On-chip optical filters with designable characteristics based on an   interferometer with embedded silicon photonic structures
  We demonstrate chip-scale flat-top filters at near-infrared wavelengths using negative index photonic crystal based Mach Zehnder interferometers. Supported by full three-dimensional numerical simulations, we experimentally demonstrate a new approach for engineering high-pass, low-pass, band-pass, and band-reject filters, based on designing the photonic band diagram both within the band-gap frequency region and away from it. We further show that our approach can be used to design filters that have tunable multi-level response for different sections of the spectrum and for different polarizations. This configuration enables deterministic control of the bandwidth and the rejection ratio of filters for integrated photonic circuits. 
S. Kocaman, M. S. Aras, N. C. Panoiu, M. Lu, and C. W. Wong
physics.optics