TROUBLESHOOTING
Replacing the Battery
1. Turn off the module and remove the two screws on the back
panel with a Phillips screwdriver. (See Fig. 1.)
2. Remove the back panel and replace the battery.
3. Replace the back panel.
4. Check the battery level as described above.
Basic Optical Test
To quickly test whether a photodetector appears to be working,
you can perform a simple DC optical test:
1. Turn the detector on.
2. Using a voltmeter or oscilloscope, measure the output voltage
from the Bias Monitor on the front panel. (With no light on the
detector, the Bias Monitor voltage should be <10 mV.)
3. Couple some CW light into the photodetector.
4. With the voltmeter or oscilloscope, you should observe a DC
output voltage. If you know the optical power and wavelength,
you can calculate the expected output voltage (
V
out
) using the
expression:
V
out
= P
in
• R • G
, where
P
in
is the input optical power
(watts),
R
is the photodetector’s responsivity (A/W), and
G
is the
amplifier’s transimpedance gain (V/A). The gain of the bias
monitor port is 1000 V/A.
If the output voltage appears to be low, then the fiber connector
might be dirty. If a dirty connector is suspected, see Cleaning the
Fiber Connector below.
Cleaning the Fiber Connector
The high-speed photodetectors have an internal fiber connector
and a fiber pigtail that brings the input light to the detector. If the
fiber connector is dirty, this can block the input light so that light
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