Throughout optics and photonics, phase is normally controlled via an optical path difference. Although much less common, an alternative means for phase control exists: a geometric phase (GP) shift occurring when a light wave is transformed through one parameter space, e.g., polarization, in such a way as to create a change in a second parameter, e.g., phase. In thin films and surfaces where only the GP varies spatially—which may be called GP holograms (GPHs)—the phase profile of nearly any (physical or virtual) object can in principle be embodied as an inhomogeneous anisotropy manifesting exceptional diffraction and polarization behavior. Pure GP elements have had poor efficiency and utility up to now, except in isolated cases, due to the lack of fabrication techniques producing elements with an arbitrary spatially varying GP shift at visible and near-infrared wavelengths. Here, we describe two methods to create high-fidelity GPHs, one interferometric and another direct-write, capable of recording the wavefront of nearly any physical or virtual object. We employ photoaligned liquid crystals to record the patterns as an inhomogeneous optical axis profile in thin films with a few μm thickness. We report on eight representative examples, including a GP lens with F/2.3 (at 633 nm) and 99% diffraction efficiency across visible wavelengths, and several GP vortex phase plates with excellent modal purity and remarkably small central defect size (e.g., 0.7 and 7 μm for topological charges of 1 and 8, respectively). We also report on a GP Fourier hologram, a fan-out grid with dozens of far-field spots, and an elaborate phase profile, which showed excellent fidelity and very low leakage wave transmittance and haze. Together, these techniques are the first practical bases for arbitrary GPHs with essentially no loss, high phase gradients (∼rad/μm), novel polarization functionality, and broadband behavior.

Fabrication of ideal geometric-phase holograms with arbitrary wavefronts

A new polarization-independent and fast-response adaptive microlens array using a polymer-stabilized blue phase liquid crystal is proposed. With a curved top electrode and planar bottom electrode, gradient electric fields are generated and lens-like phase profile obtained. Optimization process leads to an ideal parabolic phase profile for suppressing spherical aberration.

Polarization independent adaptive microlens with a blue-phase liquid crystal.

A switchable Fresnel zone plate lens is demonstrated using a polymer-stabilized liquid crystal. The fabrication process is relatively simple and the device can be operated below 10 volts with fast response time. Such a device works well for a linearly polarized light.

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Switchable Fresnel lens using polymer-stabilized liquid crystals

An introduction to the technology of liquid crystal on silicon (LCOS) devices leads on to a discussion of the application areas which have been and are being opened up by the development of phase-only devices.

The Applications and Technology of Phase-Only Liquid Crystal on Silicon Devices

This paper describes an evolutionary approach to design flat multiwavelength achromatic lenses based on subwavelength plasmonic nanoparticles Our lattice evolution algorithm achieved desired optical responses by tuning the arrangement of the phase units on a discrete square lattice Lattice lenses consisting of a single type of nanoparticle could operate at any wavelength in the visible to near-infrared regime (540–1000 nm) by tailoring the localized surface plasmon resonance When the unit cells were expanded to anisotropic particle shapes, the planar optics could selectively focus light depending on the polarization of incident light Finally, the algorithm realized efficient multiobjective optimization and produced achromatic lattice lenses at up to three wavelengths (λ = 600 nm, λ = 785 nm, and λ = 980 nm) using multiple different nanoparticle shapes

Plasmonic Lattice Lenses for Multiwavelength Achromatic Focusing.

Static and dynamic Fresnel zone lenses were fabricated in quartz glass by means of microstructuring techniques. Two types of on-axis and offaxis lenses with different focal lengths and of different apertures were designed to operate at wavelengths of 1·52 μm and 633 nm. The blazed profile of the onaxis and off-axis lenses was approximated by up to 16 and up to four discrete levels respectively. Dynamic, that is electrically switchable, lenses have been realized by filling the structured surface with liquid crystal. The optical properties of the lenses, such as the focal spot sizes and the diffraction efficiencies, were investigated. Further the switching behaviour of the dynamic lenses was studied. The design and fabrication of the static and dynamic, on-and off-axis Fresnel zone lenses as well as their optical and switching properties will be presented.

Static and dynamic Fresnel zone lenses for optical interconnections

A solid immersion lens based on diffraction (dSIL) is proposed as an alternative to the conventional design based on refraction. A design analogous to a Fresnel zone plate is derived in accordance with the Huygens–Fresnel principle. Fabrication of a binary dSIL is achieved by electron-beam lithography and reactive-ion etching on LaSF35, with index n=2.014. Measurement of the point-spread function is performed with near-field optical microscopy. The results are in accord with the expected resolution enhancement of a factor n with respect to the diffraction limit.

Diffraction-based solid immersion lens

Solid Immersion Lenses (SILs) have an outstanding potential for applications in future generations of optical data storage systems. We report the realization of a diffractive Solid Immersion Lens (dSIL) which is the diffractive analog of the refractive hemispherical SIL. Here, inside the medium the propagation angles of the first order diffracted waves point in the same direction as the incident angles from outside the SIL. We realized two types of dSILs: binary phase elements were fabricated in a highly refracting glass (LaSF35) by direct 3-beam writing and successive reactive ion etching, and dSILs with a blazed profile were manufactured in photoresist by holographic lithography. The minimum distance between adjacent zones in the diffracting structure is in the range of one wavelength. Polarization dependencies and phase impacts have to be consideration in the design of an optical element with features this small. In comparison to the lithographically realized binary phase grating, the holographic elements have the advantage of high diffraction efficiency.

Diffractive solid immersion lenses: characterization and manufacturing

Diffractive beam-splitting elements with a large fan angle of about 45° were realized as binary phase elements for application in a commercial laser device operating at the wavelength of 635 nm. The fan-out elements designated to split a laser beam into a line of 43 equal power spots were fabricated in silica by means of microstructuring techniques and replicated in acrylate by ultraviolet curing. Two different gratings have been designed using scalar unidirectional iterative methods, based on the iterative discrete on-axis and on the direct binary search algorithms. The optical properties of both gratings obtained by these scalar methods were compared with simulations based on rigorous electromagnetic calculations in order to verify and control the application-relevant specifications. The experimentally measured optical performance of the replicated fan-out elements is in good agreement with the theoretical predictions. The complete procedure for realizing the linear beam splitters, that is the ...

Theoretical and experimental properties of a binary linear beam-splitting element with a large fan angle

Reflective micro-optical components for shaping non-diffracting beam arrays were fabricated by proportional transfer of continuous resist profiles into silica and silicon via e-beam writing and gray-tone lithography. Low dispersion multiplexing of 10-fs pulses was demonstrated.

Margit Ferstl

Papers

Static and dynamic Fresnel zone lenses for optical interconnections

Diffraction-based solid immersion lens

Diffractive solid immersion lenses: characterization and manufacturing

Theoretical and experimental properties of a binary linear beam-splitting element with a large fan angle

Lithographically fabricated micro-optical array beam shapers for ultra-short pulse lasers