1、 TSB-4979 August 2013Practical Considerations for Implementation of Encircled Flux Launch Conditions in the Field NOTICE TIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating inter
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19、ITATIONS. TIA TSB-4979 iiTIA TSB-4979 Practical Considerations for Implementation of Encircled Flux Launch Conditions in the Field FOREWORD III 1 SCOPE. 1 2 BACKGROUND 1 3 METHOD 1- UNIVERSAL CONTROLLER 2 4 METHOD 2 MATCHED CONTROLLER 4 5 GUIDANCE FOR OTDRS 5 6 GENERAL CONSIDERATIONS AND BEST PRACTI
20、CES 6 7 REFERENCES 7 TIA TSB-4979 iiiTIA TSB-4979 Practical Considerations for Implementation of Encircled Flux Launch Conditions in the Field Foreword Several IEC, ISO and TIA standards such as TIA-526-14-B, IEC 61280-4-1 Ed. 2.0 and IEC/ISO 14763-3 define the desired launch condition using a metri
21、c called encircled flux (EF) when testing a multimode cable plant. While these standards provide guidelines for testing multimode fiber, there is no document to describe how EF compliance is achieved outside of a lab. A purpose of this document is to identify user-friendly, low complexity solutions
22、for implementing multimode launch conditions that meet EF-based requirements. To that end, this document describes two possible implementation methods. The first method can be used with any light source, be it overfilling or underfilling, from any test supplier considered a “universal controller”. T
23、he second method is a light source and launch cord combination (the launch cord could include a controlling device), perhaps from a specific test supplier, that together meet the EF requirements considered a “matched controller”. This document describes the advantages and disadvantages of each imple
24、mentation method. This document also provides uncertainty of measurements and best practices advice. It is not the intent of this TSB to provide users a prescriptive method for implementing EF compliance, nor is it required that they construct equipment to produce or verify the launch condition. Rat
25、her, it is the responsibility of manufacturers of test equipment to offer devices that have been built and tested for EF compliance. From TIA Project No. TIA-PN-4979, formulated under the cognizance of TIA TR42.11, Subcommittee on Fiber Optic Systems. Key words: source, launch, encircled flux, multi
26、mode, attenuation testing, fiber optic testing, light source, OTDR, reference grade, launch cord, LED, mode filter. TIA TSB-4979 iv(this page left blank) TIA TSB-4979 1 1 Scope This Telecommunications Systems Bulletin (TSB) describes two methods for implementing light sources to fulfill compliance r
27、equirements for the EF launch condition. The EF guidelines can be used for field testing optical attenuation of installed multimode cabling for 850 nm and 1300 nm containing 50 m and, when required, 62.5 m graded-index fibers. Since the most common high-speed applications currently run at 850 nm on
28、50 m cabling, for dual wavelength sources its best to align the launch condition to the 850 nm EF target, then allow the 1300 nm launch to fall where it may. In almost all cases, the 1300 nm response will remain within its EF template also. This approach reduces 850 nm launch uncertainty, possibly a
29、t the expense of the 1300 nm launch. Despite this trade-off, this is an improvement over other launch conditions. Since the EF template is different for 50 m and 62.5 m cabling, two diffferent launch controllers are needed. One specific launch controller adjusted for 50 m EF response and another one
30、 adjusted for 62.5 m EF response are needed. This applies to all types of controllers used with single or dual wavelength sources. The purpose of this EF launch condition is to provide: 1. Consistency of field measurements when different sources are used; reducing loss measurement uncertainty from g
31、reater than 40 % to less than 10 % on a dB basis. 2. A provisional worst-case launch condition for IEEE 802.3 (Ethernet) and INCITS T11 (Fibre Channel) compliant transceivers used in high-speed networks (1Gbps). 3. A template for compliance at the output of launch cords. 4. Comparable insertion loss
32、 of a single connection and/or splice at both 850 nm and 1300 nm. 5. Increased harmonization of a metric that defines multimode launch conditions for testing. Although the focus of this document is to assist field personnel in understanding alternative EF launch condition implementation options, the
33、 concepts in this TSB may be applicable to certain lab testing situations where EF launch condition compliance is required. Note: The source launch conditions are specified for the launch cord output. It is presumed that equipment, as supplied, has been verified by the manufacturer to produce the sp
34、ecified launch measured per TIA-455-203-A (FOTP-203-A) or IEC 61280-1-4 Ed. 2.0 2 Background Throughout the history of optical fiber communication systems, the types of light sources and methods to measure test source launch conditions have evolved and improved. These evolutions and improvements, fr
35、om time to time, have resulted in updated industry Standards which have required modification to test measurement practices. In some cases, only the test methods have been impacted and changed. In many cases though, test equipment improvements have required the introduction of new and improved testi
36、ng sources. TIA TSB-4979 2Over the years, many standards have addressed multimode launch conditions. As such, light sources typically used in measuring attenuation on multimode fiber may produce differing launch conditions. These differing launch conditions commonly cause measurement variations. Att
37、enuation measurement experiments using different test instruments that meet outdated launch prescriptions have shown high variations. For example, attenuation variations can occur when two different light sources or different launch cords are used. Despite these issues legacy test equipment complian
38、t to early test standards has typically remained in service in the field. A dilemma thus exists in knowing if the test equipment currently being deployed in the field meets the requirements of the specified installation test methods. The most recent launch condition metric is EF. This metric has bee
39、n applied to define the launch condition limits of 850 nm transmitters for such applications as 4G, 8G, and 16G Fibre Channel, and 10G, 40G and 100G Ethernet. It is also being applied to specify the launch condition of test sources used to verify attenuation of the cabling over which these applicati
40、ons operate. In fact, the target launch condition of the test source is set to represent the worst case launch of these applications. Thus measurements performed with an EF compliant launch will render a repeatable conservative measurement of the loss experienced by these applications. When the EF-c
41、ompliant launch was first introduced, there were many types of test light sources in the field and users were left wondering how their equipment (optical loss test sets, stand-alone light sources, and OTDRs) could meet this new requirement. Since the launch condition for these many “legacy” sources
42、cannot be known, and in order to prevent large-scale instrument replacement, a device was needed and developed that could be attached as a retrofit to these various light sources that conditions the launch in a new way. In order to produce compliant output from the widely ranging native launch condi
43、tions of legacy sources, such devices are relatively complex. As new test sources were developed, they could be optimised to allow for simpler external conditioning devices that can be handled more similarly to the mandrels prescribed in prior launch condition standards. In the following sections, t
44、hese two basic implementation methods are described. The first method describes the universal controller initially introduced for EF compliance. The second method describes an alternative implementation using the matched controller that mimics what users of current equipment use. In both cases the s
45、upplier of the conditioning device verifies compliance in the factory. Note: The universal and matched controllers for an OTDR may include a long length of launch cord, typically more than 100 meters. 3 Method 1- universal controller 3.1 Implementation method for legacy sources For legacy sources, t
46、he type of launch emitted is unknown. Given that, a device that re-distributes the modes, regardless of the initial launch, is needed; then the modes are filtered appropriately. This type of device, known as the universal controller is adjusted in the factory to best fit the EF template. Such config
47、uration entails a “black box” with fixed input cord, output cord and connectors. This uni-directional device is labeled with “input” and “output.” Since EF is TIA TSB-4979 3 measured at the output of the launch cord, it is necessary to have a fixed cord (pigtail) attached to the black box. These uni
48、versal controllers are available for legacy sources used in optical test sets and stand-alone light sources, as well as OTDRs. These devices are universal since they can be used with any light source and they are specified to produce an EFcompliant launch. The figure below illustrates this configura
49、tion, but the relative sizes are not to scale. Figure 1. Legacy Source with Universal Controller Legacy sources that naturally produce sufficiently-uniform mode power distributions can be conditioned to be EF compliant by applying a mandrel wrap. However, a fixed mandrel wrap prescription (e.g., 5 turns on a 22 mm mandrel) cannot be universally applied across all such legacy sources to achieve EF compliance. In general, the mandrel diameter and/or number of wraps need to be adjusted for EF compliance. Note: Some legacy equipment could be tuned to be EF compliant i
