# Waveguides with Absorbing Boundaries: Nonlinearity Controlled by an Exceptional Point and Solitons

## TL;DR

This paper demonstrates the existence of stable guided solitons in waveguides with absorbing boundaries, where exceptional points in the spectrum enable control over effective nonlinearity and soliton type, with potential for practical manipulation.

## Contribution

It introduces a novel mechanism where exceptional points in waveguide spectra enable nonlinearity control and soliton formation in absorbing boundary waveguides.

## Key findings

- Stable TE and TM solitons exist in waveguides with absorbing boundaries.
- Exceptional points cause effective nonlinearity to switch between focusing and defocusing.
- Nonlinearity can be manipulated via the properties of the absorbing cladding.

## Abstract

We reveal the existence of continuous families of guided single-mode solitons in planar waveguides with weakly nonlinear active core and absorbing boundaries. Stable propagation of TE and TM-polarized solitons is accompanied by attenuation of all other modes, i.e. the waveguide features properties of conservative and dissipative systems. If the linear spectrum of the waveguide possesses exceptional points, which occurs in the case of TM-polarization, an originally focusing (defocusing) material nonlinearity may become effectively defocusing (focusing). This occurs due to the geometric phase of the carried eigenmode when the surface impedance encircles the exceptional point. In its turn the change of the effective nonlinearity ensures the existence of dark (bright) solitons in spite of focusing (defocusing) Kerr nonlinearity of the core. The existence of an exceptional point can also result in anomalous enhancement of the effective nonlinearity. In terms of practical applications the nonlinearity of the reported waveguide can be manipulated by controlling the properties of the absorbing cladding.