Ultra-compact, broadband adiabatic passage optical couplers in thin-film lithium niobate on insulator waveguides

Yi Xin Lin, Mohammadreza Younesi, Hung Pin Chung, Hua Kung Chiu, Reinhard Geiss, Quan Hsiang Tseng, Frank Setzpfandt, Thomas Pertsch, Yen Hung Chen

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


We report the first demonstration of broadband adiabatic directional couplers in thin-film lithium niobate on insulator (LNOI) waveguides. A three LN-waveguide configuration with each waveguide having a ridge cross section of less than 1 square micron, built atop a layer of SiO2 based on a 500-µm-thick Si substrate, has been designed and constructed to optically emulate a three-state stimulated Raman adiabatic passage system, with which a unique counterintuitive adiabatic light transfer phenomenon in a high coupling efficiency of >97% (corresponding to a >15 dB splitting ratio) spanning telecom S, C, and L bands for both TE and TM polarization modes has been observed for a 2-mm long coupler length. An even broader operating bandwidth of >800 nm of the device can be found from the simulation fitting of the experimental data. The footprint of the realized LNOI adiabatic coupler has been reduced by >99% compared to its bulk counterparts. Such an ultra-compact, broadband LNOI adiabatic coupler can be further used to implement or integrate with various photonic elements, a potential building block for realizing large-scale integrated photonic (quantum) circuits in LN.

Original languageEnglish
Pages (from-to)27362-27372
Number of pages11
JournalOptics Express
Issue number17
StatePublished - 16 Aug 2021


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