Pavlos P. Manousiadis

Synthesis and properties of novel star-shaped oligofluorene conjugated systems with BODIPY cores

Summary Star-shaped conjugated systems with varying oligofluorene arm length and substitution patterns of the central BODIPY core have been synthesised, leading to two families of compounds, T-B1–T-B4 and Y-B1–Y-B4, with T- and Y-shaped motifs, respectively. Thermal stability, cyclic voltammetry, absorption and photoluminescence spectroscopy of each member of these two families were studied in order to determine their suitability as emissive materials in photonic applications.

Wide field-of-view fluorescent antenna for visible light communications beyond the étendue limit

Visible light communications (VLC) is an important emerging field aiming to use optical communications to supplement Wi-Fi. This will greatly increase the available bandwidth so that demands for ever-higher data rates can be met. In this vision, solid-state lighting will provide illumination while being modulated to transmit data. An important obstacle to realizing this vision are receivers, which need to be inexpensive, sensitive, fast, and have a large field of view (FoV). One approach to increasing the sensitivity of a VLC receiver is to increase the area of the receiver’s photodetector, but this makes them expensive and slow. An alternative approach is to use optical elements to concentrate light, but conservation of etendue in these elements limits their FoV. In this paper, we demonstrate novel antennas that overcome these limitations, giving fast receivers with large collection areas and large FoV. Our results exceed the limit of etendue, giving an enhancement of light collection by a factor of 12, with FoV semi-angle of 60°, and we show a threefold increase in data rate.

Demonstration of 2.3 Gb/s RGB white-light VLC using polymer based colour-converters and GaN micro-LEDs

This paper presents a demonstration of polymer based colour-converters and GaN micro-LEDs for red-green-blue based white-light visible-light-communication. By applying an optimised orthogonal-frequency-division-multiplexing scheme, an aggregate-rate of 2.3 Gb/s is demonstrated.

A simple wide field of view concentrator for free space visible light communications

The optical gain of a simple new type of wide field of view optical concentrator is predicted and easy modifications that will significantly increase its gain without changing its field of view are identified.

A saturated red color converter for visible light communication using a blend of star-shaped organic semiconductors

We report a study of blends of semiconducting polymers as saturated red color converters to replace commercial phosphors in hybrid Light emitting diodes (LEDs) for visible light communication (VLC). By blending two star-shaped organic semiconductor molecules, we found a near complete energy transfer (>90% efficiency) from the green-emitting truxene-cored compound T4BT-B to the red-emitting boron dipyrromethene (BODIPY) cored materials. Furthermore, we have demonstrated the capability of these materials as fast color converters for VLC by measuring their intrinsic optical modulation bandwidth and data rate. The measured 3 dB modulation bandwidth of blends (∼55 MHz) is more than 10 times higher than commercially available LED phosphors and also higher than the red-emitting BODIPY color converter alone in solution. The data rate achieved with this blend is 20 times higher than measured with a commercially available phosphor based color converter.

BODIPY star-shaped molecules as solid state colour converters for visible light communications

In this paper, we study a family of solid-state, organic semiconductors for visible light communications. The star-shaped molecules have a boron-dipyrromethene (BODIPY) core with a range of side arm lengths which control the photophysical properties. The molecules emit red light with photoluminescence quantum yields ranging from 22% to 56%. Thin films of the most promising BODIPY molecules were used as a red colour converter for visible light communications. The film enabled colour conversion with a modulation bandwidth of 73 MHz, which is 16 times higher than that of a typical phosphor used in LED lighting systems. A data rate of 370 Mbit/s was demonstrated using On-Off keying modulation in a free space link with a distance of ∼15 cm.

Polymer colour converter with very high modulation bandwidth for visible light communications

For white light data communications, broadband light emitting materials are required, whose emission can be rapidly modulated in intensity. We report the synthesis, photophysics and application of a novel semiconducting polymer for use as a high bandwidth colour converter, to replace commercial phosphors in white LEDs. The high modulation bandwidth (470 MHz) is 140 times higher than that measured using a conventional LED phosphor.

A comparative study of optical concentrators for visible light communications

Given the imminent radio frequency spectrum crunch, Visible Light Communication (VLC) is being proposed as an alternative wireless technology allowing for scalable connectivity to potentially millions of mobile and Internet-of- Things (IoT) devices. A VLC system uses a photo-detector (PD) receiver that converts the optically modulated light from a light source into a modulated electrical signal. The corresponding receiver electrical bandwidth is typically inversely proportional to the PD active area. Consequently, to construct a high-speed VLC link, the PD active area is often substantially reduced and an optical concentrator is used to enhance the receiver collection area. However, to achieve high concentrating factor, the link field-of-view (FOV) needs to be narrow due to the étendue conservation in linear passive optical systems. This paper studies a Fluorescent Concentrator (FC) that breaks this étendue conservation. The FC is not only based on reflective and refractive principles but also makes use of fluorescence process. A comparison between the FC and conventional optical concentrators, namely Compound Parabolic Concentrator (CPC) is also investigated. The trade-off between received signal strength and incoming link angle is demonstrated over 60° coverage. Experimental results show that performance degradation as the link angle increases using FC-based receivers is significantly lower than for conventional CPC.

Microstructured organic semiconductors: Lasers sensors and visible light communications

Directly patterned thin films hold many advantages over other methods of micro-structuring organic semiconductors. We show that solvent immersion imprint lithography is able to create a wide variety of organic semiconductor photonic devices that can be used for applications including laser sensors and visible light communications.