Source: http://proxy.osapublishing.org/optica/abstract.cfm?uri=optica-6-3-380
Timestamp: 2019-04-23 13:29:24+00:00

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Integrated photonics is a powerful platform that can improve the performance and stability of optical systems while providing low-cost, small-footprint, and scalable alternatives to implementations based on free-space optics. While great progress has been made on the development of low-loss integrated photonics platforms at telecom wavelengths, the visible wavelength range has received less attention. Yet, many applications utilize visible or near-visible light, including those in optical imaging, optogenetics, and quantum science and technology. Here we demonstrate an ultra-low-loss integrated visible photonics platform based on thin-film lithium niobate on an insulator. Our waveguides feature ultra-low propagation loss of 6 dB/m, while our microring resonators have an intrinsic quality factor of 11 million, both measured at 637 nm wavelength. Additionally, we demonstrate an on-chip visible intensity modulator with an electro-optic bandwidth of 10 GHz, limited by the detector used. The ultra-low-loss devices demonstrated in this work, together with the strong second- and third-order nonlinearities in lithium niobate, open up new opportunities for creating novel passive and active devices for frequency metrology and quantum information processing in the visible spectrum range.
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Fig. 1. (a)–(c) Finite element simulation of TE00 waveguide mode near three different wavelengths: 635 nm, 850 nm, and 1550 nm; wW=480 nm is waveguide width and wT=120 nm is LN slab thickness. (d) False-color SEM micrograph of the waveguide cross section. (e) 2D AFM scan on LN waveguide. (f) AFM line profile of LN waveguide.
Fig. 2. (a) SEM micrograph of a fabricated microring resonator (radius=100 μm). (b) SEM image of the coupling region.
Fig. 3. (a) Measured transmission spectrum of TFLN microring cavity near 635 nm wavelengths. (b)–(d) Fit of the resonance dips to Lorentzian function at wavelengths of 637 nm, 730 nm, and 800 nm, respectively. Experimental data shown as blue dots and fit function shown as red line.
Fig. 4. (a) Mask layout of fabricated device. (b) Measured transmission of cascaded Y-splitter tree as a function of number of Y-splitter branches. The orange line shows a linear fit with a slope of −3.21 dB/splitter. (c) Dark field optical microscope image of the unbalanced MZI. Scale bar: 50 μm. (d) Measured transmission spectrum of the MZI showing extinction ratios of ∼30 dB. Inset: SEM micrograph of Y-splitter section. Scale bar: 2 μm.
Fig. 5. (a) Optical image of the fabricated LN amplitude modulator. (b) Measured normalized transmission versus applied DC voltage showing a half-wave voltage of 8 V for a 2-mm-long device at a wavelength of 850 nm. Measured electro-optical response of the amplitude modulator. (c) The 3-dB cutoff frequency is ∼10 GHz, limited by the detector. Inset: Measured electrical insertion loss (S21 parameters) shows an electrical (3-dB) bandwidth of 17 GHz.

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