The use of a triangular cyclic interferometer for obtaining two counter-propagating optical beams which are accurately collinear is described, and its performance including the tolerance sensitivity is analysed. A novel technique for facilitating fringe observation has led to the realisation of an instrument with a demonstrated angular alignment capability of 1 mu rad. The new design permits real-time monitoring of the interferometer. The whole alignment operation of the interferometer relies on visual observation of interference fringes.