Silicon-Based TM0-to-TM3 Mode-Order Converter Using On-Chip Shallowly Etched Slot Metasurface

Chenxi Zhu,Xin Hu,Zhe Kang,Yue Dong,Bo Zhang,Yi Ni,Yin Xu,Peipeng Xu

doi:10.3390/photonics8040095

Abstract

Mode-order converters drive the on-chip applications of multimode silicon photonics. Here, we propose a TM0-to-TM3 mode-order converter by leveraging a shallowly etched slot metasurface pattern atop the silicon waveguide, rather than as some previously reported TE-polarized ones. With a shallowly etched pattern on the silicon waveguide, the whole waveguide refractive index distribution and the corresponding field evolution will be changed. Through further analyses, we have found the required slot metasurface pattern for generating the TM3 mode with high conversion efficiency of 92.9% and low modal crosstalk <−19 dB in a length of 17.73 μm. Moreover, the device’s working bandwidth and the fabrication tolerance of the key structural parameters are analyzed in detail. With these features, such devices would be beneficial for the on-chip multimode applications such as mode-division multiplexing transmission.

Highlights

Silicon photonics has attracted intensive research interest as an excellent platform for developing some ultradense on-chip photonic integrated circuits, due to its high refractive index contrast, low cost and compatibility with mature complementary metal-oxidesemiconductor (CMOS) technologies [1,2,3,4]
In order to solve this issue, high-performance mode-order converters which can change the input fundamental mode into the higherorder mode are the pivotal components for the on-chip mode-division multiplexing (MDM) applications [6,8,9,10]
Faced with more mode channel requirements of high-capacity on-chip MDM transmission [7,8], TM-polarized mode-order converters should be developed and their structures cannot refer to the TE-polarized ones directly due to their different polarization states

Summary

Introduction

Silicon photonics has attracted intensive research interest as an excellent platform for developing some ultradense on-chip photonic integrated circuits, due to its high refractive index contrast, low cost and compatibility with mature complementary metal-oxidesemiconductor (CMOS) technologies [1,2,3,4]. Some prevailing optimization methods (e.g., deep learning and topology optimization [16,17,18]) have been used to find the optimal structure pattern at the cost of quite time-consuming iterative calculations and complex patterns for the device fabrication Compared with these latest reports, some classical structures such as Mach−Zehnder interferometers (MZI) [19,20] and Bragg gratings [21,22] are still employed to realize the mode-order conversion due to their simple structures, high performance and clear working mechanisms. We found that this shallowly etched slot scheme had some scalability for the mode-order conversion, and more higher-order modes could be generated using such etched multimode waveguide structures Based upon these unique features, the proposed scheme and related devices would well support the on-chip multimode applications [26,27], such as on-chip MDM systems

Materials and Methods

Findings

Conclusions