Cascaded identical resonant grating reflection filters are shown to exhibit flattened spectral responses when the individual filter elements are cascaded π out of phase. Off resonance, the net response of a cascaded arrangement is given approximately by the sum of the individual filter responses. Cascading filters π out of phase thus result in a reduction in the off-resonance reflection levels and correspondingly an increase in the spectral bandpass ratio. The spectral bandpass ratio is a figure of merit used to gauge the flatness of a response and is defined as the ratio of the linewidth at an efficiency of 90% to the linewidth at an efficiency of 10%. Cascading two and three filters in this manner results in respective increases in the spectral bandpass ratio of three times and more than five times that of a single filter.
© 2002 Optical Society of America
Donald K. Jacob, Steven C. Dunn, and M. G. Moharam, "Flat-Top Narrow-Band Spectral Response Obtained from Cascaded Resonant Grating Reflection Filters," Appl. Opt. 41, 1241-1245 (2002)