EXFO CT440 Series, User Manual

Page: 53 / 169

Performing Measurement Scans
CT440
47
Performing a Measurement Using the Analog In BNC Connector
Performing a Measurement Using the Analog In BNC
Connector
The CT440 enables you to measure an electric signal through the
Analog In
BNC input port
during the scan. You can measure the voltage of the electric signal or the optical power of
the signal.
The most common case requiring this kind of measurement happens when the output of
the DUT cannot be collected into a fiber or because of unacceptable losses. In such case,
free-space photodetectors are used, providing an electrical output that feed the
Analog In
BNC input (voltage input from 0-5 V High impedance) and plotted simultaneously with the
results obtained on the detectors of the front panel array.
The voltage information might not be relevant and specific operations on the output
recorded files should be done to allow comparisons. For this reason, an internal conversion
of the measured data into optical power might be required, which you can set in the
Referencing window as explained in the following procedure.
System Setup
To build your detection system using the Analog In BNC port as an external detector, follow
these instructions concerning the BNC connections:

If your photodetector has a 50 Ω output (0-5 V), you need an adaptation with a BNC
50 Ω termination (see the setup example below)

If you have a high impedance output (0-5 V) photodetector, you can directly connect it
to the
Analog In BNC input of the CT440.
Example
To use the Analog In BNC input port as an external detector, you can build your detection
system as illustrated below. We recommend the PDA20C InGaAs transimpedance amplified
photodetector from Thorlabs.
I
MPORTANT
On CT440 with PDL option: PDL measurement is not guaranteed if you use the
Analog In BNC interface.
AC/DC Power
Supply
LDS1212-1
Photodetector
(PDA20C for example)
Optical
input
BNC
output
BNC 50 Ω
termination
BNC T adapter
BNC cable
BNC Analog input
(0-5 V High impedance)