Optical Spectrum Analyzers
Chapter 5: Using the Free-Space Input
Rev D, June 16, 2022
Page 18
Figure 13. Example Setup for Aligning the Free-Space Input
5.3.2. Adjust Software Settings
Once the system is roughly aligned, disable the alignment beam in order to see a signal in the main software
window. Change the acquisition settings to Low Resolution, and for Redstone OSA305 Low Sensitivity or for
OSA20xC Medium Sensitivity. OSA20xC users should now open the “Signal” window under the Instrument
menu and click the “Auto” box below the applicable detector to toggle to “Manual” mode; opening the “Free-
space Alignment” window automatically manages these settings for Redstone OSA305. Adjust the gain level(s)
such that a strong signal is achieved while not saturating the detector(s); a signal value in the range of 10% to
80% is suggested. It is recommended to start a time series measurement of the signal and/or power via the
Long-Term functionality found in the Analysis menu to get a reading of how the signal value and detected input
power changes as the two mirrors are adjusted.
