Supercontinuum generation (SCG) enables ultrashort optical pulses to broaden dramatically in nonlinear materials, providing a powerful tool for spectroscopy and fundamental physics. Ultraviolet SCG (UV-SCG), in particular, allows direct probing of electronic transitions below 400 nm. In contrast to fiber- and bulk-based systems, on-chip SCG promises highly compact sources with millimeter-scale footprints. However, realizing UV-band SCG on-chip remains challenging, as most integrated photonic materials strongly absorb below 350 nm and exhibit normal dispersion that disrupts phase-matching, limiting efficient spectral broadening.
In a new paper published in Light: Science & Applications , the team led by Professor Daoxin Dai from Zhejiang University, China, and co-workers have demonstrated ultraviolet-C to mid-infrared supercontinuum on a chip, leveraging the exceptional transparency window and second-order nonlinearity of lithium tantalate. A key innovation is the introduction of chirped periodically poled lithium tantalite (PPLT) with submicron ferroelectric domains. Utilizing 3-wave-mixing processes under quasi-phase-matching conditions, they created the shortest ultraviolet wavelength ever reported from a chip—below 270 nm—while reaching 2400 nm in the mid-infrared, covering more than three octaves with just 100 pJ pulse energy on a chip for the first time. This work establishes thin-film lithium tantalate as a versatile platform for full-spectrum nonlinear photonics, opening new possibilities for integrated ultraviolet sources.
In this study, the researchers have overcome a longstanding fabrication challenge in achieving submicron ferroelectric domains, enabling multi-period poling designs with domain sizes ranging from 0.95 to 10 μm for UV-to-MIR spectral engineering. By strategically engineering cascaded second-harmonic generation and sum-frequency generation, they demonstrate the first on-chip SCG reaching the deep-UV region at 270 nm. Simultaneously, mid-infrared spectral broadening is achieved through difference-frequency generation within the same waveguide. Such nonlinear processes generates a supercontinuum exceeding three octaves, achieved even with remarkably low pump energy of 100 pJ. These scientists summarize the operational principle of their supercontinuum source on chip:
“We chose thin-film lithium tantalate (LT), a rapidly emerging integrated photonics platform, for supercontinuum generation, leveraging its exceptional transparency window and strong second-order nonlinearity. Thin-film LT combines near-zero birefringence, outstanding ultraviolet transparency extending down to 260 nm and spanning a broad spectral range from 260 to 5500 nm, an enhanced optical damage threshold, and χ² nonlinear coefficients (~21 pm/V) comparable to those of lithium niobate. These unique properties make LT an ideal platform for ultraviolet supercontinuum generation and broadband spectral engineering.”
"The structure comprises three key sections with distinct waveguide widths and poling periods," they explained. "The first section enables cascaded χ² processes for near-infrared supercontinuum generation, the second facilitates up-conversion to produce ultraviolet and visible light, and the third supports down-conversion for mid-infrared emission."
"This ultraviolet supercontinuum source is also designed to target the characteristic absorption bands of environmental pollutants, including SO₂ (~300 nm), O₃ (~300 nm), acetone (~279 nm), and α,β-unsaturated carbonyl compounds such as crotonaldehyde (~290 nm), thereby providing a versatile tool for industrial process monitoring and environmental analytics," the researchers forecast.
Light: Science & Applications
Ultraviolet-C to Mid-infrared Supercontinuum Generation in Periodically Poled Lithium Tantalate Waveguides