Broadband integrated beam splitter using spatial adiabatic passage.

T Lunghi,S Tascu,A M Apetrei,M Bellec,F Doutre,N Belabas,M P De Micheli,A P Rambu,S Tanzilli,O Alibart

doi:10.1364/oe.26.027058

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±0.03 and 0.48±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 π. Thanks to their independence to material dispersion, these devices represent simple, elementary components to create achromatic and versatile photonic circuits.

Highlights

The ability to coherently control the spatial degree of freedom of optical beams is fundamental in integrated optics
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
Spatial adiabatic passage (SAP) [2] currently emerges as a novel approach to fully transfer an optical beam from a waveguide to another one [3]

Summary

Introduction

The ability to coherently control the spatial degree of freedom of optical beams is fundamental in integrated optics. Spatial adiabatic passage (SAP) [2] currently emerges as a novel approach to fully transfer an optical beam from a waveguide to another one [3] This mechanism has shown a remarkable robustness against fabrication imperfections and wavelength dispersion. Chung et al [9] propose an alternative architecture based on 2-folded-SAPs and showed numerically an extremely broad achromatic response Both these works focused only on the amplitude splitting capabilities but we show here that SAP design can be adapted to engineer 50/50 beam splitters with a phase relationships between the output beams being either 0 or π all over the full bandwidth. 2-foldedSAP provides two output beams in phase while f-SAP provides two beams of opposite phase independently of the wavelength

Spatial adiabatic passage in theory

Findings

Conclusion