Spectral compression of single-photon wave packets by sum-frequency conversion in slow-light waveguides

A slow-light scheme is proposed for simultaneous frequency conversion and spectral compression of a weak optical pulse, which may be in any quantum state including a single-photon state. Such a process plays crucial roles in schemes for constructing quantum networks. Assuming that appropriate slow-light waveguides can be fabricated, theoretical modeling shows that a 3-ps signal pulse can be converted by sum-frequency generation (SFG) into a pulse with duration in the ns regime with a corresponding spectral compression factor of the order of 1000 and a useful intrinsic efficiency up to 83%. With this design, deleterious spatial-temporal oscillations are suppressed because the continual delay of the SFG field suppresses back-conversion from SFG to the signal field. Independent of the input pulse shape (if it is short enough), the converted pulse will have a near-exponential rising shape, which is suitable for temporal-mode matching into an optical cavity.