Chapter 3 Product Overview - THORLABS LCC3111H User Manual

Liquid Crystal Noise Eater
Chapter 3: Product Overview
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.
Page 4