Fibre Bragg and Long-Period Grating Applications

It is possible to induce permanent changes in the refractive index of an optical fibre by exposing its core to ultraviolet light. If such exposure is carried out using an interferometer or through a phase mask it is possible to write a periodically varying refractive index grating within the core of a fibre. The reflectivity, bandwidth and central wavelength of such a Bragg structure are defined by the period and length of the phase mask and exposure time used. If the spacing of the Bragg planes is varied across the length of the grating it is possible to produce a chirped grating, in which different wavelengths can be considered to be reflected from different points along the grating.

We use fibre Bragg gratings as

• narrowband retroreflectors for providing feedback at a specific wavelength in fibre lasers (both in short pulse and single frequency lasers)

• filters for multichannel wavelength-division multiplexed (WDM) communications systems.

• fibre dispersion compensators in fibre links, or spectral manipulators of optical pulses as in a chirped pulse amplification (CPA) system.

In our group, we had the first demonstration of the use of chirped fibre gratings for fibre dispersion compensation. Currently we are working on the implementation of super-stepped chirp gratings for dispersion compensation over ever-increasing span lengths and bandwidths.

Relevant publications

A. Boskovic, J. R. Taylor And R. Kashyap: '40 times dispersive broadening of femtosecond pulses and complete recompression in a chirped fiber grating', Optics Communications, 119, pp.51-55 (1995)

R. Kashyap, S. V. Chernikov, P. F. Mckee And J. R. Taylor: '30ps chromatic dispersion compensation of 400fs pulses at 100 Gbits/s in optical fibers using an all-fiber photoinduced chirped reflection grating', Electronics Letters, 30, pp.1078-1080 (1994)

A. Boskovic, M. J. Guy, S. V. Chernikov, J. R. Taylor And R. Kashyap: 'All-fiber diode-pumped, femtosecond chirped pulse amplification system', Electronics Letters, 31, pp.877-879 (1995)

S. V. Chernikov, J. R. Taylor And R. Kashyap: 'All-fiber dispersive transmission filters based on fiber grating reflectors', Optics Letters, 20, pp.1586-1588 (1995)

M. J. Guy, S. V. Chernikov, J. R. Taylor And R.Kashyap: 'Low-loss fiber Bragg grating transmission filter based on a fiber polarization splitter', Electronics Letters, 30, pp.1512-1513 (1994)

M.J. Guy, S. V. Chernikov, J. R. Taylor, D. G. Moodie And R. Kashyap:'Generation of transform-limited optical pulses at 10-GHz using an electroabsorption modulator and a chirped fiber Bragg grating', Electronics Letters, 31, pp.671-672 (1995)

K. Rottwitt, M. J. Guy, A. Boskovic, D. U. Noske, J. R. Taylor And R. Kashyap: 'Interaction of uniform phase picosecond pulses with chirped and unchirped photosensitive fiber Bragg gratings', Electronics Letters, 30, pp.995-996 (1994)

D. U. Noske, M.J. Guy, K. Rottwitt, R. Kashyap And J. R. Taylor: 'Dual-wavelength operation of a passively mode-locked figure-of-8 ytterbium-erbium fiber soliton laser', Optics Communications, 108, pp.297-301 (1994)

M. J. Guy, J. R. Taylor And R. Kashyap: 'Single-frequency erbium fiber ring laser with intracavity phase-shifted fiber Bragg grating narrow-band-filter', Electronics Letters, 31, pp.1924-1925 (1995)

For more information on fibre Bragg gratings

R. Kashyap: 'Photosensitive optical fibres: devices and applications', Optical Fiber Technology, 1, pp. 17-34 (1994)

 

We would like to thank Raman Kashyap of BT Laboratories for his collaboration in this work.