High-accuracy long distance alignment using single-mode optical fiber and phase plate

A long distance alignment technique is developed using the combination of a single-mode optical fiber and a phase plate. The characteristics of the diffraction pattern of a Gaussian beam passing through a π step phase plate are analyzed theoretically. The feasibility of the method is validated in theory and with computer-simulation, and the factors affecting the alignment precision are discussed. The reliability of the alignment technique is demonstrated when it is used in the measurement of the straightness of a 12 m-track, in which measured results using the new technique coincide very well with those using an HP5528 dual frequency laser interferometer.