Optical Nonreciprocity Research Articles

Nonreciprocal cavity dark-state polariton and quantum statistics

Optical nonreciprocity plays an essential role in optical information communication and information processing. Based on electromagnetically induced transparency, a nonreciprocal cavity dark-state polariton (DSP) could be achieved using spin-biased cold atoms. The DSP induces a nonreciprocal window with high transmission and low insertion loss around the cavity resonant frequency. By decreasing the strength of the control field, the contribution of the atom excitation dominates the behavior of the DSP, which exhibits a narrow cavity linewidth and thus a long lifetime of cavity photons in the form of the DSP. Further, we investigate the nonreciprocity for the statistical properties of the system in the single-atom ($N=1$) and multiatom ($N>1$) cases. Due to the existence of DSP, the photon statistics leads to totally different profiles for the light propagating in both directions in the two cases. In the single-atom ($N=1$) case, the light in the form of DSP shows apparent sub-Poissonian distribution simultaneously with relatively high transmission and a narrow bandwidth corresponding to the one-photon excitation due to quantum interference. Such a quasiparticle may provide a platform for novel applications in nonreciprocal quantum devices and quantum simulation.

Nonreciprocity of Optical Absorption in the Magnetoelectric Antiferromagnet CuB2O4

The change in the absorption spectra due to reversal of the direction of light propagation (nonreciprocity of absorption) is a consequence of a simultaneous violation of both time-reversal and spatial-inversion symmetries. Here, we report on a high-resolution spectroscopic study of absorption nonreciprocity in the noncentrosymmetric multiferroic CuB2O4 below the antiferromagnetic transition temperature TN = 21 K in the commensurate phase in magnetic fields up to 0.5 T. The study was performed in a broad spectral region covering several exciton transitions, which all are followed by an anomalously rich structure due to the multiple exciton-magnon-phonon satellites. Two components were resolved for the spectral line near 1.4 eV corresponding to the exciton transition between the ground and the first excited state. A quantitative theory of the optical absorption and nonreciprocity at this line was developed. The theory takes into account the interference between the electric and magnetic dipole contributions to the absorption and gives an adequate explanation of the relevant effects.

Optical Transitions and Nonreciprocity in Spatio‐Temporally Periodic Layers of Spherical Particles

AbstractAn extension of the photonic layer multiple scattering methodology to dynamic spherical scatterers, which exhibit a periodic time‐varying response, is presented. The applicability of the method is demonstrated on specific examples of single‐ and bi‐layers of periodically modulated high‐refractive‐index spherical particles arranged on a square lattice. The results provide compelling evidence for strong and tunable inelastic scattering effects under the triple resonance condition, fulfilled for optical transitions between neighboring high‐Q lattice modes of the appropriate symmetry, which originate from multipolar Mie resonances. A consistent interpretation of the underlying mechanisms is provided and potential applications in the design of nonreciprocal devices are discussed.

Efficient optical isolator via dual-Raman process with chiral nonlinearity

A scheme for optical nonreciprocity is proposed via dual-mode Raman process in thermal atoms. We investigate a far-detuned nonlinear Raman process, with the assistance of the Doppler effect to achieve chiral optical nonlinearity. The resulting Kerr nonlinear absorption is subject to a direction-dependent Doppler shifts seen by the thermal atoms. Moreover, the inter-channel Raman interference could significantly enhance Kerr nonlinear absorption for probe field, leading to the enhancement of the optical nonreciprocity. Simulation results show that the isolation ratio could reach 41 dB and the insertion loss is about 0.16 dB, with bandwidth up to 2π ×48 MHz. Furthermore, the sensitivity of the system is investigated under different strengths of the control and Raman fields.

Emergent optical nonreciprocity and chirality-controlled magneto-optical resonance in a hybrid magneto–chiral metamaterial

Broken spatial and time reversal symmetries in materials often give rise to new emergent phenomena in the interaction between light and matter. The combination of chirality and broken time reversal symmetry in a magnetic field leads to magneto–chiral phenomena, such as the nonreciprocity of transmission. Here, we construct a terahertz hybrid metamaterial that combines the natural optical activity of a chiral metallic gammadion bilayer and the magneto-optical activity of semiconductor indium antimonide in a magnetic field. We report a resonant magneto–chiral effect that leads to polarization-independent nonreciprocal optical transmittance. Furthermore, we discover a magneto-optical Faraday effect that is resonantly controlled by the natural optical activity of the chiral gammadion bilayer. Unlike optical activity due to chirality, the novel Faraday effect is odd under time reversal. Both phenomena are activated by a modest magnetic field, which may open doors for their potential applications in polarization-independent optical isolation and highly efficient polarization control at terahertz frequencies.

The effect of optical non-reciprocity in multilayer nanostructure systems based on Bi

The effect of optical non-reciprocity in multilayer nanostructure systems based on Bi

Magnetic-free unidirectional polarization rotation and free-space optical isolators and circulators

Optical nonreciprocity is an essential concept in optical signal processing and communication. The traditional way to achieve nonreciprocity is using magneto-optical nonreciprocal polarization rotation, which is incompatible with existing on-chip integration due to the applied magnetic field. Here, we theoretically and experimentally realize unidirectional polarization rotation with a magnetic-free mechanism using atomic ensembles. Free-space isolators and circulators are further formed based on the nonreciprocity of polarization rotation. As only one direction of the signal changes its polarization, the forward transmission and backward isolation can be adjusted separately. Compared with the existing magnetic-free circulators that rely on high-Q factor cavities or Mach–Zehnder interferometers, we experimentally realized circulators in free space. This dramatically simplifies the magnetic-free circulator structure and provides better stability.

All-fiber optical nonreciprocity based on parity-time-symmetric Fabry-Perot resonators

Nonreciprocal light transmission in an all-fiber platform is critical in modern optical communication systems, which can avoid the packaging and integration process required in current devices based on magneto-optical or nonlinear materials. Here we propose and demonstrate an all-fiber device with remotely tunable isolation ratio and switchable isolation direction by constructing two mutually coupled Fabry-Perot (FP) resonators with identical geometry and balanced gain and loss. By controlling the pumping power, strong optical nonreciprocity is achieved due to gain saturation nonlinearity that is enhanced by the broken parity-time symmetry. Nonreciprocal light transmission with an isolation ratio of 8.58 dB at 1550 nm and an insertion loss of 2.5 dB is demonstrated. The isolation bandwidth is 125 MHz, which is determined by the bandwidths of the two coupled FP resonators. The proposed approach provides an all-fiber solution for a remotely tunable and optically controlled isolator, which may find applications in software-defined optical networks.

Nonlinear optical nonreciprocity in a surface plasmon–exciton coupled asymmetric cavity system

Nonlinear optical nonreciprocity in a surface plasmon–exciton coupled asymmetric cavity system

Nonreciprocal vortex isolator via topology-selective stimulated Brillouin scattering

Optical nonreciprocity, which breaks the symmetry between forward and backward propagating optical waves, has become vital in photonic systems and enables many key applications. So far, all the existing nonreciprocal systems are implemented for linearly or randomly polarized fundamental modes. Optical vortex modes, with wavefronts that spiral around the central axis of propagation, have been extensively studied over the past decades and offer an additional degree of freedom useful in many applications. Here, we report a light-driven nonreciprocal isolation system for optical vortex modes based on topology-selective stimulated Brillouin scattering (SBS) in chiral photonic crystal fiber. The device can be reconfigured as an amplifier or an isolator by adjusting the frequency of the control signal. The experimental results show vortex isolation of 22 decibels (dB), which is at the state of the art in fundamental mode isolators using SBS. This device may find applications in optical communications, fiber lasers, quantum information processing, and optical tweezers.

Optical Nonreciprocity in Double Optomechanical Systems with Quadratic Coupling

In this paper, the optical nonreciprocal phenomena in double optomechanical systems with quadratic coupling are studied. Our model belongs to an optomechanical system in which three coupling modes coexist, that is, the two cavity fields are coupled with the mechanical oscillator at the same time and the couplings are in the form of quadratic interactions. In addition, there is a linear coupling mode between the two cavity fields. In the entire system, each cavity field is effectively coupled by a control field and a probe field simultaneously. The expression of the transmission coefficient of the probe field is obtained by solving the dynamic evolution equation satisfied by the system. Using numerical analysis, we analyze the change in transmission coefficient of the probe field under the conditions of different physical parameters. The results show that we can realize optical nonreciprocal transmission in this system. Appropriate choices about physical parameters can achieve perfect nonreciprocity. Our theoretical scheme to realize optical nonreciprocal transmission in a double optomechanical system provides a theoretical basis for optical circulators, cyclic amplifiers and directional amplifiers.

Spatial Nonreciprocal Transmission and Optical Bistability Based on Millimeter‐Scale Suspended Metasurface

AbstractWhen light interacts with microscopic objects at the micro‐ and nano‐scale, the momentum exchange between photons and objects can be very significant. While the optical radiation pressure at the same level is usually too weak to change the mechanical state of macro‐scale objects at millimeter scale or beyond. Suspended metasurfaces with excellent mechanical and optical properties are ideal candidates for light‐matter interactions. Here, without sound insulation conditions, the spatial optical nonreciprocity based on an optomechanical system with a 2 mm × 2 mm × 110 nm Si3N4 suspended metasurface at the telecom wavelength is demonstrated, with peak wavelength shift up to 1.1 pm, which is about 4.0 times of the full width at half maximum, together with optical bistability at only about 10 W cm−2 input intensities, which is more than 4 orders of magnitude lower than traditional nonlinear optical mechanism. This work may pave new avenues for spatially nonreciprocal devices and bistable devices, and benefit the applications such as precision sensing, cavity quantum optomechanics, and all‐optical switching.

Nonreciprocity with Structured Light Using Optical Pumping in Hot Atoms

Nonreciprocal transmission of structured light has possible applications in high-capacity optical communication and high-dimensional signal processing. Here, we demonstrate the magnet-free and cavity-free optical nonreciprocity of an orbital-angular-momentum (OAM) beam using optical-pumping technology with the assistance of the Doppler effect in hot atoms. By using optical pumping to induce a direction-dependent population transfer of the ground-state atoms, we realize optical nonreciprocity for the signal laser that is carrying OAM. Interestingly, an isolation ratio close to 30 dB and maximum transmission over 0.86 can be achieved simultaneously without the use of an optical cavity. Due to the unique amplitude and helical phase profile of the structured light, our proposal may open an avenue for exploring the singularity characteristics of optical nonreciprocity using structured light.

Optical Nonreciprocity in Rotating Diamond with Nitrogen‐Vacancy Color Centers

AbstractA method to realize optical nonreciprocity in rotating nano‐diamond with nitrogen‐vacancy (NV) centers is theoretically proposed here. Because of the relative motion of the NV center with respect to the propagating fields, the frequencies of the fields are shifted due to the Doppler effect. When the control and probe fields are incident to the NV center from the same direction, the two‐photon resonance still holds as the Doppler shifts of the two fields are the same. Thus, due to the electromagnetically‐induced transparency, the probe light can pass through the NV center nearly without absorption. However, when the two fields propagate in opposite directions, the probe light cannot effectively pass through the NV center as a result of the breakdown of two‐photon resonance.

Nonreciprocal light propagation induced by a subwavelength spinning cylinder.

Nonreciprocal optical devices have broad applications in light manipulations for communications and sensing. Non-magnetic mechanisms of optical nonreciprocity are highly desired for high-frequency on-chip applications. Here, we investigate the nonreciprocal properties of light propagation in a dielectric waveguide induced by a subwavelength spinning cylinder. We find that the chiral modes of the cylinder can give rise to unidirectional coupling with the waveguide via the transverse spin-orbit interaction, leading to different transmissions for guided wave propagating in opposite directions and thus optical isolation. We reveal the dependence of the nonreciprocal properties on various system parameters including mode order, spinning speed, coupling distance, and various losses. The results show that higher-order chiral modes and larger spinning speed generally give rise to stronger nonreciprocity, and there exists an optimal cylinder-waveguide coupling distance where the optical isolation reaches the maximum. The properties are sensitive to the material loss of the cylinder but show robustness against surface-roughness-induced loss in the waveguide. Our work contributes to the understanding of nonreciprocity in subwavelength moving structures and can find applications in integrated photonic circuits, topological photonics, and novel metasurfaces.

Optical nonreciprocity via transmissive time-modulated metasurfaces

Abstract The frequency mixing property of time-modulated metasurfaces, attributed to the well-known phenomenon of temporal photonic transition, has led to several exotic functionalities in the last lustrum. Based on this concept, we demonstrate the possibility of achieving nonreciprocal responses in the near-infrared regime via combining a time-modulated platform and a static high-Q metasurface. In particular, the temporal metasurface is designed to up-convert the incident tone to the first higher-order harmonic, while the static platform is implemented to establish a filtering behavior with respect to the incident frequency. It is shown that while the receiver port acquires the transmitted signal in the forward direction, the amount of received power becomes negligible under the time-reversal scenario, which indicates the presented configuration exhibits different optical responses from opposite directions. In addition, the role of operating wavelength and the modulation frequency on the power isolation level are investigated, and it is demonstrated that by appropriate selection, the isolation level can reach −30 dB. Since this is the first time a nonreciprocal response is obtained in the near-infrared regime via a pure temporal modulation, we believe the idea of this paper can be of utmost importance in various applications, such as tunable optical isolators.

Fundamental Distinction of Electromagnetically Induced Transparency and Autler–Townes Splitting in Breaking the Time‐Reversal Symmetry

AbstractDespite the essential difference in underlying physics, electromagnetically induced transparency (EIT) and Autler–Townes splitting (ATS) are difficult to be discriminated because they cause resemble absorption and dispersion to a probe electromagnetic field. They are mainly discerned in the sense of absorption profile fitting. Here, the breakdown of the time‐reversal symmetry (TRS), namely optical nonreciprocity in the EIT and ATS configurations are experimentally observed by using warm rubidium atoms. The microscopic Doppler effect due to atomic thermal motion causes strong optical nonreciprocity to the probe field in the EIT configuration. In stark contrast, the propagation of the probe field is primarily reciprocal in the ATS configuration. The experimental observations in this study objectively distinguish the EIT and ATS effects in the fundamental physics of breaking the TRS. This experiment proves a concept of using the TRS as a testbed for discerning fundamental physical effects.

Chiral Quantum Optics and Optical Nonreciprocity Based on Susceptibility‐Momentum Locking

AbstractThe progress in chiral light–matter interaction in the quantum regime leads to emergence of chiral quantum optics and quantum nonreciprocity. Spin‐momentum locking is at the heart of chiral quantum optics. In this short review, the basic knowledge of optical nonreciprocity and susceptibility‐momentum locking (SML) is introduced as a novel mechanism for conducting chiral quantum optics. Various approaches achieving optical nonreciprocity based on SML are also reviewed. A perspective regarding the challenges in this direction will also be provided.

Magneto-optical nonreciprocity without chirality: Archimedean spirals on InSb.

We report the observation of magneto-optical nonreciprocity in Faraday geometry in a hybrid metamaterial consisting of an Archimedean spiral metasurface and semiconductor InSb that serves as the magneto-optical medium. None of the metamaterial constituents possesses chirality, which is usually a necessary ingredient for optical nonreciprocity in natural materials when the light travels along the magnetic field direction. We also find that our metamaterial can serve as an optical element for polarization control via magnetic field. Another significant property of our hybrid metamaterial is the emergence of the four different transmittance states, which are observed for the four combinations of the positive and negative magnetic field and the direction of the wavevector of light.

Ultra-strong nonreciprocal amplification with hot atoms

Optical nonreciprocity plays an important role in optical communication and signal processing. Here, we propose and demonstrate a magnetic-free optical nonreciprocal amplification based on a far-detuned four-wave mixing process in hot atoms. The absorption of the probe field can be significantly reduced by the large detuning. In our experiment, with just one pump field, an ultra-strong forward gain of 45 dB is achieved while the backward one keeps a near unit transmission. The experimental realization of ultra-strong nonreciprocal amplification may have applications for the generation of strong nonreciprocal quantum correlations.