The feasibility of tungsten-bronze oxides for optical lenses in powerful lasers is summarized. T. B type transparent ferroelectric oxide has excellent properties for a high electro-optical effect and a high nonlinear optical effect such as Second Harmonic Generation (SHG), but the reproductibility in growing crystals is poor. Using the melting method, the authors have grown T. B type Ba//2Na//1// minus //xLi//xNb//5O//1//5 ferroelectric single crystals and obtained some results concerning ferroelectric properties.