A planar optical waveguide has sets of diffractive elements, each routing between input and output optical ports diffracted portions of an input optical signal. The diffractive elements are arranged so that the impulse response function of the diffractive element set comprises a reference temporal waveform or its time-reverse. A planar optical waveguide has NM sets of diffractive elements, each routing between corresponding input and output optical ports corresponding diffracted portions of an input optical signal. The NM diffractive element sets, NM input optical ports, and N 1M optical switches enable routing of an input optical signal any of the N input optical sources to any of the M output optical ports based on the operational state of the corresponding 1M optical switch.