Tip of the Week – 21 Jan 2011

Posted   Filed under Tip of the Week.

Tip of the Week: Below are a few measurement units commonly used in fiber networks, which are often misused. Fiber loss or component insertion loss, unit:  dB   Typical measurement instrument: power meter and light source   Common use: fiber span and component optical loss measurement.    Note: loss in dB is always indicated as a positive value. Example, fiber loss of 5 dB, not -5 dB.  Also loss is dependent on transmission   wavelength. Fiber loss is higher at 1310nm than 1550nm for the same fiber length. Fiber attenuation, aka attenuation coefficient, unit: dB/km   (loss per 1 km length of fiber)   Typical measurement instrument: OTDR   Common use: fiber cable specifications   Note: always positive value.  Typical attenuation for a good fiber is 0.35 dB/km @1310nm and 0.23 dB/km at 1550nm Optical power, unit:  dBm  (referenced to 1 mW of optical power, 0 dBm = 1 mW)   Typical measurement instrument: power meter and light source   Common use:  optical power measurement in fiber span   Note: can be positive or negative value. Negative value means the power is less than 1 mW. Chromatic dispersion  “CD”, unit:  ps/nm   Typical measurement instrument: CD test set   Common use: fiber span or component measurement   Note: can be positive or negative value. Chromatic dispersion coefficient unit:  ps/(nm.km)   (chromatic dispersion per 1 km length of fiber)   Typical measurement instrument: CD test set   Common use: fiber cable specification   Note: can be positive or negative value Polarization mode dispersion “PMD”, unit:  ps   Typical measurement instrument: PMD test set   Common use: fiber span and component measurement   Note: always positive value. Polarization mode dispersion coefficient, unit:  ps/√km   (PMD per 1 km length of fiber)   Typical measurement instrument: PMD test set   Common use: fiber cable specification   Note: always positive value. Optical signal to noise ratio “OSNR”, unit:  dB/nm   (dB with resolution bandwidth “RBW” in nm)   Typical measurement instrument: optical spectrum analyzer (OSA)   Common use:  OSNR measurement in fiber span   Note: always positive value. OSA peak power, unit: dBm/nm   (dBm power with resolution bandwidth “RBW” in nm)   Typical measurement instrument: optical spectrum analyzer (OSA)   Common use: optical power measurements in DWDM system.  Not the same as total power measured with power meter.   Note, can be positive or negative value Notes:  dB = decibel, relative measurement between input and output, dB = -10log(PowerOut/PowerIn)  dBm = absolute measurement referenced to 1 mW, 0dBm = 1mW, equation dBm = 10log(Power/1mW)  ps = picosecond  nm = nanometer  km = kilometer  mW = milliWatt Pertinent Products/Services: ** NEW **  DWDM LiteTM  M-ROADM, Manual Reconfigurable Add-Drop Multiplexer Now have the ability to add-drop 2 to 40 channels in any DWDM link (2 to 18 in CWDM links) at a economical price!  Our M-ROADM product features include : 
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Contact us for more details and pricing.  To view all our products and services, surf to http://www.TelecomEngineering.com/products.htm To learn more about this topic and other fiber optic network topics, refer to my following books (publisher McGraw-Hill): “Planning Fiber Optic Networks”, ISBN 0-07-1499199 available from Amazon.com .  Table of contents can be seen here :  http://www.TelecomEngineering.com/products/resources/planningfibernetworks.htm , “Fiber Optic Installer’s Field Manual”, ISBN 0-07-135604-5 available from Amazon.com. Table of contents can be seen here http://www.TelecomEngineering.com/products/resources/field-manual.htm .  Did you miss last week’s Tip?  If so feel free to peruse this month’s archived Tips at http://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 USA, Inc.  Toll Free:  1.888.250.1562   www.TelecomEngineering.com