Experimental observation of inter-orbital coupling

TL;DR

This paper experimentally demonstrates inter-orbital coupling in photonic lattices, revealing new ways to control orbital states and proposing applications in photonic mode conversion and multiplexing.

Contribution

It provides the first experimental evidence of fundamental and excited orbital states coupling across different spatial positions in photonic lattices.

Findings

Fundamental and excited orbital states can couple in photonic lattices.

A full characterization of an asymmetric double-well potential was performed.

A phase beam splitter configuration was proposed for photonic multiplexing.

Abstract

Inter-orbital coupling refers to the possibility of exciting orbital states by otherwise orthogonal non-interacting modes, a forbidden process in photonic lattices due to an intrinsic propagation constant detuning. In this work, using a femtosecond laser writing technique, we experimentally demonstrate that fundamental and excited orbital states can couple each other when located at different spatial positions. We perform a full characterization of an asymmetric double-well like potential and implement a scan method to effectively map the dynamics along the propagation coordinate. Our fundamental observation constitutes also a direct solution for a spatial mode converter device, which could be located in any position inside a photonic glass chip. By taking advantage of the phase structure of higher-order photonic modes and the effective negative coupling generated, we propose a trimer configuration as a phase beam splitter ($\pi$-BS), which could be of great relevance for multiplexing and interference-based photonic concatenated operations.