Add-drop-filter,
2D simulation of a configuration with the following specification: background refractive index nb = 1.0, refractive index of the guiding regions ng = 3.2, resonator dimensions L = W = 1.54 µm, waveguide width w = 0.2 µm, gap width g = 0.29 µm, resonator separation d = 0.72 µm.

The parameters resemble the values of C. Manolatou, M.J. Khan, S. Fan, P.R. Villeneuve, H.A. Haus, and J.D. Joannopoulos, Coupling of modes analysis of resonant channel add-drop filters, IEEE Journal of Quantum Electronics, 35(9):1322--1331, 1999.
All calculations are meant for TE polarization, i.e. Ey is the single nonvanishing component of the electrical field.

 
Spectral response of the filter element:
The device is excited in port A by the guided mode of the lower waveguide with the specified vacuum wavelength λ. PB - PD and PA are the relative power transmissions to ports B, C, and D, and the relative power reflected into port A. Note that the curves related to PA, PC, and PD are almost superimposed. The links at the positions indicated by the the blue tick marks lead to illustrations of the time dependent electric field.

1.365 µm 1.409 µm 1.459 µm 1.473 µm 1.487 µm 1.5 µm 1.532 µm 1.555 µm 1.571 µm 1.613 µm 1.677 µm 1.684 µm 1.698 µm

 
The pronounced resonance at 1.532 µm:
Note that the colour levels of the images linked to this figures are adjusted to the individual field / energy range; colour levels in plots belonging to different wavelengths are not comparable.

1.526 µm 1.528 µm 1.53 µm 1.531 µm 1.5317 µm 1.532 µm 1.5324 µm 1.533 µm 1.534 µm 1.536 µm 1.538 µm

 
Caution: The simulations assume vanishing electromagnetic fields at x = +/-5 µm; the presence of these artificial boundaries may influence the results.