Figure 2: Schematic representation of the structure of the integrated devices.
From: Suppression law of quantum states in a 3D photonic fast Fourier transform chip
Internal structure of the four-mode (a) and eight-mode (b) integrated interferometers implementing the qFFT over the optical modes. In the eight-mode case, the Barak and Ben-Aryeh algorithm requires an additional relabelling of the output modes (not shown in the figure), namely 2↔5 and 4↔7, to obtain the effective Fourier transformation. The mode arrangement has been chosen in a way to minimize bending losses. The insets show the actual disposition of the waveguides in the cross-section of the devices. The modes coupled together in each step (Li) of the interferometer are joined by segments. The implemented phase shifts in each step (Pi) are also indicated.
