10 • Troubleshooting
NEW FOCUS, Inc.
Basic Optical Test
To quickly test the photodiode in your receiver, run
this simple DC optical test.
1.
Turn the receiver on.
2.
Using a voltmeter or oscilloscope, measure the
output voltage from the Bias Monitor on the front
panel of the bias supply.
With no light on the detector, the Bias Monitor
voltage should be <5 mV.
3.
Illuminate 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) as shown in
Figure 2, 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 is low, then contact New Focus to
arrange for a repair (see “Customer Service” on
page 13).
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
