Broken-supersymmetry is used to define a reflectionless active cavity capable of amplifying electromagnetic radiation in the visible. The approach is analytical through the use of the Darboux transform for the generation of the optical potential and the calculation of its solution, while the transmission/reflection spectra evaluation is done with the Transfer Matrix method. Interestingly, the proposed device behaves as a dynamic optical filter amplifying radiation arriving at large angles while for other directions is almost completely transparent. Thus, simply by rotation different functionalities can be obtained. In addition the active filter is reflectionless for all wavelengths and angles of incidence. The necessary Kramers-Kronig relations are also satisfied being the model compatible with the Drude model at high frequency i.e. far from absorption resonances.

We study the possibility to obtain structural colors through the use of supersymmetric transformations in optics such as the Darboux transform. Structural colors were originally discovered by studying the interference of light with natural photonics structures giving rise to vivid and spectacular tonalities. They differ fundamentally from ordinary colors based on light absorption at particular wavelengths, as they result from light interference only. To treat interference analytically, we make use of the Darboux transform to define materials with continuously varying spatial distributions of the refractive index that are exactly solvable for the electric field. Consequently, it is possible to calculate analytically the Transfer Matrix linked to the definition of the transmission and reflection coefficients. Interestingly, by using gain, anomalous transmission/reflection (i.e. larger than one) can be obtained, the physical system being open towards the external environment (the system is using external energy in order to increase both transmission and reflection). The generated active optical cavity can thus be used to amplify the incoming light in the desired spectral-angular region. The calculated refractive index distributions can be realized in practice as 1D multi-layered structures corresponding to optical filters in the visible.