Dense wave division multiplexing has aligned cutting edge laser optics, electronics and modulation technologies to maximize the efficiency of optical fiber data transmission. This successful conglomeration has been the byproduct of a coordinated, end-to-end approach to DWDM development, installation, testing and maintenance practices.
During all these phases of a DWDM networks lifecycle inspection of the fiber end faces and connectors is critical to ensure reliable operation. In order to be efficient inspection tools must not only allow you to see the fiber end face they must also automate the whole test process, the FiberChek Probe microscope is a handheld solution capable of auto-focus, auto pass/fail analysis, auto data storage and automated fiber inspection workflows.
Fiber testing is essential during DWDM network construction, both before and after MUX/De-MUX equipment is installed in order to ensure first time service activation and reliable networks. Conventional fiber testing tools such as VFL and fiber end inspection tools can be used with conventional OTDR testing equipment, that uses standard 1310/1550nm test wavelengths, to characterize distances to and losses from connection/splice points and find issues such as excessive optical losses and bends in the main/core/common fibers in DWDM networks.
Once MUX/De-MUX connections have been completed, standard/conventional OTDR tools become less useful as by the very nature of the MUX/DeMUX devices those 1310 & 1550nm wavelengths are blocked (filtered out). What is required to characterize the DWDM links end to end are more specialized OTDR that operate at the exact DWDM service wavelengths so they can validate specific wavelength routes. For example the VIAVI DWDM OTDR module is a tunable C-band OTDR which will do just that and allow characterization of DWDM links end-to-end through MUX and De-MUX. Having an integrated tunable laser source (via the OTDR test port) also enables a basic continuity test before service turn-up. While the Smart Link Mapper (SLM) feature provides an icon-based view of the OTDR trace to simplify the interpretation of test results and to clearly identify common DWDM link components/elements and any faults.
DWDM Turn-up Testing
To verify channel performance and wavelength provisioning over live metro/access links a DWDM Optical Channel Checker Module can be used to accurately assess wavelengths and power over the complete spectrum.
An Optical Spectrum Analyzer (OSA) is an additional tool for active DWDM systems that can verify transmitted wavelengths and power levels and most importantly OSNR. The OSA-110 series OSA module is a compact CWDM and DWDM test solution that is compatible with the T-BERD/MTS-6000A and -8000 platforms. The OSA-110 features full-band measurement capability, high optical resolution and built-in wavelength calibration to ±.05nm accuracy.
Network Monitoring with a Remote Fiber Test System and DWDM
Hardware: A remote fiber test system can provide around-the-clock OTDR monitoring in a rack-mounted solution. Automated, rack-mounted optical test units can be applied to test fiber carrying DWDM transmissions via scan routine or on demand test for specific troubleshooting and restoration use cases for 5G, FTTH, and high-speed business services. VIAVI DWDM test equipment such as the OTU-5000 with 1625-1650 nm is designed to test at an out of band wavelength that does not interfere with the active DWDM transmissions. These wavelengths are reserved for test. The OTU-8000 with a tune-able DWDM module enables testing multiple branches in a DAA network such that testing can be conducted in band on a specific transmission wavelength assigned to a node beyond a DEMUX or out of band with a wavelength reserved for test. With scalability beyond 1000 ports, both Optical Test Heads free up valuable technical resources while providing detailed, instant fault alerts with location details with integrated mapping functionality.
Software: The ONMSi remote fiber test system for core, access, metro and FTTH applications is software that controls and tracks all data obtained by the OTUs. It is designed to give your team a network wide view to fiber health and team resolution progress as an essential DWDM test solution that establishes a centralized, high-visibility portal for overall network integrity data. This includes construction test, long-term performance monitoring and intrusion detection (security).
For smaller, private or single links in the network such as data centers and industrial sites, the SmartOTU software is a stand-alone solution for continuous in-service fiber or dark fiber monitoring and fault detection. The SmartOTU can be deployed out of the box without a server or training requirements.
Locating and repairing faulty DWDM network links quickly, and without disrupting existing traffic, is the key to avoiding excessive downtime or SLA penalties. OTDR tests at specific DWDM wavelengths can be performed on the live network to avoid service interruption. Optical Channel Checkers (OCC) and OSA can also become valuable DWDM troubleshooting tools by using power and wavelength analysis to pinpoint anomalies. Test solutions which include additional features to validate SFP/SFP+ transceivers and even program tunable transceiver devices will significantly reduce Mean Time To Repair (MTTR).