Solitons can be described as self-reinforcing particle-like wave packets formed as a result of the balance between nonlinearity and dispersion.
Solitons occur in plasmas, cold atoms, lasers, and hydrodynamics. They are produced when a laser field is restricted to a circular resonator with ultra-low loss, generating several solitons moving around the resonator.
In general, the solitons move at the same speed and they hardly come close to each other. But the collision of solitons into one other can divulge crucial basic physics of the system, such as the properties of the host resonator and its nonlinearity.
The main aim for scientists in the fields of soliton physics and nonlinear dynamics is to illustrate and regulate soliton collisions in optical microresonators.
A paper related to this study was published in Physical Review X journal. The scientists at Tobias Kippenberg’s laboratory at Ecole Polytechnique Federale De Lausanne (EPFL) have currently designed a new and effective technique for producing soliton collisions in microresonators.
The method involves using two lasers to produce two different soliton species in a crystalline whispering gallery mode resonator, where each species has a specific traveling speed.
The scientists input two laser fields in the microresonator, inducing two soliton species, the speed discrepancy between which can be controlled easily. Thus, solitons with distinct speeds collide into each other.
Based on the variation between the speeds of the solitons, different solitons can either cross each other or bind with each other once they collide. As every collision takes place in minimal time, traditional methods cannot divulge the behaviors of individual solitons.
In this context, the scientists investigated the solitons by using a pulse train generated by high-speed modulators. The interference between the solitons and the pulses produces electronic signals that can be recorded and examined. This enables the scientists to compare the outcomes with theoretical simulations that precisely estimate the experimental outcomes.
This phenomenon demonstrates how powerful these solitons can be in optical microresonators.
During the soliton collision an individual soliton’s shape can be significantly distorted, and its energy exhibits dramatic vibrations. Yet, they can survive the strong impact from the collision, and they can unite with or disengage from each other after the collision.
Wenle Weng, Study First Author, EPFL
The study proposes a simple yet strong platform to investigate transient nonlinear dynamics and complicated soliton interactions. However, it can also help produce soliton-based optical telecommunications and synchronized frequency combs.
The binding and collision mechanisms can be employed to build frequency combs with unusual structures for optical metrology, as well as to improve the bandwidth of frequency combs.
The study was financially supported by the Swiss National Science Foundation and the Defense Advanced Research Projects Agency, Defense Sciences Office (U.S.).