GPU accelerated toolbox for real-time beam-shaping in multimode fibres.

We present a GPU accelerated toolbox for shaping the light propagation through multimode fibre using a spatial light modulator (SLM). The light is modulated before being coupled to the proximal end of the fibre in order to achieve arbitrary light patterns at the distal end of the fibre. First, the toolbox optimises the acquisition time of the transformation matrix of the fibre by synchronous operation of CCD and SLM. Second, it uses the acquired transformation matrix retained within the GPU memory to design, in real-time, the desired holographic mask for on-the-fly modulation of the output light field. We demonstrate the functionality of the toolbox by acquiring the transformation matrix at the maximum refresh rate of the SLM - 204 Hz, and using it to display an on-demand oriented cube, at the distal end of the fibre. The user-controlled orientation of the cube and the corresponding holographic mask are obtained in 20 ms intervals. Deleterious interference effects between the neighbouring points are eliminated by incorporating an acousto-optic deflector (AOD) into the system. We remark that the usage of the toolbox is not limited to multimode fibres and can be readily used to acquire transformation matrix and implement beam-shaping in any other linear optical system.