Nonlinear optical-frequency conversion has greatly expanded the practical utility of lasers and has exhibited significant scientific and technological potential in many fields. For achieving high conversion efficiency, phase matching between interacting waves is a necessary condition.

However, despite considerable efforts, there are very few practical methods for achieving quasiperfect phase matching in homogeneous crystals. Phase matching remains impossible in principle. The key issue is that the refractive indices associated with the interacting waves are difficult to control precisely.

Recently, researchers at Shanghai Institute of Optics and Fines Mechanics (SIOM) of Chinese Academy of Sciences proposed and demonstrated a new phase-matching method based on the linear electro-optic effect, termed“voltage-tuning phase-matching” (VTPM).It can achieve quasiperfect phase matching and has numerous remarkable advantages. They demonstrated experimentally temperature-insensitive FHG, and analyzed numerically Angle- and wavelength-dependent FHG. They established a basic theoretical framework for applying nonlinear materials using the proposed method.

The study was published in PHYSICAL REVIEW LETTERS
(http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.043901)

The experimental and analytical results support the feasibility and superiority of the method. Thus, this method paves the way for the design of novel nonlinear optical devices and provides a new perspective for the further study of nonlinear optical interactions. Moreover, this idea can endow materials with normally nonexistent characteristics, which may open an avenue for expanding the applications of conventional nonlinear materials and even low birefringence and isotropic materials. They anticipate that this method will have far-reaching implications in the field of nonlinear optics.

This work is supported by the National Natural Science Foundation of China

FIG. 1. Schematic of (a) SHG under condition of phase mismatch and (b) SHG with VTPM.(Image by Cui Zijian)