Issue link: https://www.e-digitaleditions.com/i/1066130
44 I ICT TODAY The best guidance currently available for testing MPOs is the IEC technical report, 61282-15. Like a TSB within TIA, technical reports offer guidance but not requirements. Within the IEC's SC 86C Working Group 1, there is work being done on an MPO testing standard that would be published as 61280-4-5. That document will likely be out in about a year. TIA's TR-42.11 committee is working on an addendum to the 568.3-D standard that references the IEC technical report within the ANSI standards. WHAT TO TEST When looking inside standards for link and channel testing, both ANSI/TIA and ISO/IEC specify two tiers of certification. Within the TIA standards, this is Tier 1 and Tier 2 testing; within ISO/IEC, it is called basic and extended. Tier 1 (basic) is required. It tests loss, length and polarity of a fiber optic system. These are the tests that cabling vendors must submit for warranty coverage. Tier 2 (extended) is optional. It is done with an optical time domain reflectometer (OTDR) that provides information about each connection, splice and cable segment in the link and offers a graphical representation of the components and their performance. Some companies may choose to extend Tier 1 tests with an OTDR test, but only Tier 1 testing is required. Fiber end face inspection and certification is defined in the IEC 61300-3-35 standard. It has always been important that fiber end faces are in pristine condition prior to mating, but with MPO connections, it becomes critically important because there are multiple fibers in a single connector, and contamination on the end face has a much greater impact. Ensuring a clean connector for all 8, 12 or 24 fibers on an MPO end face is more challenging than for a typical LC or SC, especially when considering that a singlemode fiber has a core only 9 microns in diameter and a multimode fiber only 50 microns. Since the surface area of the MPO connector is larger, there is a greater surface on which debris can land. In addition, the bulkhead adapter provides a larger space for the debris to enter. Once contamination is present, it can easily migrate from one fiber to another within the same array. The more fibers in the array, the higher the risk. If there is any dirt in the mix on one of the fiber end faces or on the ferrule when making the connection, that debris will shatter and move all over the connector. Furthermore, this debris often creates air gaps that can prevent light from traveling down some of the fibers which will create back reflections and insertion loss on any fiber that is affected. For evaluation of fiber end faces, the IEC 61300- 3-35 Basic Test and Measurement Procedures Standard for Fiber Optic Interconnecting Devices and Passive Components contains specific cleanliness grading criteria to assess pass or fail certification for inspection of a fiber end face. With specific criteria for different connector types and fiber size, IEC 61300-3-35 certifies the cleanliness of a fiber end face based on the number and size of scratches and defects found in each region of the end face, FIGURE 7: IEC 61300-3-35 sets the requirements for connector quality. There are limits to the size and quantity of defects that can appear in each zone. CLADDING Zone Example: Multimode MPO Connector Requirements CORE Zone ZONE NAME (Diameter) no limit <= 5µm 0>5µm 4 <= 5µm none > 5µm no limit <= 5µm 0>5µm no limit < 2µm 5 from 2-5µm none > 5µm SCRATCHES DEFECTS The main challenge of Tier 1 testing an MPO system is setting the reference in different scenarios, because it depends on whether the system is pinned or unpinned. A. CORE Zone (0-65µm) B. CLADDING Zone (65-115µm)