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FAQ1: Many optical system designers are selecting micro-electro-mechanical
systems (MEMS) based Variable Optical Attenuators (VOA). Why should I consider
using liquid crystal based VOAs instead?
Liquid crystal (LC) technology provides a more reliable platform
for optical components than micro-electro mechanical systems (MEMS).
This is due to the fact that LC based components have no moving
parts, which make them both durable and resistant to internal and
ambient disturbances. MEMS components, on the other hand, many of
which use rotating micro-mirrors, suffer from several problems,
including:
- Friction - Repeated cycling of MEMS devices can cause mechanical degradation and eventual
failure through frictional wear.
- Deformation-Repeated cycling of MEMS devices can cause failure through repeated material
deformation.
- Vibration - The resonance vibration of the moving parts is typically between
a few hundred Hz to 1 KHz due to their small mass, which is in
the same range of environmental vibration. Vibration resulting
from the cooling fan oscillation and ambient acoustic or seismic
disturbances negatively impact the ability of MEMS mirrors to
focus, which must be accurate to the millionth degree. In addition,
the excess vibration impact increases the possibility of material
failure.
- Stiction - Whenever
two MEMS elements touch each other, there is always the possibility
that they will stick together caused by molecular force or electrostatic
forces.
Lightwaves2020
has carried out an experiment to demonstrate the fact that MEMS
components are extremely vulnerable to ambient disturbances, while
their LC based counterparts are not. The experiment involved placing
a LC and an electrostatic actuated MEMS based variable optical attenuator
(VOA) on an ultrasonic stage during operation and measuring the
effect of vibration on output power. The experimental setup is shown
below:
The
following oscilloscope results were then recorded:
As shown, the
output power of the LC VOA remained stable for the duration of the
experiment, whereas the MEMS VOA oscillated widely.
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