Mode hybridization analysis in thin film lithium niobate strip multimode waveguides

Archana Kaushalram,Gopalkrishna Hegde,Srinivas Talabattula

doi:10.1038/s41598-020-73936-x

Archana Kaushalram, Gopalkrishna Hegde + Show 1 more

Open Access

https://doi.org/10.1038/s41598-020-73936-x

Copy DOI

Abstract

Mode hybridization phenomenon in air-cladded X-cut Y-propagating and Z-propagating thin film lithium niobate strip multimode waveguides is numerically studied and a mathematical relation between structural parameters leading to hybrid modes is formulated. Dependence of hybrid modes on waveguide dimensions, sidewall angles and wavelength is also analyzed. The results obtained are used to design lithium niobate on insulator (LNOI) taper for converting fundamental TM mode to higher order TE mode, and an optimum length for achieving a high conversion efficiency of 99.5% is evaluated. Birefringent Y-propagating LN and isotropic Z-propagating LN tapers are compared in terms of length, figures of merit, and fabrication tolerance. Tapers exhibit a broad bandwidth of 200 nm with an extinction ratio less than − 18 dB. The results of mode hybridization analysis are useful in design optimization of adiabatic tapers, tunable time delays, optical interconnects, mode converters and demultiplexers for mode division multiplexing (MDM) applications.

Highlights

That strongly depend on shift in hybrid points resulting from fabrication errors like sidewall angles and width deviations are studied in detail
Mode hybridization in air-cladded strip multimode waveguides on X-cut Lithium niobate on insulator (LNOI) and SOI is analyzed numerically to obtain mathematical relation between structural parameters leading to hybrid modes
Relation between width and height that lead to transverse electric (TE) polarization fraction of 0.4–0.6 is found to be a two-term Power series in Y-propagating and 3 rd order polynomial in Z-propagating LN strip waveguides

Summary

Introduction

That strongly depend on shift in hybrid points resulting from fabrication errors like sidewall angles and width deviations are studied in detail. The horizontal ( Eh) and vertical ( Ev) electric field components for hybrid mode at point A are shown in Fig. 2 and is observed that Eh and Ev are almost equal. In X-cut Y-propagating LN, qTE modes see an extraordinary index ( ne), while qTM modes see an ordinary index (no), which results in birefringence or velocity difference between these modes. In X-cut Z-propagating LN, with Z being the optic axis of the crystal, both qTE and qTM modes see an ordinary index (no), which is Scientific Reports | (2020) 10:16692 |.

Methods

Findings

Conclusion