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fibre bragg grating
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TUNABLE FIBRE BRAGG GRATING
FBG can be tuned to adjust the properties of the grating such as dispersion, bandwidth, centre wavelength.
=
: Bragg Wavelength
: Period
: Effective Refractive Index
TUNING TECHNIQUES
Thermal Tuning of FBG Strain Tuning of FBG Piezoelectric Tuning of FBG Optical Tuning of FBG
THERMAL TUNING of FBG
32 Divided thin-film heater deposited on the silica substrate
which are individually controlled.
The tuning the FBG properties are performed by the precise control of the temperature distribution of the chirped
grating
STRAIN TUNING of FBG
The group delay can be linearly adjusted when a linear strain is induced by a change in the
rotation angle change.
The dispersion can be tuned effectively tuned between a range of 495.5 to 1406.0 ps/nm
corresponding to the rotation angle
A displacement force is applied to the free end of a cantilever beam unto which a CFBG
is attached
Tunable dispersion ranging from 178 to 2126 ps/nm, corresponding to a large range of 3-db bandwidth from 0.42 to 5.04 nm, is realized by
using a 10 cm-long CFBG with an original bandwidth of 1.61 nm
PIEZOELECTRIC TUNING of FBG
A versatile and compact Mechanism F or tuning the properties of a CFBG using a
segmented piezoelectric stack with
individually controlled segments.
By applying appropriate voltages to the independently controlled constituent
segments, it is shown that the dispersion can be varied from -8770 to -940ps/nm
with an increase in bandwidth from -0.03 to -0.32nm
DISADVANTAGES
The above tuning mechanism are limited by the following
Bulky Remote Tuning Active Devices Tuning Speed Complex and expensive structures Anisotropic producing birefringence
Optical Tuning of FBG
The change in the resonance wavelength of the FBG was reversible
sand repeatable
A FBG was side polished and overlaid with photo-responsive liquid crystal (PRLC) to realise a photo-induced
wavelength shift in the FBG
An advancement to this employed a surface grating which is side polished and then
coated with PRLC.
An interesting feature of this device is that, the re-configurability and tunability of the
device makes it possible for use in an all optically programmable and tunable fibre
grating
EFFECT OF EXTERNAL PERTURBATIONS ON OPTICALLY TUNABLE FIBRE GRATINGS
Using an optically tunable FBG in an environment subject to perturbation such as
strain and pressure can induce an error in the accuracy of an optically tuned grating.
Achieve a fixed centre wavelength of operation for
telecommunication applications
INDEPENDENT CHANNEL OPTICALLY TUNABLE CFBG
Independent channel tuning of multi-channel CFBG property
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