  We apply the supersymmetric Darboux transformation to the optical Helmoltz
wave equation to generate analytically complex-valued PT-symmetric potentials
(physically a graded refractive index dielectric). PT-symmetry is then
spontaneously broken controlling the amplitude of the imaginary part of the
refractive index distribution. Consequently a resonance is detectable which is
related to a singularity of the S matrix, responsible for extraordinary high
transmission and reflection peaks in the scattering spectra. We demonstrate how
controlling the resonance we can achieve different amplification rates up to
four order of magnitude at the exact singular point. Total transmission and
very high reflection can be also obtained. All the visible portion of the
spectrum can be spanned by enlarging the spatial width of the potential. All
these potentials can be unified in a single device with the capability to
dynamically control the imaginary part of the refractive index, thus defining a
tunable dynamical optical filter behaving as a perfect amplifier, a transparent
barrier or a high efficiency mirror.
