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 .

No abstract

A theoretical analysis of the aberration losses of the microoptic directional coupler recently being used in optical communication systems has been carried out. We show that our results are consistent with those obtained experimentally and that the minimum insertion loss does not occur at the paraxial length (which has been used in the experiments), but at an optimum length, which is slightly less. However, the tolerance in the positioning of the output fiber is less for the optimum length than for the paraxial length, although the increased loss at the optimum length due to poor positional adjustments within the tolerance value is still considerably smaller than the minimum loss at the paraxial length.

No abstract

Numerical studies of ray-trace aberrations of a curved graded-index medium as a function of launching conditions and refractive-index profile are reported. The variation of meridional and skew ray aberrations with the launching angle for specific point objects shows that the axis of symmetry of the medium shifts on curving. Further, the aberrations of rays emanating from a point object increase or decrease with curvature, depending on the position of the object point with respect to the new axis of symmetry.