Tunable and efficient ultraviolet generation in nanophotonic lithium niobate

Kavli Affiliate: Scott K. Cushing

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| Summary:

On-chip ultraviolet sources are of great interest for building compact and
scalable atomic clocks, quantum computers, and spectrometers; however, few
material platforms are suitable for integrated ultraviolet light generation. Of
these materials, thin-film lithium niobate is the most competitive due to its
ability to be quasi-phase-matched, optical confinement, and nonlinear
properties. Here, we present efficient (197 $pm$ 5 %/W/cm$^{2}$) second
harmonic generation of UV-A light in a periodically poled lithium niobate
nanophotonic waveguide. We achieve on-chip ultraviolet powers of 30 $mu$W,
demonstrating the potential for compact frequency-doubling of common near-IR
laser diodes. By using a large cross section waveguide (600 nm film thickness),
we achieve insensitivity to fabrication errors, and can attain first-order
quasi-phase-matching with relatively long poling periods (>1.5 $mu$m). The
device also demonstrates linear wavelength tunability using temperature. By
varying the poling period, we have achieved the shortest reported wavelength
(355 nm) generated through frequency doubling in thin-film lithium niobate. Our
results open up new avenues to realize ultraviolet on-chip sources and
chip-scale photonics.

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