Ultra-broadband fabrication-tolerant mode division (de)multiplexer on thin film Lithium niobate

Abstract

Mode division (de) multiplexers based on asymmetric directional coupler are designed and analysed on the emerging thin film lithium niobate platform in rib, buried and strip waveguide configurations. Rib configuration offers a large bandwidth of ∼215 nm with a crosstalk level lower than −10 dB, and provides a large fabrication tolerance of ±50 nm. Strip configuration exhibits a better crosstalk of −19.7 dB at the design wavelength of 1550 nm, and has a reasonable fabrication tolerance of ±30 nm. Performance of (de) multiplexers on all three waveguide configurations are analysed in terms of modal crosstalk, mode conversion efficiency, bandwidth, along with fabrication tolerance to width and sidewall angle. The influence of electro-optic effect on the coupling length of lithium niobate mode multiplexers is also investigated. © 2020 Elsevier B.V.