2D GeP as a Novel Broadband Nonlinear Optical Material for Ultrafast Photonics

A new member of the IV-V compounds, germanium-phosphorus (Ge-P) compounds, has been shown in experiment and theory to have a tunable bandgap (E-g), excellent chemical stability, strong in-plane anisotropy, and wide-range optical absorption, all indicating a promising future in electronic and optoelectronic applications. In this work, the application potential of Ge-P compounds as nonlinear optical (NLO) materials in ultrafast photonics is studied for the first time. The strong light-matter interaction, broad and tunable E-p, and broadband and strong optical response make GeP a likely NLO material for photonics, especially in infrared photonic devices. In addition, 2D GeP nanosheets are mixed with poly(vinylidene fluoride) (PVDF) to obtain a GeP@PVDF composite film, which further improves the stability of the GeP and, for the development of organic photonic devices, helps to slow its degradation. From Z-scan data and fitting results, it is found that GeP has an excellent broadband NLO response. Moreover, using the GeP@PVDF composite film as a saturable absorber, a high-stability femtosecond laser with a 722 fs pulse width is obtained in the telecommunications band. Preliminarily, Ge-P compounds display excellent optical properties suggesting that they may be used as NLO materials in advanced photonic devices.