Applications of Fibre Optic Ring Resonators Using Laser Diodes

It is demonstrated that fibre optic ring resonators are well suited for use as spectral discriminators for the measurement of spectral line width and for the stabilization of the spectral line width of external-cavity laser diodes. Although the measuring method is very simple, accuracies within - 10 and - 20 per cent were obtained in the spectral line width ranges above 1 MHz and 300 kHz, respectively. The spectral line width is stabilized by the automatic phase control of feedback light. Moreover, the operation point of the fibre optic ring resonator is stabilized by automatic frequency control of the laser. The principles, experimental results and problems are described in detail.