Diffractive beam shaping elements for high power fibre coupling

In this paper, we discuss the design and fabrication of diffractive elements for coupling applications involving multiple fibres. We present a diffractive beam homogeniser for coupling to a fibre bundle. The flexibility of diffractive optics for fibre coupling is demonstrated by elements combining homogenising and beam splitting functions for coupling to two or four individually mounted fibres. The two way fan out was designed as a binary element to minimise the computational time and fabrication complexity. The element had a diffraction efficiency of 54%, which was considered to be too low. This was addressed in the design of the four way fan out which was designed as a 16 level element. Again the geometry was chosen to minimise the computational time required. The efficiency of the four way fan out is approximately 80%.