Optical wireless communications

Optical wireless communications (OWC) is a form of optical communication in which unguided visible, infrared (IR), or ultraviolet (UV) light is used to carry a signal.

OWC systems operating in the visible band (390–750 nm) are commonly referred to as visible light communication (VLC). VLC systems take advantage of light emitting diodes (LEDs) which can be pulsed at very high speeds without noticeable effect on the lighting output and human eye. VLC can be possibly used in a wide range of applications including wireless local area networks, wireless personal area networks and vehicular networks among others.[1] On the other hand, terrestrial point-to-point OWC systems, also known as the free space optical (FSO) systems,[2] operate at the near IR frequencies (750–1600 nm). These systems typically use laser transmitters and offer a cost-effective protocol-transparent link with high data rates, i.e., 10 Gbit/s per wavelength, and provide a potential solution for the backhaul bottleneck. There has also been a growing interest on ultraviolet communication (UVC) as a result of recent progress in solid state optical sources/detectors operating within solar-blind UV spectrum (200–280 nm). In this so-called deep UV band, solar radiation is negligible at the ground level and this makes possible the design of photon-counting detectors with wide field-of-view receivers that increase the received energy with little additional background noise. Such designs are particularly useful for outdoor non-line-of-sight configurations to support low power short-range UVC such as in wireless sensor and ad-hoc networks.

History

The proliferation of wireless communications stands out as one of the most significant phenomena in the history of technology. Wireless technologies have become essential much more quickly during the last four decades and they will be a key element of society progress for the foreseeable future. The radio-frequency (RF) technologies wide-scale deployment has become the key factor to the wireless devices and systems expansion. However, the electromagnetic spectrum where the wireless systems are deployed is limited in capacity and costly according to its exclusive licenses of exploitation. With the raise of data heavy wireless communications, the demand for RF spectrum is outstripping supply and they become to consider other viable options for wireless communication using the upper parts of the electromagnetic spectrum not just RF.

Optical wireless communication (OWC) refers to transmission in unguided propagation media through the use of optical carriers, i.e., visible, infrared (IR), and ultraviolet (UV) band. Signalling through beacon fires, smoke, ship flags and semaphore telegraph [3] can be considered the historical forms of OWC. Sunlight has been also used for long distance signalling since very early times. The earliest use of sunlight for communication purposes is attributed to ancient Greeks and Romans who used their polished shields to send signals by reflecting sunlight during battles.[4] In 1810, Carl Friedrich Gauss invented the heliograph which involves a pair of mirrors to direct a controlled beam of sunlight to a distant station. Although the original heliograph was designed for geodetic survey, it was used extensively for military purposes during the late 19th and early 20th century. In 1880, Alexander Graham Bell invented the photophone, known as the world’s first wireless telephone system.

The military interest on photophone however continued. For example, in 1935, the German Army developed a photophone where a tungsten filament lamp with an IR transmitting filter was used as a light source. Also, American and German military laboratories continued the development of high pressure arc lamps for optical communication until the 1950s.[5] In modern sense, OWC uses either lasers or light emitting diodes (LEDs) as transmitters. In 1962, MIT Lincoln Labs built an experimental OWC link using a light emitting GaAs diode and was able to transmit TV signals over a distance of 30 miles. After the invention of laser, OWC was envisioned to be the main deployment area for lasers and many trials were conducted using different types of lasers and modulation schemes.[6] However, the results were in general disappointing due to large divergence of laser beams and the inability to cope with atmospheric effects. With the development of low-loss fiber optics in the 1970s, they became the obvious choice for long distance optical transmission and shifted the focus away from OWC systems.

Current status

Over the decades, the interest in OWC remained mainly limited to covert military applications,[7] and space applications including inter-satellite and deep-space links.[8] OWC’s mass market penetration has been so far limited with the exception of IrDA which became a highly successful wireless short-range transmission solution.[9] Development of novel and efficient wireless technologies for a range of transmission links is essential for building future heterogeneous communication networks to support a wide range of service types with various traffic patterns and to meet the ever-increasing demands for higher data rates. Variations of OWC can be potentially employed in a diverse range of communication applications ranging from optical interconnects within integrated circuits through outdoor inter-building links to satellite communications.

Photo: ESA; Example of possible ultra-long OWC on inter-satellite European Data Relay Satellite (EDRS) system
OWC long range inter-buildings communications idea for Istanbul Skyline

Applications

Based on the transmission range, OWC can be studied in five categories:

  1. Ultra-short range OWC: chip-to-chip communications in stacked and closely packed multi-chip packages.[10]
  2. Short range OWC: wireless body area network (WBAN) and wireless personal area network (WPAN) applications under standard IEEE 802.15.7, underwater communications.[11]
  3. Medium range OWC: indoor IR and visible light communications (VLC) for wireless local area networks (WLANs) and inter-vehicular and vehicle-to-infrastructure communications.
  4. Long range OWC,: inter-building connections, also called Free-Space Optical Communications (FSO).
  5. Ultra-long range OWC: inter-satellite links.

Recent trends

References

  1. ↑ M. Uysal and H. Nouri, “Optical Wireless Communications – An Emerging Technology”, 16th International Conference on Transparent Optical Networks (ICTON), Graz, Austria, July 2014
  2. ↑ A. Khalighi and M. Uysal, “Survey on Free Space Optical Communication: A Communication Theory Perspective”, IEEE Communications Surveys and Tutorials.
  3. ↑ A. A. Huurdeman, The Worldwide History of Telecommunications, Wiley Interscience, 2003.
  4. ↑ G. J. Holzmann and B. Pehrson, The Early History of Data Networks (Perspectives), Wiley, 1994.
  5. ↑ M. Groth, "Photophones revisited".
  6. ↑ E. Goodwin, "A review of operational laser communication systems," Proceedings of the IEEE, vol. 58, no. 10, pp. 1746–1752, Oct. 1970.
  7. ↑ D. L. Begley, "Free-space laser communications: a historical perspective," Annual Meeting of the IEEE, Lasers and Electro-Optics Society (LEOS), vol. 2, pp. 391–392, Nov. 2002, Glasgow, Scotland.
  8. ↑ H. Hemmati, Deep Space Optical Communications, Wiley-Interscience, 2006
  9. ↑ Infrared Data Association (IrDA).
  10. ↑ Christoforos Kachris and Ioannis Tomkos, "A survey on optical interconnects for data centers", IEEE Communications Surveys & Tutorials, vol. 14, no. 4, pp. 1021–1036, Oct. 2012. doi:10.1109/SURV.2011.122111.00069
  11. ↑ F. Hanson and S. Radic, "High bandwidth underwater optical communication", Applied Optics, ISSN 0003-6935 vol. 47, no. 2, pp. 277–283, Jan. 2008. OCLC 263929596
  12. ↑ http://www.ieee802.org/15/pub/IEEE%20802_15%20WPAN%2015_7%20Revision1%20Task%20Group.htm
  13. ↑ Paul Anthony Haigh, Francesco Bausi, Zabih Ghassemlooy, Ioannis Papakonstantinou, Hoa Le Minh, Charlotte Fléchon, and Franco Cacialli. "Visible light communications: real time 10 Mb/s link with a low bandwidth polymer light-emitting diode" Optics Express Vol. 22, Issue 3, pp. 2830-2838 (2014) doi:10.1364/OE.22.002830 February 2014.
  14. ↑ The Smart Lighting Engineering Research Center

Further reading


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