Future quantum information networks operated on telecom channels require qubit transfer between different wavelengths while preserving quantum coherence and entanglement. Qubit transfer is a nonlinear optical process, but currently the types of atoms used for quantum information processing and storage are limited by the narrow bandwidth of up-conversion available. Therefore, how to achieve high efficiency broadband frequency conversion in chip scale is a rather important topic.

Here we present the first experimental demonstration of broadband and high-efficiency quasi-phase matching second-harmonic generation (SHG) in a chip-scale periodically poled lithium niobate thin film. We achieve a large bandwidth of up to 2 THz for SHG by satisfying quasi-phase matching and group-velocity matching simultaneously. Furthermore, by changing the film thickness, the central wavelength of the quasi-phase matching SHG bandwidth can be modulated from 2.70 μm to 1.44 μm. The reconfigurable quasi-phase matching lithium niobate thin film provides a significant on-chip integrated platform for photonics and quantum optics.

This work is done by Prof. Yuping Chen and Prof. Xianfeng Chen’s group. The results were published in Photonics Research entitled“Broadband Quasi-phase matching in MgO: PPLN film” (https://doi.org/10.1364/PRJ.6.000954). In this work we demonstrated the first chip scale broadband and high efficiency frequency second harmonic generation. It is of much importance for future quantum information processing and storage.

LN crystal is applied in many applications due to its unique nonlinear and quantum optical properties. Domain inversion is an effective way for quasi-phase matching and get high efficiency second harmonic generation. Due to large second order nonlinear coefficient, LN is thought to be an important supplementary material for silicon photonic chip material avoiding crosstalk problems when applied to large powers. At the same time the fine response to mechanic, heat and sound waves also make it a qualified platform. The advent of LN thin film revolutionized the industry and make highly efficient, low cost devices possible. It attracted much attention in the recent years.

OLAB has focused on bulk PPLN devices and waveguides. We realized polarization control, filter, phase modulator and so on in this platform. But for fast response modulators and low power consumption we need to integrated all the devices to chip scale. In this way large enhancement of nonlinear interactions will be realized and many new phenomena can be discovered.