In this work, we present the results of numerical modelling of nonlinear pulse propagation in multimode optical fibers leading to discretized conical emission.

Nonlinear optics is a branch of optics dealing with phenomena that are a consequence of light-induced modifications to the optical properties of matter. Optical fibers are a very attractive medium for studying nonlinear phenomena. Due to the small size of the core and the geometry of the fibers, which allows light to propagate over very long distances, the waveguides can show non-linearity even for relatively low power of the initial pulses.

The significant part of the research on nonlinear phenomena in optical fibers concerns single-mode optical fibers. Due to their design, they allow only one mode to propagate for a given light frequency. In practice, they are used in fiber-optic networks to transmit information. Recently, the interest in multimode fibers brought interesting results concerning spatiotemporal nonlinear effects and intermodal frequency conversion [1–3]. This interest is related to the potential use of multimode optical fibers in telecommunications networks. In this type of fibers, for a given frequency, there are many spatial distributions of the guided light. Sending information in different modes allows for a further multiplication of throughput, although it requires the development of methods of sending, redirecting and receiving information in many modes simultaneously [4].

Multimode optical fibers can support multiple guided modes for a given wavelength. Their number is determined by the optical frequency and the refractive index profile of investigated fiber. Each guided mode propagates in a specific manner, which could be shown as its electromagnetic field distribution. Identification of linearly polarized (LP) modes is based on determining the number of extremes along two field cross-sections: radial and transversal. The field distribution of the same mode could be slightly different depending on wavelength and reflective index profile.

At the same time, we can think of a multimode fiber as a transition material between a bulk material and a single-mode fiber. This makes them ideal for exploring the connection between nonlinear phenomena occurring in these two material mediums. One of such nonlinear phenomena is a conical emission…

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Source: towardsdatascience.com