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

We thank EPSRC for financial support from the UP-VLC Programme Grant (EP/K00042X/1). I.D.W.S. and P.J.S. are Royal Society Wolfson Research Merit Award holders. The research data supporting this publication can be accessed at http://dx.doi.org/10.17630/20163d03-6cc2-43b6-915c-d271f5220454.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 - 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 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.PostprintPublisher PDFPeer reviewe

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

Authors would like to acknowledge the EPSRC for financial support for the UP-VLC (EP/K00042X/1). PJS and IDWS also acknowledge Royal Society Wolfson Research Merit Awards.We report a study of blends of semiconducting polymers as saturated red color converters to replace commercial phosphors in hybrid 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.PostprintPeer reviewe

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

We thank EPSRC for financial support from the UP-VLC Project Grant (EP/K00042X/1). I.D.W.S. and P.J.S. are Royal Society Wolfson Research Merit Award holders.For white light data communications, broad-band 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.Publisher PDFPeer reviewe

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 whilst 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. 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 étendue in these elements limits their field-of-view. In this letter we demonstrate novel antennas that overcome these limitations, giving fast receivers with large collection areas and large fields of view. Our results exceed the limit of étendue, giving an enhancement of light collection by a factor of 12, with field of view semi-angle of 60° and we show a 3-fold increase in data rate

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

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

Data link using wide field of view optical antenna based receiver

In this paper we describe the construction and fabrication of a VLC link that used novel micro-LEDs as a transmitter, and a planar fluorescent optical concentrator at the receiver. The link operates at 20Mbit/s and can transmit video streams between laptop computers