Optical Nonreciprocity Research Articles

Broadband optical nonreciprocity by emulation of nonlinear non-Hermitian time-asymmetric loop

Broadband and power-stable optical nonreciprocity is highly desirable for practical implementation of optical isolation of coherent sources and receivers in high-speed data-processing systems. Here, we experimentally demonstrate a 2 × 2 waveguide-coupler system that produces broadband optical nonreciprocity based on simple emulation of nonlinear non-Hermitian time-asymmetric loop. The coupler system consists of five lumped optical components including two linear attenuators and two saturable amplifiers. Under moderate operation conditions which are routinely obtainable with commercial erbium-doped fiber amplifiers, we obtain 20 dB isolation ratio persisting over the entire gain bandwidth of the amplifier and over a wide incident-intensity range from 0.1 mW to 10 kW. The isolation ratio can be enhanced up to 70 dB with the forward transmission efficiency adjustable at any desired stable point by tuning amplifier’s internal dissipation in principle. Therefore, our result strongly encourages further experimental development of broadband on-chip optical isolators which have been elusive so far.

Cavity-Induced Optical Nonreciprocity Based on Degenerate Two-Level Atoms.

We developed and experimentally realized a scheme of optical nonreciprocity (ONR) by using degenerate two-level atoms embedded in an optical ring cavity. For the degenerate transition Fg = 4 ↔ Fe = 3, we first studied the cavity-transmission property in different coupling field configurations and verified that under the strong-coupling regime, the single-dark-state peak formed by electromagnetically induced transparency (EIT) showed ONR. The stable ground-state Zeeman coherence for Λ-chains involved in the degenerate two-level system was found to be important in the formation of intracavity EIT. However, different from the three-level atom-cavity system, in the degenerate two-level system, the ONR effect based on intracavity EIT occurred only at a low probe intensity, because the cavity-atom coupling strength was weakened in the counter-propagating probe and coupling field configuration. Furthermore, ONR transmission with a high contrast and linewidth-narrowing was experimentally demonstrated.

Counterpropagating optical solitary waves in orientation-modulated nematic liquid crystals

We investigate counterpropagating optical solitary waves – nematicons – in non-homogeneously oriented nematic liquid crystals. A non-symmetric angular distribution of the optic axis versus beam propagation provides the solitons with direction-dependent trajectories. By performing numerical experiments in realistic planar samples, we launch nematicons in opposite directions and examine the resulting non-specular transmission in terms of optical nonreciprocity and isolation.

Nanoscale optical nonreciprocity with nonlinear metasurfaces

Optical nonreciprocity is manifested as a difference in the transmission of light for the opposite directions of excitation. Nonreciprocal optics is traditionally realized with relatively bulky components such as optical isolators based on the Faraday rotation, hindering the miniaturization and integration of optical systems. Here we demonstrate free-space nonreciprocal transmission through a metasurface comprised of a two-dimensional array of nanoresonators made of silicon hybridized with vanadium dioxide (VO2). This effect arises from the magneto-electric coupling between Mie modes supported by the resonator. Nonreciprocal response of the nanoresonators occurs without the need for external bias; instead, reciprocity is broken by the incident light triggering the VO2 phase transition for only one direction of incidence. Nonreciprocal transmission is broadband covering over 100 nm in the telecommunication range in the vicinity of λ = 1.5 µm. Each nanoresonator unit cell occupies only ~0.1 λ3 in volume, with the metasurface thickness measuring about half-a-micron. Our self-biased nanoresonators exhibit nonreciprocity down to very low levels of intensity on the order of 150 W/cm2 or a µW per nanoresonator. We estimate picosecond-scale transmission fall times and sub-microsecond scale transmission rise. Our demonstration brings low-power, broadband and bias-free optical nonreciprocity to the nanoscale.

Broadband nonreciprocal gyromagnetic metasurface via magnetic Kerker-type dimers

Optical nonreciprocity, stemming from the deviation of the Lorentz reciprocity theorem, holds significant interest in the realm of optics and electromagnetics. Here, we propose and experimentally demonstrate broadband nonreciprocal transmission via a low-biased magnetic Kerker-type dimer metasurface. The designed magneto-optical metasurface comprises three layers of metal sandwiched between two gyromagnetic near-zero thickness slabs. The Kerker-type dimers broaden the isolation bandwidth utilizing multiple resonances where the double-stacked metallic disks act as Kerker-type dipoles, enhancing the transmissibility of the metasurface. The multipole decomposition reveals that the magnetic dipole contribution arising from magnetization is the primary cause of the metasurface's nonreciprocal response. Microwave measurement demonstrates that the bandwidth for an isolation ratio exceeding 10 dB is over 3 GHz. The broadband nonreciprocal performance remains relatively stable, exhibiting strong robustness against the bias disturbance. Our findings provide an alternative avenue for enhancing broadband nonreciprocity transmission under a low-biased magnetic field.

Optical nonreciprocity in an asymmetric cavity containing two asymmetrically arranged atoms

Optical nonreciprocity in an asymmetric cavity containing two asymmetrically arranged atoms

Optical Nonreciprocity in a Multimode Cavity Optomechanical System Controlled by Dynamic Casimir Force

AbstractThe phenomenon of nonreciprocity arises from the disruption of time reversal symmetry, enabling the one‐way transfer of signals through specific channels. In the framework of cavity optomechanics, this symmetry breaking is attributed to a nonuniform radiation pressure force resulting from the interaction between light and matter. This study investigates a hybrid cavity optomechanical system (COMS) comprising two optical modes, directly coupled to each other via photon hopping interaction and indirectly via a common mechanical excitation in the form of a movable mirror, and an additional parallel metallic plate that induces a dynamical Casimir force (DCF) interaction between the plates. The two optical cavities are driven by two strong laser fields, accompanied by two weak probe classical fields from each port. The primary focus lies in exploring the nonreciprocal behavior of the light field across ports one and two, strongly manipulated by the DCF. The DCF plays a pivotal role in providing extra degrees of flexibility and manipulation in controlling the nonreciprocal signal transmission by modifying the resonance conditions of the fields within the hybrid COMS and is responsible for the amplification and swapping of information between the two ports.

Unidirectional photonic reflector using a defective atomic lattice

Based on the broken spatial symmetry, we propose a scheme for engineering a unidirectional photonic reflector using a one-dimensional atomic lattice with defective cells that have been specifically designed to be vacant. By trapping three-level atoms and driving them into the regime of electromagnetically induced transparency, and through the skillful design of the number and position of vacant cells in the lattice, numerical simulations demonstrate that a broad and high unidirectional reflection region can be realized within the EIT window. This proposed unidirectional reflector scheme provides a new platform for achieving optical nonreciprocity and has potential applications for designing optical circuits and devices of nonreciprocity at extremely low energy levels. Published by the American Physical Society 2024

Nonreciprocal Dissipation Engineering via Strong Coupling with a Continuum of Modes

Optical nonreciprocity plays a key role in almost every optical system, directing light flow and protecting optical components from backscattered light. Controllable forms of on-chip nonreciprocity are needed for the robust operation of increasingly sophisticated photonic integrated circuits (PICs) in the context of classical and quantum computation, networking, communications, and sensing. However, it has been challenging to achieve wideband, low-loss optical nonreciprocity on-chip. In this paper, we demonstrate strong coupling and Rabi-like energy exchange between photonic bands, possessing a continuum of modes, to unlock nonreciprocity and frequency translation over wide optical bandwidths in silicon. Using a traveling-wave phonon field to drive indirect interband photonic transitions, we demonstrate band hybridization that enables an intriguing form of nonreciprocal dissipation engineering. Using the converted mode to create a nonreciprocal dissipation channel, we demonstrate a frequency-neutral, low-loss (less than 1 dB) isolator with high nonreciprocal contrast (more than 14 dB) and broad operating bandwidth (more than 59 GHz). Additionally, through the implementation of complete interband conversion, we demonstrate a high extinction (more than 55 dB) optical frequency translation operation with near-unity efficiency. Published by the American Physical Society 2024

Phase and detuning control of the unidirectional reflection amplification based on the broken spatial symmetry.

In order to achieve the tunable unidirectional reflection amplification in a uniform atomic medium that is of vital importance to design high-quality nonreciprocal photonic devices, we propose a coherent closed three-level Δ-type atomic system by applying a microwave field, and a strong coupling field of linear variation along the x direction to control a probe field. In our scheme, the linearly increased coupling field destroys the spatial symmetry of probe susceptibility and effectively suppresses the reflection of one side; the microwave field constructs closed loop transitions to amplify the probe field and causes phase changes. The numerical simulation indicates that the unidirectional reflection amplification is sensitive to the relative phase ϕ and the coupling detuning Δc. Our results will open a new route toward harnessing optical non-reciprocity, which can provide more convenience and possibilities in the experimental realization.

Optical reciprocity-nonreciprocity-amplification conversion based on degenerate four-wave mixing

Optical nonreciprocity plays an important role in optical communication and quantum networks. In this research, we propose and demonstrate a conversion scheme of magnetic-free dual-channel optical reciprocal amplification (RA) and nonreciprocal amplification (NRA) based on the multiple degenerate four-wave mixing (FWM) process in hot atoms. In our experiment, the dual-channel NRA works with the action of a single pump field based on the establishment of FWM in the same direction and breaking in the opposite direction. Based on stable ground-state Zeeman coherence, by introducing a counter-propagating pump field again, NRA can be changed to RA in the opposite direction of the two original amplified conjugate signals. Moreover, the frequencies of RA signals are very dependent on those of co-propagating pump fields. The experimental realization of NRA-RA conversion may have applications for multichannel angular momentum spatial multiplexing and quantum gate manipulation.

Efficient optical nonreciprocity based on four-wave mixing effect in semiconductor quantum well

Optical nonreciprocity has been a popular research topic in recent years. Semiconductor quantum wells (SQWs) play a key role in many high-performance optoelectronic devices. In this paper, we propose a theoretical scheme to achieve nonmagnetic optical nonreciprocity based on the four-wave mixing effect in SQW nanostructures. Using the experimentally available parameters, the nonreciprocal behavior of the probe field in forward direction and backward direction is achieved through this SQW, where both nonreciprocal transmission and nonreciprocal phase shift have high transmission rates. Furthermore, by embedding this SQW nanostructure into a Mach-Zender interferometer, a reconfigurable nonreciprocal device based on high transmission nonreciprocal phase shift that can be used as an isolator or a circulator, is designed and analyzed. The device can be realized as a two-port optical isolator with an isolation ratio of 92.39 dB and an insertion loss of 0.25 dB, and as a four-port optical circulator with a fidelity of 0.9993, a photon survival probability of 0.9518 and a low insertion loss with suitable parameters. Semiconductor media have the advantages of easier integration and tunable parameters, and this scheme can provide theoretical guidance for implementing nonreciprocal and nonreciprocal photonic devices based on semiconductor solid-state media.

Berry-Curvature Engineering for Nonreciprocal Directional Dichroism in Two-Dimensional Antiferromagnets.

In two-dimensional antiferromagnets, we find that the mixed Berry curvature can be attributed as the geometrical origin of the nonreciprocal directional dichroism (NDD), which refers to the difference in light absorption between opposite propagation directions. This Berry curvature is closely related to the uniaxial strain in accordance with the symmetry constraint, leading to a highly tunable NDD, whose sign and strength can be tuned via strain direction. We choose the lattice model of MnBi_{2}Te_{4} as a concrete example. The coupling between mixed Berry curvature and strain also suggests the magnetic quadrupole of the Bloch wave packet as the macroscopic order parameter probed by the NDD in two dimensions, which is distinct from the multiferroic order P×M or the spin toroidal and quadrupole order within a unit cell in previous studies. Our work paves the way for the Berry-curvature engineering for optical nonreciprocity in two-dimensional antiferromagnets.

Nonreciprocal optomechanically induced transparency and enhanced ground-state cooling in a reversed-dissipation cavity system.

We explore the prospects of phase-modulated optical nonreciprocity and enhanced ground-state cooling of a mechanical resonator for the reversed-dissipation system, where the dissipative coupling between two cavities is realized through the adiabatic elimination of a low-Q mechanical mode, while a high-Q mechanical mode interacts with two mutually coupled cavities, forming a closed-loop structure. This unique system facilitates the nontrivial phenomenon of optomechanically induced transparency (OMIT), which exhibits asymmetry due to the frequency shift effect. We also observe the emergence of parity-dependent unidirectional OMIT windows (appearing under the phase-matching condition), which can be dynamically modulated by both the phase factors and the strength of the dissipative coupling. Furthermore, our study delves into the ground-state cooling effect operating within the reversed-dissipation regime. Intriguingly, the cooling effect can be significantly enhanced by carefully engineering dissipative complex coupling, such as in the phase-matching condition. The potential applications of this scheme extend to the fabrication of ideal optical isolators in optical communication systems and the manipulation of macroscopic mechanical resonators at the quantum level, presenting exciting opportunities in quantum technologies.

Nonreciprocal propagation of optical pulses in a one-dimensional photonic crystal with two Weyl semimetal-based defects

We investigated the nonreciprocal propagation properties of an optical pulse in a one-dimensional photonic crystal containing Weyl semimetal-based defect layers. High optical nonreciprocity, without the need for high-intensity input light sources or external magnetic fields, is the most essential property of the Weyl semimetal. The transfer matrix and Fourier transform techniques are used to obtain the time envelopes of the transmitted pulses. It is demonstrated that the transmitted pulse may attain two different time envelopes by reversing the impinging direction of the input pulse. Then, the effects of the input pulse carrier frequency and time width on the characteristics of the transmitted pulse are presented and shown that reversing the impinging direction of the input pulse has a significant effect on the length and energy of the transmitted pulse. The results may have applications in designing pulse-shaping filters and transferring digital data.

Optical nonreciprocity in multilayer nanoisland systems of [Ag–Al2O3] N

We study the effect of optical nonreciprocity in [Ag–Al2O3] N multilayer structures. The percolation threshold for Ag films was found to be . An anomalously large optical nonreciprocity effect was found in the structures with Ag island layers. This effect appeared as a change in the reflected light polarization () when the sample was rotated around its axis from the initial position by 180∘. The effect magnitude reached . We suggest that a possible mechanism for the optical nonreciprocity effect in these structures can be related to the excitation of localized plasmons in Ag islands. We show that essentially depends on the interlayer and intralayer interaction between Ag layers in multilayer structures and is suppressed in the case of strong intralayer and interlayer interaction of plasma oscillations.

Coupling of QD-based PhC nanocavity with two mechanical modes: an approach to tunable optical switching and sensing applications

We theoretically study the dynamical change in the amplification of the output probe field spectra of a hybrid optomechanical system consisting of double mechanical modes coupled to a photonic crystal (PhC) nanocavity. The PhC cavity is also embedded with a quantum dot (QD) (two-level system) and simultaneously driven by an external pump and a probe field. We show that multiple number of transparency windows that appear can be controlled by the QD-cavity coupling strength and also the Fano profiles are directly measured by the resonant frequency of the mechanical mode. We also show the optical transition from bistability to tristability/multistability by adjusting the switching threshold of the system parameters. These results can also be used to study frequency optical nonreciprocity and all-optical switches in multi-resonator photonic devices.

Nonreciprocal photonic quantum router via synthetic magnetism

Nonreciprocal photon transmissions at the single-quantum level play crucial roles in optical information processing. Here, we propose to develop a nonreciprocal photonic quantum router via synthetic magnetism, which can route photons of an input quantum state in one direction but block them in the other direction. Our model is based on a superconducting circuit of linearly coupled microwave cavities, and the Lorentz reciprocity is broken by synthesizing an effective magnetic field for photons. As a result, an input quantum signal from a given direction can be delivered on-demand to either of the two output ports, but it from the opposite direction is completely absorbed. Our scheme does not involve strong static magnetic fields and optical nonlinearity for generating the desired optical nonreciprocity. It is, therefore, expected to be a key ingredient for the construction of on-chip quantum networks.

Chirality Induced Nonreciprocity in a Nonlinear Optical Microresonator

AbstractOn‐chip optical nonreciprocity is one of the essential functions to fully advance the development of integrated optical systems, which remains technically challenging in many aspects. There is a great need for mechanisms and approaches to facilitate the large‐scale implementation of nonreciprocal light propagation. Recently, unconventional phenomena, such as chiral optical modes and directional light propagation, have been unraveled at exceptional points (EPs), which are unique degeneracies in the energy spectrum and eigenspace of non‐Hermitian systems. Here, this work theoretically and experimentally demonstrates that by steering a single microresonator with thermo‐optic nonlinearity to chiral EPs, nonreciprocal light propagation is achieved with an isolation ratio up to 24 dB and insertion loss less than 0.5 dB. The nonreciprocity is dependent on the chirality and could be optimized near the EPs. Their results pave new avenues for the nonreciprocal control of light propagation enabled by non‐Hermitian degeneracies and hold great potential for microscale and nanoscale on‐chip nonreciprocal devices.

Tunable sum-frequency generation in modal phase-matched thin film lithium niobate rib waveguides.

In this work, we report a highly efficient and tunable on-chip sum-frequency generation (SFG) on a thin-film lithium niobate platform via modal phase matching (e + e→e). It provides on-chip SFG a solution with both high efficiency and poling-free by using the highest nonlinear coefficient d33 instead of d31. The on-chip conversion efficiency of SFG is approximately 2143%W-1 with a full width at half maximum (FWHM) of 4.4 nm in a 3-mm-long waveguide. It can find applications in chip-scale quantum optical information processing and thin-film lithium niobate based optical nonreciprocity devices.