Spatiotemporal Aspects of Nonlinear Wave Propagation in Multimode Fiber

Nonlinear wave propagation in optical fiber is a rich and fascinating subject. From a purely-scientific point of view, fibers provide convenient and reproducible experimental settings for a broad range of nonlinear dynamical processes. Qualitatively new phenomena are still being discovered. The major advances of the past 20 years are dominated by phenomena that occur in single-mode fiber (SMF).

In multimode waveguides, light encounters an environment with dimensionality that exceeds 1D but is effectively below the 3D of free space. Wave propagation depends on the optical guiding characteristics and the excitation conditions. The complexity of the problem increases once nonlinear effects come into play: all the eigenmodes (which may number in the thousands) tend to strongly affect each other through nonlinear processes. Rich and complex dynamics are possible in nonlinear multimode environments.

Fiber Lasers that Generate Ultrashort Light Pulses

Short-pulse optical techniques have had major scientific and technological impact. Some of the fastest processes in nature can be observed directly with ultrashort (picosecond or femtosecond) optical pulses. Researchers now perform measurements with attosecond time resolution. In parallel, efforts are underway to apply ultrafast lasers in areas with broader societal impact, such as manufacturing and health care. Ultrafast science is dominated by solid-state lasers, which are outstanding laboratory tools. Inexpensive, robust instruments will enable applications in a much broader range of settings.

Fiber lasers offer major practical advantages owing to their waveguide nature, efficient power-handling, and low cost. These are thoroughly-exploited in high-average power continuous-wave lasers.  However, generation of pulses with high peak power remains a serious challenge owing to uncontrolled nonlinear effects, which in turn arise from the waveguide medium.

We figure out new ways for light to propagate inside single-mode optical fiber, which allow stable pulses to form despite large nonlinear effects.  We start by finding solutions to the nonlinear partial differential equations that govern pulse propagation, and then we try to build something in the lab that will support the desired solutions.  Our work ranges from analytic theory to practical aspects of working lasers.  Currently, much of our motivation comes from the needs of scientists who are trying to do sub-cellular imaging deep in biological tissue.

Video Resources:

“Spacetime instability of light in multimode optical fiber”
Trying real hard to be accessible, we describe our recent work trying to understand the behavior of intense pulses of light in multimode optical fibers, motivated by high power fiber lasers and telecommunications. The work highlighted here is described in the paper in Nature Photonics

“Spatiotemporal Dynamics of Optical Pulse Propagation in Multimode Fibers”
In this OSA webinar (originally streamed on 6/22/2016), Frank discusses several areas of our ongoing work in multimode optical fiber. The slides can be downloaded here.

“Interdimensional Nonlinear Optics in Multimode Fibers”
As part of Cornell’s Summer Graduate Student STEM Colloquium (7/18/2016), Logan Wright gives an informal talk on nonlinear optics in multimode fibers, aimed at the educated non-specialist.

You should love optical fibers. They are an integral part of the internet-age global infrastructure. In industry and medicine, lasers based on optical fiber are a rapidly growing market, providing unprecedented cost:performance and reliability. All these technologies, based on single-mode fiber, are nearing their fundamental limits, and panic for the anticipated ‘capacity crunch’ is building. In other words, we’re screwed.

Fortunately, something called ‘multimode fiber’ has the potential for unparalleled unscrewing. In this talk, I will explain what multimode fibers are, and review recent work studying how short pulses of light behave inside them. I will explain what I mean by ‘interdimensional’ and show that nonlinear optical pulses called ‘multimode solitons’ can provide a basis for understanding complex 4-D nonlinear wave behavior in MMFs. In some limits, their dynamics can be understood using a classical “fat duck on a trampoline” model. Finally, I will discuss prospects for multimode fibers in several important applications, including things like high-speed internet, neural networks, and ridiculously (!!!) high-power lasers.