APPENDICES
11
APPENDIX 3: INSIDE THE PHOTODETECTOR MODULE
Inside the photodetector module is a gold-plated microwave
housing that contains the high-frequency circuitry. This housing
is bolted to a printed-circuit board which regulates the bias for the
photodiode and amplifies the DC photocurrent for the monitor
port. The optical signal is brought from the front-panel connector
to the microwave housing with a <0.2-meter, 9-µm core fiber.
Although the material and modal dispersion per unit length of this
fiber can be high at certain wavelengths, there is no degradation
in frequency response since the fiber is less than 0.2 meters long.
The fiber is protected by a sheet metal flange to prevent damage
while changing the battery. A simplified schematic is provided in
Fig. 2 for your reference.
Fig. 2a. Simplified schematic diagram of the 100X series photodetector
modules.
–
+
–
+
Batt
Chk
Microwave
Housing
Photodiode
Microwave
Output
Connector
V
-
V
+
V
+
V
-
V
+
On/Off
Bias
Monitor
V
-
V
-
