ways. One can mention the use of spiral phase plates, [ 3,4 ] computer generated holograms, [ 5,6 ] optical mode conversion, [ 7 ] lasing on higher-order modes of resonators, [ 8 ] light propagation in uniaxial crystals, [ 9,10 ] and space-variant birefringent retarders with formed [ 11 ] or natural [ 12 ] birefringence. Since then, these approaches have been improved and singular photonic technologies have emerged, a large set of products being now available to generate vortex beams. Still, from a practical point of view, mature options remain those relying on bulk and macroscopic optical elements.Quite naturally, research efforts have been made to miniaturize singular optical devices. For instance, femtosecond 3D direct laser writing technique has been proposed to fabricate microscopic spiral phase plates [ 13 ] and easy-prototyping of almost arbitrary singular microoptical elements with standard optical quality is now achievable. [ 14,15 ] On the other hand, self-engineered topological defects of liquid crystals have been shown to behave as small-scale optical vortex generators based on spinorbit interaction of light. In particular, the initial approach based on droplets (1−10 µm diameter) [ 16 ] evolved toward the use of thin (10−100 µm thick) fi lms whose effi ciency, diversity, tunability, and reconfi gurability stand with more than decent fi gures of merit. [17][18][19][20] Another approach consists to functionalize existing integrated optics subsystems with singular features, for instance, by twisting weakly deformed fi bers [ 21 ] or by using corrugated ring microresonators coupled to waveguides. [ 22 ] Of course, above few examples do not aim at providing an exhaustive list of recent progresses and, in order to partly fi ll this gap, one may refer to ref.[ 23 ] for a review of several strategies toward the elaboration of compact singular photonic devices. In particular, the use of ultrathin (i.e., with subwavelength thickness) artifi cially structured surfaces received a growing interest since a few years, as summarized in several recent reviews. [24][25][26][27] The common denominator of these approaches is subwavelength structuring of ultrathin material layer that confers "meta"-properties to it, from which originates the terminology of optical "meta"-surfaces.In this work, we address the particular case of optical vortex generation with topological charge up to | | 10 = , in the visible domain, by using nanostructured metallic thin fi lms following an approach introduced by Hasman's group in the early 2000s in the mid-infrared domain. [ 11 ] The idea consists to benefi t from the spinorbit interaction of light owing to azimuthally varying artifi cially birefringent waveplates made of inhomogeneous subwavelength Submicron-thick gold fi lms endowed with subwavelength patterning allow on-demand topological shaping of light, hence the precise delivery of optical orbital angular momentum. Several kinds of metallic metasurfaces enabling the generation of optical vortices with arbitrary topological charges...

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Three dimensional (3D) fast (< 0.5 hour) printing of micro-optical elements down to sub-wavelength resolution over 100 µm footprint areas using femtosecond (fs-)laser oscillator is presented. Using sub-1 nJ pulse energies, optical vortex generators made of polymerised grating segments with an azimuthally changing orientation have been fabricated in SZ2080 resist; width of polymerised rods was ∼ 150 nm and period 0.6-1 µm. Detailed phase retardance analysis was carried out manually with Berek compensator (under a white light illumination) and using an equivalent principle by an automated Abrio implementation at 546 nm. Direct experimental measurements of retardance was required since the period of the grating was comparable (or larger) than the wavelength of visible light. By gold sputtering, transmissive optical vortex generators were turned into reflective ones with augmented retardance, ∆n × h defined by the form birefringence, ∆n, and the height h = 2d where d is the thickness of the polymerised structure. Retardance reached 315 nm as measured with Berek compensator at visible wavelengths. Birefringent phase delays of π (or λ/2 in wavelength) required for high purity vortex generators can be made based on the proposed approach. Optical vortex generators for telecom wavelengths with sub-wavelength patterns of azimuthally oriented gratings are amenable by direct laser polymerisation.