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Appl Opt. 2006 Mar 10;45(8):1777-84.

Form-birefringent space-variant inhomogeneous medium element for shaping point-spread functions.

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  • 1University of California, San Diego, Department of Electrical and Computer Engineering, 9500 Gilman Drive, La Jolla, California 92093-0407, USA.


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 degrees, 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.

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