ABSTRACT
A transparent variable diffractive spiral axicon (DSA) based on a single LC cell is presented. The manufactured DSA can be switched between 24 different configurations, 12 convergent and 12 divergent, where the output angle is varied as a function of the applied topological charge. The active area of the device is created using a direct laser writing technique in indium-tin oxide coated glass substrates. Liquid crystal is used to modulate the phase of the incoming beam generating the different DSA configurations. The DSA consists in 24 individually driven transparent spiral shaped electrodes, each introducing a specific phase retardation. In this article, the manufacture and characterization of the tunable DSA is presented and the performance of the DSA is experimentally demonstrated and compared to the corresponding simulations.
ABSTRACT
A compact and cost effective NIR-VIS-UV lidar echo emulator (LEE) was designed and manufactured as a compact breadboard. The LEE is an application specific optical pulse shaper delivering a short lidar return (echo) in the ns range overlapped with a long lidar return in the µs range with a repetition rate from 100 Hz - 500 Hz. The short echo power levels are in the range from 0.2-200 nW, whereas the long echo powers from 0.1-25 pW. The coarse power tuning between the two kind of echoes is done using variable attenuators. LEE provides three operation modes: short echo, long echo, or both echoes overlapped. In the overlapping mode, the power difference between the echoes exceeds 60 dB.
ABSTRACT
Optical waveguides in photonic integrated circuits are traditionally passive elements merely carrying optical signals from one point to another. These elements could contribute to the integrated circuit functionality if they were modulated either by variations of the core optical properties, or by using tunable claddings. In this work, the use of liquid crystals as electro-optically active claddings for driving integrated waveguides has been explored. Tunable waveguides have been modeled and fabricated using polymers. Optical functions such as variable coupling and optical switching have been demonstrated.
ABSTRACT
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.
ABSTRACT
Nanoimprint lithography has become a useful tool to prepare elements containing nanoscale features at quite reasonable cost, especially if the fabrication elements are created in the own laboratory. We have designed and fabricated a whole nanoimprint manufacturing system and analyzed the resulting surfaces using ad hoc packages developed on an open-software AFM image analysis suite. To complete the work, a number of polymers have been thoroughly studied in order to select the best material for this implementation. It turned out that the best alternative was not always the same, but depended on the application. A comparative study of the polymers, which takes into account the values and dispersion of numerous sample parameters, has been carried out. As a large number of samples was prepared, an automatized procedure for characterization of nanoimprint surfaces had to be set up. The procedure includes figures of merit for comparative purposes. Materials without the requirement of a solvent were found to be superior for most nanoimprint applications. A large dispersion of the samples was found.
ABSTRACT
This paper reports on the design, fabrication and characterization of an all-organic photonic integrated circuit working as a switching polarizer for visible light (630nm), combining organic waveguides and liquid crystals that can be electrically driven. The device was made in commercially available epoxy by laser direct writing lithography. A device with a 2dB loss and a 20dB extinction ratio for both polarizations, was simulated; the manufactured devices proved the working principle of the design. The results have led to the design of a switching polarization splitter, in which a careful choice of waveguide material and liquid crystal can lead to devices working on a wide range of wavelengths.
ABSTRACT
Nanoimprint lithography (NIL) is an imprinting technique which has experienced an increasing popularity due to its versatility in fabrication processes. Commercial NIL machines are readily available achieving high quality results; however, these machines involve a relatively high investment. Hence, small laboratories often choose to perform NIL copies in a more rudimentary and cheaper way. A new simple system is presented in this document. It is based on two devices which can be made in-house in plastic by using a 3D printer or in aluminum. Thus, the overall manufacturing complexity is vastly reduced. The presented system includes pressure control and potentially temperature control. Replicas have been made using a sawtooth grating master with a pitch around half micrometre. High quality patterns with low density of imperfections have been achieved in 2.25 cm2 surfaces. The material chosen for the negative intermediary mould is PDMS. Tests of the imprint have been performed using the commercial hybrid polymer Ormostamp®.
ABSTRACT
A photonic crystal fiber selectively filled with silver nanoparticles dispersed in polydimethylsiloxane has been numerically studied via finite elements analysis. These nanoparticles possess a localized surface plasmon resonance in the visible region which depends on the refractive index of the surrounding medium. The refractive index of polydimethylsiloxane can be thermally tuned leading to the design of polarization tunable filters. Filters found with this setup show anisotropic attenuation of the x-polarization fundamental mode around α(x) = 1200dB/cm remarkably higher than the y-polarization mode. Moreover, high fiber birefringence and birefringence reversal is observed in the spectral region of the plasmon.
ABSTRACT
The 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.
