Tunable and efficient ultraviolet generation with periodically poled lithium niobate.

Area of Science:

• Photonics
• Materials Science
• Quantum Technologies

Background:

• Integrated ultraviolet (UV) sources are crucial for compact atomic clocks, quantum computers, and spectrometers.
• Thin-film lithium niobate (TFLN) offers excellent properties like sub-micron modal confinement and strong nonlinearity for integrated photonics.
• Challenges like fabrication sensitivity, photorefractive effects, and losses have limited TFLN's UV applications.

Purpose of the Study:

• To demonstrate efficient UV-A light generation in a periodically poled lithium niobate nanophotonic waveguide.
• To overcome limitations of standard quasi-phase matching for UV generation in TFLN.
• To explore the potential of TFLN for compact, on-chip UV sources.

Main Methods:

• Fabrication of periodically poled lithium niobate nanophotonic waveguides.
• Utilizing large cross-section waveguides for first-order UV quasi-phase matching.
• Employing temperature for linear wavelength tunability.
• Achieving second harmonic generation (SHG) of UV-A light.

Main Results:

• Efficient second harmonic generation (SHG) with a normalized efficiency of 197 ± 5%/W/cm².
• Generation of on-chip UV powers up to approximately 30 µW.
• Demonstration of linear wavelength tunability via temperature control.
• Achieved the shortest reported wavelength (355 nm) for frequency doubling in TFLN by varying poling periods (>1.5 µm).

Conclusions:

• Efficient UV-A light generation is achievable in TFLN nanophotonic waveguides.
• The developed method overcomes previous limitations for UV applications in TFLN.
• This work paves the way for compact, chip-scale UV sources by frequency doubling near-IR laser diodes.