Astrophotonics is the discipline of applying photonic technology in instrumentation to address problems in astronomy and astrophysics. Photonic devices known as fibre Bragg gratings (FBGs) can be used as highly selective filters for removal of unwanted light prior to dispersion in a spectrograph. It has been shown that FBGs are well suited to the problem of removing atmospheric molecular emission lines from ground-based near- infrared observations. This thesis describes the development of a new generation of FBGs for this purpose, inscribed within multi-core fibres (MCFs) which contain multiple single- mode cores within one cladding. A new component, the polished capillary tube (PCT), was modelled, fabricated and tested; results showed that this was an effective device for improving the uniformity of gratings within MCFs. Following this a protocol for temperature tuning of gratings relative to one another was developed and tested. Finally, this thesis describes the development of a new instrument for inscribing gratings in fibres. When MCF technology reaches maturity, they will be used in astronomical instruments for atmospheric suppression, and will also have applications wherever photonics is used.