Fiber Optics. XII. A Technique for Launching an Arbitrary Mode on an Optical Dielectric Waveguide

A spatial-filtering technique is described which provides a means for launching an arbitrary mode on a fiber-optical waveguide. Appropriate amplitude and phase filters are used to discriminate against unwanted modes. These are inserted in the pupil of a launching lens which focuses collimated light onto the end of the guide. A double-path illuminating system is generally needed to obtain the required input polarization. The method is evaluated both theoretically and experimentally, and the agreement is found to be good within the practical limitations of cross-sectional irregularities in the nominally circular optical fibers.