Abstract

We experimentally characterize the properties of an element that generates a doughnutlike point-spread function by converting the linearly polarized incident field to radially or azimuthally polarized light utilizing space-variant inhomogeneous medium (SVIM) form-birefringent subwavelength structures. To fabricate the high-aspect-ratio SVIM structures, we developed a chemically assisted ion-beam-etching process that permits control of the fabricated form-birefringent structure profile to optimize the effect of birefringence and the impedance mismatch on the substrate–air interface. Fabricated elements perform efficient polarization conversion for incident angles as large as 30°, where the extinction ratio is found to be better than $4.5$. The intensity distribution in the far field shows that our SVIM device generates a doughnut point-spread function that may prove useful for various applications.

© 2006 Optical Society of America

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