The design and characterisation of a reconfigurable multi-level spiral phase plate is shown. The device is based on a pie-shape liquid-crystal structure with 24 slices driven by custom electronics that allow independent excitation control of each electrode. The electrooptical cell was manufactured using maskless laser ablation lithography and has shown an unprecedented high fill factor. The topological charge can be dynamically changed between 1, 2, 3, 4, 6, 8 and 12. The device has been calibrated and characterised at 632.8 nm but can be employed at any wavelength in the visible and near infrared spectrum, just modifying the driving parameters of the electrodes. The experimental results have been compared to predictions derived from simulations. An excellent correspondence between theoretical and experimental result has been found in all cases.

Visible light communication systems can be used in a wide variety of applications, from driving to home automation. The use of wearables can increase the potential applications in indoor systems to send and receive specific and customized information. We have designed and developed a fully organic and flexible Visible Light Communication system using a flexible OLED, a flexible P3HT:PCBM-based organic photodiode (OPD) and flexible PCBs for the emitter and receiver conditioning circuits. We have fabricated and characterized the I-V curve, modulation response and impedance of the flexible OPD. As emitter we have used a commercial flexible organic luminaire with dimensions 99 × 99 × 0.88 mm, and we have characterized its modulation response. All the devices show frequency responses that allow operation over 40 kHz, thus enabling the transmission of high quality audio. Finally, we integrated the emitter and receiver components and its electronic drivers, to build an all-organic flexible VLC system capable of transmitting an audio file in real-time, as a proof of concept of the indoor capabilities of such a system.

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Liquid crystal properties make them useful for the development of security devices in applications of

SummaryThe inclusion of nanoparticles modifies a number of fundamental properties of many materials. Doping of nanoparticles in self-organized materials such as liquid crystals may be of interest for the reciprocal interaction between the matrix and the nanoparticles. Elongated nanoparticles and nanotubes can be aligned and reoriented by the liquid crystal, inducing noticeable changes in their optical and electrical properties. In this work, cells of liquid crystal doped with high aspect ratio multi-walled carbon nanotubes have been prepared, and their characteristic impedance has been studied at different frequencies and excitation voltages. The results demonstrate alterations in the anisotropic conductivity of the samples with the applied electric field, which can be followed by monitoring the impedance evolution with the excitation voltage. Results are consistent with a possible electric contact between the coated substrates of the LC cell caused by the reorientation of the nanotubes. The reversibility of the doped system upon removal of the electric field is quite low.

Passive liquid crystal (LC) devices are becoming an interesting alternative for the manufacturing of photonic devices in spatial applications. These devices feature a number of advantages in this environment, the lack of movable parts, and of exposed electronics being among the most outstanding ones. Nevertheless, the LC material itself must demonstrate its endurance under the harsh conditions of space missions, including launch and, perhaps, landing. In this paper, we present the environmental testing of an LC device for space applications. A number of LC based beam steering devices were manufactured, characterized, and tested in a series of destructive and nondestructive tests defined by the European Space Agency (ESA). The purpose was to evaluate the behavior and possible degradation of the LC response in simulated space environments. Device fabrication and testing was done within an ESA-funded project, whose purpose was the design, manufacturing, and characterization of adaptive optical elements, as well as the execution of qualification tests on the devices in space-simulated conditions.

Abstract-An analytical, complete framework to describe the current-voltage (I-V) characteristics of organic diodes without the use of previous approaches, such as injection or bulk-limited con duction is proposed. Analytical expressions to quantify the ratio between injection and space-charge-limited current from experi mental I-V characteristics in organic diodes have been derived. These are used to propose a numerical model in which both bulk transport and injection mechanisms are considered simultane ously. This procedure leads to a significant reduction in comput ing time with respect to previous rigorous numerical models. In order to test the model, different diode structures based on two different polymers: poly(2-methoxy-5-{3',7'-dimethyloctyloxy}-pphenylenevinylene) (MDMO-PPV) and a derivative of the poly(2,7-fluorene phenylidene) [PFP:(CN) 2 ], have been fabricated. The present model is excellently fitted to experimental curves and yields the microscopic parameters that characterize the active layer.