Analytical beam propagation model of micro-lensed fibers for wavelength selective switch

Micro-lensed fibers require some features such as low coupling loss and wide tolerance to function in wavelength selective switch (WSS). In this paper, Fourier optics and scalar diffraction theory are used to analyze the major beam propagation and transformation by switching different focus length micro-lens in WSS. A hemispheric micro-lens array is then etched with designed optimum focal length. In experiment, a method is proposed for measuring the insertion loss (IL) and coupling efficiency of a fiber coupling micro-lens in WSS. The theoretical calculations of the spot size at any distance from micro-lens agree well with experimental results. The experimental coupling efficiency can reach up to 70%.