Page 169 - Photodetection and Measurement - Maximizing Performance in Optical Systems

Control of Ambient Light

162 Chapter Seven

polarization state variation remains, but this is much smaller. The simplicity of
such fiber-interferometers means that they can often be integrated into complex
machinery such as high-speed actuators. If the object’s direction is known, fre-
quency-shifting is not required. The collinear back-scatter geometry means that
calibration is not necessary, as one detected fringe means a motion of l/2 for
the source in use.
The control and suppression of unwanted light can often be as difficult, and
as expensive, as detection of the wanted light signal. Success often appears to
be down to a random series of trials and errors. Nevertheless, a methodical
approach of understanding the origin and eventual absorption of every possi-
ble light source, combined with a bit of pencil-and-paper ray-tracing, will
usually get you to that success more quickly.

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