Theoretical and experimental studies of the electromagnetic coupling between parallel, passive, glass-fiber waveguides and active (Nd3+-doped laser) resonators are reported. Predicted evanescent-wave coupling strengths are verified to within a factor of two. Far-field interference patterns of these phase-locked, optical waveguides manifest a high degree of coherence and give the predicted asymmetry. Coupling of two fiber lasers is also demonstrated through common-cavity end-mirror reflectors; a high-frequency self-Q-switching action is found when the fiber ends are not rigidly mounted.
N. S. KAPANY, J. J. BURKE, K. L. FRAME, and R. E. WILCOX, "Coherent Interactions between Optical Waveguides and Lasers," J. Opt. Soc. Am. 58, 1176-1182 (1968)