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Step 4: Calibrating and Adjusting the
1550 nm Circuit
Use the following procedure to make calibration
adjustments to the 1550 nm laser diode circuit.
4-1. Adjust the dc power supply to 9 V ±0.25 V.
Connect the supply's positive lead to BT1+;
connect the negative lead to BT1-.
4-2. Set up the DMM to measure dc volts less than
2 V. Connect the negative probe to TP2 (Gnd)
and the positive to the side of R2 furthest
from the board edge. To calculate current in
the 1550 nm laser drive use the equation
I = V/22.
4-3. Use a singlemode fiber patch cable to connect
the laser source to the OPM. Set the OPM to
measure 1550 nm.
WCaution
In the following steps, do not exceed
the laser diode's maximum operating
current of 60 mA. Doing so can damage
the laser diode. If the current reaches
60 mA before the optical power reading
reaches -9.2 dBm, clean the ST
connectors or repair the laser source.
4-4. Set the laser source to 1550 nm. Turn R31 to
the full clockwise position.
WCaution
In the next step, slow the adjustment rate
on R40 as the optical power reading
approaches -14 dBm. If you turn R40 too
quickly, you might overshoot the -9.2 dBm
target and exceed the laser diode's
maximum current of 60 mA.
4-5. Adjust R40 clockwise until either the power
reading is -9.2 dBm ±0.1 dB or the current
reaches 60 mA. A typical current value is
15 mA at -9.2 dBm. If the current reaches
60 mA before the power reading reaches
-9.2 dBm, the laser source requires repair.
Calibration adjustments for Serial Numbers ≥ 79130000
4-6. With the laser source set to 1550 nm, verify
that the power reading is -9.2 dBm ±0.1 dB.
4-7. Adjust the 1550 nm external potentiometer
(R31) counterclockwise to verify that the
laser source output is adjustable to -11.2 dBm
±0.1 dB.
4-8. Adjust R31 until the laser source output reads
-10.0 dBm ± 0.1 dB.
Step 5: Adjusting the 2 kHz Modulated
Signal
5-1. Connect an oscilloscope across TP1 and TP2
(Gnd).
5-2. Set the laser source
position. Set the 1550/1310 switch to
MOD
1310.
5-3. Verify that the signal frequency is 2 kHz
±100 Hz with a duty cycle of 50% ±5%.
Adjust R29 as necessary.
5-4. Set the 1550/1310 switch to 1550 and reverify
signal frequency is 2 kHz ±100 Hz with a
duty cycle of 50% ±5%.
Step 6: Reassembly and Final Test
6-1. Remove the singlemode cable from the laser
source. Put the dust cap onto the laser source
optical ST connector.
6-2. Apply insulating varnish, such as red GLPT,
to all potentiometers adjusted.
6-3. Put the board back in the case. Put the case
halves together and install the four Phillips
screws. Reinstall the lock washers and nuts to
the CW/MOD and 1550/1310 switches.
Install a 9 V battery and the battery door.
6-4. Run the performance tests as described in the
earlier section "Performance Tests".
Service Information Sheet
switch to the
CW/MOD
9
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