Reflection and transmission of waves in surface-disordered waveguides

TL;DR

This paper investigates how surface disorder affects wave reflection and transmission in multimode waveguides, revealing anomalous scattering effects, mode selectivity, and coexistence of transport regimes through numerical simulations.

Contribution

It provides new insights into surface scattering effects on wave transport, highlighting the coexistence of ballistic, diffusive, and localized regimes in surface-disordered waveguides.

Findings

Larger transverse momentum modes are more strongly scattered.

Surface scattering causes mode selectivity and anomalous backscattering.

Multiple transport regimes coexist within the same waveguide.

Abstract

The reflection and transmission amplitudes of waves in disordered multimode waveguides are studied by means of numerical simulations based on the invariant embedding equations. In particular, we analyze the influence of surface-type disorder on the behavior of the ensemble average and fluctuations of the reflection and transmission coefficients, reflectance, transmittance, and conductance. Our results show anomalous effects stemming from the combination of mode dispersion and rough surface scattering: For a given waveguide length, the larger the mode transverse momentum is, the more strongly is the mode scattered. These effects manifest themselves in the mode selectivity of the transmission coefficients, anomalous backscattering enhancement, and speckle pattern both in reflection and transmission, reflectance and transmittance, and also in the conductance and its universal fluctuations. It is shown that, in contrast to volume impurities, surface scattering in quasi-one-dimensional structures (waveguides) gives rise to the coexistence of the ballistic, diffusive, and localized regimes within the same sample.