A unique type of fibre device
called a Polarization Maintaining Fiber Coupler may maintain the
polarization state while optical signals are being transmitted. Modern optical
fibre communication systems, optical fibre sensing, interferometry, and quantum
optics can all benefit greatly from this device. This article will provide a
detailed introduction to the polarization-maintaining fibre coupler's
operation, structural features, and performance attributes.
The fundamental working principle
of a polarization-maintaining fibre coupler
The evanescent field coupling
effect between optical fibres is the fundamental operating concept of
polarization-maintaining fibre couplers. In order to accomplish coupling and
optical power distribution, the light field delivered in one
polarization-maintaining optical fibre will enter the other optical fibre as evanescent
waves when their cores are sufficiently close to one another. You must learn
about the Polarization Maintaining Fiber Splitter.
Polarization-maintaining fibre
couplers must simultaneously satisfy two requirements, in contrast to standard
single-mode fibre couplers:
- Reach a particular ratio of optical power
distribution.
- Keep the input light's polarisation state at the
output end.
- Method for maintaining polarisation
Polarization-maintaining fibre
couplers' capacity to sustain polarisation states is largely dependent on:
- Alignment of the matching primary axis:
Precise alignment of the two connected polarization-maintaining fibres
with their fast and slow axes is required; these are typically done in one
of two configurations: "principal axis parallel" or
"principal axis cross."
- High birefringence maintenance: To prevent
the polarisation state from being arbitrarily altered, the coupling
procedure must considerably lessen the fiber's initial high birefringence
features.
- Selective coupling of modes: Crosstalk
between distinct polarisation modes is suppressed by permitting only
coupling between the same polarisation modes.
Polarisation extinction ratio
and coupling efficiency
Two primary metrics are used to
assess a polarization-maintaining coupler's performance:
The ratio of the optical power at
the input to the optical power at the output is known as the coupling
efficiency.
The logarithmic value of the ratio of the power in the intended polarisation state to the power in the orthogonal polarisation state is known as the polarisation extinction ratio (PER), which is a measurement of the device's capacity to retain polarisation state.
A high polarisation extinction ratio and a precisely adjustable coupling ratio are characteristics of an ideal Polarization Maintaining Fiber Coupler.
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