Fabrication of Chalcogenide Glass Based Hexagonal Gapless Microlens Arrays via Combining Femtosecond Laser Assist Chemical Etching and Precision Glass Molding Processes

Abstract

Chalcogenide glasses (ChGs) are emerging as critical infrared (IR)-enabled materials in advanced IR optical systems by the wealth of their transparency in the key wide infrared (IR) transmission window. However, fabrication of ChG-based integrated micro-optical components in an efficient and economical way remains a huge challenge. In this paper, a 3D close-packed hexagonal microlens array (MLA) possessing over 6000 convex hexagonal micro-lenslets with the size of tens of micrometers within a footprint of 10 mm × 10 mm on a Ge20Sb15Se65 ChG surface was successfully fabricated via a precise thermal-mechanical molding process. The master mold of ChG MLA was firstly fabricated by a femtosecond laser-assisted chemical etching process and then transferred on to the surface of the ChG via a precision thermo-mechanical molding process, which resulted in a convex MLA. The morphology, imaging and focusing performances of the as-prepared ChG MLA were investigated and demonstrated the advancement of the method. Meanwhile, the IR transmittance and x-ray diffraction image of the ChG MLAs were measured to verify the structural and compositional stability of the ChG under the given molding conditions. The combined results proved a new route to mass production of miniaturized gapless ChG MLAs for advanced infrared micro-optics.

Theoretical and Experimental Study on Hot-Embossing of Glass-Microprism Array without Online Cooling Process

“…The shape of the microprism was approximately trapezoidal, which was consistent with simulation analysis (see Figure 6b). Therefore, this proves that the glass-microprism array could be molded without online cooling, and molding efficiency was significantly improved compared with the micro-hot-embossing time of 138 min in [28].…”

“…Generally, the hot-embossing glass-microlens cycle is long due to its long cooling time to eliminate thermal stress [27]. A hexagonal-microlens array was fabricated via a precise thermal-mechanical embossing process, but the time of the glass-embossing process reached 138 min with cooling time of 88 min [28]. Refractive lens and diffractive gratings were developed, but the total time of hot embossing lasted about 250 min, including the cooling time of 120 min [29].…”

Fabrication of a Chalcogenide Glass Microlens Array for Infrared Laser Beam Homogenization

“…The magnified image of the quasi-periodic MLA in Figure 3 clearly shows that the prepared MLA along the Y-axis has an irregular shape, a smooth surface, and a high filling factor (up to 100%). The molding conditions were determined from a previous study, which examined the effect of temperature and pressure on the plasticity of ChG, as shown in Table 2 [22]. To prevent the ChG from breaking, a slow cooling process followed by a rapid cooling process was chosen for the cooling stage.…”

“…ChG has excellent optical properties, specifically: (1) a transparent region covering 1.064 µm lasers and three infrared atmospheric windows of 1~3 µm, 3~5 µm, and 8~12 µm; (2) a low refractive index temperature coefficient and a low dispersion; and (3) high optical uniformity. Since its introduction in the 1950s, ChG has been widely used in infrared lenses [22,23], fiber-optic lasers [24], guided-wave photonic devices [25], and phase-change materials [26]. Therefore, chalcogenide glass with a microlens array can be used to homogenize infrared beams.…”

Fabrication Large-scale Diffractive Lens Arrays on Chalcogenide Glass by Means of Step-and-Repeat Hot Imprinting and Non-Isothermal Glass Molding

“…The focusing and imaging performance of diffractive lens depends on the form accuracy and surface nish of its feature. Many methods for the manufacture of diffractive lens arrays have been extensively investigated, including laser direct writing [5][6][7], focused ion beam [8], and photolithography [9]. By increasing the number of orders, the optical properties of the multiorder diffractive optical elements fabricated by lithography can be obviously improved.…”