Massively Degenerate Coherent Perfect Absorption in Gradient-Index Fibers

TL;DR

This paper introduces a compact, scalable multimode coherent perfect absorber using gradient-index fibers, enabling efficient absorption of complex light fields for applications in photonics and light harvesting.

Contribution

It demonstrates a novel fiber-based CPA leveraging the self-imaging property of GRIN fibers for near-degenerate rephasing of multiple modes, overcoming previous limitations.

Findings

Achieves field-of-view reflectivities below 1% for realistic parameters.

Supports highly efficient absorption of complex multimode fields.

Provides a practical, scalable solution for multimode absorption in fiber systems.

Abstract

Coherent perfect absorbers (CPAs) have recently attracted considerable attention due to their ability to enhance light--matter interaction. By exploiting interference, CPAs enable even weakly absorbing materials to achieve complete absorption under appropriate excitation conditions. Generalizing this concept to the simultaneous absorption of arbitrary multimode input states remains challenging, however, since conventional implementations typically operate only for a single or a very small number of input channels. Here, we propose a compact realization of a multimode coherent perfect absorber based on a gradient-index (GRIN) fiber. Using the self-imaging property of the fiber, the bulky free-space architecture of previous approaches is replaced by a monolithic waveguiding platform that supports near-degenerate rephasing of many spatial modes. We show that standard GRIN profiles optimized for minimal intermodal dispersion enable highly efficient absorption of complex multimode fields, with field-of-view reflectivities well below \(1\%\) for realistic parameters. This approach provides a practical and scalable route toward efficient multimode absorption in fiber-based and integrated photonic systems, with potential applications in light harvesting, optical control, and imaging.