Ultrashort pulse propagation in near-field periodic diffractive structuresby use of rigorous coupled-wave analysis

We present a method for near-field analysis of ultrashort optical pulse pro pagation in periodic structures-including subwavelength and resonant gratin g structures-based on the integration of Fourier spectrum decomposition and rigorous coupled-wave analysis (RCWA). We discuss the spectral decompositi on, including considerations for computational. efficiency, tile applicatio n of the RCWA method to compute tile internal and external fields of the st ructure, and the synthesis of the resulting fields to obtain the time-domai n solution. We apply this tool to the analysis of two photonic structures: (1) a nanostructured polarization-selective mirror that exhibits the desire d broadband performance characteristics when operated at the design wavelen gth but yields strongly diminished polarization selectivity and modulation of the pulse envelope at an offset wavelength and (2) a two-mode coupled wa veguide structure that produces from one incident pulse two transmitted pul ses whose temporal separation depends on the waveguide geometry, In both ex amples, we apply our new modeling tool to investigate the near fields and f ind that near-field effects are critical in determining the performance cha racteristics of nanostructured devices. Furthermore, detailed observation a nd understanding of near-field phenomena in nanostructures may be applied t o the design of novel photonic devices. (C) 2001 Optical Society of America .