Fiber Channel / FICON Singlemode Recommendation for 8 APC connectivity systems

Transcription

1 Fiber Channel / FICON Singlemode Recommendation for 8 APC connectivity systems WHITEPAPER Whitepaper: Lichtlauf Poarität - Codierung Autor: Harald Jungbäck Seite 1 von 5

2 Reflections: A singlemode (SM) problem! Within the recent years more and more transmission problems occur at increasing SM Fiber Channel (FC) and IBM FICON SM data rates, even the link attenuation and length specifications of the FC und FICON standard and of the used transceivers are fulfilled. According to the current state of knowledge, the transmission problems are caused by too high reflection of fiber optic singlemode connection with 0 physical contact (PC) ferrules. The reflections running back to the laser transmitter, disturbing its function and eventually affecting the signal to noise ratio of the transmission signal negatively. The first problems already occurred on the upgrade from FC SM 1Gbit/s to 2Gbit/s, which however could be eliminated by simple cleaning of the connections. On the increase from 2 to 4 Gbit/s the transmission problems gained heavily, but mostly could be fixed by simple cleaning of the connections, too. Reflections in singlemode fiber optic connections can be caused by errors of the geometry of the connector ferrule`s end faces like apex offset and undercut, next to the most common reasons contamination and defects like scratches etc. of the light propagating 9µm singlemode fiber cores. Finally, all errors mentioned above causing imperfect physical contact of the 9µm singlemode fiber cores of the singlemode fibers linked via connections. Imperfect physical contact of the 9µm singlemode fiber cores is the reason of reflections in connections, because there is no glass-to-glass transition but glass-to contamination or air-to glass. As already mentioned, reflections can be caused by geometry errors of the connector ferrule s end faces, in particular the parameters Apex Offset (=lateral offset of the highest points of the convex spherical end face) and Undercut = negative Fiber Height. Both and other end face geometry parameters are produced through the polishing process as a major part of the assembling of fiber optic connectors. The geometry parameters are specified in connector standards and are usually measured with Interferometer devices as shown below. Whitepaper: Fiber Channel / FICON Singlemode Author: Harald Jungbäck Page 2 of 5

3 The measurement of how many reflections within connections are attenuated, respectively are avoided, is Return Loss RL in [db]. The higher the RL of a connection, the lower the generated reflection is. Fiber Channel and IBM FICON singlemode specify RL of connections as follows: Fiber Channel Physical Interface-5 (FC-PI-5) REV 1.00 : SM optical return loss: Connectors and splices shall each have a return loss greater than 26 db as measured by the methods of IEC IBM: Has no particular RL spec for FICON SM, only the following generic spec, valid for all types of singlemode connectors, resp. connections, to be found in the Planning Guide: System Planning for Fiber Optic Links (ESCON, FICON, Coupling Links, and Open System Adapters) GA Table 5-5 Note 2: Singlemode connectors and splices must meet a minimum return loss specification of 28 db. For multimode (MM) fiber optic connections the same facts are applicable. They cause reflections as well if their commonly 50µm fiber cores do not have sufficient physical contact. But multimode reflections have very low intensity and through this they do not disturb the transmission, why the RL of MM connections are only specified to min. 20 [db]. Most of the Fiber Channel applications are multimode. Even though the upgrades are fast increasing, we are not aware of any transmission problems caused by reflections. It is to fear that the reflection caused transmission problems at the upcoming 8 and 16 Gbit/s singlemode Fiber Channel and FICON will raise. Thus, the requirements on Return Loss RL of fiber optic connections cannot be high enough. Common in the market for SM fiber optic connections with 0 physical Contact (PC) ferrules are RL values of 40 to 50 [db], but measured against reference connectors of measurement cables of certain high quality. The before mentioned, in the first view low SM RL specifications of FC and FICON, allow the conclusion to be fulfilled simply and securely even by market common 0 PC singlemode connectors. But as experience demonstrates, in particular the gaining reflection caused transmission problems, the statement above is not a matter of fact. In the daily reality of data center operation, with all the obstacles like contaminated connector end faces and randomly mated each-to-each connections, the RL values specified in connector data sheets are often not to reach. Reflection caused transmission problems of Fiber Channel and FICON singlemode only can be excluded by the use of fiber optic singlemode connectors with 8 Angled Physical Contact (APC) ferrules! SM 8 APC connections do not send the reflected light, which is caused through contamination or end face geometry errors, back into the transmitting fiber, but they reflect the light out of the SM 9µm fiber core into the fiber cladding. Whitepaper: Fiber Channel / FICON Singlemode Author: Harald Jungbäck Page 3 of 5

4 SM 8 APC connections even have in the worst case of no physical contact of the 9µm fiber cores, glass-air-glass transition, minimum 50 [db] Return Loss RL and through this they give the highest possible operation reliability for reflection critical applications like SM FC and FICON. Hence our recommendation: Use at the latest of 8 Gbit/s SM Fiber Channel and FICON only SM 8 APC connections in your cabling infrastructure. For attachment of common SM Fiber Channel and FICON Transceivers 0 PC connectors must be used, 8 APC in the cabling infrastructure only. Use hybrid 0 PC to 8 APC equipment cords to attach equipment to your 8 APC infrastructure. Pay attention on clean connector ferrule end faces, in particular their fibers, of 8 APC connectors as close as you must do on 0 PC! Fiber optic connector ferrule end faces with singlemode 9/125µm fiber under 400x magnification Avoid contamination transmission problems caused by inspecting and cleaning the end faces of your fiber optic connectors! Whitepaper: Fiber Channel / FICON Singlemode Author: Harald Jungbäck Page 4 of 5

5 About Rosenberger OSI: Since 1991, Rosenberger Optical Solutions & Infrastructure (Rosenberger OSI) has been an expert in innovative fiber optic cabling infrastructure and service solutions for Datacom, Telecom and Industrial. The products and services can be found wherever largest amounts of data have to be transferred quickly and securely. In addition to the development and production of a broad portfolio of fiber optic and copper cabling systems, Rosenberger OSI also offers a variety of services such as planning, installation and maintenance of cabling infrastructure. Rosenberger OSI employs about 600 people in Europe and has been a part of the globally operating Rosenberger Group since 1998, a worldwide leading provider of high-frequency-, high-voltage-, and fiberoptic-connection solutions headquartered in Germany. For further information, please visit: Rosenberger-OSI GmbH & Co. OHG Optical Solutions & Infrastructure Endorferstr Augsburg GERMANY Phone: info-osi@rosenberger.com Rosenberger is a registered trademark of Rosenberger Hochfrequenztechnik GmbH & Co. KG. All rights reserved. Rosenberger 2017 Transfer to third party only by authority of Rosenberger-OSI GmbH & Co. OHG- All rights reserved Created: Valid since: