Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol Investigation of third-order optical nonlinearities of copper doped germanium-gallium-sulfur chalcogenide glasses Xiaoyu Zhang a,b , Feifei Chen a,b,⁎ , Ruiqiang Lin a,b , Yicong Huang a,b , Shixun Dai a,b , Qiuhua Nie a,b , Xianghua Zhang c , Wei Ji d a Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies, Ningbo University, Ningbo 315211, China b Key Laboratory of Photoelectric Detection Materials and Devices of Zhejiang Province, Ningbo University, Ningbo 315211, China c Laboratory of Glasses and Ceramics, University of Rennes 1, 35042 Rennes Cedex, France d Department of Physics, National University of Singapore, 2 Science Drive 3, 117551, Singapore ARTICLE INFO Keywords: Chalcogenide glasses Raman spectroscopy and scattering Optical properties Nonlinear optics ABSTRACT A series of copper doped germanium‑gallium‑sulfur (GGS-Cu) chalcogenide glasses were synthesized by melt- quenching method. Raman spectra showed that the introduction of Cu could alter the main structure of GGS network, leading to modification of thermal, mechanical and optical properties of the GGS glasses, even at very low doping level. Femtosecond Z-scan measurements were employed to study the third-order optical non- linearities (TONL) of the GGS-Cu glasses at wavelength of 1550 nm. Significant improvement of TONL perfor- mance due to the Cu doping was observed, and its possible mechanism was studied. 1. Introduction The development of all-optical communication network requires photonic devices with small size, low energy consumption as well as fast processing speed. High optical nonlinear fibers have been considered as a key component for the fabrication of such devices due to their small modefield radius that would keep the propagation light power density at very high level [1]. In various fiber materials, chalcogenide glasses (ChGs) that refer to a category of glass constructed by chalcogen elements (S, Se, and Te) have attracted considerable attentions for their large third-order nonlinear susceptibility (χ (3) , at least two orders of magnitude larger than that of silica glasses) and fast nonlinear response time (< 200 fs) [2,3], as well as their very wide transmission range (0.4–25 μm), thus they have great potentials in realization of key devices in all-optical communication network as well as integrated photonic systems that based on infrared technologies [4,5]. In various kinds of ChGs, most of them are As-based glasses, how- ever, As is a highly toxic element, therefore some new glass composi- tions without As have draw people's attention [6,7]. In particular, sul- fide glasses based on germanium‑gallium‑sulfur (Ge-Ga-S, GGS) ternary system have been intensively studied for its visible transparency, high chemical stability, as well as its flexibility of glass property modifica- tion by means of changing chemical composition and post treatments [8–10], which made GGS ChGs a promising candidate for optics device fabrication. However, as compared to other category of ChGs (i.e. Se- and Te-based), sulfide glasses are known to manifest relatively small third-order optical nonlinearities (TONL), thus then many attempts had been made to engineer TONL properties of GGS ChGs for higher χ (3) value [11–13]. It have been reported that introduction of noble metal, such as Ag and Au could modify optical properties of the GGS ChGs and improve their TONL performance [13,14]. Copper as a common noble metal is known to have the capacity to inhibit the appearance of pho- toinduced phenomena in ChGs [15], and its enhancement to TONL properties of ChGs had also been reported [16]. However, few studies were conducted on Cu doped GGS ChGs, and its influence on optical properties as well as inner structural order of GGS ChGs remains un- clear. On the other hand, little is known about the TONL properties of GGS-based at telecom wavelength of 1550 nm. In this paper, we introduced copper to GGS (GGS-Cu) ChGs by melt- quenching method. Different from Ag and Au doping as reported in previous studies [13,14], the variation of GGS glass network induced by Cu doping is firstly observed in present study by Raman spectra. TONL properties of the GGS-Cu glasses are studied by femtosecond Z-scan technique at the wavelength of 1550 nm, and the significant enhance- ment of TONL properties by the introduction of Cu is observed and the possible mechanism is discussed. 2. Experimental GGS glass with the molar composition of 10Ga-25Ge-65S (referred http://dx.doi.org/10.1016/j.jnoncrysol.2017.09.002 Received 23 June 2017; Received in revised form 9 August 2017; Accepted 1 September 2017 ⁎ Corresponding author at: Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies, Ningbo University, Ningbo 315211, China. E-mail address: chencyin@sina.com (F. Chen). Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx 0022-3093/ © 2017 Published by Elsevier B.V. Please cite this article as: Zhang, X., Journal of Non-Crystalline Solids (2017), http://dx.doi.org/10.1016/j.jnoncrysol.2017.09.002