Abstract 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.
Abstract 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.
We study the two-color nonreciprocal effects of transmission and reflection in cold atoms driven into the tripod configuration and confined in a moving optical lattice. Our numerical results show that a very high contrast of the forward-backward transmission up to around 92% (reflection up to around 85%) is observable near the sharp edges of two tunable photonic band gaps at lattice speeds of several meters per second. Such two-color optical nonreciprocity is attained in fact by breaking the time-reversal symmetry with asymmetric Doppler shifts and can be dynamically manipulated by varying the driving and coupling field detunings, the probe pulse length, the atomic lattice velocity, etc.
Multi-band signal propagation and processing play an important role in quantum communications and quantum computing.In recent years, optical nonreciprocal devices such as an optical isolator and circulator are proposed via various configurations of atoms, metamaterials, nonlinear waveguides, etc.In this work, we investigate all-optical controlled nonreciprocity of multi-band optical signals in thermal atomic systems.Via introducing multiple strong coupling fields, nonreciprocal propagation of the probe field can happen at some separated frequency bands, which results from combination of the electromagnetically induced transparency (EIT) effect and atomic thermal motion.In the proposed configuration, the frequency shift resulting from atomic thermal motion takes converse effect on the probe field in the two opposite directions.In this way, the probe field can propagate almost transparently within some frequency bands of EIT windows in the opposite direction of the coupling fields.However, it is well blocked within the considered frequency region in the same direction of the coupling fields because of destruction of the EIT.Such selectable optical nonreciprocity and isolation for discrete signals may be greatly useful in controlling signal transmission and realizing selective optical isolation functions.
Abstract Hot atoms can exhibit non-magnetic optical non-reciprocal transmission due to their chiral properties, which are characteristic of most alkali metal atoms. In fact, the nonreciprocity in hot atoms depends on the propagation direction of the coupling field due to the Doppler effect. Herein, the reciprocal to non-reciprocal conversion based on the single- and double-dark states is realized by controlling the bidirectional coupling fields in a three-level electromagnetically induced transparent medium coupled with a ring cavity. Tuning the frequency difference between the two coupling fields causes the multi-frequency-channel reciprocity and nonreciprocity manipulation to occur. The experimental proof can be applied to quantum communications and quantum networks, such as optical transistors, all-optical switching or routing and logic gate operation.
Owing to the potential applications in all-optical quantum information processing and quantum optical networks, magnet-free optical non-reciprocity transmission has attracted great interest and has been studied in many fields, such as parity-time-symmetry enhanced nonlinearity, optomechanical systems, photonic crystal, cold atomic Bragg lattices, chiral quantum optics, and hot atoms. In particular, the random thermal motion of hot atoms can be a useful resource to realize optical non-reciprocity. Here in this work, based on the susceptibility-momentum-locking of atomic thermal motion and the strong coupling characteristics of cavities, a magnetic-free optical reciprocity-nonreciprocity transmission conversion scheme is designed and realized through the atom-cavity compound system. Theoretical and experimental analysis show that the coupling field conditions determine the nonreciprocity of the system. Under the action of single traveling-wave field, the nonreciprocity in hot atoms depends on the propagation direction of the coupling field due to the Doppler effect. Therefore, by changing the opening and closing of the opposite coupling field, the two-way single channel optical nonreciprocal transmission based on intracavity electromagnetically induced transparency can be controlled. When the two coupling fields propagate simultaneously in the opposite directions, however, the cavity transmission changes from single-dark-state to double-dark-state peaks, in which the reciprocity outputs depend on the frequency difference between the two coupling fields. By tuning the frequency difference, the two-way multi-channel reciprocal-nonreciprocal transmission regulation based on double dark polar peaks can be realized. The study can be applied to all-optical quantum devices and quantum information processing, such as optical transistors, optical switching and routing, and quantum gate manipulation.
We theoretically investigate narrowband nonreciprocal transmission in a Doppler-broadened five-level M-type atomic medium. After Doppler averaging, the M-type system retains a narrow near-resonant electromagnetically induced transparency window that is narrower than that of a standard three-level Λ system. This spectral narrowing is associated with the decreasing separation between the two inner dressed states as atomic velocity increases. The transparency window exhibits pronounced direction-dependent transmission, with high forward transmission and strong suppression in the reverse direction. The transparency linewidth and forward-backward probe transmission can be controlled via two independent driving fields, while the central transparency frequency is kept essentially unchanged. The resulting narrowband nonreciprocity supports high forward transmission together with strong suppression in the reverse direction, which is suitable for frequency-selective optical filtering and nonreciprocal optical transmission in thermal atomic media. Our scheme with these specific features is geared towards enabling compact vapor-cell-based nonreciprocal devices for quantum network applications.
We numerically investigate two-channel pulse propagation dynamics in a degenerate tripod-type four-level atomic medium under the combined influence of an external magnetic field and a relative phase. The results show that an external magnetic field is used as a “knob” to switch between transparent and absorptive regimes of the probe pulse by the on/off state of the magnetic field within suitable frequency and phase domains. By tuning the magnitude of the magnetic field, the transparency spectrum can be reversibly transformed between single- and double-window structures, enabling stable pulse propagation in a single- or dual-channel. In addition, the relative phase strongly modifies the probe absorption profile and provides an efficient means to control pulse propagation dynamics. These findings suggest promising applications in pulse propagation, multi-channel switching, and optical storage for communication systems.