Fibre gratings and devices for sensors and lasers

Abstract

Although mainstream grating writing, more often than not using single photon excitation of germanosilicate based defects with CW 244 nm light, remains the key technology for complex devices it is now being complemented by a whole host of processes which can enhance and tailor the properties of both conventional and not-so-conventional fibre Bragg gratings. Further, processes for writing of gratings in non-germanosilicate fibres have also continued to develop and include multi-photon excitation directly into the band edge of the glass. It is now possible to custom tailor a gratings property based on the application and the nature of production as well as custom tailor the grating writing process to suit the type of fibre and application. Examples and suggestions where these can benefit sensors and lasers are outlined.The various diffraction orders produced through a phase mask during UV direct writing of Bragg gratings -the two brightest are the +1 and −1 orders whilst the central zero order is suppressed most. This method remains the most commonly used approach to fibre Bragg grating writing, including in very large diameter fibres.

Regenerated Fibre Bragg Gratings

“…For a general review on photosensitivity and grating types, see [Canning 2008a]. Another variant with superior high temperature stability is the so-called "chemical composition grating (CCG)" [Fokine 2002] where a periodic index modulation can be regenerated after erasure of the UV induced type-I grating written in H-loaded germanosilicate fibre, which happens to contain fluorine, if annealed ~1000°C.…”

Grating writing in structured optical fibers

“…Gratings are now readily written into both photosensitive and non-photosensitive structured optical fibers of various sorts using a range of photosensitive mechanism -a specific review of these mechanisms can be found elsewhere [35]. Figure 4 shows the type of fibers into which gratings have been successfully written.…”

Femtosecond pulse written fiber gratings: a new avenue to integrated fiber technology

“…Type II gratings are modifications above the damage threshold of the host material. The most recent addition are Type R gratings that form out of annealed Type I gratings after prolonged heating [81].…”