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| Wavelength-division multiplexing | |
|---|---|
| Name | Wavelength-division multiplexing |
| Invented | 1970s |
| Related | Optical fiber, Dense wavelength-division multiplexing |
Wavelength-division multiplexing
Wavelength-division multiplexing (WDM) is an optical multiplexing technique that increases bandwidth by combining multiple optical carrier signals on a single optical fiber by using different wavelengths (i.e., colors) of laser light. Developed alongside advances in optical fiber research, WDM is integral to modern telecommunications, linking developments in semiconductor lasers, optical amplifiers, and fiber manufacturing, and enabling large-scale backbone networks, metropolitan rings, and submarine links.
WDM evolved from laboratory advances associated with Bell Labs, Corning Incorporated, AT&T, ITU-T, and NIST, connecting breakthroughs from John B. MacChesney era materials research to commercialization by Lucent Technologies and Alcatel-Lucent. Early demonstrations involved cooperation among RSRE, British Telecom, and NTT researchers who leveraged erbium-doped fiber amplifier progress attributed to groups at NTT and Bellcore. Regulatory and standardization activity from ITU, ETSI, and national agencies shaped channel grids and spectrum allocation. Major carriers such as Verizon Communications, AT&T Inc., Deutsche Telekom, Orange S.A., and consortiums managing SEA-ME-WE 3 and MAREA adopted WDM to scale capacity on existing fiber routes.
WDM has several categories widely adopted by vendors like Cisco Systems, Huawei Technologies, Nokia, Ciena Corporation, and Infinera. Coarse WDM (CWDM) and dense WDM (DWDM) differ in channel spacing standardized by bodies such as ITU-T. DWDM enabled high-channel-count systems used by internet backbone providers including Level 3 Communications and content companies like Google and Facebook for data center interconnects. Other variants include wavelength-routing systems deployed by metropolitan operators like BT Group and submarine-specific implementations used by consortia such as SEA-ME-WE 4 and TAT-14. Reconfigurable optical add-drop multiplexers (ROADMs) and flex-grid systems influenced by OIF and MEF provide dynamic spectral allocation, while spectrum-sliced elastic optical networks have been explored in academia at MIT, Stanford University, University of Cambridge, and Tsinghua University.
Core components include lasers, multiplexers/demultiplexers, optical amplifiers, filters, and fiber, supplied by manufacturers such as Finisar, NeoPhotonics, Sumitomo Electric Industries, and Fujitsu. Semiconductor distributed feedback lasers (DFB lasers) and tunable lasers developed by teams at EPFL and Bell Labs provide narrow linewidth sources; arrayed waveguide gratings (AWGs) and thin-film filters from Mitsubishi Electric or JDS Uniphase implement multiplexing. Erbium-doped fiber amplifiers (EDFAs) from Optical Coating Laboratory Inc. and Raman amplifiers used by Telefonica extend reach. Passive components trace to material advances by Corning Incorporated and manufacturing lines in Japan and Germany; active switching technologies have been commercialized by Infinera and Ciena for coherent transponders and digital signal processors (DSPs). Connectorization and fiber types reference standards promulgated by IEC and TIA.
WDM is implemented in point-to-point links, ring topologies favored by municipal carriers like KPN and Telekom Austria, and mesh architectures used by national backbones such as China Telecom and NTT East. Subsea trunking projects like SEA-ME-WE 5 and MAREA rely on WDM for per-fiber capacity aggregated across repeaters supplied by manufacturers including Alcatel Submarine Networks and SubCom. Data center interconnects use WDM for short-reach dense links in deployments by Amazon Web Services, Microsoft Azure, and hyperscale cloud providers. Network functions virtualization and software-defined networking experiments from Open Networking Foundation and ETSI NFV integrate WDM control via GMPLS or SDN controllers developed by vendors like Juniper Networks and research groups at Carnegie Mellon University.
Capacity scales with channel count, modulation formats, and spectral efficiency; advances in coherent detection, carrier-phase estimation, and forward error correction by research at Bell Labs, Nokia Bell Labs, and Huawei drove spectral efficiencies used by operators such as Sprint Corporation and Vodafone. Nonlinear impairments (Kerr effect, four-wave mixing) and dispersion management studied at University College London and Politecnico di Milano limit per-channel power and spacing. Amplifier noise figures, optical signal-to-noise ratio (OSNR) metrics codified by ITU-T and technique trade-offs examined by IEEE conferences define reach and bit-error-rate performance. Flex-grid and super-channel approaches pushed by IETF drafts and industry groups increase per-fiber throughput but require advanced DSP and programmable ROADMs.
WDM underpins long-haul backbone transport for carriers like AT&T, Verizon, and NTT, submarine cables linking continents such as Asia-America Gateway, metro rings for municipal providers like CityFibre, and data center interconnects used by Google Cloud Platform and Meta Platforms. Enterprises deploy CWDM for campus links and service providers use DWDM for wavelength leasing products bought by financial firms on trading networks in New York and London. Research and defense labs including Los Alamos National Laboratory and Sandia National Laboratories use specialized WDM for sensing and high-bandwidth telemetry; scientific facilities such as CERN and observatories coordinate fiber networks for data acquisition.
Standards and grid definitions are set by ITU-T series (notably G.692 and G.694.1) and interoperability testing by ISO, IEEE 802.3 working groups, and the Optical Internetworking Forum. Protocols for control planes include GMPLS standardized in IETF working groups and extensions for flex-grid in ITU-T and OIF specifications; vendor consortia like Metro Ethernet Forum and testing regimes at European Telecommunications Standards Institute facilities validate multi-vendor systems. Operational best practices reference documents from Carrier Ethernet initiatives and training programs run by Telecommunications Training Institute affiliates.
Category:Optical networking