We discuss the possibility of observing and measuring coupling among the modes of a multimode fiber by using a fiber resonator. If both the injected and spurious modes are simultaneously at resonance, both modes appear at the resonator output and their power ratio is proportional to the power coupling coefficient. This result is based on perturbation theory whose limits of validity are discussed. We also discuss the problem of mode identification and the difficulties of power measurements that are caused by overlapping of modes in the far-field radiation pattern of the resonator.
© 1977 Optical Society of AmericaPDF Article