Fig. 4: Forming trapped states using frequency mirror implemented by coupled-resonators.
a Optical image (false-color) of the device. A long racetrack shape cavity (cavity 1) with FSR1 of 10.46 GHz is used to generate the frequency crystal. A rectangular shape (cavity 2) with FSR2 of 302.9 GHz is coupled to the cavity 1 to provide the frequency mirrors. Metal electrodes (light yellow) provides the efficient microwave modulation. Thermal heater (orange) can tune the position of the mirrors by varying the resonances of cavity 2. b Illustration of the coupling between two resonators when the coupling strength satisfies \(2\mu\) > FSR1 or \(\mu\) is comparable with FSR1. In this case, rather than having two-mode splitting of resonances of cavity 1, the single resonance of cavity 2 couples to multiple resonances of cavity 1, forming multi-hybrid modes and leading to a gradual reduction of FSR1. c Measured transmission spectrum of the device. The FSR1 gradually changes from ~10.5 GHz (uncoupled value) to ~8.5 GHz and then goes back to ~10.5 GHz, indicating the strong coupling in presence of the resonance of cavity 2. d FSR1 as a function of wavelength. The FSR1 features dips with periodicity equal to the FSR2, thus confirming the strong coupling between the two cavities. e Reflection at the mirror leads to constructive/destructive interference at every other lattice points. In addition, the mirror formed by coupling of multiple resonances supports trapped state, and provides >30 dB suppression of transmitted optical energy.
