User Guide

Liquid Crystal Noise Eater Chapter 3: Product Overview
Page 2 CTN017430-D02
Chapter 3 Product Overview
Thorlabs’ Liquid Crystal Noise Eaters are precision instruments for stabilizing and
attenuating laser power. The noise eater consists of a variable attenuator (liquid
crystal wave plate and polarizer), a calibrated beam splitter, and a servo controller
to control the modulator, as depicted in the block diagram below.
Figure 1 Noise Eater Block Diagram
Linearly polarized light is input into the liquid crystal retarder, which, together with
the output polarizer, acts as a variable retarder. A beamsplitter then sends a small
part of the beam to a feedback loop consisting of a photodiode and control servo.
The servo compares the optical signal to a preset signal level and applies the
appropriate adjustment voltage until the optical signal reaches the desired level.
The noise eater can also be used as a variable attenuator even without the
presence of noise. By adjusting the resistance of the potentiometer, the user can
set the desired output power level.