Flattopped tunable wavelength-division-multiplexer filter design

We present what is to our knowledge the first design of a tunable optical filter with a flattopped passband. The filter consists of a Fabry-Perot etalon with multiple reflection gratings as dielectric mirrors. Wavelength tunability is achieved by modulation of the refractive indices of the cavity and the dielectric mirrors. Specifically, a filter with a 1-nm linewidth and a 40-nm wavelength-tuning range is designed for applications in wavelength-division-multiplexing (WDM) optical fiber communication systems. We also discuss several factors, including absorption and variations of other design parameters, that may affect the performance of the filter.