Abstract
A lithium niobate on an insulator ridge waveguide allows constructing high-density photonic integrated circuits thanks to its small bending radius offered by the high index contrast. Meanwhile, the significant mode-field mismatch between an optical fiber and the single-mode lithium niobate waveguide leads to low coupling efficiencies. Here, we demonstrate, both numerically and experimentally, that the problem can be solved with a tapered single mode fiber of an optimized mode field profile. Numerical simulation shows that the minimum coupling losses for the TE and TM mode are 0.32 dB and 0.86 dB, respectively. Experimentally, though without anti-reflection coating, the measured coupling losses for TE and TM mode are 1.32 dB and 1.88 dB, respectively. Our technique paves a way for a broad range of on-chip lithium niobate applications.
Highlights
Lithium niobate on insulator (LNOI) is an emerging platform which has shown promising potential for integrated photonics due to its numerous advantages of high refractive-index contrast, wide transparent window (0.35-5 μm), large nonlinear coefficient, and excellent electro-optic characteristics [1,2,3,4,5]
Photonic devices based on LNOI, including waveguides [6,7], microring resonators [1, 8], microdisk resonators [9,10,11], and photonic crystal cavities [12,13] have been developed
One major obstacle of integrated LNOI photonics for the practical applications is the lack of efficient light coupling mechanism, especially between standard single-mode optical fibers and single-mode lithium niobate (LN) waveguides, which can greatly degrade the device performances [4,26]
Summary
Lithium niobate on insulator (LNOI) is an emerging platform which has shown promising potential for integrated photonics due to its numerous advantages of high refractive-index contrast, wide transparent window (0.35-5 μm), large nonlinear coefficient, and excellent electro-optic characteristics [1,2,3,4,5]. One major obstacle of integrated LNOI photonics for the practical applications is the lack of efficient light coupling mechanism, especially between standard single-mode optical fibers and single-mode LN waveguides, which can greatly degrade the device performances [4,26].
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