Wavelength-dependent loss measurements in polysilicon modified optical fibres

The recent advancements in on-chip silicon photonics has lead to the demonstration of a number of compact optoelectronic devices owing to the unique material properties of the semiconductor. Although to date most of the major advancements have been based on single-crystal silicon waveguides, lately there has been an increased interest in polycrystalline structures for integrated devices as the deposition process is easier, allowing for more design flexibility. As a photonics material, polysilicon offers good optical and electronic properties but it is typically associated with large losses due to scattering off grain boundaries and surface imperfections at the core-cladding interface. This paper presents measurements of the optical losses of silicon core fibres as a function of wavelength. These fibres are fabricated by depositing silicon inside a silica capillary template using a high-pressure processing technique. To quantify the wavelength dependent losses of silicon fibres, cut-back measurements are performed by filtering the output of a supercontinuum source to yield an average launch power of ~0.5 mW. A loss of ~8 dB/cm at 1.55 mum is obtained, comparable with the lowest losses reported in the literature. Good agreement with a lambda^-4 fit indicates that the losses are primarily due to Rayleigh scattering.