Physics

We present a novel method for forming radially and azimuthally polarized beams by using computer-generated subwavelength dielectric gratings. The elements were deposited upon GaAs substrates and produced beams with a polarization purity of 99.2% at a wavelength of 10.6 mm. We have verified the polarization properties with full space-variant polarization analysis and measurement, and we show that such beams have certain vortexlike properties and that they carry angular momentum.

Polarization beam-splitters and optical switches based on subwavelength quasi-periodic structures are presented. By locally controlling the orientation and period of the subwavelength grooves, birefringent elements for which the optical axes vary periodically, are realized. We present a theoretical discussion of these elements, as well as a detailed description of the design and realization procedures. We show experimental results for infra-red radiation at a wavelength of 10.6 lm. Ó

Space-variant Pancharatnam-Berry phase optical elements based on computer-generated subwavelength gratings are presented. By continuously controlling the local orientation and period of the grating we can achieve any desired phase element. We present a theoretical analysis and experimentally demonstrate a Pancharatnam -Berry phase-based diffraction grating for laser radiation at a wavelength of 10.6 mm.

We present a novel method for forming linearly polarized axially symmetric beams with various polarization orders that is based on computer-generated space-variant subwavelength gratings. We introduce and experimentally demonstrate that our space-variant polarization state manipulations are accompanied by a phase modification of a helical structure that results from the Pancharatnam -Berry phase. We have verified the polarization properties of our gratings for laser radiation at 10.6-mm wavelength.

Propagation-invariant vectorial Bessel beams with linearly polarized axial symmetry based on quantized Pancharatnam -Berry phase optical elements are described. The geometric phase is formed through the use of discrete computer-generated space-variant subwavelength dielectric gratings. We have verified the polarization properties of our elements for laser radiation at 10.6-mm wavelength and also demonstrated propagation-invariant, controlled rotation of a propeller-shaped intensity pattern through the simple rotation of a polarizer.

Quantized Pancharatnam-Berry phase diffractive optics using computer-generated space-variant subwavelength dielectric grating is presented. The formation of the geometrical phase is done by discrete orientation of the local subwavelength grating. We discuss a theoretical analysis and experimentally demonstrate a quantized geometrical blazed phase of polarization diffraction grating, as well as polarization dependent focusing lens for infrared radiation at wavelength 10.6 m.

Spiral phase elements with topological charges based on space-variant Pancharatnam-Berry phase optical elements are presented. Such elements can be achieved by use of continuous computer-generated space-variant subwavelength dielectric gratings. We present a theoretical analysis and experimentally demonstrate spiral geometrical phases for infrared radiation at a wavelength of 10.6 mm.

The formation of spiral phase elements producing helical beams with different topological charges is presented. The elements consist of discrete space-variant subwavelength dielectric gratings. We demonstrate our approach by fabricating elements for circularly polarized laser radiation with a wavelength of 10.6 lm. The resulting helical phases, as well as the birefrigent parameters of the element, are measured by analyzing the polarization-dependency of the elements along with the self-interference characteristics of the emerging beams.

Space-variant polarization manipulation of enhanced nondirectional thermal emission in a narrow spectral peak is presented. The emission is attributed to surface phonon-polariton excitation from space-variant subwavelength SiO 2 gratings. Polarization manipulation was obtained by discretely controlling the local orientation of the grating. We experimentally demonstrated thermal emission in an axially symmetric polarization distribution. Theoretical calculations based on rigorous coupled-wave analysis are presented along with experimental results.

Is it possible to achieve thermal radiation excited by surface waves having a coherence length much larger than what one might anticipate from the behavior of surface waves on a flat interface? We demonstrate an extraordinary coherent thermal radiation from coupled resonant cavities; each of them supports standing wave surface polaritons. The coupling is implemented by surface standing waves between the cavities. As a result, the spatial coherence length is increased by an order of magnitude compared with that of delocalized surface waves.

A new class of vectorial vortex based on coherent addition of two orthogonal circularly polarized Bessel beams of identical order but with different propagation constants is presented. The transversely spacevariant axially symmetric polarization distributions of these vectorial fields rotate as they propagate, while they maintain a propagation-invariant Bessel intensity distribution. These properties were demonstrated by use of discrete space-variant subwavelength gratings for 10.6 m CO 2 laser radiation. The polarization properties were verified by both full space-variant polarization analysis and measurements. Rotating intensity patterns are also demonstrated by transmitting the vectorial vortices through a linear polarizer.

A method for polarimetric measurement that uses a discrete space-variant subwavelength dielectric grating is presented. One retrieves the polarization state by measuring the far-field intensity of a beam emerging from the grating followed by a polarizer. The analysis for a partially polarized, quasi-monochromatic beam is performed by use of the beam coherence polarization matrix along with an extended van Cittert-Zernike theorem. We experimentally demonstrate polarization measurements of both fully and partially polarized light.

An optical encryption method based on a geometrical phase produced by space-variant polarization manipulation is presented. The decrypted picture is retrieved either by a polarization measurement of the beam emerging from the encrypted element or by a single intensity measurement of the beam transmitted through the encrypted element followed by an optical key element. Both elements are realized by use of computer-generated space-variant subwavelength dielectric gratings. Theoretical analyses of the optical concept are presented along with experimental results.

We present a unique method for real-time polarization measurement by use of a discrete space-variant subwavelength grating. The formation of the grating is done by discrete orientation of the local subwavelength grooves. The complete polarization analysis of the incident beam is determined by spatial Fourier transform of the near-field intensity distribution transmitted through the discrete subwavelength dielectric grating followed by a subwavelength metal polarizer. We discuss a theoretical analysis based on Stokes-Mueller formalism, as well as on Jones calculus, and experimentally demonstrate our approach with polarization measurements of infrared radiation at a wavelength of 10.6 m.

A novel method for real-time polarization measurement is presented. The method is based on a space-variant wave plate that we realized as a computer-generated space-variant subwavelength dielectric grating. The Stokes parameters of the incident beam are determined by Fourier analysis of the space-variant intensity transmitted through the grating and an analyzer. We discuss the design and realization of such wave plates and demonstrate our technique with polarization measurements of both polarized and partially polarized CO 2 -laser radiation at a wavelength of 10.6 mm.

We present a novel method for the formation of a complete depolarizer that is based on a polarization-state scrambling procedure over the space domain. Such an element can be achieved by use of cascaded, computergenerated, space-variant subwavelength dielectric gratings. We introduce a theoretical analysis and experimentally demonstrate a depolarizer for infrared radiation at a wavelength of 10.6 mm.

Self-imaging of a periodic space-variant polarized field is demonstrated. The field is created by use of space-variant subwavelength dielectric gratings. Our observations include self-imaging of the fields at the Talbot planes as well as the translation of incident polarization variation into intensity modulation at certain planes. We demonstrate the formation of a one-dimensional nondiffracting beam with uniform intensity and a nontrivial polarization structure.

We demonstrate an extraordinary quasimonochromatic thermal emission with high spatial coherence length ͑l c Ͼ 2400͒ and a quality factor Q = 2320 at radiation frequencies that are much smaller than the plasma frequency of metal ͑ p ͒. This emission is achieved by forming a plasmonic bandgap, which is obtained by a periodic structure on a metallic surface. Such a structure modifies the dynamics of the surface wave and results in a van Hove singularity ͓Van Hove, Phys. Rev. 89, 1189 ͑1953͔͒ in the spectral density of states while maintaining a large coherence length.

Transformation and inverse transformation between a free-space linearly polarized beam and the vectorial vortex mode of a circular hollow waveguide by use of Pancharatnam-Berry phase optical elements is proposed. Demonstration was achieved by fabricating GaAs subwavelength gratings and utilizing a 300 m diameter hollow metallic waveguide for 10.6 m wavelength CO 2 laser radiation. The mode transformations and the excitation of a single vectorial mode inside the hollow waveguide were verified by full polarization measurements. In addition, the inverse mode transformation of the single vectorial mode excitation in the waveguide enabled us to experimentally obtain a linearly polarized bright spot with a high central lobe.

We propose and analyze a general approach for coupling a free space uniformly polarized beam to a desired hollow waveguide mode, thus enabling a single mode operation. The required spatial polarization state manipulation is achieved by use of inhomogeneous anisotropic subwavelength structures. Demonstration is obtained by coupling a linearly polarized CO 2 laser beam at a wavelength of 10.6µm to the TE 01 , TM 01 , EH 11 , EH 21 , and EH 31 modes of a 300µm diameter dielectric-coated hollow metallic waveguide. Full polarization and intensity analysis of the beam at the waveguide's inlet and outlet ports indicates a high coupling efficiency to a single waveguide mode. Finally, shaping the waveguide mode to a nearly diffraction limited linearly polarized beam and to a radially polarized vectorial vortex are also demonstrated.