Ultrashort broadband polarization beam splitter based on a combined hybrid plasmonic waveguide

Ken-Wei Chang,Chia-Chien Huang

doi:10.1038/srep19609

Abstract

We propose an ultracompact broadband polarization beam splitter (PBS) based on a combined hybrid plasmonic waveguide (HPW). The proposed PBS separates transverse-electric (TE) and transverse-magnetic (TM) modes using a bent lower HPW with vertical nanoscale gaps and a straight upper HPW with a horizontal nanoscale gap, respectively, without relying on an additional coupling region. This design considerably reduces the length of the PBS to the submicron scale (920 nm, the shortest PBS reported to date) while offering polarization extinction ratios (PERs) of ~19 dB (~18 dB) and insertion losses (ILs) of ~0.6 dB (~0.3 dB) for the TE (TM) mode over an extremely broad band of 400 nm (from λ = 1300 nm to 1700 nm, covering entirely second and third telecom windows). The length of the designed PBS can be reduced further to 620 nm while still offering PERs of 15 dB, realizing a densely photonic integrated circuit. Considering the fabrication tolerance, the designed PBS allows for large geometrical deviations of ±20 nm while restricting PER variations to within 1 dB, except for those in the nanoscale gaps smaller than 10nm. Additionally, we also address the input and ouput coupling efficiencies of the proposed PBS.

Highlights

We propose an innovative design for a Polarization beam splitters (PBSs) based on a combined HPW (CHPW) consisting of two parts: a bent lower HPW deposited on a SOI platform and formed by a high-index silicon (Si) core sandwiched between two low-index nanoscale layers of silicon dioxide (SiO2) and Ag and a straight upper HPW formed by a nanoscale layer of SiO2 sandwiched between Si and Ag layers
TE and TM modes are supported by the bent lower and straight upper HPWs, respectively, without the requirement of a coupling region that is typically indispensable in directional couplers (DC)-based PBSs
The bent lower HPW structure is formed by a Si core that is sandwiched successively between SiO2 and Ag layers, and the straight upper HPW structure (Fig. 1(a)) that is stacked on the lower part is formed by a horizontal SiO2 layer sandwiched between Si and Ag

Summary

Introduction

TE and TM modes are supported by the bent lower and straight upper HPWs, respectively, without the requirement of a coupling region that is typically indispensable in DC-based PBSs. The key idea allows the length of the proposed PBS to be shortened to the submicron scale while retaining satisfactory PERs and broad operating bandwidths. Note that the novel design of the proposed PBS allows TE and TM modes to be separated by the bent lower and straight upper HPW structures, respectively, without the requirement of a coupling region, making the length of the designed PBS extremely short.

Results

Conclusion