Optical Nonreciprocity Research Articles

Ultra-high optical nonreciprocity with a coupled triple-resonator structure

Optical transmission nonreciprocity as a widely investigated phenomenon is essential to various applications. Many sophisticated mechanisms have been proposed and tested for achieving the optical nonreciprocity on integrated scale, but the technical barriers still exist to their practical implementation. To have an ultra-high transmission nonreciprocity, we consider a simple physical mechanism of optical gain saturation applied to a structure of three mutually coupled cavities or fiber rings. The gain saturation processes in two of its components creates a significantly enhanced optical nonreciprocity that satisfies the requirements for the realistic applications. The structure enjoys two advantages of its wide working bandwidth and the flexibility in choosing its components. Moreover, it is possible to apply the structure to a faithful and non-reciprocal transmission of broadband pulse signals. The structure may considerably relax the constraints on the integrated photonic circuits based on the current technology.

Up‐And‐Coming Advances in Optical and Microwave Nonreciprocity: From Classical to Quantum Realm

Reciprocity is a fundamental physical principle that roots in the time‐reversal symmetry of physical laws. It allows making predictions on any arbitrary complex system's response and operation and hence simplifies the analysis. However, there are many practical situations in which it is advantageous to break reciprocity, e.g., isolators preventing wave scattering back to lasers and generators, full‐duplex systems for multiplexing transmission and receiving in the same channel, nonreciprocal cavity excitation, and protection of fragile states of superconductor quantum computers from thermal noise. The most widespread approach to time‐reversal symmetry breaking and nonreciprocity based on magnetic field biasing suffers from bulkiness, cost ineffectiveness, and loss, motivating researchers and engineers to search for more practical approaches. Herein, the up‐and‐coming advances in optical nonreciprocity, including new materials (Weyl semimetals, topological insulators, metasurfaces), active structures, time‐modulation, parity‐time (PT)‐symmetry breaking, nonlinearity combined with a structural asymmetry, quantum nonlinearity, unidirectional gain and loss, chiral quantum states and valley polarization are overviewed. A general description of nonreciprocal systems is provided and the pros and cons of the mentioned approaches to nonreciprocity are discussed.

Progress of silicon photonic devices-based Fano resonance

The development of silicon photonics provides a method of implementing high reliability and high precision for new micro-nano optical functional devices and system-on-chips. The asymmetric Fano resonance phenomenon caused by the mutual coupling of optical resonant cavities is extensively studied. The spectrum of Fano resonance has an asymmetric and sharp slope near the resonance wavelength. The wavelength range for tuning the transmission from zero to one is much narrow in Fano lineshape, therefore improving the figure of merits of power consumption, sensing sensitivity, and extinction ratio. The mechanism can significantly improve silicon-based optical switches, detectors, sensors, and optical non-reciprocal all-optical signal processing. Therefore, the mechanism and method of generating the Fano resonance, the applications of silicon-based photonic technology, and the physical meaning of the Fano formula’s parameters are discussed in detail. It can be concluded that the primary condition for creating the Fano resonance is that the dual-cavity coupling is a weak coupling, and the detuning of resonance frequency of the two cavities partly determines Fano resonance lineshapes. Furthermore, the electromagnetically induced transparency is generated when the frequency detuning is zero. The methods of generating Fano resonance by using different types of devices in silicon photonics (besides the two-dimensional photonic crystals) and the corresponding evolutions of Fano resonance are introduced and categorized, including simple photonic crystal nanobeam, micro-ring resonator cavity without sacrificing the compact footprint, micro-ring resonator coupling with other structures (mainly double micro-ring resonators), adjustable Mach-Zehnder interferometer, and others such as slit waveguide and self-coupling waveguide. Then, we explain the all-optical signal processing based on the Fano resonance phenomenon, and also discuss the differences among the design concepts of Fano resonance in optimizing optical switches, modulators, optical sensing, and optical non-reciprocity. Finally, the future development direction is discussed from the perspective of improving Fano resonance parameters. The topology structure can improve the robustness of the Fano resonance spectrum; the bound states in continuous mode can increase the slope of Fano spectrum; the Fano resonance can expand the bandwidth of resonance spectrum by combining other material systems besides silicon photonics; the multi-mode Fano resonances can enhance the capability of the spectral multiplexing; the reverse design methods can improve the performance of the device. We believe that this review can provide an excellent reference for researchers who are studying the silicon photonic devices.

On-chip optical non-reciprocity through a synthetic Hall effect for photons

We demonstrate a synthetic Hall effect for light, using an acousto-optically modulated nanophotonic resonator chain. To produce this effect, we simultaneously generate the required synthetic electric field using temporal modulation and the required synthetic magnetic field using spatial modulation of the resonator chain. We show how the combination of these synthetic fields transverse to the direction of light propagation can be used to produce non-reciprocal optical transmission, as a basis for new photonic and topological devices.

Reconfigurable nonreciprocity with low insertion loss using a simple two-level system.

Nonreciprocal light propagation is essential to control the direction of the light flow. Here, we report the realization of magnetic-free optical nonreciprocity using a simple two-level system driven by a pump field in warm atoms. In our experiment, we not only demonstrate less than 0.5 dB of insertion loss and up to 20 dB of isolation but also provide flexible and reconfigurable operations of the isolation bandwidth, frequency, and direction. Nonreciprocal scheme with these characteristics may find important applications in photonic devices.

Optical control of the valley Zeeman effect through many-exciton interactions.

Charge carriers in two-dimensional transition metal dichalcogenides (TMDs), such as WSe2, have their spin and valley-pseudospin locked into an optically addressable index that is proposed as a basis for future information processing1,2. The manipulation of this spin-valley index, which carries a magnetic moment3, requires tuning its energy. This is typically achieved through an external magnetic field (B), which is practically cumbersome. However, the valley-contrasting optical Stark effect achieves valley control without B, but requires large incident powers4,5. Thus, other efficient routes to control the spin-valley index are desirable. Here we show that many-body interactions among interlayer excitons (IXs) in a WSe2/MoSe2 heterobilayer (HBL) induce a steady-state valley Zeeman splitting that corresponds to B ≈ 6 T. This anomalous splitting, present at incident powers as low as microwatts, increases with power and is able to enhance, suppress or even flip the sign of a B-induced splitting. Moreover, the g-factor of valley Zeeman splitting can be tuned by ~30% with incident power. In addition to valleytronics, our results could prove helpful to achieve optical non-reciprocity using two-dimensional materials.

A three-order-parameter bistable magnetoelectric multiferroic metal

Using first-principles calculations we predict that the layered-perovskite metal Bi5Mn5O17 is a ferromagnet, ferroelectric, and ferrotoroid which may realize the long sought-after goal of a room-temperature ferromagnetic single-phase multiferroic with large, strongly coupled, primary-order polarization and magnetization. Bi5Mn5O17 has two nearly energy-degenerate ground states with mutually orthogonal vector order parameters (polarization, magnetization, ferrotoroidicity), which can be rotated globally by switching between ground states. Giant cross-coupling magnetoelectric and magnetotoroidic effects, as well as optical non-reciprocity, are thus expected. Importantly, Bi5Mn5O17 should be thermodynamically stable in O-rich growth conditions, and hence experimentally accessible.

Experimental demonstration of cavity-free optical isolators and optical circulators

Cavity-free optical nonreciprocity components, which have an inherent strong asymmetric interaction between the forward- and backward-propagation direction of the probe field, are key to produce such as optical isolators and circulators. According to the proposal presented by Xia et al., [Phys. Rev. Lett. 121, 203602 (2018)], we experimentally build a device that uses cross-Kerr nonlinearity to achieve a cavity-free optical isolator and circulator. Its nonreciprocal behavior arises from the thermal motion of N-type configuration atoms, which induces a strong chiral cross-Kerr nonlinear response for the weak probe beam. We obtain a two-port optical isolator for up to 20 dB of isolation ratio in a specially designed Sagnac interferometer. The distinct propagation directions of the weak probe field determine its cross-phase shift and transmission, by which we demonstrate the accessibility of a four-port optical circulator.

Collision-Induced Broadband Optical Nonreciprocity.

Optical nonreciprocity is an essential property for a wide range of applications, such as building nonreciprocal optical devices that include isolators and circulators. The realization of optical nonreciprocity relies on breaking the symmetry associated with Lorentz reciprocity, which typically requires stringent conditions such as introducing a strong magnetic field or a high-finesse cavity with nonreciprocal coupling geometry. Here we discover that the collision effect of thermal atoms, which is undesirable for most studies, can induce broadband optical nonreciprocity. By exploiting the thermal atomic collision, we experimentally observe magnet-free and cavity-free optical nonreciprocity, which possesses a high isolation ratio, ultrabroad bandwidth, and low insertion loss simultaneously. The maximum isolation ratio is close to 40dB, while the insertion loss is less than 1dB. The bandwidth for an isolation ratio exceeding 20dB is over 1.2GHz, which is 2 orders of magnitude broader than typical resonance-enhanced optical isolators. Our work paves the way for the realization of high-performance optical nonreciprocal devices and provides opportunities for applications in integrated optics and quantum networks.

Boosting optical nonreciprocity: surface reconstruction in iron garnets

Bi-substituted iron garnet films are extensively used in the fabrication of nonreciprocal devices in optical telecommunications. The miniaturization of these devices for on-chip integration requires the development of more efficient magneto-optic materials than presently available. Recent evidence has emerged of large near-surface enhancements in the magneto-optic response in these materials. However, their operative mechanisms at the atomic and electronic levels are not as yet understood. We report significant differences in the ionic structure between surface and bulk in bismuth-substituted iron garnet materials. It is found that the unit cell is elongated normal to the surface, thus enlarging the separation between F e 3 + ions. These ions play a central role in the magneto-optic response of this material. A marked displacement of Fe ions creates gaps at the surface that are populated in the bulk. Concomitantly, surface- and bulk-sensitive measurements of spin-polarized 3d F e 3 + states show significant differences in the magnitude of L 2 edge x-ray magnetic circular dichroism, as well as differences in L 3 edge dichroism, which, in the presence of spin-orbit coupling in 3d states, can be assigned to high-energy states. An increase in magnetic circular dichroism correlates with larger Faraday rotation. These findings provide a deeper understanding of the role of the surface in the electronic transitions to excited F e 3 + 3d states, responsible for these nonreciprocal phenomena. Together with the surface reconstruction underlying these effects reported here, they provide a useful tool for the further development of improved materials technologies to advance the integration of nonreciprocal devices in optical circuits.

Nonreciprocal Metamaterial Obeying Time-Reversal Symmetry.

We introduce a class of non-Hermitian systems that break electromagnetic reciprocity while preserving time-reversal symmetry, and describe its novel polarization dynamics. We show that this class of systems can be realized using van der Waals heterostructures involving transition-metal dichalcogenides (TMDs). Our work provides a path towards achieving strong optical nonreciprocity and polarization-dependent directional amplification using compact, large-area and magnet-free structures.

Optical nonreciprocity in a three-mode optomechanical system within a common reservoir

Optical nonreciprocity in a three-mode optomechanical system within a common optical reservoir is considered. It is found that optomechanically induced nonreciprocity is generated by the interference between the incoherent coupling induced by the common reservoir and the optomechanical coupling mediated by the interactions of two optical modes with a mechanical mode. There exist two symmetric nonreciprocal regimes that respectively correspond to the forward and backward photon transmissions, and the optical nonreciprocity for the relative phase φ between the optomechanical couplings is in opposite direction to that for the phase 2 π − φ . Additionally, it is shown that the optimal nonreciprocity as well as the nonreciprocal amplification can be achieved only by adjusting the optomechanical couplings. To compare nonreciprocity induced by incoherent coupling with that in the case of coherent coupling, we consider the optomechanically induced nonreciprocity created by interference between the optomechanical and direct couplings between the two optical modes. The nonreciprocal behaviors and their differences in these two cases are explained by using analytic findings.

Optical nonreciprocity in a piezo-optomechanical system**Project supported by the National Natural Science Foundation of China (Grant Nos. 61941501, 61775062, 11574092, 61378012, and 91121023), the Doctoral Program of Guangdong Natural Science Foundation, China (Grant No. 2018A030310109), the Doctoral Project of Guangdong Medical University, China (Grant No. B2017019), and the Open Project of the Key Laboratory of Low Dimensional Quantum Structures and

We theoretically study the optical nonreciprocity in a piezo-optomechanical microdisk resonator, in which the cavity modes and the mechanical mode are optically pumped and piezoelectrically driven, respectively. For asymmetric optical pumping and different piezoelectrical drivings, our system shows some nonreciprocal optical responses. We find that our system can function as an optical isolator, a nonreciprocal amplifier, or a nonreciprocal phase shifter.

Light-induced magnetism in plasmonic gold nanoparticles

Strategies for ultrafast optical control of magnetism have been a topic of intense research for several decades because of the potential impact in technologies such as magnetic memory, spintronics, and quantum computation, as well as the opportunities for non-linear optical control and modulation in applications such as optical isolation and non-reciprocity. Here we report the first experimental quantification of optically induced magnetization in plasmonic Au nanoparticles due to the inverse Faraday effect (IFE). The induced magnetic moment in nanoparticles is found to be ~1,000x larger than that observed in bulk Au, and ~20x larger than the magnetic moment from optimized magnetic nanoparticle colloids such as magnetite. Furthermore, the magnetization and demagnetization kinetics are instantaneous within the sub-picosecond time resolution of our study, supporting a mechanism of coherent transfer of angular momentum from the circularly polarized excitation to the orbital angular momentum of the electron gas.

Broadband optical nonreciprocity in an N-type thermal atomic system

Nonreciprocal propagation of light plays a very important role and attracts a great deal of research interest in quantum optics and quantum information sciences for the intriguing physics and the vast prospective applications. In order to enhance the nonreciprocal bandwidth of light, we investigate nonreciprocal propagation of the weak probe field by controlling two strong control fields in a cavity-free N-type thermal Rb87 atomic system. From the theoretical analysis, it is found that, the linewidth of the EIT windows and thus the nonreciprocal bandwidth for the probe field are mainly determined by the intensities of the control fields Ω1 and Ω2. For proper Ω1, nonreciprocal bandwidth of the probe field can be significantly enhanced by increasing Ω2, which implies the probability of generating more than 100 MHz bandwidth for optical nonreciprocity. The principle experimental demonstration in the Rb87 thermal atomic system is consistent with the theoretical analysis, and we obtain ∼60 MHz nonreciprocal bandwidth in experiments. Our work may provide references for all-optical nonreciprocal quantum devices such as optical isolator, circulator and router in optical information processing.

Realization of Nonlinear Optical Nonreciprocity on a Few-Photon Level Based on Atoms Strongly Coupled to an Asymmetric Cavity.

Optical nonreciprocity is important in photonic information processing to route the optical signal or prevent the reverse flow of noise. By adopting the strong nonlinearity associated with a few atoms in a strongly coupled cavity QED system and an asymmetric cavity configuration, we experimentally demonstrate the nonreciprocal transmission between two counterpropagating light fields with extremely low power. The transmission of 18% is achieved for the forward light field, and the maximum blocking ratio for the reverse light is 30dB. Though the transmission of the forward light can be maximized by optimizing the impedance matching of the cavity, it is ultimately limited by the inherent loss of the scheme. This nonreciprocity can even occur on a few-photon level due to the high optical nonlinearity of the system. The working power can be flexibly tuned by changing the effective number of atoms strongly coupled to the cavity. The idea and result can be applied to optical chips as optical diodes by using fiber-based cavity QED systems. Our work opens up new perspectives for realizing optical nonreciprocity on a few-photon level based on the nonlinearities of atoms strongly coupled to an optical cavity.

Multiwavelength Magnetic-Free Optical Isolator by Optical Pumping in Warm Atoms

Achieving multiwavelength nonreciprocal optical devices, which can realize nonreciprocal (perfect one-way) transmission for two or more wavelengths at the same time, without magnetic materials is challenging, but is highly desirable for densely integrated multiwavelength photonic components. The authors experimentally realize multiwavelength magnetic-free optical nonreciprocity using optical pumping of warm ${}^{85}$Rb atoms, with the assistance of Doppler effect. This scheme may have advantages in decreasing the number of optical isolators, and thus can reduce the complexity of an integrated multiwavelength system.

Achievement of unidirectional air waveguide with extra-broad operation bandwidth in magneto-optical photonic crystals with a triangle lattice

We have presented a coupling structure of two-dimensional (2D) magneto-optical photonic crystals (MOPCs) with a triangular lattice. The numerical calculation of photonic band structure is performed based on the finite element method. The result shows that photonic band gap of 2D MOPCs with a triangular lattice is much larger than that of 2D MOPCs with a square lattice or a honeycomb lattice under the same applied external magnetic field, i.e., working bandwidth of 2D MOPCs with a triangular lattice is much larger than that of the other two MOPCs. We have studied the coupling effect of one-way edge modes in 2D MOPCs with a triangle lattice, and achieved a unidirectional air waveguide with high-transmission, strong nonreciprocity and extra-broad operation bandwidth. Furthermore, we have qualitatively analyzed waveguide transmission characteristics based on S-parameter method, and illustrated the effective operating bandwidth and the optimum operating frequency for optical waveguide nonreciprocity devices according to different transmission losses in application.

Optomechanically induced nonreciprocity based on mechanical driving

Nonreciprocal devices are indispensable for providing highly desirable functionalities for optical circuitry. Here, we propose to take advantage of the interference between optomechanical interaction and mechanical driving to create optical nonreciprocal transmission in a double-cavity optomechanical system. We derived essential conditions for ideal optomechanically induced optical nonreciprocity and analysed properties of optical nonreciprocal transmission, especially in blue-detuned regime. These results can be used to control optical transmission in quantum information processing.

Perfect optical nonreciprocity in a double-cavity optomechanical system

Nonreciprocal devices are indispensable for building quantum networks and ubiquitous in modern communication technology. Here, we use optomechanical interaction and linearly-coupled interaction to realize optical nonreciprocal transmission in a double-cavity optomechanical system. The scheme relies on the interference between the two interactions. We derive the essential conditions to realize perfect optical nonreciprocity in the system, and analyse the properties of optical nonreciprocal transmission and the output fields from mechanical mode. These results can be used to control optical transmission in quantum information processing.