User Guide

Liquid Crystal Noise Eater Chapter 5: Operation
Rev A, September 21, 2021 Page 9
5.4. Setting the Output Power Level
The noise eater operates by varying how much of the signal is attenuated in order
to reach the target output power and attenuate the noise. Since the noise eater
can attenuate the signal but not amplify it, the clean output beam can only have a
power as high as the minimum power level of the noisy signal. In practice, to
remove all noise without unnecessarily attenuation the signal power, the output
power level should be set to slightly lower than the minimum power of the noisy
signal.
There are two methods to maximize the output power while still maintaining a clean
output signal. One method uses an external device such as an optical power
meter, while the other uses the LED indicator on the noise eater.
Figure 8 Example of a noisy input beam and set output levels.
5.4.1. Maximizing the Output Power Using an External
Measurement Device
To set the target output to a point that attenuates all noise, but does not
unnecessarily attenuate the signal’s power, first observe the characteristics of the
noise of the signal, either by using the statistics screen on the Thorlabs’ PM200
optical power meter, or using a detector and an oscilloscope. Once the minimum
power level of the noisy signal is established, adjust the output power of the noise
eater to an output level slightly below the minimum of the noisy signal.
To set the output power, use the following procedure:
1. After mounting and connecting the noise eater, set the power selector to
the highest value, and turn the knob all the way counterclockwise to
maximize the output power.
2. Using an optical power meter or a detector and oscilloscope, record the
minimum output power of the signal. Note: Depending on the