<title>Diffraction of cylindrical waves due to elliptical and rectangular apertures</title>

Abstract

Operation of some optical devices such as a surface plasmon resonance compact sensor relies on cylindrical waves. On the contrary, optical power is usually transmitted via collimated beams. A holographic grating structure may serve in coupling of a collimated laser beam and its transformation into the beam with the cylindrical wave front, and the vice versa transformation on outcoupling. The paper deals with the role of an aperture shape in focusing of the cylindrical waves. Elliptical and rectangular apertures are discussed, and the transversal as well as longitudinal diffraction in the zone of the focal line is studied. A special feature of this problem is that in the focal plane the Fraunhofer diffraction takes place only in the direction perpendicular to the focal line. The Fresnel difracton causes a modulation along the focal line. A consequence of the elliptical aperture is that the focal line is not illuminated uniformly: illumination declines from the center to the ends. For practical purposes the rectangular aperture turn out to be much more suitable.