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Measuring Power from a Fiber Optic Cable
Overview
One of many important measurements in the fi ber optic industry is that of optical power.
Transmitting information using fi ber optic links depends on suffi cient optical power
traveling through the optical fi ber, connectors, and other elements in which light could
be lost. Enough power must reach the receiver so that the data can be distinguished from
random noise. By measuring the optical power at various points in a fi ber optic link, proper
operation can be confi rmed or faulty components pinpointed.
Procedure for measuring output power
The procedure for measuring optical power in a fi ber optic cable end is similar to the initial
checkout of the test set. During the checkout, you actually measured optical power, using
the built-in LED as an optical source, and the test cable as a delivery system. The following
procedure is more general since the source can be a transmitter from a fi ber optic link, or
another piece of test equipment.
1.
Put the protective cap on the “DETECTOR” receptacle and set the “DISPLAY
SELECTOR SWITCH” to 20 µW. Turn on the test set by pressing the “ON/OFF”
switch.
2.
If the meter does not read zero (± 0.02 µW), refer to the section titled “SERVICE
AND MAINTENANCE” and follow the “Zeroing” procedure. Remove the
protective cap.
3.
Set the “DISPLAY SELECTOR SWITCH” to 20 mW or the highest expected
power to be measured. Set the “WAVELENGTH” switch to the closest value of
wavelength for the transmitter or optical source. For visible sources choose 650
nm; for infrared sources select 850 nm. If you are using the built in LED optical
source in the Fiber Optic Test Set, select 650 nm.
4.
Attach one end of a connectorized cable to the external optical source or
transmitter. If you are using the built-in LED, remove the protective cap from
the receptacle and insert the connector. See Figure 2. Insert the remaining
connector into the “DETECTOR” receptacle.
When making measurements with
un-connectorized cable ends or fi ber, gently insert them into the appropriate
receptacles on the test set. Do not apply pressure beyond what is required to seat
the ends or internal components may be damaged.
5.
If the cable has connectors, make sure the source end of the cable is inserted into
the remote optical transmitter or fi ber optic light source. Insert the connector for
the receiver or delivery end into the “DETECTOR” receptacle on the test set.
When measuring power from an un-connectorized cable end or fi ber, gently
insert it into the detector receptacle. Do not apply pressure beyond what is
required to seat the fi ber or the detector may be damaged.
It is assumed the
transmitter side of the cable has a connector or other low-loss launch interface.
