Enhanced wavelength conversion to advance quantum information networks

Advancements in quantum information technology are paving the way for faster and more efficient data transfer. A key challenge has been ensuring that qubits, the fundamental units of quantum information, can be transferred between different wavelengths without losing their essential properties, such as coherence and entanglement. As reported in Advanced Photonics, researchers from Shanghai Jiao Tong University (SJTU) recently made significant strides in this area by developing a novel method for broadband frequency conversion, a crucial step for future quantum networks.

The SJTU team focused on a technique using X-cut thin film lithium niobate (TFLN), a material known for its nonlinear optical properties. They achieved broadband second-harmonic generation—an important process for converting light from one wavelength to another—with a remarkable bandwidth of up to 13 nanometers. This was accomplished through a process called mode hybridization, which allows for precise control over the frequency conversion in a micro-racetrack resonator.

(a) Schematic of the birefringent racetrack resonator on X-cut TFLN, where SH-band light experiences a mode-hybridization in the half-circle waveguide. (b) Principle of SQPM. Inset: varying SQPM SHG intensity with the periodically inverted efficient nonlinear coefficient (m=5), and a comparison among the SHG processes under the perfect phase-matching (PPM), QPM, SQPM, and phase mismatching (PMM). (c) Effective refractive indices of the hybrid mode in SH-band and TE0 mode in FW-band in the half-circle waveguide, and the vector mismatch dispersion between them. (d) Average vector mismatch dispersion versus different FW wavelengths, which is positive in the straight waveguide and negative in the half-circle waveguide. Credit: T. Yuan, J. Wu, et al., doi 10.1117/1.AP.6.5.056012

According to corresponding author Professor Yuping Chen, “An efficient second-order nonlinear process with widely-tunable pump bandwidth has been a long-pursued goal, owing to the extensive applications in wavelength division multiplexing networks, ultrashort pulse nonlinearity, quantum key distribution, and broadband single-photon source generation.” She adds, “Thanks to the great progress in fabrication technology on the TFLN platform, this work will pave the way to chip-scale nonlinear frequency conversion between the ultrashort optical pulses and even the quantum states.”  

This breakthrough could have wide-ranging implications for integrated photonic systems. By enabling on-chip tunable frequency conversion, it opens the door to enhanced quantum light sources, larger capacity multiplexing, and more effective multichannel optical information processing. As researchers continue to explore these technologies, the potential for expanding quantum information networks grows, bringing us closer to realizing their full capabilities in various applications.

For details, see the original Gold Open Access article by T. Yuan, J. Wu, et al., “Chip-scale nonlinear bandwidth enhancement via birefringent mode hybridization,” Adv. Photon. 6(5), 056012 (2024), doi 10.1117/1.AP.6.5.056012