FIBER COUPLING EFFICIENCY FOR RANDOM LIGHT AND ITS APPLICATIONS TO LIDAR

Employing the van Cittert-Zernike theorem of classical coherence theor y, we derive a general expression for the efficiency with which quasi- monochromatic random light can be coupled to an optical fiber by means of a lens. For the important case of a source with Gaussian intensity distribution, we obtain and discuss the dependence of the coupling ef ficiency to single-mode fibers on the lens-to-fiber coupling geometry as well as on the ratio of lens size to speckle size. A specialization to the emerging fields of both incoherent and coherent fiber-based li dar applications shows that a maximum coupling efficiency of similar t o 42% can be obtained for a monostatic system. (C) 1998 Optical Societ y of America.