Transition between coupled-resonator-induced transparency and absorption

Electromagnetically induced transparency and absorption in atomic systems have applications such as slow-light generation. Coupled-resonator-induced transparency (CRIT) and absorption (CRIA) are the optical analogy to them. Here we theoretically and experimentally study CRIT and CRIA in two directly coupled whispering-gallery-mode microresonators. The theoretical results give conditions for observing CRIT and CRIA, and predict that a transition between them will happen if we change the coupling strength between the two microresonators or the coupling strength between the fiber taper and the first microresonator. The experimental results demonstrate the transitions between CRIT and CRIA using a microsphere coupled to a sausagelike microresonator. The obtained results give some guidelines to observe CRIT and CRIA.