Appendix Ii: Inside The Photodetector - New Focus 1480 User Manual

Appendix II:
Inside the Photodetector
Figure 3:
Simplified
schematic of
the Models
1480 & 1481
photodetector
modules
20 • Appendix II: Inside the Photodetector
A gold-plated microwave housing inside the
photodetector module 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 9-cm fiber.
The fiber is protected by a sheet metal flange to prevent
damage while changing the battery. A simplified
schematic is provided below.
Microwave
Microwave
Housing
Connector
Photodiode
+
V
Output
–
+
+
V
-
V
-
V
Batt
Chk
+
V
–
+
-
V
-
V
NEW FOCUS, Inc.
Bias
Monitor
On/Off