Optical networking
Optical networking is a means of communication that uses signals encoded in light to transmit information in various types of
Types
Fiber-optic networks
The most common
Free-space optical networks
Free-space optical networks can also be used to set up temporary terrestrial networks e.g. to link LANs on a campus.
Components
Components of a fiber-optical networking system include:
- Fiber. Multi-mode or single-mode.
- Laser or LED light source.
- Multiplexer/demultiplexer, also called mux/demux, filter, or prism. These can include Optical Add/Drop Multiplexer (OADM) and Reconfigurable Optical Add/Drop Multiplexer (ROADM).
- Optical switch, to direct light between ports without an optical-electrical-optical conversion
- Optical splitter, to send a signal down different fiber paths.
- Circulator, to tie in other components, such as an OADM.
- Optical amplifier.
- Wave division multiplexer.
Transmission Medium
At its inception, the telecommunications network relied on
It was clear that light waves could have much higher bit rates without crosstalk. In 1957,
The first fiber-optic system for live telephone traffic was in 1977 in Long Beach, Calif., by
Optical Amplification
The capacity of fiber optic networks has increased in part due to improvements in components, such as optical amplifiers and optical filters that can separate light waves into frequencies with less than 50 GHz difference, fitting more channels into a fiber. The
Wavelength Division Multiplexing
Using optical amplifiers, the capacity of fibers to carry information was dramatically increased with the introduction of wavelength-division multiplexing (WDM) in the early 1990s. AT&T's Bell Labs developed a WDM process in which a prism splits light into different wavelengths, which could travel through a fiber simultaneously. The peak wavelength of each beam is spaced far enough apart that the beams are distinguishable from each another, creating multiple channels within a single fiber. The earliest WDM systems had only two or four channels—AT&T, for example, deployed an oceanic 4-channel long-haul system in 1995.[9] The erbium-doped amplifiers on which they depend, however, did not amplify signals uniformly across their spectral gain region. During signal regeneration, slight discrepancies in various frequencies introduced an intolerable level of noise, making WDM with greater than 4 channels impractical for high-capacity fiber communications.
To address this limitation, Optelecom, Inc. and General Instruments Corp. developed components to increase fiber bandwidth with far more channels. Optelecom and its head of Light Optics, engineer David Huber and Kevin Kimberlin co-founded Ciena Corp in 1992 to design and commercialize optical telecommunications systems, the objective being an expansion in the capacity of cable systems to 50,000 channels.[10] [11] Ciena developed the dual-stage optical amplifier capable of transmitting data at uniform gain on multiple wavelengths, and with that, in June 1996, introduced the first commercial dense WDM system. That 16-channel system, with a total capacity of 40 Gbit/s,[12] was deployed on the Sprint network, the world's largest carrier of internet traffic at the time.[13] This first application of all-optical amplification in public networks[14] was seen by analysts as a harbinger of a permanent change in network design for which Sprint and Ciena would receive much of the credit.[15] Advanced optical communication experts cite the introduction of WDM as the real start of optical networking.[16]
Capacity
The density of light paths from WDM was the key to the massive expansion of fiber optic capacity that enabled the growth of the Internet in the 1990s. Since the 1990s, the channel count and capacity of dense WDM systems has increased substantially, with commercial systems able to transmit close to 1 Tbit/s of traffic at 100 Gbit/s on each wavelength.[17] In 2010, researchers at AT&T reported an experimental system with 640 channels operating at 107 Gbit/s, for a total transmission of 64 Tbit/s.[18] In 2018, Telstra of Australia deployed a live system that enables the transmission of 30.4 Tbit/s per fiber pair over 61.5 GHz spectrum, equal to 1.2 million 4K Ultra HD videos being streamed simultaneously.[19] As a result of this ability to transport large traffic volumes, WDM has become the common basis of nearly every global communication network and thus, a foundation of the Internet today.[20] [21] Demand for bandwidth is driven primarily by Internet Protocol (IP) traffic from video services, telemedicine, social networking, mobile phone use and cloud-based computing. At the same time, machine-to-machine, IoT and scientific community traffic require support for the large-scale exchange of data files. According to the Cisco Visual Networking Index, global IP traffic will be more than 150,700 Gbits per second in 2022. Of that, video content will equal 82% of all IP traffic, all transmitted by optical networking.[22]
Standards and protocols
References
- ^ "Elon Musk is about to launch the first of 11,925 proposed SpaceX internet satellites — more than all spacecraft that orbit Earth today". Business Insider. Retrieved 15 April 2018.
- ^ "Google Laser-Beams the Film Real Genius 60 Miles Between Balloons". WIRED. Retrieved 16 April 2018.
- ^ Newton, Casey (21 July 2016). "Inside the test flight of Facebook's first internet drone". TheVerge.com.
- ISBN 978-0-470-50511-3.
- ^ Dutta, Niloy, K. (2014). Fiber Amplifiers and Fiber Lasers. World Scientific. pp. vi.
{{cite book}}
: CS1 maint: multiple names: authors list (link) - ^ Chadha, Devi (2019). Optical WDM Networks. p. 8.
- ^ Agrawal, Govind P. (2002). Fiber-Optic Communications Systems. John Wiley & Sons, Inc.
- ^ Nemova, Galina (2002). Optical Amplifier. p. 139.
- ISBN 0080513212, 9780080513218
- ^ Aurweek, Steve (May 17, 1993). ""Optelecom, HydraLite become partners"". The Baltimore Sun.
- ^ Hecht, Jeff. ""OSA Centennial Snapshots. Boom, Bubble, Bust: The Fiber Optic Mania". The Optical Society and Optics and Photonics News. October 2016.
- ^ Markoff, John (March 3, 1997). "Fiber-Optic Technology Draws Record Stock Value". New York Times.
- ^ Sprint (June 12, 1996). ""New Technology Allows 1600 Percent Capacity Boost"". PR Newswire. Kansas City, MO.
- ^ Gilder, George (December 4, 1995). ""Angst and Awe on the Internet"". Forbes ASAP.
- ^ Goldman Sachs (July 30, 1997). "Ciena Corporation: Breaking the Bandwidth Barrier". Technology: Telecom Equipment, US Research Report.
- ^ Cvijetic, Milorad and Djordjevic, Ivan B. (2013). Advanced Optical Communication Systems and Networks. Artech House.
{{cite book}}
: CS1 maint: multiple names: authors list (link) - S2CID 20600739.
- ^ Zhou, X., et al., “64-Tb/s (640×107-Gb/s) PDM-36QAM transmission over 320km using both pre- and post-transmission digital equalization,” 2010 Conference on Optical Fiber Communication/National Optical Fiber Engineers Conference, March 2010, San Diego, CA
- ^ Rohan, Pierce (January 24, 2018). "A world-record speed achieved on Telstra's transmission network". Computer World.
- ^ Grobe, Klaus; Eiselt, Michael (2013). Wavelength Division Multiplexing: A Practical Engineering Guide. John T. Wiley & Sons. p. 2.
- ISBN 978-1-60807-555-3
- ^ Cisco Visual Networking Index: Forecast and Methodology, 2013-2018, https://www.cisco.com/c/en/us/solutions/collateral/service-provider/visual-networking-index-vni/white-paper-c11-741490.html