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Since optical vortex (OV) beams possess an additional degree of freedom, orbital angular momentum, the beams can be utilized to enhance signal modulation in optical communication technologies by mode division multiplexing and information encoding. In particular, tunable OV devices with wavelength adjustment and channel switching generate wide interest among researchers. This paper demonstrates tunable OV generator based on a grid‐patterned liquid crystal (GPLC) cell. The device, which is capable of producing an array of OV beams, offers an electrically controllable conversion between scalar vortices and vector vortices and controllable optical vortex density. In addition, the GPLC device is tunable to optimize its performance over a broad range of wavelengths. [ABSTRACT FROM AUTHOR]

Featured Application: Optical Communications; Snapshot Polarimetry; Micromachining; Particle Manipulation. We use a tunable commercial liquid-crystal device tuned to a quarter-wave retardance to study the generation and dynamics of different types of hybrid vector beams. The standard situation where the q-plate is illuminated by a Gaussian beam is compared with other cases where the input beam is a vortex or a pure vector beam. As a result, standard hybrid vector beams but also petal-like hybrid vector beams are generated. These beams are analyzed in the near field and compared with the far field distribution, where their hybrid nature is observed as a transformation of the intensity and polarization patterns. Analytical calculations and numerical results confirm the experiments. We include an approach that provides an intuitive physical explanation of the polarization patterns in terms of mode superpositions and their transformation upon propagation based on their different Gouy phase. The tunable q-plate device presents worthy advantages, since it allows a compact and efficient generation of pure and hybrid vector beams to study these effects. [ABSTRACT FROM AUTHOR]

Highlights • Q-plates with diameter of 0.4 mm were made in ∼ 1 min using femtosecond-laser processing. • Periods of gratings of 0.4 μ m and 0.8 μ m with a groove width of ∼ 200 nm were made by ablation. • The optical properties of the q -plates were verified and showed a ~3% efficiency of spin-orbital conversion. Abstract Fast fabrication of micro-optical elements for generation of optical vortex beams based on the q -plate design is demonstrated by femtosecond (fs) laser ablation of gold film on glass. Q-plates with diameter of ∼ 0.5 mm were made in ∼ 1 min using galvanometric scanners with writing speed of 5 mm/s. Period of gratings of 0.8 μ m and groove width of 250 nm were achieved using fs-laser ablation at λ = 343 nm wavelength. Phase and intensity analysis of optical vortex generators was carried out at 633 nm wavelength and confirmed the designed performance. Efficiency of spin–orbital conversion of the q -plates made by ablation of 50-nm-thick film of gold was ∼ 3 %. Such gratings can withstand thermal annealing up to 800 °C. They can be used as optical vortex generators using post-selection of polarisation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Porous nanostructured sculptured multilayer with axisymmetric optical activity. • Wavelength dependent response through multilayer optical design. • Optical activity switchable through liquid infiltration within the pore structure. • To be considered as thin film radial polarization converters. Abstract A radial polarization converter is a super-structured optical retarder that converts a conventional linearly polarized light beam into a structured beam with radial or azimuthal polarization. We present a new type of these sophisticated optical elements, which is made of porous nanostructured sculptured single thin films or multilayers prepared by physical vapor deposition at an oblique angle. They are bestowed with an axisymmetric retardation activity (with the fast axis in a radial configuration). In particular, a Bragg microcavity multilayer that exhibits a tunable transmission peak in the visible range with a retardance of up to 0.35 rad has been fabricated using this methodology. Owing to the highly porous structure of this type of thin films and multilayers, their retardance could be switched off by liquid infiltration. These results prove the possibility of developing wavelength dependent (through multilayer optical design) and switchable (through vapor condensation or liquid infiltration within the pore structure) radial polarization converters by means of oblique angle physical vapor deposition. [ABSTRACT FROM AUTHOR]

In this work, we performed a Mueller matrix imaging analysis of two commercial optical components usually employed to generate and manipulate vector beams—a radial polarizer and a liquid-crystal q-plate. These two elements generate vector beams by different polarization mechanisms—polarizance and retardance, respectively. The quality of the vector beams relies on the quality of the device that generates them. Therefore, it is of interest to apply the well-established polarimetric imaging techniques to evaluate these optical components by identifying their spatial homogeneity in diattenuation, polarizance, depolarization, and retardance, as well as the spatial variation of the angles of polarizance and retardance vectors. For this purpose, we applied a customized imaging Mueller matrix polarimeter based on liquid-crystal retarders and a polarization camera. Experimental results were compared to the numerical simulations, considering the theoretical Mueller matrix. This kind of polarimetric characterization could be very helpful to the manufacturers and users of these devices.

We use a tunable commercial liquid-crystal device tuned to a quarter-wave retardance to study the generation and dynamics of different types of hybrid vector beams. The standard situation where the q-plate is illuminated by a Gaussian beam is compared with other cases where the input beam is a vortex or a pure vector beam. As a result, standard hybrid vector beams but also petal-like hybrid vector beams are generated. These beams are analyzed in the near field and compared with the far field distribution, where their hybrid nature is observed as a transformation of the intensity and polarization patterns. Analytical calculations and numerical results confirm the experiments. We include an approach that provides an intuitive physical explanation of the polarization patterns in terms of mode superpositions and their transformation upon propagation based on their different Gouy phase. The tunable q-plate device presents worthy advantages, since it allows a compact and efficient generation of pure and hybrid vector beams to study these effects.

We demonstrate a physical model of photoalignment and photopatterning based on rotational diffusion in solid azo-dye nanolayers. We also highlight the new applications of photoalignment and photopatterning in display and photonics such as: (i) liquid crystal (LC) E-paper devices, including optically rewritable LC E-paper on flexible substrates as 3D E-paper, as well as optically rewritable technology for photonics devices; (ii) photonics LC devices, such as LC Switches, polarization controllers and polarization rotators, variable optical attenuators, LC filled photonic crystal fiber, switchable diffraction grating; (iii) patterned micro-polarizer array using photo-alignment technology for image sensor; (iv) electrically tunable liquid crystal q-plates; (v) electrically switchable liquid crystal Fresnel lens; (vi) liquid crystal optical elements with integrated Pancharatnam-Berry phases. We are sure, that in the field of (LC), the main point is no longer display research, but new photonic applications of LC are emerging in telecommunication, fiber optical communication systems, sensors, switchable lenses, LC light converters and other LC photonics devices.

Liquid-crystal polymer q -plates are commercial devices for generating vector beams at the design wavelength where the device exhibits half-wave (HW) retardance. Since they are not voltage addressable, the operational wavelength remains fixed. In this work we perform a broadband spectral characterization of the q -plate retardance as a function of wavelength, ϕ ( λ ), and identify the wavelengths with retardance values relevant for vector beam generation ( π , π /2, and 3 π /2). The wavelength is then used as a tuning parameter to change the device performance from a HW q-plate to a positive-QW or a negative-QW q -plate. These performances are analyzed using the Jones matrix formalism. We present a simple procedure to derive the polarization distribution of the vector beams expected at these QW wavelengths, as a superposition of the input polarization state and the output state of a HW q -plate. Experimental results using the red and blue lines of an Ar-Kr laser and an IR laser diode of 980 nm confirm the theoretical predictions. We show that for input linearly polarized light of 980 nm and 488 nm the device generates hybrid vector beams (where the ellipticity varies with the azimuthal angle), while for 647 nm pure radial vector beams with constant ellipticity are obtained. These results could extend the use of commercial q -plates for multicolour vector beam applications. [ABSTRACT FROM AUTHOR]

The new photonics applications of liquid crystals are highligthed: LC photonics elements for passive optical network systems, such as LC switches, sensors, lenses, LC light converters, optically and electrically rewritable E-paper. Special attention will be paid to photoalignment technology for LC photonics and emergent display devices. [ABSTRACT FROM AUTHOR]

We present the use of a q-plate device operating at the 1550 nm telecommunications wavelength. A prototype liquid-crystal device from Citizen Holdings Co. is deonstrated to be useful for the generation of vector beams and orbital angular momentum transfer at this important wavelength. [ABSTRACT FROM AUTHOR]

We demonstrate a physical model of photoalignment and photopatterning based on rotational diffusion in solid azo-dye nanolayers. We also highlight the new applications of photoalignment and photopatterning in display and photonics such as: (i) liquid crystal (LC) E-paper devices, including optically rewritable LC E-paper on flexible substrates as 3D E-paper, as well as optically rewritable technology for photonics devices; (ii) photonics LC devices, such as LC Switches, polarization controllers and polarization rotators, variable optical attenuators, LC filled photonic crystal fiber, switchable diffraction grating; (iii) patterned micro-polarizer array using photo-alignment technology for image sensor; (iv) electrically tunable liquid crystal q-plates; (v) electrically switchable liquid crystal Fresnel lens; (vi) liquid crystal optical elements with integrated Pancharatnam-Berry phases. We are sure, that in the field of (LC), the main point is no longer display research, but new photonic applications of LC are emerging in telecommunication, fiber optical communication systems, sensors, switchable lenses, LC light converters and other LC photonics devices. [ABSTRACT FROM AUTHOR]