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