Long Length/Small Core Step-Index Silicon Core Fiber Fabricated by Improved Powder-in-Tube Process

The development of silicon-core fibers have drawn strong interest over the last decade. Indeed, silicon is a material offering interesting properties such as mid-wave infrared transparency (1-7 μm), high refractive index (3.48 @ 1.55 μm) and large third order non linearity (≈ 1.5×10 ^-13 cm ² /W). Until now, three fabrication processes have been developed to achieve glass-clad silicon-core fibers: the high-pressure microfluidic chemical deposition method [1], the molten core method from silicon rods [2] and the powder-in-tube method [3]. This last one shows a very high potential to achieve hybrid optical fibers as it allows not only to use a wide range of materials but it is also compatible with the stack-and-draw process; in this way, many different designs of fibers can be especially drawn. Unfortunately, fibers fabricated by this method are very short, only a few centimetres long because of the mechanical stresses accumulation at the interface between the two materials which have different thermal expansion coefficients (Si: 3×10 ^-6 K ^-1 ; SiO ₂ : 5×10 ^-7 K ^-1 ), and because of the presence of air between the grains.