Optical Diode Made from a Moving Photonic Crystal

Abstract

Optical diodes controlling the flow of light are of principal significance for optical information processing. They transmit light from an input to an output, but not in the reverse direction. This breaking of time reversal symmetry is conventionally achieved via Faraday or nonlinear effects. For applications in a quantum network, features such as the abilities of all-optical control, on-chip integration, and single-photon operation are important. Here we propose an all-optical optical diode which requires neither magnetic fields nor strong input fields. It is based on a "moving" photonic crystal generated in a three-level electromagnetically induced transparency medium in which the refractive index of a weak probe is modulated by the moving periodic intensity of a strong standing coupling field with two detuned counterpropagating components. Because of the Doppler effect, the frequency range of the crystal's band gap for the probe copropagating with the moving crystal is shifted from that for the counterpropagating probe. This mechanism is experimentally demonstrated in a room temperature Cs vapor cell.

Breaking temporal symmetries for emission and absorption

“…The concept is based on imparting a suitable form of momentum biasing that breaks time-reversal symmetry, achieved with mechanical motion or with spatiotemporal modulation (20)(21)(22)(23)(24)(25)(26)(27)(28)(29). In this paper, for the first time to our knowledge, we apply these concepts to emitting/absorbing systems, showing that it is possible to realize magnetic-free nonreciprocal structures that can emit without absorbing from the same direction over a broad frequency range.…”

Non-Hermitian Degeneracies and Unidirectional Reflectionless Atomic Lattices

“…Such proposals have obvious advantages of real-time all-optical reconfigurable capabilities and implicit disadvantages of intractable field modulations and considerable symmetry errors. Large optical nonreciprocities may also be achieved by exploiting the asymmetric Doppler shift in moving atomic Bragg mirrors [20], and proofof-principle experiments have been carried out [21].The great interest in PT-symmetric complex media stemmed, however, from the non-Hermitian extensions of quantum mechanics and quantum field theories [22,23], and it is perhaps worth going back to the essential nonHermitian behavior of light transport to get a broader picture on reciprocity violations and unidirectional reflectionlessness. Take, e.g., a typical one-dimensional (1D) light scattering process as shown in Fig.…”

“…Such proposals have obvious advantages of real-time all-optical reconfigurable capabilities and implicit disadvantages of intractable field modulations and considerable symmetry errors. Large optical nonreciprocities may also be achieved by exploiting the asymmetric Doppler shift in moving atomic Bragg mirrors [20], and proofof-principle experiments have been carried out [21].…”

Parity-time-antisymmetric atomic lattices without gain

“…However, they cannot be directly used to implement unidirectional light transport and its manipulation [8,9], an essential and more difficult task than others in all-optical networks. In this respect, only in recent years significant progress has been made by considering moving photonic crystals of driven atoms [10,11] and optical materials with parity-time (P T ) symmetry [12,13]. As compared to traditional photonic crystals, P T -symmetric materials are periodically modulated not only in terms of the real part n but also the imaginary part n of the refractive index n, exhibiting a delicate balance of gain and loss alternately along the modulation direction.…”