100% reflectivity Bragg reflectors produced in optical fibres by single excimer laser pulses

It is shown for the first time that fibre gratings with reflectivities in excess of 99.8% and fractional bandwidths of 0.005 (7.5 nm or 970 GHz at 1550 nm) can be written by interferometric side exposure of a fibre core to a single 40 mJ UV pulse of 20 ns duration at 248 nm. These highly efficient reflectors are formed by a new mechanism in which the core glass fuses, resulting in a very large periodic modulation of the refractive index. They are stable at temperatures as high as 800 degrees C.