Add-drop multiplexers (ADMs) are elements of integrated optical circuits. They are also called resonant notch-filters (or more generally, optical ring resonators). A multiplexer is used to add or extract signals at specific frequencies / wavelengths from a network path. Rigorous 3D simulation of ADMs is necessary for design and optimization of such devices.

Fig. 1: Geometry of an add-drop multiplexer.

Figure 1 shows the geometry of an add-drop multiplexer: Two silicon waveguides with rectangular cross section run parallel to each other. A ring resonator with the same cross section and with a diameter of 10 microns is placed between the waveguides. When a signal enters one of the ports at a frequency far away from the ring resonance it will be transmitted straight through the corresponding waveguide. When it enters at resonance frequency, it will be dropped to the opposite port.

Fig. 2: Discretization of part of the computational domain.

Figure 2 shows part of the discretization of the computational domain (mesh generated with JCMgeo).

Fig. 3: Real part of the electric field distribution (x-component) in a pseudocolor representation (visualization: JCMview).

Figure 3 shows an electromagnetic field distribution (real part of the x component of the electric field) at a frequency close to resonance (wavelength around 1550 nm). Clearly the resonantor stores most of the field energy. The displayed data is obtained from an export of the 3D field data to a 2D plane through the center of the waveguides.

Fig. 4: Transmission spectrum to two ports for a multiplexer with diamter of 10microns. Transmission spectra and other data can be obtained from post-processing on the computed near fields. This allows to quantify resonance frequencies, widths, free spectral range, losses, etc.

Figure 4 shows the transmission spectra to the different channels of the add-drop multiplexer.
JCMsuite allows to handle simulations at high accuracy of the results for ring resonator diameters of up to about 40 microns (on standard computers with extended RAM).