Fabrication of ideal geometric-phase holograms with arbitrary wavefronts

Abstract

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.

ON-SKY PERFORMANCE ANALYSIS OF THE VECTOR APODIZING PHASE PLATE CORONAGRAPH ON MagAO/Clio2

“…This orientation pattern, as well as any other arbitrary pattern, can be embodied by a liquid crystal layer structure, whichlocally aligns its fast axis to a photo-alignment layer. The geometric phase is inherently achromatic, but leakage terms (which in this case take the shape of the regular PSF) can emerge if the retardance is not exactly half-wave (Mawet et al 2009;Snik et al 2012;Kim et al 2015). A typical APP phase design is antisymmetric in the pupil function, which results in a D-shaped dark hole next to the star.…”

High-performance geometric phase elements in silica glass

“…Thus, the desired phase pattern of the wave is directly encoded in the optical axis orientation and is equal to twice the rotation angle of the local retarder. However, despite the numerous techniques enabling the manufacturing of high-efficiency elements, 6,[14][15][16][17][18] the limited technological flexibility and low material durability, e.g., liquid crystals with a damage threshold of 0.2 J/cm 2 , prevent these elements from being widely integrated in consumer electronics or high-power laser applications. Here we propose a direct-write ultrafast laser nanostructuring of silica glass as an alternative method which is capable of fabricating geometric phase optics.…”

Ferroelectric Liquid Crystal Dammann Grating by Patterned Photoalignment

“…In this way, a customized LC director distribution can be achieved to offer special designed optical functions. Many photonic devices can be achieved via patterned alignment, including patterned retarders [9,10], Q-plates [4,5], LC gratings [11,12], LC lenses [13][14][15], and polarization converters [16][17][18], etc., which could find many important applications in beam shaping [4], imaging system [13,14], Complementary Metal Oxide Semiconductor (CMOS) sensor system [19] and 3D display [10], etc.…”

“…The most important property and advantage of the LC DG is that the grating is electrically tunable, which offers great potential to benefit lots of optical applications such as optical communication and beam shaping. Moreover, the working principle of LC DG is unique since it uses the geometric phase [15] instead of the conventional dynamic phase which is controlled by optical path difference. For the LC DG, the electrically switching speed is critical important which plays key role in optical applications.…”