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

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.

Near-infrared demonstration of computer-generated holograms implemented by using subwavelength gratings with space-variant orientation.

We provide an experimental demonstration of novel form-birefringent computer-generated holograms at wavelengths of 1.55 and 10.6 microm.

Compact and integrated TM-pass waveguide polarizer.

A novel integrated TM-pass waveguide polarizer with a subwavelength-wide slot is introduced and theoretically analyzed. With a proper design of the slot, the waveguide can be used as a single polarization waveguide to guide only TM polarization modes of the light signal. With 26 microm length of this TM-pass polarizer, our computer simulations predict the insertion loss of 0.

Form-birefringence structure fabrication in GaAs by use of SU-8 as a dry-etching mask.

A thin layer of a SU-8 submicrometer pattern produced by holographic lithography was directly used as the dry-etching mask in a chemically assisted ion-beam-etching system. With optimized etching parameters, etching selectivity of 7:1 was achieved together with a smooth vertical profile. As an application, a half-wavelength retardation plate for a 1.

Implementation of a graded-index medium by use of subwavelength structures with graded fill factor.

We present a novel configuration for the implementation of subwavelength-based graded-index devices. The proposed concept is based on the etching of one-dimensional subwavelength gratings into a high-index slab waveguide to achieve the desired effective index distribution. A graded-index profile can be achieved by gradually modifying the duty ratio of the grating along the horizontal axis, while the beam is confined in the vertical direction by the slab waveguide.

Design, fabrication and characterization of subwavelength computer-generated holograms for spot array generation.

We report the analysis, design, fabrication and experimental characterization of novel subwavelength computer-generated holograms that produce uniform symmetric spot array. We distinguish between a polarization-sensitive and polarization-insensitive far-field reconstruction and show that a linearly polarized incident illumination is required in the former case in order to generate a symmetric reconstruction. The polarization-insensitive case generates a symmetric response independent of the illumination polarization.

Engineering space-variant inhomogeneous media for polarization control.

Novel devices for converting a linear polarization state to radial or azimuthal polarization states are realized by use of space-variant inhomogeneous media on a subwavelength scale. The two designs presented use form birefringence to locally transform the polarization state. The devices are fabricated in a GaAs substrate for operation in the far-infrared wavelength range.