Nonlinear DFB phase-shifted structure: all-optical, low-intensity switching device

Recently ultrafast optical switching in nonlinear distributed-feedback (DFB) structures has attracted considerable attention. An increase of the DFB device´s input intensity changes its photonics band structure and, consequently, shifts the position of its stop gaps, allowing the transmission at previously forbidden frequencies. The analysis of uniform, nonlinear DFB devices in both CW and time-dependent regime has demonstrated the possibilities for switching and bistable applications; however, relatively high input intensities required here have hindered the practical use of these concepts - a problem recently addressed by the non-uniform grating design Phase-shifted DFB devices are promising but have attracted little attention for intensity switching. First proposed by Shank and Haus, phase-shifted and especially λ/4-shifted structures have been extensively used, most notably for fabrication of single-mode semiconductor lasers. The authors present such a structure and its transmission band in the case where a linear, zero-gain optical medium and λ/4-shift is used. One intuitively expects that even a small input intensity would be enough to significantly change the position and the shape of the central transmission peak - a feature readily usable for low-intensity, all-optical switching. In order to justify such an expectation, we apply a set of stationary, coupled-mode nonlinear equations to each uniform region of the structure