Optic-electronic-optic (OEO) interferometer enabling coherent optical add-drop multiplexing

We present the first experimental demonstration of an optic-electronic-optic (OEO) interferometer, relying on coherent detection, real-time digital signal processing (DSP), and electro-optic in-phase/quadrature (I/Q) remodulation in one of the interferometer paths. We experimentally quantify the performance of our system and demonstrate the add-drop functionality of an optical quadrature phase-shift keying (QPSK) signal. Long-term stable operation is achieved by implementing an endless active phase stabilization into the DSP.