Tip of the Week – 15 Apr 2013

Posted   Filed under Tip of the Week.

Tip of the Week: Back to Basics When measuring values in a fiber optic network, below are a few of the basic units you may come across.
    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 (such as DWDM or CWDM mux) Note: loss in dB is always indicated as a positive value. Example, fiber loss of 5 dB, not -5 dB. Also optical fiber loss is dependent on transmission wavelength. Fiber loss is higher at 1310nm than 1550nm for the same fiber length. Be sure to use the proper wavelength laser source and power meter.
    Fiber attenuation, aka attenuation coefficient, unit: dB/km (loss per 1 km unit 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 at 1310nm and 0.23 dB/km at 1550nm
    Optical power, unit: dBm (referenced to 1 milli-Watt of optical power, 0 dBm = 1 mW) Typical measurement instrument: power meter and light source (test source or transceiver) Common use: absolute optical power measurement 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 unit 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 square root 1 km unit 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 for DWDM systems 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 necessarily the same value as total power measured with power meter. Note, can be positive or negative value
    Transmission rate: Gbps or Gb/s, Mbps or Mb/s, bps or b/s Typical measurement instrument: BER test set Common use: equipment specifications, link design (x bits per second) Note, this is the physical later transmission rate and is not the same as data rate
    Data rate: GBps or GB/s, MBps or MB/s, Bps or B/s Typical measurement instrument: Data test set Common use: information throughput (x bytes per second) Note, this is the rate information is being transferred and is not the same as the transmission rate
    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 bps or b/s = bits per second Bps or B/s = bytes per second
Pertinent Products/Services: * Now Available new DWDM Optical Power Meter * The DWDM Lite Power meter allows you to easily measure DWDM signal powers and wavelengths in your fiber and on any port of your DWDM multiplexer. Measurement range from 1526.43nm (channel 64) to 1563.86nm (channel 17). It works like a mini optical spectrum analyzer (OSA). When connected to the common fiber out of a DWDM multiplexer, it identifies and shows all DWDM channels in the fiber and their individual channel powers. This tool is a great help for technicians deploying and debugging DWDM systems, measuring channel loss, and equalizing channel powers in EDFA applications. Features:
  • Simultaneous measurement of all DWDM channel powers in C-Band
  • identifies which DWDM channels are present in a fiber
  • dynamic range -40dBm to +10dBm
  • computer interface
  • portable with rechargeable lithium-polymer battery
  • compact and portable, dimensions 3 x 6 x 1.4 inches
  • great price
Applications:
  • Passive DWDM networks
  • EDFA DWDM networks to aid in channel power balancing
  • ROADM Networks
More details here: https://telecomengineering.com/product_type/test-equipment/ ** Also available for CWDM networks.