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Visible Light Communication

Visible Light Communication (VLC) on flexible substrates: state of art

The ever-increasing demand for digital communication systems is pushing the scientific community to develop new technological sectors. One of these is certainly represented by optical band communication, known as visible light communication (VLC). The visible band of the electromagnetic spectrum has undisputed advantages, from its width to the possibility of transferring a huge amount of data at zero licensing costs. The frequencies of use of the VLC range from 400 THz to 800 are preferable to those currently used (microwaves and radio frequencies) in several fields. One advantage is that VLC is limited only by material obstacles, while it is not subject to electromagnetic perturbations, making this communication system ideal for indoor environments. Moreover, VLC can ensure a large bandwidth, increasing the density of information in strategic sectors such as information and communication technology, computer science, and medicine. Undoubtedly, conventional technology, based on inorganic semiconductors and metals, would allow the development of already highly reliable VLC technology. Nonetheless, it shows technological limitations, such as large area scalability, for large screens and displays, mechanical inflexibility, elevated production costs and, last but not least, the possibility of making devices that cannot be worn or even inserted into fabrics and clothes. There remains therefore a large window of applications for VLC requiring the development of low cost, large area, low dissipation, low polarization voltage technology, wearable devices, such as that of visible light sources and detectors based on the semiconductive properties of small organic molecules. Moreover, the ability of some organic materials to modulate visible light over the entire spectrum makes them unique compared to inorganic semiconductors. It is clearly unlikely that organic diodes and transistors could substitute conventional semiconductor technology. Instead, it is more reasonable to hypothesize a side by side of the two technologies, where organic devices can offer technological solutions, impossible with conventional semiconductors or which would require the use of large resources, with consequent increase in production costs. Nowadays, the state of development of organic electronics has reached considerable steps forward, that it is already an integral part of commercial devices, such as mobile phones, televisions, and in general in all those applications where large, very clear, and bright displays are required, keeping at the same time production costs relatively low. A further aspect that has identified organic electronics as the only technological solution is undoubtedly the recent development of folding screen devices, where conventional electronics inevitably fails.

So far, there has been a great development of organic electronics, especially for light sources, such as OLEDs. In parallel, also the use of organic electronics as photodetectors is increasing in number [1], even if not so intense as organic light sources. The use of organic phototransistors (OPTs) as visible light detectors has been demonstrated [1, 2], as well as OPTs have been coupled to inorganic and organic scintillators for detecting radiation, as protons in medical applications [3]. Up to now, about organic VLC systems, a modulated demonstrator [4] has been developed, which have paved the way for a more consistent development of VLC systems based on organic semiconductors. One of the main limit in using organic VLC systems seems to be the maximum speed that organic devices can get. However, recently, an important advance has been done in this direction. Indeed, in [5] is showed that an organic device for VLC are capable of ensuring data transmission speeds of the order of hundreds of kb/s. This result was even overcome in [6], in which a light modulation, similar to orthogonal frequency division multiplexing, was employed. The possibility of Ethernet-type transmission has also been tested, as reported in [7]. Currently, the maximum transmission rate for VLC achieved with organic devices is 500 Mb/s [8].

In support of the chance of obtaining substantial advances in flexible organic devices, we find an intense international development of organic electronics, which now occupies a strategic sector in the ever-increasing demand for low-cost electronics, made on non-conventional large-area substrates, such as plastics, very thin plastic films, and paper, which are flexible and, in some cases, even wearable [9]. Recent development has led organic electronics to be seen as an industry in its own right, often referred to as “printed electronics industry”. The development expectations for printed electronics are truly impressive, coming to estimate [10] a value around 330 billion dollars in the near future (expected already in 2027), compared to the current market for Si-based electronics, that is in the order of 225 billion dollars [11].

Bibliography

  1. K. J. Baeg et al., Organic Light Detectors: Photodiodes and Phototransistors, Adv. Mater. 25, 4267, 2013.
  2. Y. Bonnassieux et al., The 2021 flexible and printed electronics roadmap, Flex. Print. Electron. 6, 023001, 2022.
  3. Calvi S et al., Flexible fully organic indirect detector for megaelectronvolts proton beams, NPJ Flexible Electronics 5, 1-11 (2023)4. C. Vega-Colado et al., An All-Organic Flexible Visible Light Communication System, Sensors 18, 3045, 2018.
  4. P. A. Haigh et al., Exploiting equalization techniques for improving data rates in organic optoelectronic devices for visible light communications, J. Lightwave Technol., 30, 3081, 2012.
  5. S.T. Le et al., 10 Mb/s visible light transmission system using a polymer light-emitting diode with orthogonal frequency division multiplexing, Opt. Lett. 39, 3876, 2014.
  6. P.A. Haigh et al., Exploiting equalization techniques for improving data rates in organic optoelectronic devices for visible light communications. J. Lightwave Technol. 30, 3081, 2012.
  7. P.A. Haigh et al., Visible light communications: Real time 10 Mb/s link with a low bandwidth polymer light-emitting diode. Opt. Express, 22, 2830, 2014.
  8. Y. Zhang et al., Aggregation-induced emission luminogens as color converters for visiblelight communication. ACS Appl. Mater. Interfaces 10, 34 418, 2018.
  9. A. Nathan et al., Flexible Electronics: The Next Ubiquitous Platform. Proc. IEEE 100, 1486, 2012.
  10. R. Das and P. Harrop, RFID Forecasts, Players and Opportunities 2011–2021 (Santa Clara, CA: IDTechEx-2021).