Multimode Fluoroindate Optical Fiber Coupler

Mid-Infrared wavelengths are attracting research attention because of its implications in a plethora of applications, including optical spectroscopy, chemical sensing, thermal imaging, light sources, and comb generation [1], [2]. However, the level of technological maturity is still limited because of the absence of the essential building blocks that are commercially available in silica optical fiber, such as couplers and splitters [3]. When considering soft glasses couplers (i.e. made of chalcogenide or fluoride glasses) fabricated by fused biconical taper, the main drawbacks concerns the fragility, the need for precise temperature and tension control, and the surface crystallization that leads to high excess loss [3]. Regarding fluoride optical fibers, side-polished bonding has been demonstrated in zirconium fluoride glass as well as couplers made via fused biconical tapering technique [2]. The latter technique is considered superior to side-etching and side-polishing in terms of reliability and repeatability [4]. In this manuscript, for the first time, the fabrication of a $2\times 2$ optical coupler based on fluoroindate optical fibers is reported. The $2\times 2$ optical coupler is fabricated via Vytran® GPX -2400 glass processing system. Two identical pieces of IFG MM (0.30) 100/160 (Le Verre Fluoré, Bruz, France) are cleaved through Vytran® LDC-400 optical fiber cleaver. The optical fibers are inserted in the low-index capillary and fused via Vytran ^® GPX-2400 glass filament processing system. The optical fibers are not twisted to avoid additional bend loss. The entire structure is securely clamped in the fiber holding blocks, making sure not to induce high transverse strain, and is tapered down to approximately 15% of the initial diameter, exploiting a filament starting power $P=12.2W$ .