Tunable optical group delay in an active waveguide semiconductor resonator

We investigate a novel optical filter with specific application to tunable optical delay lines. The structure consists of cascaded chirped grating and phase-shifter sections, providing two optical cavities which generate a wide range of potential filter responses. The active waveguide nature of the filter allows current-controlled tunability of both the spectral response and the corresponding group delay. The filter is studied experimentally and theoretically for both transmission and reflection schemes, highlighting the tradeoffs. We demonstrate that continuous group delay tunability of 43 ps can be achieved in reflection with small power variation by optimizing the injection currents.