A configurable wavelength demultiplexer using periodic filter chains

Abstract

The ability to select an arbitrary wavelength out of a large set of wavelengths is important for future dense wavelength division multiple access (DWDM) systems. Current approaches use a spectrometer to demultiplex the wavelengths and use a switch at each wavelength to select or deselect that particular wavelength at the output. In a DWDM system with N wavelengths, N number of switches at each receiver need to be employed in order to select an arbitrary wavelength using the conventional approach. Since switches are active components, this is undesirable when N is large. A better scaling can be achieved if we can arrange a series of configurable filters in a way that half of the spectral energy is filtered out when the input spectrum is passed through each successive stage of the filter. So the first stage filters out half of the spectrum. The second stage filters out another half of the spectrum that is left from the output of the first stage, etc. Optical filters are usually interferometric devices which generate periodic complementary outputs at the same time, such as a Mach-Zehnder interferometer (MZI). The filters used at different stages could be MZIs for which the periodicity is controlled by varying the optical path differences between the two arms of the MZI. To generate more square like transmission functions, a periodic cavity structure in a form similar to a one-dimensional photonic crystal may be used.