26.01.18 – EPFL researchers have discovered a new mechanism that can trigger stable dissipative Kerr solitons to breathe. The work is published in Physical Review X.

Optical microresonators are devices that can confine light by reflecting it internally. These structures can support stable and self-consistent optical pulses known as temporal dissipative Kerr solitons (DKS), which will not deform over propagation (i.e. no change in the temporal duration, the power, etc.). Physically, this phenomenon is the result of a double balance effect working on DKS in the microresonator, namely between the cavity dispersion and the nonlinearity on the one hand, and on the other hand, between the dissipation (loss of the cavity) and the parametric gain from an external light source. Since being stable, such solitons represent a self-organized dissipative temporal structure which can be found in a wide range of fields, and mathematically described by a generalized driven, dissipative and detuned nonlinear Schrödinger equation – Lugiato–Lefever equation. Moreover, the light coupled out of the microresonator consists of an ultra-fast pulse train whose spectrum corresponds to a series of discrete, equally spaced frequency lines, forming an optical frequency comb. These frequency combs can be applied to spectroscopy, optical telecommunication, and low-noise microwave generation. However, dissipative solitons can destabilize and begin to oscillate (in the power as well as in the pulse duration), a behavior called breathing (see “Breathing Optical Solitons”). This introduces instability in a frequency comb system and is harmful to applications.

EPFL researchers have deeply studied the dynamics of breathing optical solitons and most recently, they discovered a new mechanism that can trigger stable DKS to breathe.

The study is based on the fact that microresonators are often multimode, which means that they can guide light waves in more than one spatial pattern in the transverse direction and with different velocities in the propagation direction. In such cases, energy exchange between the soliton in one mode and the optical waveform in another can occur, which leads to the soliton breathing (cf. the figure above). This new regime is called a dynamic inter-mode breather soliton, and it can occur in configurations where dissipative Kerr solitons are normally stable. In this work, Dr. Hairun Guo and his colleagues performed both experiments and numerical simulations, and they observed an out-of-phase power oscillation in between the two modes, indicating the energy exchange between the soliton and another waveform in the microresonator.

Compared to other regimes, inter-mode breather solitons reveal a novel type of instability in microresonator-based frequency combs, which highlights rich nonlinear dynamics of dissipative temporal structures in multi-mode microresonators, but should be avoided in applications.

Reference

H. Guo, E. Lucas, M. H. P. Pfeiffer, M. Karpov, M. Anderson, J. Liu, M. Geiselmann, J. D. Jost, T. J. Kippenberg. Intermode Breather Solitons in Optical Microresonators. Physical Review X 7, 041055, 06 December 2017. DOI: 10.1103/PhysRevX.7.041055