Ultrafast All-Optical Switching of Telecom Single Photons

Low-loss, rapid switching solutions are vital to the development of several applications in quantum information science. Fast routers form an integral component of multiplexing schemes that enable quantum resources such as single-photon generation, long-distance entanglement swapping for quantum communication, and exotic quantum state creation for quantum metrology. The Pockels effect in bulk, electro-optic crystals is a relatively low-loss solution, but suffers from slow switching rates (∼10 MHz) and a high voltage demand of several kilovolts. While on-chip electro-optic modulators address the high voltage problem and offer scalability, these typically suffer from high insertion losses. A simple, yet elegant approach to attain both low losses (< 0.6 dB) and up to THz switching rates is to utilize cross-phase modulation in an optical fiber. A pump pulse induces birefringence in the fiber and a co-propagating signal pulse (of a different wavelength) experiences a nonlinear phase shift as it "walks over" the pump pulse, due to their different group velocities in the fiber. Using this technique, we demonstrate a ∼30 GHz, all-optical switch for 1590-nm photons from a heralded single-photon source, achieving a signal-to-noise ratio of ∼160:1.