Reflectivity spectra evolution in grating structures with fractionally organized gaps

Gratings with quarter-wavelength gaps separating subgratings have been analyzed extensively in the literature, where they have found applications for distributed feedback lasers, filters, etc. In these structures, the gaps always had quarter-wavelength lengths. We modify these structures by starting with a quarter-wavelength gap, but ordering the subsequent gaps following a scaling factor of 0.8. The subgratings are assumed to be uniform and to have equal lengths. The reflectivity spectra of these gratings are analyzed by using the transfer matrix method, with emphasis on the wavelength range near the central lobe. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 42–45, 2001.