15-GHz & 25-GHz Photodetectors
Troubleshooting • 13
Troubleshooting
Testing the Photodiode
The photodiode can be damaged by electrostatic
discharge or excessive optical power, which can lead to
an increased dark (or
offset
) voltage. A damaged
photodiode can result in a degraded responsivity and
frequency/impulse response. See “Checking the DC-
Offset Voltage,” below.
Checking the DC-Offset Voltage
1.
With no light on the photodetector, turn the
detector on.
2.
Use a voltmeter to measure the Bias Monitor
output voltage. This voltage is the DC offset plus
dark current.
3.
If the output is >10 mV, then the detector is
probably damaged and will need to be returned to
New Focus.
If the output is <10 mV, then perform the Basic
Optical Test described below.
Basic Optical Test
To quickly test the photodiode in your receiver, run
this simple DC optical test.
1.
Turn the receiver on.
1480 FC Det revA.fm Page 13 Monday, March 13, 2000 2:55 PM
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