Abstract

The traditional method for measuring spatial coherence is to use Young's double slit arrangement or some similar variant. Although quick and easy, this technique has some drawbacks, particularly in replacing and realigning successive sets of apertures. A new method is described using single-mode optical fibers to sample the beam, and a γ-coupler to combine the light from the two points. As one fiber end is translated along the fiber axis (perpendicular to the wavefront), fringes are observed at the output. This method has the added advantage of being able to compare any two arbitrarily chosen points on the wavefront, and symmetry does not have to be assumed. Spatial coherence functions for several different lasers have been measured and compared with results using the classical method. Visibility is measured as a function of aperture spacing and of bias current (for laser diodes). No fringes are observed for below lasing threshold operation of laser diodes or for a light emitting diode (LED).

© 1989 Optical Society of America