VIAVI provides the industry with testing solutions to build, deploy and manage passive DWDM networks.
How VIAVI Enables DWDM Systems
Over the past forty years, the physical characteristics of single-mode optical fiber have continued to evolve as breakthroughs in manufacturing have removed waterpeaks that limit performance while wavelength utilization and modulation formats have continued to increase carrying capacity exponentially. Dense Wavelength Division Multiplexing (DWDM) is an important milestone in the evolution of fiber optic transmission technology.
At the start of the network lifecycle, there is manufacturing and new development of passive DWDM devices where verifying full characterization of wavelength dependence performance is critical. As Cable and Telco service providers continue to evolve their networks, pushing fiber deeper, moving networking elements closer to subscribers and serving smaller subscriber groups (in order to increase service speeds and offerings) DWDM is becoming an essential enabler for those HFC Distributed Access Architecture (DAA) and xDSL/Gfast networks.
While wireless providers utilizing Centralized RAN (C-RAN) as a key architectural feature have also realized the benefits of DWDM, which will be a necessity as 5G adoption ratchets capacity demands even further. Passive Optical Network (PON) owner/operators have begun to leverage the advantages of DWDM technology overlaid on existing E-PON and G-PON networks delivering Fiber to the Home (FTTH). And finally, massive hyperscale and multi-tenant data center (MTDC) operators are deploying high-capacity DWDM solutions in their optical data center interconnect (DCI) networks.
By staying ahead of the DWDM technology curve, VIAVI has armed the industry with the test solutions needed to navigate the activation, maintenance and troubleshooting challenges of passive DWDM networks.
What is WDM?
Wavelength Division Multiplexing is a technique that allows multiple frequencies (or wavelengths) to be transmitted over the same fiber simultaneously. This is accomplished by the use of optical transmitters or transceivers with outputs tuned to individual and specific wavelengths so that there are distinct and non-overlapping transmission channels.
Coarse Wavelength Division Multiplexing (CWDM) uses wavelengths between 1260nm and 1670nm (the O, E, S, C, L and U transmission bands) and allows up to 18 individual channels to be created within this region, carrying any combination of voice, data or video with channels spaced 20nm apart. CWDM is a cost-effective solution for relatively low-bandwidth deployments however, because CWDM signals cannot be amplified, there are no broadband optical amplifiers capable of supporting that range, distances are limited to 80km.
Dense Wavelength Division Multiplexing (DWDM) takes WDM to the next level by decreasing channel spacing to 0.8nm or less and shrinking the operational wavelength range. This can produce 80 or more channels or lanes of traffic, opening the door to more high speed, high bandwidth applications.
Amazingly, all DWDM wavelengths reside within the narrow 1525nm to 1565nm region known as the C-Band. This area is utilized due to the relatively low (0.25dB/km) signal loss (fiber attenuation) compared to lower wavelengths found in the O or E-bands for example. As a result of the narrow channel spacing higher-precision lasers and filtering processes are required to maintain channel integrity and minimize interference.
Passive DWDM network architecture begins with a transponder or transceiver accepting data inputs of various traffic types and protocols. This transponder performs the essential function of mapping input data onto an individual DWDM wavelength. Each individual wavelength is fed to an optical multiplexer (MUX) which filters and combines multiple wavelengths onto a single output port for transmission over the main/core/common DWDM fiber. At the receiving end wavelengths can then be separated to isolate the individual channels by using an optical demultiplexer (De-MUX), each channel is then routed to the appropriate client-side output through an additional wavelength matched transponder.
Because DWDM technology overlaps the CWDM frequency band, a “hybrid” solution can also be selected. This type of hybrid system leaves the CWDM MUX and deMUX hardware in place, inserting DWDM wavelengths on top of existing channels in the 1530 to 1550nm range, thereby creating up to 28 additional channels. A hybrid CWDM/DWDM system can provide a significant capacity boost without requiring new fiber installation or wholesale infrastructure changes.
An Optical Add Drop Multiplexer (OADM) is an optional component of DWDM architecture that can be added to either passive or active networks to facilitate the addition or subtraction of a specified wavelength from a mid-stream location on the main/core/common DWDM fiber. Bidirectional architecture includes transmitters and receivers at both ends of the circuit as well as combination MUX/De-MUX devices.
For long-haul networks, DWDM architecture gains complexity with the addition of active system components needed to compensate for optical losses that will make signal reception and data recovery impossible. An Erbium Doped Fiber Amplifier (EDFA) can be used as a booster or launch amplifier to boost the optical power levels just as they leave the MUX while a pre-amplifier performs the same function prior to entering the DeMUX. Additional inline amplifiers might also be included. Passive networks, without EDFA, minimize this complexity.
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