Long cavity length composite cavity fibre laser with single longitudinal mode and narrow linewidth

The composite cavity fibre laser (CCFL) is demonstrated for its capability in maintaining single longitudinal mode operation, whilst having longer cavity length than typical distributed Bragg reflector or distributed feedback fibre lasers, and hence also higher output power. These two attributes should enable the CCFL to be useful in sensing applications. A long cavity length CCFL can be fabricated simply by writing three spectrally matched Bragg gratings directly into a continuous length of doped fibre. This is analogous to the use of feedback cavities in semiconductor laser designs to maintain single longitudinal mode. Results from in-house fabrications show that long cavity length CCFLs can be fabricated to have single longitudinal mode and narrow linewidth characteristics similar to that of a distributed feedback fibre laser, and also significantly higher output power.