Optical fibre-based devices (e.g. fibre gratings) play an important role
in the optical communications and sensing industry. One type of fibre
grating, the long-period grating (LPG), is becoming more and more
popular as a simple and versatile component for a number of applications
in optical engineering. Long period grating is obtained by introducing a
periodic refractive index modulation in the core of an optical fibre.
The phase matching condition causes light to couple from core mode to
forward propagating cladding mode. These cladding modes attenuate
rapidly on propagation and thus resulting in distinct resonance bands in
transmission spectrum. The sensitivity of LPGs to various external
perturbations and their ability to manipulate selectively light
propagating in optical fibres make them well-suited to creating
fibre-based devices. LPGs can be used in various applications, for
example as gain equalisers for erbium-doped fibre amplifiers, as channel
routers in optical add-drop multiplexers and as sensors. LPGs are
typically fabricated by exposing photosensitive optical fibre to
ultraviolet light