Defects and calibration in universal programmable photonic circuits with interlaced DFRFT layers*

Universal programmable photonic circuits are photonic platforms which can be controlled to perform arbitrary NxN transformations (usually restricted to U(N) or SU(N)). In recent years, research has been conducted on a promising class of universal structures consisting of alternating phase shift layers and a general transformation. One such important transformation, the Discrete Fourier Transform, can be generalized into what is known as the Discrete Fractional Fourier Transform (DFrFT). Using DRrRT's we have shown that universality can be achieved with N + 1 phase layers [1]. We extend this analysis by showing that universality is not compromised by perturbations of the transformation layers and consider the effect of defects in the phase components [2].