Broadband integrated beam splitter using spatial adiabatic passage

TL;DR

This paper presents a robust, broadband integrated beam splitter on lithium niobate using spatial adiabatic passage, achieving achromatic splitting over 130 nm and enabling phase control for versatile photonic circuits.

Contribution

The authors demonstrate a simple, robust, and broadband beam splitter based on spatial adiabatic passage, overcoming dispersion and fabrication challenges of traditional designs.

Findings

Achieves splitting ratio of approximately 0.5 over 1500-1630 nm

Demonstrates phase control with relative phase 0 or π

Device is robust against fabrication imperfections and dispersion

Abstract

Light routing and manipulation are important aspects of integrated optics. They essentially rely on beam splitters which are at the heart of interferometric setups and active routing. The most common implementations of beam splitters suffer either from strong dispersive response (directional couplers) or tight fabrication tolerances (multimode interference couplers). In this paper we fabricate a robust and simple broadband integrated beam splitter based on lithium niobate with a splitting ratio achromatic over more than 130 nm. Our architecture is based on spatial adiabatic passage, a technique originally used to transfer entirely an optical beam from a waveguide to another one that has been shown to be remarkably robust against fabrication imperfections and wavelength dispersion. Our device shows a splitting ratio of 0.52$\pm $0.03 and 0.48$\pm $0.03 from 1500\,nm up to 1630\,nm. Furthermore, we show that suitable design enables the splitting in output beams with relative phase 0 or $\pi$. Thanks to their independence to material dispersion, these devices represent simple, elementary components to create achromatic and versatile photonic circuits.