No abstract

In this paper we have given accurate empirical expressions for the straightforward analytical determination of the fundamental mode field (and also the corresponding spot size) in single-mode optical fibers from the far field measurements. The procedure is based on the use of the earlier reported Gaussian Hankel approximation for the near field pattern which has been shown to describe the modal pattern for graded index single-mode fibers with good accuracy.

A new approach to the design of holographic concave gratings is presented, in which a grating is treated as if it were composed of many small plane gratings, i .e . of local elementary gratings . A wavefront of the diffracted wave is constructed from the waves diffracted from the local elementary gratings . The expression of the focal curves is represented by the loci of centres of principal curvature of the wavefront . The aberration functions are defined as the differences between the direction cosines of the normal to the diffracted wave and those of the reference spherical wave . Blanks are assumed to be toric . The gratings are designed for use with Seya-Namioka monochromators and grazing incidence monochromators, and their theoretical performances are investigated by means of spot diagrams .