Abstract
Dissipative solitons can be found in a variety of systems resulting from the double balance between dispersion and nonlinearity, as well as gain and loss. Recently, they have been observed to spontaneously form in Kerr nonlinear microresonators driven by a continuous wave laser, providing a compact source of coherent optical frequency combs. As optical microresonators are commonly multimode, intermode interactions, which give rise to avoided mode crossings, frequently occur and can alter the soliton properties. Recent works have shown that avoided mode crossings cause the soliton to acquire a single-mode dispersive wave, a recoil in the spectrum, or lead to soliton decay. Here, we show that avoided mode crossings can also trigger the formation of breather solitons, solitons that undergo a periodic evolution in their amplitude and duration. This new breather soliton, referred to as an intermode breather soliton, occurs within a laser detuning range where conventionally stationary (i.e., stable) dissipative Kerr solitons are expected. We experimentally demonstrate the phenomenon in two microresonator platforms (crystalline magnesium fluoride and photonic chip-based silicon nitride microresonators) and theoretically describe the dynamics based on a pair of coupled Lugiato-Lefever equations. We show that the breathing is associated with a periodic energy exchange between the soliton and a second optical mode family, a behavior that can be modeled by a response function acting on dissipative solitons described by the Lugiato-Lefever model. The observation of breathing dynamics in the conventionally stable soliton regime is relevant to applications in metrology such as low-noise microwave generation, frequency synthesis, or spectroscopy.
- Received 7 June 2017
DOI:https://doi.org/10.1103/PhysRevX.7.041055
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Optical microresonators are devices that can confine light by reflecting it internally. They can support stable and self-consistent laser pulses known as dissipative Kerr solitons—a self-organized dissipative temporal structure that can be found in a wide range of fields. These solitons are the result of the double balance between the dispersion and nonlinearity on the one hand, and between the losses and the parametric gain from an external source on the other. The light coupled out of the microresonator thus consists of a pulse train whose spectrum corresponds to a series of discrete, equally spaced frequency lines, forming an optical frequency comb. These combs can be applied to spectroscopy, optical telecommunication, and low-noise microwave generation. However, dissipative solitons can destabilize and begin to oscillate, a behavior called breathing. This introduces instability in a frequency comb system and is harmful to applications. We discovered a new mechanism that can trigger breather soliton behavior.
Microresonators are often multimode, which means that they can guide light waves in more than one 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. This new regime is called a dynamic intermode breather soliton, and it can occur in configurations where dissipative Kerr solitons are normally stable.
Compared to other regimes, intermode breather solitons reveal a novel type of instability in microresonator-based frequency combs, which highlights the rich nonlinear dynamics of dissipative temporal structures in multimode microresonators but should be avoided in applications.