Formation of helical beams by use of Pancharatnam-Berry phase optical elements

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 10.6microm .     

Space-variant Pancharatnam-Berry phase optical elements with computer-generated subwavelength gratings

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 10.6microm.     

Pancharatnam-Berry phase of optical systems

We present simple closed-form expressions for evaluating the overall and the Pancharatnam-Berry phase introduced by an optical system with either orthogonal or nonorthogonal eigenpolarizations. The formulas provide a meaningful connection with the Pancharatnam-Berry phase associated with nonclosed paths on the Poincaré sphere.     

Vectorial vortex mode transformation for a hollow waveguide using Pancharatnam-Berry phase optical elements

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 microm diameter hollow metallic waveguide for 10.6 microm 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.     

Interfering Bessel beams for optical micromanipulation

We examine the properties of interfering high-order Bessel beams. We implement an experimental setup that allows us to realize these interferograms, using interfering Laguerre-Gaussian beams and an axicon. We demonstrate the use of such beams for controlled rotation of microscopic particles in optical tweezers and rotators. The self-healing properties of interfering Bessel beams allow the simultaneous manipulation and rotation of particles in spatially separated sample cells.     

Polychromatic vectorial vortex formed by geometric phase elements

We propose the use of a geometric phase, obtained by spatial polarization state manipulations, for the formation of polychromatic vectorial vortices. Experimental demonstration is obtained by using Pancharatnam-Berry phase optical elements formed by a space-variant subwavelength grating etched on a GaAs wafer. We further demonstrate formation of scalar and unpolarized polychromatic vortices.     

Addressing atoms in optical lattices with Bessel beams

A method of synthesizing localized optical fields with zeros on a periodic lattice is analyzed. The applicability to addressing atoms trapped in optical lattices with low cross talk is discussed.     

Distortion correction by phase conjugation of nonparaxial vectorial beams: a general proof

We present a general proof of the distortion-correction theorem, that is, of the possibility of correcting wave distortion by the technique of optical phase conjugation. The proof is valid for fully vectorial nonparaxial propagation in the presence of a tensorial refractive-index perturbation and backscattering of the incident field.     

Generation of nondiffracting Bessel beams by use of a spatial light modulator

A laser beam with phase singularities is an interesting object to study in optics and may have important applications in guiding atoms and molecules. We explore the characteristics of a singularity in a nondiffracting Bessel beam experimentally by use of a programmable spatial light modulator with 64-level phase holograms. The diffraction efficiency with 64-level phase holograms is greatly improved in comparison with that obtained with a binary grating. The experiments show that the size and deflection angle of the beam can be controlled in real time. The observations are in agreement with scalar diffraction theory.     

Generation and amplification of pulsed Bessel beams by seeding an optical parametric amplifier

By using two very different seed pulses we demonstrate that the spatiotemporal gain properties of a chi(2) optical parametric amplifier can be exploited as an efficient conical reshaping mechanism leading to the generation and amplification of a pulsed Bessel beam.     

The generation of Bessel beams at millimetre-wave frequencies by use of an axicon

An axicon is used to generate a Bessel beam at 90 GHz in the millimetre-wave region of the spectrum. The Bessel beam has a central intensity maximum of approximately 4 mm in diameter that is maintained over a propagation distance greater than 60 mm.     

Beam wander relieved optical switch using Bessel beams in turbulent atmosphere

The digital micro-mirror device(DMD)-based optical switch has the advantages of high-speed channels reallocation, miniaturization, stability, and large capacity for short reach optical communication in the datacenter.However, thermal turbulent atmosphere in the datacenter would cause perturbations and channel crosstalk for the optical switch. The self-healing optical beams such as the Bessel beams have the non-diffraction property to mitigate the turbulence issue. Here, we propose and demonstrate a Bessel beams enabled DMD-based optical switch to improve the stability and performance of optical communication in turbulent atmosphere. We statistically characterize the beam wanders of the Gaussian and Bessel beams in turbulent atmosphere at temperatures of 60°C and 80°C. We build the two-channel optical switch communication system and measure the bit error rate of the 15 Gbit/s on–off keying signals transmitted by the Gaussian and Bessel beams at temperatures of 60°C and 80°C, respectively. The optical switch using the Bessel beams shows lower bit error rates with weaker fluctuations compared with the Gaussian beams. The DMD-based optical switch using the Bessel beams has the potential for practical optical communication applications in the datacenter.     

Generation of the determined vectorial vortex beams by use of an achromatic axially symmetric waveplate

Optical Review - We review the generation of the determined vectorial vortex beams in the terahertz (THz) beams at frequencies of 0.16 and 0.36 THz, and intense middle infrared pulsed beam at...     

Fabrication of planar optical phase elements

A method is described for obtaining thin film planar optical phase elements using photolithographic and specially developed evaporation/etching techniques. As an example of the method, the fabrication of a phase Fresnel zone plate in which the outermost zone measures 4.3 microns, is described.     

Stochastic optimization of quantized diffraction optical elements to form longitudinal intensity distributions

A stochastic approach to optimization of quantized diffraction optical elements (DOEs) intended to form specified longitudinal intensity distributions is considered.     

Angular spectrum of quantized light beams

We introduce a generalized angular spectrum representation for quantized light beams. By using our formalism, we are able to derive simple expressions for the electromagnetic vector potential operator in the case of (a) time-independent paraxial fields, (b) time-dependent paraxial fields, and (c) nonparaxial fields. For the first case the well-known paraxial results are fully recovered.     

Diffractive phase elements that synthesize color pseudo-nondiffracting beams

The design of diffractive phase elements (DPE's) for generating color pseudo-nondiffracting beams (PNDB's) in a multiple-wave illuminating system by the conjugate-gradient method is described. The axial-intensity distributions for dual-color PNDB's generated by the DPE's are shown. The color PNDB's behave as segmented axial-intensity distributions; in each of segments only one color persists. The sequence of wavelength components in the color PNDB's can be arbitrarily preset. Three-dimensional plots of a dual-color PNDB indicate the characteristics of a beam with high transverse resolution.     

Conversion of high-order Laguerre-Gaussian beams into Bessel beams of increased, reduced or zeroth order by use of a helical axicon

We propose a new method for transformation of a Laguerre-Gaussian beam of azimuthal index l and radial index n = 0 (LG_l,0) into a vortex, diverging or nondiverging Bessel beam, which can have increased or decreased phase singularity order, or into a zeroth order Bessel beam, by means of a helical axicon. The Bessel beam divergence or nondivergence depends upon the waist position of the input Laguerre-Gaussian beam, regarding the plane where the helical axicon is situated.The expressions for the amplitude and the intensity distribution of the diffracted wave field, in the process of Fresnel diffraction, are deduced using the stationary phase method. The theoretical analysis for the vortex radius and the maximum propagation distance of the Bessel beams obtained is presented.     

Generation of spiraling high-order Bessel beams

Spiraling Bessel beams of arbitrary order are created by illuminating an apertured axicon and a hologram with a single-ringed Laguerre–Gaussian beam. The high-order beam rotates around the propagating axis with a hollow center and can be regarded as the hollow spiraling beam. Such beams have distinct advantages, which offer a direct method for micro-fabrication applications, especially for cold atom guiding, due to their inherent central hollow region and their non-diffracting feature.