Doppler difference velocimetry using a 2-core photonic crystal fibre

In this paper we describe the first use of a two core photonic crystal fibre for fringe projection for use in a Doppler difference velocimeter. The two-core fibre, with a core separation of 17 /spl mu/m, projects a series of fringes when both cores are illuminated with 633 nm light simultaneously. Light scattered from moving particles is coupled into a separate multi-mode (50/125 /spl mu/m) receiving fibre and detected using a silicon detector and amplifier. The measured reflection intensity signal is processed in the frequency domain to obtain the velocity component of the moving particle.