Imprinting gradient refractive index micro-structure in GeS2–Ga2S3–KCl glass for broadband diffraction grating

Abstract

A gradient refractive index (GRIN) microstructure covering visible to middle infrared wavelength is imprinted in chalcohalide glass through a simple and inexpensive microthermal poling process. The effects of poling voltage (U), temperature (T), and time (t) on diffraction, morphology, elemental distribution and transmittance of the glass are thoroughly investigated. An effective imprinting formation region of GRIN microstructure based on the U and T values is observed under a fixed t of 30 min. Deformation of morphology and diffraction order increase with increasing U and T saturated at approximately 750 V and 150 °C respectively. The process can be divided into three stages, adding voltage, maintaining voltage and decreasing temperature. During the front two stages, K+ ions depletion layer forms in subsurface of sample anode-side, accompanied by the transformation of homopolar bonds Ga–Ga and S–S into heteropolar bond Ga–S. Moreover, most parts of K+ ions migrate back to the depletion layer during the last stage.