4-9
Extech Reporter
UNIT 4
Optical Loss
Definition: the amount of optical power that is lost through the link under test due to the attenuation of the
passive components of the link (i.e. optical fiber, interconnections, and splices).
Units: dB
Calculation: (Light Source Reference Power) - (Measured Power)
Total Allowable System Loss
Light
Source
Reference
Power (dBm)
INVALID
OPERATING
MARGIN **
Minimum
Required
Power (dBm)
Measured
Power (dBm)
PASS
OPERATING MARGIN
or
SYSTEM OVERHEAD
Optical Loss
FAIL
Pass/Fail
Definition: the rating a link receives when its Measured Power is compared to its System Reference
Power, based upon the attenuation parameters or loss values specified by cabling standards. A link
passes when Measured Power is greater than the System Reference Power. A link fails when Measured
Power is less than the System Reference Power.
Units: N/A
Calculation: N/A
Total Allowable System Loss
Light
Source
Reference
Power (dBm)
INVALID
OPERATING
MARGIN **
Minimum
Required
Power (dBm)
Measured
Power (dBm)
PASS
OPERATING MARGIN
or
SYSTEM OVERHEAD
Optical Loss
FAIL
** If the Measured Power is greater than the Light Source Reference Power, then the circuit will receive an Invalid Operating Margin error, indicating an invalid test condition. Circuit test results receiving this error
should be considered as a FAIL.
In other words, more light is received through the whole link from end to end than was received through the single reference patch cable. This is physically impossible since this would indicate GAIN in the system
rather than LOSS.
This condition usually occurs when the reference was set up incorrectly. The correct sequence of steps to set a reference follow:
1) MULTIMODE ONLY - wrap the reference cable seven (7) times around a 0.7” mandrel (0.7” for 62.5um, and 0.9” for 50um) and secure.
2) Connect the ends of the reference cable to the power meter detector port and the appropriate light source port.
3) Power ON and set the units to the same wavelength.
4) Set the reference (or “ZERO”) in the power meter using the procedure in the operations guide.
The most important part of certification testing is to ensure that the integrity of the reference (or “ZERO”) is maintained.
Two factors to keep in mind are:
– Do NOT remove the patch cord from the light source port until all tests have been completed
– MULTIMODE ONLY - do NOT allow the patch cord to unwrap from the mandrel
Interpreting Extech Reporter Screens and Reports, cont.
