A ring resonator is a very useful device that acts as a high-Q filter for applications that require wavelength selectivity. This type of device has many resonances, and only these resonant wavelengths are coupled to the output waveguide. All other wavelengths are allowed to pass uncoupled through the input waveguide, hence the ring resonator is essentially an optical notch filer, with numerous stop bands.
In this application example, a ring resonator will be analyzed using FDTD. First, a pulse response is used to determine the spectrum of resonances, and then a CW simulation is used to demonstrate the propagation through the device, at one of the resonant wavelengths.