Polarization- and wavelength-agnostic nanophotonic beam splitter

David González-Andrade,Christian Lafforgue,Delphine Marris-Morini,Xavier Le Roux,Eric Cassan,Laurent Vivien,Aitor V Velasco,Mathias Berciano,Elena Durán-Valdeiglesias,Carlos Alonso-Ramos,Pavel Cheben

doi:10.1038/s41598-019-40497-7

Abstract

High-performance optical beam splitters are of fundamental importance for the development of advanced silicon photonics integrated circuits. However, due to the high refractive index contrast of silicon-on-insulator platforms, state-of-the-art nanophotonic splitters are hampered by trade-offs in bandwidth, polarization dependence and sensitivity to fabrication errors. Here, we present a new strategy that exploits modal engineering in slotted waveguides to overcome these limitations, enabling ultra-broadband polarization-insensitive optical power splitters with relaxed fabrication tolerances. The proposed splitter design relies on a single-mode slot waveguide that is gradually transformed into two strip waveguides by a symmetric taper, yielding equal power splitting. Based on this concept, we experimentally demonstrate −3 ± 0.5 dB polarization-independent transmission for an unprecedented 390 nm bandwidth (1260–1650 nm), even in the presence of waveguide width deviations as large as ±25 nm.

Highlights

Silicon-on-insulator (SOI) platforms are becoming established as an enabling technology for next-generation photonic circuits for a wide range of applications, including telecom and datacom applications[1,2,3], radio-over-fibre systems[4,5], bio-sensing[6,7], LIDAR8 and absorption spectroscopy[9,10], to name a few
The single-mode operation of the slot waveguide is of fundamental importance to our device because it mitigates any wavelength-dependent beating between different waveguide modes, which is the main phenomenon limiting the bandwidths of Directional couplers (DCs) and Multimode interference couplers (MMIs)
We have proposed and experimentally demonstrated an ultra-broadband and polarization-independent optical beam splitter based on a single-mode slot waveguide with a symmetric slot-to-strip transition

Summary

Introduction

Silicon-on-insulator (SOI) platforms are becoming established as an enabling technology for next-generation photonic circuits for a wide range of applications, including telecom and datacom applications[1,2,3], radio-over-fibre systems[4,5], bio-sensing[6,7], LIDAR8 and absorption spectroscopy[9,10], to name a few. Directional couplers (DCs) are based on two parallel waveguides separated by a gap, enabling straightforward tuning of the power-splitting ratio by adequately selecting the coupling length Due to their mode-beating-based operational principle, DCs are intrinsically narrowband in nature and suffer from a low tolerance to fabrication errors and a strong polarization dependence[17,18,19]. Halir et al have experimentally demonstrated a device with a bandwidth broader than 300 nm[37] Their subwavelength engineered MMI presents insertion loss and imbalance below 1 dB over a 325 nm wavelength range, in addition to a compact footprint of only 3.25 × 25.4 μm[2], but operates only for TE polarization. We propose and experimentally demonstrate a new beam splitter concept based on modal-engineered slotted waveguides This design provides ultra-broadband and polarization-independent operation with relaxed fabrication tolerances. Our experimental results demonstrate a near-ideal transmission of −3 ± 0.5 dB in an unprecedented bandwidth of 390 nm for both the TE and TM polarizations

Methods

Results

Conclusion