Tip of the Week – 05 Jan 2011

Tip of the Week: If your fiber network uses optical amplifiers then you will likely need to measure optical signal to noise ratio (OSNR). OSNR is a ratio of the signal optical power to noise power in a fiber and is typically measured in unit dB.  It is specified for fiber optic transceivers as a minimum value for a given bit error rate (typically 10-12).  Typical minimum transceiver OSNR is 24 dB for OC192/10GigE transceivers and 18 dB for OC48 transceiver (refer to individual transceiver specs for correct value). Optical amplifiers introduce noise into the fiber link and if the link design is not proper, this noise can overwhelm the signal and cause bit errors even if the optical signal power is well within specification.  If your network does not contain optical amplifiers, then the fiber signal noise level is generally very low and OSNR does not need to be considered (except for some cases where WDM, DWDM and CWDM units are deployed). OSNR is commonly measured with an optical spectrum analyzer (OSA), which by the way is very expensive.  The OSA is also used to accurately measure signal power when noise is present.  Measuring signal power with a standard power meter will provide an inaccurate reading since the meter will show both the combined signal and noise power. A simple test that can be performed to illustrate amplifier noise, is to connect an optical power meter to an optical amplifier (EDFA) output port when it’s input port is not connected (note some optical amplifiers will automatically shut down if there is no input power).  The power meter will read a noise power level even with no input into the amplifier.  This is the normal noise generated by the amplifier and does not mean that the amplifier is defective. Pertinent Products/Services: Need help installing, provisioning, testing, debugging and maintaining your fiber network? Give us a call toll free 888-250-1562.  We can provide you will these services during normal business hours or as 24×7 emergency support. Our expertise includes:
  • fiber optic, Ethernet, SONET networks
  • DWDM and CWDM systems
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  • optical amplifier systems (EDFA, SOA, Raman)
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Contact us toll free 1-888-250-1562 or email at info@TelecomEngineering.com for more details and pricing. To learn more about this topic and other fiber optic network topics, refer to my following books (publisher McGraw-Hill): Did you miss last week’s Tip?  If so feel free to peruse this month’s archived Tips at https://www.telecomengineering.com/About_us/Tip_of_week/tipofweek.htm Contacts: For information about our products and pricing contact us at toll free 1-888-250-1562 . If you have any questions regarding this tip or other fiber networking concerns, please feel free to email me at BChomycz@TelecomEngineering.com. To unsubscribe from this email newsletter Click Here or reply to this email and in subject line place “Unsubscribe”. To add a new subscription to this email newsletter Click Here or reply to this email and in subject line place “Subscribe”. Please feel free to forward this email to other industry professionals that may be interested in this newsletter. *Note: All prices shown are in US$ and products are shipped FOB Minnesota, USA. Prices may change without notice. Bob Chomycz, P.Eng. President Telecom Engineering, Inc. Telecom Engineering USA, Inc. Toll Free:  1.888.250.1562 www.TelecomEngineering.com