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1、TIA/EIA TELECOMMUNICATIONS SYSTEMS BULLETIN ITM-20 Enhanced Bandwidth Performance over Laser-Based, Multimode Fiber Local Area Networks TSB62-20 FEBRUARY 2001 TELECOMMUNICATIONS INDUSTRY ASSOCIATION The Telecommunications Industry Association represenis the communications sector of Eisctrtlnis Irrau
2、stries Alliance Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted without license from IHS -,-,- NOTICE TIMEIA Engineering Standar
3、ds and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his
4、particular need. Existence of such Standards and Publications shall not in any respect preclude any member or nonmember of TIMEIA from manufacturing or selling products not conforming to such Standards and Publications, nor shall the existence of such Standards and Publications preclude their volunt
5、ary use by those other than TIMEIA members, whether the standard is to be used either domestically or internationally. Standards, Publications and Bulletins are adopted by EIA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, TIA/EIA does not assume a
6、ny liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard, Publication, or Bulletin. Technical Bulletins are distinguished from TIMEIA Standards or Interim Standards, in that they contain a compilation of engineering data or information useful to t
7、he technical community, and represent approaches to good engineering practices that are suggested by the formulating committee. This Bulletin is not intended to preclude or discourage other approaches that similarly represent good engineering practice, or that may be acceptable to, or have been acce
8、pted by, appropriate bodies. Parties who wish to bring other approaches to the attention of the formulating committee to be considered for inclusion in future revisions of this Bulletin are encouraged to do so. It is the intention of the formulating committee to revise and update this Bulletin from
9、time to time as may be occasioned by changes in technology, industry practice, or government regulations, or for other appropriate reasons. (From Project No. 4892, formulated under the cognizance of the TIA FO-2.2 Subcommittee on Digital Multimode Systems. ) Published by TELECOMMUNICATIONS INDUSTRY
10、ASSOCIATION 2001 Standards and Technology Department 2500 Wilson Boulevard Arlington, VA 22201 PRICE: Please refer to the current Catalog of ELECTRONIC INDUSTRIES ALLIANCE STANDARDS and ENGINEERING PUBLICATIONS or call Global Engineering Documents, USA and Canada (1-800-854-7179) International (303-
11、397-7956) All rights reserved Printed in U.S.A. Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted without license from IHS -,-,- C
12、opyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted without license from IHS -,-,- Copyright Telecommunications Industry Association
13、Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted without license from IHS -,-,- TSB-62-20 ITM-20 Enhanced Bandwidth Performance over Laser.Based. Multimode Fiber Local Area Networ
14、ks Contents . Foreword III 1 Introduction 1 2 Background and History . 2 2.1 Launch Conditioning 2 2.2 Source Near Field 2 2.2.1 Mode Power Distribution 2 2.2.2 Encircled Flux . 3 2.3 Encircled Flux Round Robins . 4 2.4 Encircled Flux and Link Performance 5 2.5 The Validation Experiment . 6 2.6 Rest
15、ricted Mode Launch Fiber Bandwidth . 8 2.7 Enhanced Bandwidth Criteria . 9 2.8 Risk Assessment 10 3 Recommendation . 11 4 Normative references . 12 Annex A (informative) 13 Annex B (informative) 19 i Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS
16、 Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted without license from IHS -,-,- TSB-62-20 This page left blank. ii Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/111
17、1111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted without license from IHS -,-,- TSB-62-20 ITM-20 Enhanced Bandwidth Performance over Laser-Based, Multimode Fiber Local Area Networks Foreword From TIA Project No. 4892 formulated under the cogni
18、zance of TIA FO-2.2.1, Subcommittee on Modal Dependence of Bandwidth. This bulletin is part of the series of test methods included within TINEIA TSB-62. There are two annexes, which are informative. Key words: bandwidth, effective modal bandwidth, encircled flux, launched power distribution, restric
19、ted mode launch, restricted mode launch bandwidth iii Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted without license from IHS -
20、,-,- TSB-62-20 This page left blank. iv Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted without license from IHS -,-,- TSB-62-20
21、 1 Introduction 1.1 Intent This bulletin describes and gives background information for the laser source and fiber selection criteria required to achieve enhanced bandwidth performance over local area networks (LANs) based on multimode fiber links and laser sources. Such a link is shown in Figure 1.
22、 Figure 1 - Basic link addressed by this bulletin. These criteria come from developments in the TIA Working Group on the Modal Dependence of Bandwidth (FO-2.2.1) (the Working Group) from 1997 to 2000. Without appropriate source and fiber selection criteria, fiber link lengths for LANs must be set ve
23、ry conservatively to minimize risk of link failure. The Working Group has developed and tested new test procedures that characterize the laser source near field and the multimode fibers bandwidth performance under restricted launch conditions. Limiting the allowable range of these source and fiber p
24、arameters assures that a link will meet enhanced bandwidth performance conditions with an acceptable risk of link failure (below 1%) for maximum link lengths. Shorter links will have lower risks of link failure. 1.2 Scope Although the methodology described here to characterize both sources and fiber
25、 may be broadly applicable to different source and fiber types, the specific selection criteria addressed in this bulletin are only applicable to LANs based on short-wavelength (830 - 860 nm) laser sources and graded-index 62.5/125 m optical fibers. Short-wavelength networks based on graded-index 50
26、/125 m fiber alread perform at gigabit-per-second data rates over link lengths of up to 550 meters , criteria for enhanced network performance is therefore less urgent for these networks. Nevertheless, enhanced network performance for 50/125 m fiber systems (e.g. 1 O gigabit-per-second systems) is c
27、urrently (as of September 2000) under consideration in the Working Group. Y. 1 Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted w
28、ithout license from IHS -,-,- TSB-62-20 2 Background and History The move toward high-speed (2 1 gigabit-per-second) LANs requires the greater modulation capabilities of laser sources like the Vertical Cavity Surface Emitting Laser (VCSEL) or the edge-emitting semiconductor laser diode. Unlike the l
29、ess coherent light emitting diode (LED), laser sources typically excite only a subset of the fiber modes available. This change in source property together with the inter- modal dispersion properties of the fiber requires that both source and multimode fiber be characterized and/or modified especial
30、ly for high-speed LAN applications. 2.1 Launch Conditioning The Working Group began looking into short-wavelength (-850 nm) laser source characterization in the spring of 1998. Characterization of the multimode fiber would follow later that same year. This work followed work that the Group performed
31、 in association with the I EEE 802.3 Gigabit Ethernet standardization effort. There, it was found that laser launch conditioning led to more predictable worst-case bandwidth performance. In particular, an offset single-mode fiber launch into multimode fiber employed with 1300 nm laser sources and im
32、plemented with a special hybrid patchcord gave a bandwidth performance that predictably met or exceeded the overfilled launch (OFL) performance specification of the 62.5 pm core multimode fibeQ. This result allowed the adoption of an acceptably long link length of 550 meters for the Gigabit Ethernet
33、 1000BASE-LX standard. No such launch conditioning was prescribed for the short-wavelength (-850 nm) 1 000BASE-SX Gigabit Ethernet standard, and the resulting link length for 62.5 m fiber was less than 300 m. The Working Group realized that conditioning the launch of the short-wavelength sources mig
34、ht lead to significant improvement in allowable link length, particularly for 62.5 m fiber. Unlike the offset launch solution employed for the 1300 nm sources, the solution for the short-wavelength sources would ideally involve no external patchcord. This was desired to preserve the low-cost potenti
35、al of the short-wavelength sources. A simple restriction of allowable source launch characteristics might yield the desired performance enhancement. The Working Group began by looking at the near-field properties of the laser source. 2.2 Source Near Field 2.2.1 Mode Power Distribution Initially, the
36、 Working Group attempted to characterize the near field of the source by applying a measurement of the mode power distribution produced by the laser source in a length of multimode fiber. This measurement is described in EIA/TIA ITM-3. It quickly became apparent, however, that such an approach was n
37、ot 2 Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted without license from IHS -,-,- TSB-62-20 satisfactory. ITM-3 assumes that a
38、ll modes within a mode group have the same energy. This equipartion-of-energy assumption does not generally hold for multimode fibers under 1 km in length. Energy redistribution amongst modes within a mode group occurs over longer fiber lengths, if it occurs at all. Since lasers initially excite a f
39、raction of the modes excited by an LED, this failure of energy redistribution becomes particularly important for laser source characterization. The near-field intensity as a function of radius was often observed to be non-symmetrical and non-monotonic. These near-field patterns produced non-physical
40、 computed mode power distributions, i.e. negative mode- group powers. 2.2.2 Encircled Flux The Working Group eventually settled on another measure of the laser near field, the Encircled Flux (EF). Encircled Flux is obtained from the near-field intensity pattern produced by a laser source in a 10 m l
41、ength of 62.5 m core, graded-index multimode fiber. It is the near-field pattern at the end of this fiber (as opposed to the near field at the laser source itself) that is more relevant to system performance. This is because the only relevant part of the laser source energy is that which is coupled
42、into the fiber. In general, such a near field will have a non-uniform shape that includes speckle. By integrating over radius and over all azimuthal angles, the Working Group collapsed the two-dimensional near-field information into a one-dimensional radial function, giving the fractional power laun
43、ched by a source within a given fiber radius. The complexity in the raw near-field data is avoided by exploiting the axial symmetry of the fiber, and, unlike the measurement of mode power distribution, no assumption on the equipartition of energy within mode groups is required. Typical near-field pa
44、tterns for an LED and a VCSEL source at the end of a IO-meter, graded-index, 62.5 m fiber jumper are shown in Figure 2. Note that while the near-field intensity and annular flux for the VCSEL are irregular, the encircled flux as a function of radius is smooth and monotonically increasing. Since it i
45、s the launch power distribution and not the absolute power that is of interest, the normalized encircled flux is plotted and compared. The detailed procedure for obtaining encircled flux is defined in a test procedure, ElMIA FOTP-203. 3 Copyright Telecommunications Industry Association Provided by I
46、HS under license with EIALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/29/2007 21:44:39 MDTNo reproduction or networking permitted without license from IHS -,-,- TSB-62-20 Radius (Ikm) Figure 2 - Near Fields, Intensity Profiles, Annular Flux, and Encircled Flux for an LED a
47、nd a VCSEL 2.3 Encircled-Flux Round Robins To be a useful parameter, Encircled Flux needs to correlate with link performance and be reproducibly measured from lab to lab. The latter was tested with inter-laboratory round robins. The first round-robin comparison involved 17 laser sources, 9 VCSELS an
48、d 8 edge-emitting (CD) lasers and two LEDs. The range of encircled flux encountered in this comparison is shown in Figure 3, where the shaded boxes define the source selection criteria of Table I below. Curves for sources that satisfy the criteria lie between the shaded boxes. 4 Copyright Telecommunications Industry Association Provided by IHS under license with EIALicensee=IHS Employees/1111111001, User=W