Long-period gratings on lithium-niobate waveguides : phase-matching turning points for ultra-broadband mode conversion

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Original languageEnglish
Pages (from-to)3984-3987
Journal / PublicationOptics Letters
Issue number16
Online published2 Aug 2022
Publication statusPublished - 15 Aug 2022



We analyze a polymer long-period grating (LPG) formed on the surface of a z-cut lithium-niobate (LN) few-mode waveguide for TM00-TM10 mode conversion. We identify and explore the turning points along the phase-matching curves of the LPGs for the achievement of ultra-broadband mode conversion. We fabricate a number of gratings with annealed proton-exchanged LN waveguides and our experimental results agree well with the theoretical results. A typical fabricated grating operating near the turning point provides a mode extinction ratio larger than 20 dB from 1550nm to a wavelength longer than 1700 nm, and another one provides a mode extinction ratio larger than 10 dB from 1464nm to a wavelength longer than 1700 nm. Our gratings show good thermal stability. The structure of the LPG on LN waveguide could be applied to the realization of ultrabroadband high-speed mode switches for mode-multiplexing applications.

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