User Guide

Liquid Crystal Noise Eater Chapter 5: Operation
Rev A, September 21, 2021 Page 5
Chapter 5 Operation
5.1. Selecting the Power Range
The NEL02A(/M), NEL03A(/M) and NEL04A(/M) have two selection switches at
the top of the case which are used to select the input power range. When the
high/low power switch is set to “L”, the input power range can be set from 1 mW to
30 mW, and when the status switch set to “H”, the input power range can be set
from 100 mW to 500 mW.
The NEL01A(/M) has only one selection switch which can set the input power
range at 1 mW, 3 mW, 10 mW, or 30 mW. The power selector should be set to the
lowest value that is still higher than the actual power of the laser. For example, if
the NEL01A(/M) is being used with a beam power of 8 mW at 635 nm, the selector
should be set to 10 mW.
Figure 4 Top View of the NEL02A/NEL03A/NEL04A Noise Eaters. The top of the NEL01A
housing appears the same except it does not have the L-H switch for low or high power
settings.
The NEL01A(/M), NEL02A(/M) and NEL03A(/M) noise eaters use a Silicon
detector, while the NEL04A(/M) uses a Germanium detector, as part of the
feedback loop. The responsivity of the detector is different for different
wavelengths, and so the power settings on the selector only correspond to the
design wavelength of the detector (635 nm for NEL01A(/M) and NEL02(/M), 780
nm for NEL03A(/M), 1550 nm for NEL04A(/M)). The power range at a given
wavelength is inversely proportional to the responsivity (higher responsivity value
will result lower power range value). The graph below shows the relative
responsivity of both detectors at a range of wavelengths. The tables below show
a rough estimate of the power settings at various wavelengths for each model.