Researchers from Politecnico di Milano, Italy, and Southeast University, China, have developed a novel metasurface that could enhance nonlinear optical processes, offering potential benefits for the energy sector, particularly in sensing, THz generation, and ultrafast electro-optic modulation. The team, led by Michele Celebrano and Chunhui Wang, has published their findings in the journal Nature Communications.
The researchers have created a large-area metasurface using thin-film lithium niobate (TFLN) technology. This metasurface comprises a slanted titanium dioxide (TiO2) nanograting on etchless TFLN, fabricated through scalable nanoimprint lithography. The key innovation lies in the optimal coupling of quasi-bound state in the continuum (q-BIC) modes with a narrowband pulsed laser pump, enabling efficient narrowband second-harmonic generation (SHG).
Second-harmonic generation is a nonlinear optical process where two photons with the same frequency combine to generate a new photon with twice the energy, and therefore twice the frequency and half the wavelength, of the initial photons. The demonstrated normalized SHG efficiency is 0.15% cm²/GW, which is among the highest reported for lithium niobate (LN) metasurfaces. Notably, the low pump peak intensity used in this research enables SHG even with continuous-wave pumping, making it suitable for integrated and portable photonic applications.
The researchers also achieved SHG wavelength tuning from 870 to 920 nm with stable output power and polarization control by using off-normal pump illumination. This versatility opens new opportunities for various applications, including sensing, THz generation and detection, and ultrafast electro-optic modulation of nonlinear optical signals.
In the energy sector, these advancements could lead to more efficient and compact devices for sensing and monitoring, improved THz imaging for quality control and safety inspections, and faster electro-optic modulation for high-speed data transmission and processing. The use of scalable nanoimprint lithography also ensures that these innovations can be mass-produced, making them accessible for widespread industrial applications.
The research was published in the journal Nature Communications, under the title “Efficient and tunable narrowband second-harmonic generation by a large-area etchless lithium niobate metasurface.”
This article is based on research available at arXiv.