Symmetric and asymmetric manipulations of two pulses via dynamically controlled dual-channel optical nonreciprocity

Optical nonreciprocity provides a firm basis for direction-dependent control of light transport. We propose a scheme to manipulate two counter-propagating light pulses based on dynamically controlled dual-channel optical nonreciprocity originating from the Doppler effect. This scheme is implemented in a four-level tripod-type thermal atomic medium driven by two counter-propagating control fields. Symmetric or asymmetric propagation and storage scenarios for the two probe pulses can be established by adjusting the detunings and intensities of the control fields. In particular, complete separation of the forward and backward transmission windows enables the realization of a frequency-tunable bidirectional optical isolator. Doppler shifts make the tripod system behave as two weakly coupled three-level Λ-type channels associated mainly with the forward and backward probe fields. Our proposal may have potential applications in designing direction-dependent all-optical devices for manipulating multiple optical pulses.