Optical networking

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Optical networking is a means of communication that uses signals encoded in light to transmit information in various types of telecommunications networks. These include limited range local-area networks (LAN) or wide area networks (WANs), which cross metropolitan and regional areas as well as long-distance national, international and transoceanic networks. It is a form of optical communication that relies on optical amplifiers, lasers or LEDs and wavelength-division multiplexing (WDM) to transmit large quantities of data, generally across fiber-optic cables. Because it is capable of achieving extremely high bandwidth, it is an enabling technology for the Internet and telecommunication networks that transmit the vast majority of all human and machine-to-machine information.

Contents

Types

Fiber-optic networks

The most common fiber-optic networks are communication networks, mesh networks or ring networks commonly used in metropolitan, regional, national and international systems. Another variant of fiber-optic networks is the passive optical network, which uses unpowered optical splitters to link one fiber to multiple premises for last mile applications.

Free-space optical networks

Free-space optical networks use many of the same principles as a fiber-optic network but transmit their signals across open space without the use of fiber. Several planned satellite constellations such as SpaceX's Starlink intended for global internet provisioning will use wireless laser communication to establish optical mesh networks between satellites in outer space. [1] Airborne optical networks between high-altitude platforms are planned as part of Google's Project Loon and Facebook Aquila with the same technology. [2] [3]

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:

Transmission Medium

At its inception, the telecommunications network relied on copper to carry information. But the bandwidth of copper is limited by its physical characteristics—as the frequency of the signal increases to carry more data, more of the signal's energy is lost as heat. Additionally, electrical signals can interfere with each other when the wires are spaced too close together, a problem known as crosstalk. In 1940, the first communication system relied on coaxial cable that operated at 3 MHz and could carry 300 telephone conversations or one television channel. By 1975, the most advanced coaxial system had a bit rate of 274 Mbit/s, but such high-frequency systems require a repeater approximately every kilometer to strengthen the signal, making such a network expensive to operate.

It was clear that light waves could have much higher bit rates without crosstalk. In 1957, Gordon Gould first described the design of the optical amplifier and the laser that was demonstrated in 1960 by Theodore Maiman. The laser is a source for light waves, but a medium was needed to carry the light through a network. In 1960, glass fibers were in use to transmit light into the body for medical imaging, but they had high optical loss—light was absorbed as it passed through the glass at a rate of 1 decibel per meter, a phenomenon known as attenuation. In 1964, Charles Kao showed that to transmit data for long distances, a glass fiber would need loss no greater than 20 dB per kilometer. A breakthrough came in 1970, when Donald B. Keck, Robert D. Maurer, and Peter C. Schultz of Corning Incorporated designed a glass fiber, made of fused silica, with a loss of only 16 dB/km. Their fiber was able to carry 65,000 times more information than copper.

The first fiber-optic system for live telephone traffic was in 1977 in Long Beach, Calif., by General Telephone and Electronics, with a data rate of 6 Mbit/s. Early systems used infrared light at a wavelength of 800 nm, and could transmit at up to 45 Mbit/s with repeaters approximately 10 km apart. By the early 1980s, lasers and detectors that operated at 1300 nm, where the optical loss is 1 dB/km, had been introduced. By 1987, they were operating at 1.7 Gbit/s with repeater spacing of about 50 km. [4]

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 erbium-doped optical amplifier (EDFA) was developed by David Payne at the University of Southampton in 1986 using atoms of the rare earth erbium that are distributed through a length of optical fiber. A pump laser excites the atoms, which emit light, thus boosting the optical signal. As the paradigm shift in network design proceeded, a broad range of amplifiers emerged because most optical communication systems used optical fiber amplifiers. [5] Erbium-doped amplifiers were the most commonly used means of supporting dense wavelength division multiplexing systems. [6] In fact, EDFAs were so prevalent that, as WDM became the technology of choice in the optical networks, the erbium amplifier became "the optical amplifier of choice for WDM applications." [7] Today, EDFAs and hybrid optical amplifiers are considered the most important components of wave division multiplexing systems and networks. [8]  

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

Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) have evolved as the most commonly used protocols for optical networks. The Optical Transport Network (OTN) protocol was developed by the International Telecommunication Union as a successor and allows interoperability across the network as described by Recommendation G.709. Both protocols allow for delivery of a variety of protocols such as Asynchronous Transfer Mode (ATM), Ethernet, TCP/IP and others.

Related Research Articles

<span class="mw-page-title-main">Synchronous optical networking</span> Standardized protocol

Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). At low transmission rates data can also be transferred via an electrical interface. The method was developed to replace the plesiochronous digital hierarchy (PDH) system for transporting large amounts of telephone calls and data traffic over the same fiber without the problems of synchronization.

<span class="mw-page-title-main">Optical amplifier</span> Device that amplifies an optical signal

An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback from the cavity is suppressed. Optical amplifiers are important in optical communication and laser physics. They are used as optical repeaters in the long distance fiber-optic cables which carry much of the world's telecommunication links.

<span class="mw-page-title-main">Wavelength-division multiplexing</span> Fiber-optic communications technology

In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light. This technique enables bidirectional communications over a single strand of fiber as well as multiplication of capacity.

<span class="mw-page-title-main">Optical communication</span> Use of light to convey information

Optical communication, also known as optical telecommunication, is communication at a distance using light to carry information. It can be performed visually or by using electronic devices. The earliest basic forms of optical communication date back several millennia, while the earliest electrical device created to do so was the photophone, invented in 1880.

All-silica fiber, or silica-silica fiber, is an optical fiber whose core and cladding are made of silica glass. The refractive index of the core glass is higher than that of the cladding. These fibers are typically step-index fibers. The cladding of an all-silica fiber should not be confused with the polymer overcoat of the fiber.

Hybrid fiber-coaxial (HFC) is a broadband telecommunications network that combines optical fiber and coaxial cable. It has been commonly employed globally by cable television operators since the early 1990s.

<span class="mw-page-title-main">Passive optical network</span> Technology used to provide broadband to the end consumer via fiber

A passive optical network (PON) is a fiber-optic telecommunications technology for delivering broadband network access to end-customers. Its architecture implements a point-to-multipoint topology in which a single optical fiber serves multiple endpoints by using unpowered (passive) fiber optic splitters to divide the fiber bandwidth among the endpoints. Passive optical networks are often referred to as the last mile between an Internet service provider (ISP) and its customers. Many fiber ISPs prefer this technology.

In fiber optics, a reconfigurable optical add-drop multiplexer (ROADM) is a form of optical add-drop multiplexer that adds the ability to remotely switch traffic from a wavelength-division multiplexing (WDM) system at the wavelength layer. This is achieved through the use of a wavelength selective switching module. This allows individual or multiple wavelengths carrying data channels to be added and/or dropped from a transport fiber without the need to convert the signals on all of the WDM channels to electronic signals and back again to optical signals.

<span class="mw-page-title-main">Multi-mode optical fiber</span> Type of optical fiber mostly used for communication over short distances

Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode links can be used for data rates up to 800 Gbit/s. Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link because of modal dispersion. The standard G.651.1 defines the most widely used forms of multi-mode optical fiber.

This is a list of acronyms and other initialisms used in laser physics and laser applications.

<span class="mw-page-title-main">Fiber-optic communication</span> Transmitting information over optical fiber

Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of infrared or visible light through an optical fiber. The light is a form of carrier wave that is modulated to carry information. Fiber is preferred over electrical cabling when high bandwidth, long distance, or immunity to electromagnetic interference is required. This type of communication can transmit voice, video, and telemetry through local area networks or across long distances.

Wavelength selective switching components are used in WDM optical communications networks to route (switch) signals between optical fibres on a per-wavelength basis.

<span class="mw-page-title-main">Optical mesh network</span> Optical network using a mesh topology

An optical mesh network is a type of optical telecommunications network employing wired fiber-optic communication or wireless free-space optical communication in a mesh network architecture.

<span class="mw-page-title-main">Polarization-division multiplexing</span> Method for multiplexing signals

Polarization-division multiplexing (PDM) is a physical layer method for multiplexing signals carried on electromagnetic waves, allowing two channels of information to be transmitted on the same carrier frequency by using waves of two orthogonal polarization states. It is used in microwave links such as satellite television downlinks to double the bandwidth by using two orthogonally polarized feed antennas in satellite dishes. It is also used in fiber optic communication by transmitting separate left and right circularly polarized light beams through the same optical fiber.

Fiber-optic filter is an optical fiber instrument used for wavelength selection, which can select desired wavelengths to pass and reject the others. It is Widely used in DWDM systems dynamic wavelength selection, DWDM signal separation, optical performance monitoring, field tunable optical noise filtering and optical amplifier noise suppression, etc. Optical multiplexers (couplers) makes different wavelength coupling into an optical fiber and different wavelength carries different information. At the receiving end, if you want to separate desired wavelengths from optical fiber, it is necessary to use optical filter.

A super-channel is an evolution in dense wavelength-division multiplexing (DWDM) in which multiple, coherent optical carriers are combined to create a unified channel of a higher data rate, and which is brought into service in a single operational cycle.

An erbium-doped waveguide amplifier is a type of an optical amplifier enhanced with erbium. It is a close relative of an EDFA, erbium-doped fiber amplifier, and in fact EDWA's basic operating principles are identical to those of the EDFA. Both of them can be used to amplify infrared light at wavelengths in optical communication bands between 1500 and 1600 nm. However, whereas an EDFA is made using a free-standing fiber, an EDWA is typically produced on a planar substrate, sometimes in ways that are very similar to the methods used in electronic integrated circuit manufacturing. Therefore, the main advantage of EDWAs over EDFAs lies in their potential to be intimately integrated with other optical components on the same planar substrate and thus making EDFAs unnecessary.

An optical module is a typically hot-pluggable optical transceiver used in high-bandwidth data communications applications. Optical modules typically have an electrical interface on the side that connects to the inside of the system and an optical interface on the side that connects to the outside world through a fiber optic cable. The form factor and electrical interface are often specified by an interested group using a multi-source agreement (MSA). Optical modules can either plug into a front panel socket or an on-board socket. Sometimes the optical module is replaced by an electrical interface module that implements either an active or passive electrical connection to the outside world. A large industry supports the manufacturing and use of optical modules.

Optelecom-NKF, Inc. is an American company that designs, manufactures, and markets high-bandwidth communications products, financial market data information, and business video systems.

David R. Huber is an American engineer specializing in optical networking. He is the holder and assignor of several patents in the field of optical transmission, distribution, and communication.

References

  1. ↑ "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.
  2. ↑ "Google Laser-Beams the Film Real Genius 60 Miles Between Balloons". WIRED. Retrieved 16 April 2018.
  3. ↑ Newton, Casey (21 July 2016). "Inside the test flight of Facebook's first internet drone". TheVerge.com.
  4. ↑ Argawal, G.P., Fiber-Optic Communications Systems, Fourth Edition, 2010, Wiley, Hoboken, NJ, ISBN   978-0-470-50511-3.
  5. ↑ Dutta, Niloy, K. (2014). Fiber Amplifiers and Fiber Lasers. World Scientific. pp. vi.{{cite book}}: CS1 maint: multiple names: authors list (link)
  6. ↑ Chadha, Devi (2019). Optical WDM Networks. p. 8.
  7. ↑ Agrawal, Govind P. (2002). Fiber-Optic Communications Systems. John Wiley & Sons, Inc.
  8. ↑ Nemova, Galina (2002). Optical Amplifier. p. 139.
  9. ↑ Ramaswami, R., and Sivarajan, K., Optical Networks: A Practical Perspective, Second Edition, 2001, Elsevier, Philadelphia, PA, ISBN   0080513212, 9780080513218
  10. ↑ Aurweek, Steve (May 17, 1993). ""Optelecom, HydraLite become partners"". The Baltimore Sun.
  11. ↑ Hecht, Jeff. ""OSA Centennial Snapshots. Boom, Bubble, Bust: The Fiber Optic Mania". The Optical Society and Optics and Photonics News. October 2016.
  12. ↑ Markoff, John (March 3, 1997). "Fiber-Optic Technology Draws Record Stock Value". New York Times.
  13. ↑ Sprint (June 12, 1996). ""New Technology Allows 1600 Percent Capacity Boost"". PR Newswire. Kansas City, MO.
  14. ↑ Gilder, George (December 4, 1995). ""Angst and Awe on the Internet"". Forbes ASAP.
  15. ↑ Goldman Sachs (July 30, 1997). "Ciena Corporation: Breaking the Bandwidth Barrier". Technology: Telecom Equipment, US Research Report.
  16. ↑ Cvijetic, Milorad and Djordjevic, Ivan B. (2013). Advanced Optical Communication Systems and Networks. Artech House.{{cite book}}: CS1 maint: multiple names: authors list (link)
  17. ↑ Winzer, P.J. (April 2012). "Optical Networking Beyond WDM". IEEE Photonics Journal. 4 (2): 647–651. Bibcode:2012IPhoJ...4..647W. doi:10.1109/JPHOT.2012.2189379. S2CID   20600739.
  18. ↑ 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   
  19. ↑ Rohan, Pierce (January 24, 2018). "A world-record speed achieved on Telstra's transmission network". Computer World.
  20. ↑ Grobe, Klaus; Eiselt, Michael (2013). Wavelength Division Multiplexing: A Practical Engineering Guide. John T. Wiley & Sons. p. 2.
  21. ↑ Cvijetic, M., and Djordjevic, I.B., Advanced Optical Communication Systems and Networks, 2013, Arctech House, Newton, MA, ISBN   978-1-60807-555-3
  22. ↑ 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
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