. Brasch, J. D. Jost, C. Y. Wang, N. M. Kondratiev, M. L. Gorodetsky, and T. J. Kippenberg, "Temporal solitons in optical microresonators," Nat. Photon. 8, 145–152 (2013).
6. V. Brasch, M. Geiselmann, T. Herr, G. Lihachev, M. H. P. Pfeiffer, M. L. Gorodetsky, and T. J. Kippenberg, "Photonic chip–based optical frequency comb using soliton Cherenkov radiation," Science 351, 357–360 (2016).
7. P. Marin-Palomo, J. N. Kemal, M. Karpov, A. Kordts, J. Pfeifle, M. H. P. Pfeiffer, P. Trocha, S. Wolf, V. Brasch, M. H. Anderson, R. Rosenberger, K. Vijayan, W. Freude, T. J. Kippenberg, and C. Koos, "Microresonator-based solitons for massively parallel coherent optical communications," Nature 546, 274–279 (2017).
8. P. Trocha, M. Karpov, D. Ganin, M. H. P. Pfeiffer, A. Kordts, S. Wolf, J. Krockenberger, P. Marin-Palomo, C. Weimann, S. Randel, W. Freude, T. J. Kippenberg, and C. Koos, "Ultrafast optical ranging using microresonator soliton frequency combs," Science 359, 887 (2018).
9. D. T. Spencer, T. Drake, T. C. Briles, J. Stone, L. C. Sinclair, C. Fredrick, Q. Li, D. Westly, B. R. Ilic, A. Bluestone, N. Volet, T. Komljenovic, L. Chang, S. H. Lee, D. Y. Oh, M.-G. Suh, K. Y. Yang, M. H. P. Pfeiffer, T. J. Kippenberg, E. Norberg, L. Theogarajan, K. Vahala, N. R. Newbury, K. Srinivasan, J. E. Bowers, S. A. Diddams, and S. B. Papp, "An optical-frequency synthesizer using integrated photonics," Nature 557, 81–85 (2018).
10. D. J. Moss, R. Morandotti, A. L. Gaeta, and M. Lipson, "New CMOS-compatible platforms based on silicon nitride and Hydex for nonlinear optics," Nat. Photon. 7, 597–607 (2013).
11. M. H. P. Pfeiffer, C. Herkommer, J. Liu, H. Guo, M. Karpov, E. Lucas, M. Zervas, and T. J. Kippenberg, "Octave-spanning dissipative Kerr soliton frequency combs in Si3N4 microresonators," Optica 4, 684–691 (2017).
12. Q. Li, T. C. Briles, D. A. Westly, T. E. Drake, J. R. Stone, B. R. Ilic, S. A. Diddams, S. B. Papp, and K. Srinivasan, "Stably accessing octave-spanning microresonator frequency combs in the soliton regime," Optica 4, 193–203 (2017).
13. V. Brasch, E. Lucas, J. D. Jost, M. Geiselmann, and T. J. Kippenberg, "Self-referenced photonic chip soliton Kerr frequency comb," Light Sci Appl. 6, e16202 (2017).
14. J. Liu, A. S. Raja, M. Karpov, B. Ghadiani, M. H. P. Pfeiffer, B. Du, N. J. Engelsen, H. Guo, M. Zervas, and T. J. Kippenberg, "Ultralow-power chip-based soliton microcombs for photonic integration," Optica 5, 1347–1353 (2018).
15. M. Karpov, H. Guo, A. Kordts, V. Brasch, M. H. P. Pfeiffer, M. Zervas, M. Geiselmann, and T. J. Kippenberg, "Raman Self-Frequency Shift of Dissipative Kerr Solitons in an Optical Microresonator," Phys. Rev. Lett. 116, 103902 (2016).
16. H. Guo, M. Karpov, E. Lucas, A. Kordts, M. H. P. Pfeiffer, V. Brasch, G. Lihachev, V. E. Lobanov, M. L. Gorodetsky, and T. J. Kippenberg, "Universal dynamics and deterministic switching of dissipative Kerr solitons in optical microresonators," Nat. Phys.13, 94 (2016).
17. C. Bao, J. A. Jaramillo-Villegas, Y. Xuan, D. E. Leaird, M. Qi, and A. M. Weiner, "Observation of Fermi-Pasta-Ulam Recurrence Induced by Breather Solitons in an Optical Microresonator," Phys. Rev. Lett.117, (2016).
18. E. Lucas, M. Karpov, H. Guo, M. L. Gorodetsky, and T. J. Kippenberg, "Breathing dissipative solitons in optical microresonators," Nat.Commun.8, 736 (2017).
19. H. Guo, E. Lucas, M. H. P. Pfeiffer, M. Karpov, M. Anderson, J. Liu, M. Geiselmann, J. D. Jost, and T. J. Kippenberg, "Intermode Breather Solitons in Optical Microresonators," Phys. Rev. X 7, 041055 (2017).
20. E. Lucas, G. Lihachev, R. Bouchand, N. G. Pavlov, A. S. Raja, M. Karpov, M. L. Gorodetsky, and T. J. Kippenberg, "Spatial multiplexing of soliton microcombs," Nat. Photon.12, 699–705 (2018).
21. H. Guo, C. Herkommer, A. Billat, D. Grassani, C. Zhang, M. H. P. Pfeiffer, W. Weng, C.-S. Brès, and T. J. Kippenberg, "Mid-infrared frequency comb via coherent dispersive wave generation in silicon nitride nanophotonic waveguides," Nat. Photon. 12, 330 (2018).
Biography: 

Dr. Guo obtained his Bachelor and Master degree at Shanghai University, Shanghai, China, in 2008 and 2011, respectively. In 2011, he started his PhD study at Technical University of Denmark (DTU), Denmark, where he joined the group of Ultrafast Nonlinear Optics (UNO) lead by Prof. Morten Bache. His PhD topic was “cascaded quadratic soliton compression in waveguide structures” which includes the near-infrared and mid-infrared soliton pulse formation, and soliton induced supercontinuum generations, as well as light-matter interactions in nonlinear crystals and crystal waveguides. He defended his PhD thesis and obtained the degree in 2014.

Since 2015, he joined the Kippenberg Laboratory (Laboratory of Photonics and Quantum Measurements, LPQM) atSwiss Federal Institute of Technology Lausanne (EPFL), Switzerland, and embarked on a new phase of his career as a postdoctoral scientist. His research interests were centered on microresonator based optical frequency combs andcavity dissipative soliton physics, with a focus on mid-infrared frequency comb generations in nano-photonic chip-based devices.

In 2019, he received a professorship in Photonics Engineering at Shanghai University (Shanghai, China) where now he is building up his own lab. His group will focus on the topic of optical frequency combs and ultra-fast nonlinear regimes in optical frequency metrology.

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