Entropy loading for capacity maximization of RGB-based visible light communications.

In this work, we propose and experimentally demonstrate an entropy loading technique based on probabilistic constellation shaping for a visible light communication (VLC) system. The aggregated achievable bit rate of a multi-carrier signal is maximized, considering a given pre-estimated signal-to-noise ratio. A study of the ideal number of subcarriers and signal bandwidth was performed using multiplexed red, green and blue lasers diodes with a bandwidth of 1 GHz. With a 20 degree optical diffuser, the communication system is able to cover a wide area at a free-space distance of 0.90 m, while achieving a record aggregate bit rate of 31.2 Gbit/s for single-polarization RGB-VLC systems.

Etched fiber Bragg grating probe using a regular CNC machine and a 3D printer.

Etched fiber Bragg gratings (EFBGs) have been widely employed for refractive index (RI) measurements that can be used to monitor sugar consumption during the fermentation of alcoholic beverages. EFBGs are obtained by removing the cladding of a fiber Bragg grating, which is traditionally performed by a chemical attack with hydrogen fluoride, an extremely hazardous corrosive substance that causes severe wounds and even death. To overcome such drawbacks, this technical note presents a simple, practical, and low cost method for the diameter reduction of single mode optical fibers by mechanical polishing, employing a small scale computer numerical control device and an ad hoc 3D-printed rod. The sensor probe obtained was tested using sucrose aqueous solutions with RIs between 1.333 and 1.394, measured in an Abbe refractometer. The results show a linear shift of the Bragg wavelength with respect to RI with a correlation of 0.928.

Practical splicing of poly-methyl-methacrylate plastic optical fibers.

This Engineering and Laboratory Note describes a simple, fast, cost-effective, and practical splicing technique for poly-methyl-methacrylate (PMMA) plastic optical fibers. We believe this technique can be useful for home networks, laboratory research, and educational uses. It employs a widely available, low-cost transparent adhesive combined with a suitable alignment sleeve. The fiber tips did not need to be cleaned or polished, and the polyethylene jacket did not need to be removed. The alignment between the cleaved fibers was performed by means of the jacket. Low insertion losses were measured for the main PMMA-based fiber types.

Impact of the concentration in polymer on the dynamic behavior of Polymer Stabilized Ferroelectric Liquid Crystal using Snap-shot Mueller Matrix Polarimetry.

Experimental results are presented related to the dynamic behaviour of Polymer Stabilized Ferro-electric Liquid Crystal (PSFLC) samples under external applied electric field, using Snap-shot Mueller Matrix Polarimetry (SMMP) and Mueller Matrix (MM) formalism. Different polarimetric coefficients are simultaneously extracted from each channeled spectrum measured with this full-optical SMMP technique. The impact of the concentration of polymer present into the liquid crystal cell on this dynamic behaviour is studied, permitting a direct and quick characterisation of the material. The results obtained for PSFLC are compared with those already measured for pure Surface Stabilized Ferro-electric Liquid Crystal (SSFLC) samples, which correspond to a 0% concentration in polymer.