Optical fibre angle of acceptance transformation - using graded refractive index cylindrical lens to keep response constant over cone and bent fibre for mode mixing

摘要

A lens having a graded refractive index is placed on the end of a stopped refractive index optical fibre. The system is especially useful in measurement and control instruments such as optical characterisation or colour analysers. The acceptance angle is determined by the focal length and focus of a radially graded refractive index rod lens whose index decreases as the square of the radius. Such a lens is capable of powers between 200 and 2000 dioptre without large alterations. The lens can be fixed so as to match on a priori angular acceptance template. Propagation modes in the fibre are mixed by subjecting the fibre to non periodic curves in the form of an arch without imposing stress on the fibre surface homogeneity and flatness can be measured by varying the angular incidence and measuring the fibre output with a controlled source. The response is maintained constant and equal to the axial response over a cone of acceptance.