Controllable optical quality factor in a two-ring-two-bus structure

Dynamically tuning Q factor in optical resonators is now more feasible in information processing applications, such as light storage and wavelength conversion. This paper proposed and demonstrated a new dynamically tuning Q approach that is realized in coupled two rings structure. One resonator uses an add-drop configuration, coupled to another single micro-ring. The heating causes an increase in the refractive index, which in turn causes resonant wavelength redshift. This shift is a switch to control the coupling between the two rings, to tune the linewidth of light confined in the ring, equivalent to tune the quality factor. And we adjust the detuning and coupling state between the two rings to control the light coupled into the resonator. The Q factor decreases from 56,525 to 16,450 in the transmission spectrum with the different heater power. In this way, we successfully realized a modulation of the Q from high to low states in the structure. Besides, the original coupling spacing between the two rings also has an influence on the Q factor. The larger the coupling spacing, the higher the Q factor. In addition, we also study the changes of phase and delay time in the tunable process. The results show that the change of fast light (high Q) and slow light (low Q) can be realized at the same time, which would enable applications for on-chip adjustable time delay, fast/slow light and light storage.