An active semiconductor tunable-shape optical filter and delay line

We present a novel active semiconductor optical filter consisting of a curved-waveguide distributed-feedback (DFB) section and a phase-shifter section with a highly reflective coating. Separate electrical contacts to the DFB and phase-shifter sections allow independent tuning of the gain and the phase accumulated through the structure. The waveguide curvature forms an additional cavity, leading to interesting and controllable coupled-cavity effects. We show experimental and theoretical transmission properties of this filter operating with fixed gain in the DFB and current-controlled absorption in the phase-shifter and suggest potential applications to active filter control and tunable optical delay lines.