A narrowband filter with wide free-spectral-range and independent tunability of transmission coefficients

We present an integrated filter on silicon photonics with wide free-spectral-range and sub-nm bandwidth, which is particularly suitable for programmable photonic circuit with arbitrary spectral responses. The unique feature is that its extinction ratio, namely the transmission coefficient within the bandwidth, can be independently controlled from 0 to 1 without affecting the rest optical span. Thus, a series of such building blocks with varying center wavelengths can be concentrated to form a programmable photonic circuit that can generate arbitrary spectral responses with easy control logic. The notch filter is a Mach-Zenhder-Interferometer with narrowband contra-directional couplers (CDC) and the filter performance is greatly enhanced compared with previous results. The bandwidth is reduced by a factor of 4 and the device length is only one third of previous demonstration.