Abstract
We study the external mode coupling in optical microresonators with a loss-dependent coupling coefficient. In the case of dielectric optical microresonators with localized absorption or radiation loss, the mode coupling between whispering gallery modes (WGMs) can result in a destructive interference of the mode fields in the lossy area and consequently reduce the mode loss. Once the reduction overcomes the introduced loss, the actual mode loss is reduced by increasing the loss factor. An anomalous relation between the actual mode loss and the introduced loss factor is then found, while the mode frequencies show parallel, crossing, or anticrossing behavior under different coupling conditions; such phenomena can be well explained by the analysis based on the coupling theory. The results show that the localized cavity loss can suppress the original WGMs and generate high- coupled modes, which illustrate a possible way to dynamically control the optical modes inside the microresonator.
© 2015 Optical Society of America
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