DEVELOPMENT OF A GENERALIZED THEORETICAL-MODEL FOR THE RESPONSE OF A PHASE DOPPLER MEASUREMENT SYSTEM TO ARBITRARILY ORIENTED FIBERS ILLUMINATED BY GAUSSIAN BEAMS/

We present a generalized theoretical model for the response of the pha se/Doppler (P/D) measurement system to light scattered by cylindrical fibers. This theoretical model is valid for arbitrary fiber diameters and refractive indices, for Gaussian incident beams, and it accounts f or arbitrary fiber orientations, fiber positions, and effects that are due to the two-dimensional receivers. The generalized P/D computer mo del (GPDCM) is the extension of an earlier study by the authors, combi ning past P/D simulation methodology with recent developments in model ing light scattering by tilted cylindrical fibers. A FORTRAN computer program that implements the GPDCM theoretical development was written and tested against known P/D results and physical expectations. To ill ustrate the capabilities of the GPDCM, we present computation results, comparing the effect of fiber tilt, fiber position, and receiver aper ture on the performance of P/D systems configured in backscatter and s idescatter arrangements. Calculations show that the effects of fiber t ilt and position are most pronounced in the backscatter P/D arrangemen t, resulting in broadening of the measured phase distribution. The cal culated mean phase shifts, however, were found to be essentially indep endent of the above factors. Computational results also showed that th e effect of fiber tilt and position on phase-distribution measurements can be reduced through proper choice of aperture shape and by imposit ion of threshold criteria on measurable signal characteristics such as the amplitude ratio and visibilities. The GPDCM provides a computatio nal tool that will he valuable in the design, optimization, and evalua tion of P/D fiber measurement systems. (C) 1998 Optical Society of Ame rica. OCIS codes: 290.0290, 280.1100, 120.3180.