  The employment of magneto-optical materials to fabricate photonic crystals
gives the unique opportunity to achieve optical tuning by applying a magnetic
field. In this study we have simulated the transmission spectrum of a
microcavity in which the Bragg reflectors are made with silica (SiO2) and
yttria (Y2O3) and the defect layer is made with TGG (Tb3Ga5O12). We show that
the application of an external magnetic field results in a tuning of the defect
mode of the microcavity. In the simulations we have considered the wavelength
dependence of the refractive indexes and the Verdet constants of the materials.
A tuning of the defect mode of about 22 nm with a magnetic field of 5 T, at low
temperature (8 K), is demonstrated. Furthermore, we discuss the possibility to
tune a microcavity with disordered photonic structures as reflectors. In the
presence of the magnetic field such microcavity shows a shift of resonances in
a broad range of wavelengths. This study presents a method of contactless
optical tuning.
