In this contribution, it is shown how the number of optical sources in WDM-based optical beamforming networks can be reduced. In optical beamforming networks based on several optical carriers and a dispersive medium a correspondence is established between each optical carrier and each antenna element. However, it is feasible to reduce the number of optical sources of the architecture if the optical carriers are reused by means of the combination of dispersive and non-dispersive time delays.
To sum up, this contribution shows how WDM optical beamforming architectures can be simplified combining dispersive and non-dispersive time delays to allow the use of photonic beamforming techniques in large antenna arrays. The number of optical sources of the beamformer, as well as its total size and cost, can be highly reduced using this technique. Experimental results validating the feasibility of the technique are provided.
Multi-core fiber (MCF) has been one of the main innovations in fiber optics in the last decade. Reported work on MCF has been focused on increasing the transmission capacity of optical communication links by exploiting space-division multiplexing. Additionally, MCF presents a strong potential in optical beamforming networks. The use of MCF can increase the compactness of the broadband antenna array controller. This is of utmost importance in platforms where size and weight are critical parameters such as communications satellites and airplanes. Here, an optical beamforming architecture that exploits the space-division capacity of MCF to implement compact optical beamforming networks is proposed, being a new application field for MCF. The experimental demonstration of this system using a 4-core MCF that controls a four-element antenna array is reported. An analysis of the impact of MCF on the performance of antenna arrays is presented. The analysis indicates that the main limitation comes from the relatively high insertion loss in the MCF fan-in and fan-out devices, which leads to angle dependent losses which can be mitigated by using fixed optical attenuators or a photonic lantern to reduce MCF insertion loss. The crosstalk requirements are also experimentally evaluated for the proposed MCF-based architecture. The potential signal impairment in the beamforming network is analytically evaluated, being of special importance when MCF with a large number of cores is considered. Finally, the optimization of the proposed MCF-based beamforming network is addressed targeting the scalability to large arrays.
A low-cost method to ink-jet print terahertz polarizers is presented. A liquid metal printer is used to deliver an eutectic Gallium and Indium alloy (EGaIn24.5) onto polyvinyl chloride film substrates to create flexible wire grid polarizers (10 x 20 mm) in the sub-THz band with a nominal pitch of 200 μm and 300 μm, respectively. A Terahertz Time Domain Spectroscopy (THz-TDS) setup has been used to characterize the polarizers. The experimental results have been compared with FIT (Finite Integration Technique) simulations (CST Studio) showing good agreement. The characterization of the polarizers shows an extinction ratio up to 14 dB in the 0.1-0.7 THz and low loss (<1 dB). A microscopic characterization of the polarizers shows a variance in the line spacing of about 9%. This fabrication method allows a quick and cost-effective approach for the development of sub-THz polarizers to be used in polarization-resolved spectroscopy, polarimetric quality monitoring sensors and the characterization of THz components.
A simple technique to avoid color limitations in image capture systems based on chroma key video composition using retroreflective screens and light-emitting diodes (LED) rings is proposed and demonstrated. The combination of an asynchronous temporal modulation onto the background illumination and simple image processing removes the usual restrictions on foreground colors in the scene. The technique removes technical constraints in stage composition, allowing its design to be purely based on artistic grounds. Since it only requires adding a very simple electronic circuit to widely used chroma keying hardware based on retroreflective screens, the technique is easily applicable to TV and filming studios.