Project Researcher: Jiho Han
This research project has investigated the feasibility of a holographic optical fibre that could project an arbitrary image directly from it. The most promising and immediate potential application is beam shaping, though it may also be useful for beam splitting, or low information content display, such as indicators.
A Matlab program was developed that takes a desired image and calculates the “best” phase hologram. It uses the Gerchberg-Saxton algorithm to find the phase hologram, and Rayleigh-Sommerfield’s diffraction formula with Fresnel and Fraunhofer approximations for calculating the wave propagation.
In order to experimentally demonstrate the holographic optical fibre, a FIB system is selected as the machining platform, and a fibre mount is designed to ensure geometric compatibility. A hologram for a ring shaped beam is calculated, and the features simplified to aid ease of manufacturing. On coupling a laser into the fibre, the ring beam profile results as predicted.
The figure shows the surface profile measurement of the holographic optical fibre tip, and beam measurement for the output beam. The step height in the hologram is approximately 700nm, and (Radius)/(Distance from fibre tip) for the output beam measured 0.083 as compared to the predicted 0.1.
Potential further work includes machining holograms for more complicated shapes, study on suitable integration into laser systems, and investigation for suitability for high power lasers.