Coding two-dimensional patterns into mode spectrum of silicon microcavity covered with a phase-change film

In the present study, we propose a new approach for coding two-dimensional patterns (spatial information or images) into mode spectra of a silicon microcavity. Electric field distributions associated with each cavity mode generated by the microcavity provide a basis (dictionary) for image encoding. The cavity is covered with a layer of phase-change material (Ge₂Sb₂Te₅; GST), which enables the electric field distribution to be memorized and the images to be encoded into absorption spectra via the difference in the refractive index between the crystalline and amorphous phases. In numerical simulations, a clear modification of the absorption spectra of the GST layer upon partial crystallization was demonstrated. We fabricated silicon microcavities covered with a GST layer and confirmed that spectral features originating from individual cavity modes can be greatly modified upon phase change.