User`s guide

What is an Optical Head? Getting Started with Optical Heads
Agilent 81618A/9A and Agilent 81623B/4B/6B/8B Optical Heads, Fourth Edition
15
Analog Output
The analog output is the BNC connector on the back of the optical head. It
outputs a voltage directly proportional to the strength of the optical signal
at the optical input in the current range. The analog signal is always in the
range between 0 and 2V, 2V corresponding to a full power input signal in
the current range, 0V corresponding to no input signal.
During autoranging, the level to which 2V corresponds changes. You
should disable autoranging when using the analog output.
Disabling Autoranging
Select the best range for the application using the mainframes user
interface. Select <Menu>, <Range Mode>, <Manual> and then choose
from the list of ranges.
Applications
Possible applications for the analog output are:
• to close the feedback loop controlling the current supplied to a laser
• to aid positioning the system for fiber alignment tasks
• to monitor optical power on an oscilloscope
The analog signal reacts instantaneously to the input signal, whereas the
power shown on the display is subject to averaging.
Optical input
The optical input to the optical head requires a connector adapter to match
the connector type (or bare fiber) to the optical head interface.
The optical head interface can be either threaded or a D-type magnetic
interface depending on the model of optical head (81628B is only available
with a threaded interface). See “Accessories” on page 19 for details of the
connector adapters available.
When a connector adapter is fitted it should be locked in place by
tightening the locking screws located either side of the main optical head
housing.