Nonreciprocal Photonic Devices Research Articles

Loss-induced quantum nonreciprocity

Attribute to their robustness against loss and external noise, nonreciprocal photonic devices hold great promise for applications in quantum information processing. Recent advancements have demonstrated that nonreciprocal optical transmission in linear systems can be achieved through the strategic introduction of loss. However, a crucial question remains unanswered: can loss be harnessed as a resource for generating nonreciprocal quantum correlations? Here, we take a counterintuitive stance by engineering loss to generate a vital form of nonreciprocal quantum correlations, termed nonreciprocal photon blockade. We examine a dissipative three-cavity system comprising two nonlinear cavities and a linear cavity. The interplay of loss and nonlinearity leads to a robust nonreciprocal single- and two-photon blockade, facilitated by destructive quantum interference. Furthermore, we demonstrate the tunability of this nonreciprocal photon blockade by manipulating the relative phase between the two nonlinear cavities. Remarkably, this allows for the reversal of the direction of nonreciprocity. Our study not only sheds a light on the concept of loss-engineered quantum nonreciprocity but also opens up a pathway for the design of quantum nonreciprocal photonic devices.

Ultra-compact microring optical isolator using an aluminum-substituted cobalt ferrite thin film

Yttrium iron garnets, which are typically used as magneto-optical isolators, are not suitable for monolithic integration with photonic circuits. We experimentally demonstrated an ultracompact microring optical isolator using an aluminum-substituted cobalt ferrite (CAFO) thin film directly deposited on silicon waveguides. The device footprint was only 43×71µm2. The isolator can operate without an external magnet owing to the strong remanent magnetization of the CAFO film and achieved a maximum isolation ratio of 24.7 dB at a wavelength of 1545.7 nm. Our study could facilitate integration of nonreciprocal photonic devices on Si platforms.

Amplified Nonreciprocal Reflection in a Uniform Atomic Medium with the Help of Spontaneous Emissions

It is important to elaborate on versatile strategies for achieving the perfect nonreciprocal reflection amplification, which is the key technology of high-quality nonreciprocal photonic devices. In this work, we ingeniously design a coherent four-level N-type atomic system to harness the nonreciprocal light amplification, in which the uniform distribution of atoms is driven by two strong coupling fields and a weak probe field. In our regime, the strength of the two control fields is designed with linear variation along the x direction to destroy the spatial symmetry of the probe susceptibility, leading to the nonreciprocity of the reflection. In particular, the closed-loop transitions to amplify the probe field are due to the combined effect of the control fields and spontaneous emissions. The numerical simulation indicates that the perfect nonreciprocal reflection amplification can be realized and modulated by the appropriate settings of the control fields and the detuning, Δc. Our results will open a new route toward harnessing nonreciprocity, which can provide more convenience and possibilities in experimental realization.

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.

Inducing Circularly Polarized Single-Photon Emission via Chiral-Induced Spin Selectivity.

One of the central aims of the field of spintronics is the control of individual electron spins to effectively manage the transmission of quantized data. One well-known mechanism for controlling electronic spin transport is the chiral-induced spin-selectivity (CISS) effect in which a helical nanostructure imparts a preferential spin orientation on the electronic transport. One potential application of the CISS effect is as a transduction pathway between electronic spin and circularly polarized light within nonreciprocal photonic devices. In this work, we identify and quantify the degree of chiral-induced spin-selective electronic transport in helical polyaniline films using magnetoconductive atomic force microscopy (mcAFM). We then induce circularly polarized quantum light emission from CdSe/CdS core/shell quantum dots placed on these films, demonstrating a degree of circular polarization of up to ∼21%. Utilizing time-resolved photoluminescence microscopy, we measure the radiative lifetime difference associated with left- and right-handed circular polarizations of single emitters. These lifetime differences, in combination with Kelvin probe mapping of the variation of surface potential with magnetization of the substrate, help establish an energy level diagram describing the spin-dependent transport pathways that enable the circularly polarized photoluminescence.

Silicon integrated Bi2TbFe5O12 thin films for O-band nonreciprocal photonic device applications

Silicon photonics for data communication requires key components in the O-band (1260 nm−1310 nm). However, very few studies report silicon integrated magneto-optical thin films operating at this wavelength range. In this study, we report a method to fabricate polycrystalline Bi2Tb1Fe5O12 thin films on silicon substrates for O-band nonreciprocal photonic device applications. The films are fabricated by magnetron sputtering at room temperature followed by rapid thermal annealing for crystallization. Pure garnet phase is stabilized by a Y3Fe5O12 seed layer on silicon. The film deposited on silicon-on-insulator (SOI) waveguides showed saturation Faraday rotation of −3300 ± 183 deg/cm, propagation loss of 53.3 ± 0.3 dB/cm and a high figure of merit of 61.9 ± 3.8 deg/dB at 1310 nm wavelength, demonstrating promising potential for O-band integrated nonreciprocal photonic devices.

Non-reciprocal topological photonics

The proposal and development of topological photonics have provided a new approach to fundamentally addressing the susceptibility of traditional photonic devices to defects or disorders, significantly enhancing the transmission efficiency and robustness of photonic devices. Among them, non-reciprocal topological photonics which break time-reversal symmetry and support chiral topological states are crucial branches of topological photonics. Their topological properties are characterized by non-zero Chern numbers in two dimensions or topological Chern vectors in three dimensions, exhibiting a rigorous and complete topological protection beyond that of reciprocal topological photonics. This review focuses on introducing the remarkable achievements of non-reciprocal topological photonics in exploring novel physical phenomena (chiral/antichiral edge/surface states, two-dimensional/three-dimensional photonic Chern insulators, magnetic Weyl photonics crystals, etc.) and constructing non-reciprocal robust topological photonic devices (unidirectional waveguides, broadband slow-light delay lines, arbitrarily shaped topological lasers, high-orbital-angular-momentum coherent light sources, etc.). Finally, the present status, potential challenges, and possible breakthroughs in the development of non-reciprocal topological photonics are discussed.

Perfect non-reciprocal reflection amplification in closed loop coherent gain atomic system

High-performance non-reciprocal photonic devices can improve the efficiency of optical quantum manipulation, information processing, and quantum simulation effectively. The enhanced optical signal can simultaneously amplify the weak signal output by the quantum system and isolate the sensitive quantum system from the back-scattered external noise, which is the core technology of high-performance photonic devices. In our previous work (<ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://doi.org/10.1364/OE.499738">2023 <i>Opt. Express</i> <b>31</b> 38228</ext-link>), we have achieved dynamic control of unidirectional reflection amplification based on four-wave mixing gain and the use of coupling field intensity varying linearly with position. In this work, we design a simple three-level closed loop coherent gain atomic system, setting the intensity of coupling field to be varying with position step shape to break the spatial symmetry of probe susceptibility, and achieving perfect non-reciprocal reflection light amplification. In contrast, the stepped variation of coupling field intensity is easier to adjust in experiment, greatly reducing the difficulty in the experiment. Specifically, the system introduces phase modulation. By changing the phase, the frequency region of probe gain and absorption can be switched, which makes the modulation of reflection amplification more flexible.

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.

Two-color unidirectional reflections by modulating the spatial susceptibility in a homogeneous atomic medium.

Non-reciprocal reflections of optical signals are unusual yet fascinating to achieve the imminent applications of non-reciprocal photonic devices and circuits. The complete non-reciprocal reflection (unidirectional reflection) was recently found to be achievable in a homogeneous medium, if the real and imaginary parts of the probe susceptibility satisfy the spatial Kramers-Kronig (KK) relation. We propose a coherent four-level tripod model for realizing dynamically tunable two-color non-reciprocal reflections by applying two control fields with linearly modulated intensities. We found that, the unidirectional reflection can be obtained if the non-reciprocal frequency regions are located in the electromagnetically induced transparency (EIT) windows. This mechanism is to break the spatial symmetry by the spatial modulation of susceptibility to induce unidirectional reflections, the real and imaginary parts of the probe susceptibility are no longer required to satisfy the spatial KK relation.

Interface-Mediated YIG/Ce:YIG Bilayers Structure with Enhanced Magneto-optical Properties via Pulsed Laser Deposition

For the realization of integrated nonreciprocal photonic devices for optical communication, on-chip monolithic integration of magneto-optical materials onto silicon remains a challenge. Implemented with pulsed laser deposition (PLD), a MgO interfacial layer is introduced to overcome the material incompatibilities between a silicon substrate and magneto-optical thin films of yttrium iron garnet (YIG). With a thickness of ∼40 nm, the amorphous interfacial layer of MgO can effectively inhibit interdiffusion across YIG/Si and promote the growth of a high-density, high-phase-purity polycrystalline garnet structure in the bilayer of YIG/Ce:YIG. Such modified chemistry and microstructure in YIG/Ce:YIG lead to enhanced magneto-optical properties, including an ∼38% increase in Faraday rotation and an ∼15% increase in saturation magnetization, as well as an ∼20% increase in infrared (IR) transmission. Offering dual functions of diffusion barrier and structure template, the MgO layer demonstrated herein suggests a new remedy solution to heterogeneous interfaces in advanced thin film devices.

Faraday rotation in nonreciprocal photonic time-crystals

Faraday rotation is one of the most classical ways to realize nonreciprocal photonic devices like optical isolators. Recently, the temporal analog of Faraday rotation, achieved through time-interfaces, was introduced [Li et al., Phys. Rev. Lett. 128, 173901 (2022)]. Here, we extend this concept to the periodic switching regime by introducing nonreciprocal photonic time-crystals (NPTC), formed by switching material properties of a spatially homogeneous magnetoplasma medium periodically in time. Based on a temporal transfer matrix formalism, we study the NPTC band structure and show that temporal Faraday rotation can be achieved in both momentum bands and (partial) bandgaps. When combined with the bandgaps of the NPTCs, the temporal Faraday effect can enable a unidirectional wave amplifier by extracting energy from the modulation. Our study expands the catalog of photonic time-crystals (PTCs), forging a link between photonic nonreciprocity and parametric gain and shedding light on unexplored functionalities of PTCs in wave engineering.

Enhanced Faraday rotation by a Fano resonance in substrate-free three-dimensional magnetoplasmonic structures.

Three-dimensional magnetoplasmonic nanostructures possess more novel and richer optical and magneto-optical (MO) behaviors compared with planar nanostructures, and exhibit attractive potential applications in micro-nano non-reciprocal photonic devices. However, fabrication of three-dimensional magnetoplasmonic nanostructures is difficult using the usual nanofabrication methods. This work constructs three-dimensional substrate-free Au/Co/Au structures prepared using focused ion beam (FIB) technology. In the three-dimensional split-ring structure, with y-polarized light normal incidence, a three-dimensional coupling current is formed between the vertical split-ring and the bottom square hole, which causes excitation of the Fano resonance. The Fano resonance causes a significant enhancement of the local magnetic field, resulting in a larger Faraday rotation (FR). The resonance also brings about a sign reversal of FR, which is related to the direction of the Lorentz force on electrons. Similar effects also exist in the three-dimensional nanopillar structure and the three-dimensional nanoring structure in the simulation results. Due to the high flexibility of FIB machining, the height and shape of the three-dimensional split-ring can be arbitrarily changed, which means the FR intensity and the position of the FR null point are tunable. The designed three-dimensional structures provide a new route to regulate the Faraday effect, and broaden the possibilities for the design and construction of MO devices.

On-Chip Nonreciprocal Photonic Devices Based on Hybrid Integration of Magneto-Optical Garnet Thin Films on Silicon

On-chip integration of nonreciprocal photonic devices is considered a “fundamental challenge” and the “missing link” for silicon photonics. Hybrid integration of magneto-optical (MO) materials in silicon photonic integrated circuits (PICs) shows promising potential to solve this challenge. In the past decade, the performance of silicon-integrated isolators and circulators based on hybrid integrated MO thin films has been significantly improved in terms of low insertion loss, high isolation ratio, and compact footprint. Accordingly, novel integrated magneto-photonic devices have emerged, including nonvolatile MO switch/memory, on-chip magnetometers, quantum nonreciprocal photonic devices, and topologically nontrivial lasers. In this paper, we review recent progress of on-chip nonreciprocal photonic devices based on hybrid integration of MO thin films on silicon. The configuration, operation principle, and key metrics of different types of integrated MO nonreciprocal photonic devices are summarized. In addition, the progress of on-chip electromagnets and novel MO devices are discussed.

Nonreciprocal photonic devices based onwhispering-gallery-modes microcavities

<p indent="0mm">Because the nonreciprocity has both theoretical and applicable prospects, it is desired to break through the restriction of the reciprocity principle for nonreciprocity optical transmission. Theoretically, the reciprocity principle is equivalent to the limited time reversal symmetry. To break the symmetry, the system should include nonlinearity, magneto-optical effects, or modulation in time. Some key components in the optical circuits, such as isolators, circulators, and phase shifters, are typical nonreciprocal devices. They are realized based on the Faraday effect of magneto-optical materials in traditional free-space optics. However, the magneto-optical materials are not naturally compatible with the integrated optics. Therefore, while pursuing the magneto-optical integration on a chip, people also devote to developing nonreciprocal theories and devices without magnetic materials. Whispering-gallery-modes (WGMs) optical microcavity has the advantages of small mode volume and high-quality factor. Therefore, many nonreciprocal strategies in photonic integration are based on optical microcavities. Similar to the nonreciprocal principle of the magneto-optical effect, the external bias fields (such as magnetic field, angular momentum, linear momentum, etc.) are necessary to break the time reversal symmetry. In this paper, we review the research on nonreciprocal optics in WGMs optical microcavities, and summarize recent research achievements in the following interaction categories: Magneto-optical effect, chiral coupling of atoms with energy level distribution bias, macroscopic Doppler effect with angular momentum bias, optomechanical driving, acousto-optic oscillation and nonlinear driving. Firstly, even on the chip, the magneto-optical effect is an important way to realize nonreciprocity. Nonreciprocity can be achieved by depositing/bonding magneto-optical materials on a silicon chip or using the spin-orbit interaction of WGMs in the YIG microsphere with the help of an external magnetic field. Secondly, preparing the atom to a specific Zeeman energy level can also lead to the polarization concerned interaction between the atoms and the photons, so that the nonreciprocity of the photon can be realized based on the control of the atomic ground state population. Thirdly, the Doppler effect can make the moving dielectric medium produce an additional refractive index related to the speed. Then the effective refractive index is different between the light propagating in the opposite directions. The reciprocity of the system is destroyed, thereby achieving nonreciprocity. Finally, the nonreciprocity of optomechanical systems, acousto-optic modulation, and nonlinear effects can be explained by the conservation of angular momentum of photon-phonon interactions. As a summary, some representative parameters of isolators obtained in related experiments are listed in the table. The existing solutions for nonreciprocity have also be classified in terms of angular momentum and interactions, which is beneficial to deeply understanding the existing solutions and to developing potential solutions. The research of nonreciprocity is also discussed by listing problems to be studied.

Observation of optical gyromagnetic properties in a magneto-plasmonic metamaterial

Metamaterials with artificial optical properties have attracted significant research interest. In particular, artificial magnetic resonances with non-unity permeability tensor at optical frequencies in metamaterials have been reported. However, only non-unity diagonal elements of the permeability tensor have been demonstrated to date. A gyromagnetic permeability tensor with non-zero off-diagonal elements has not been observed at the optical frequencies. Here we report the observation of gyromagnetic properties in the near-infrared wavelength range in a magneto-plasmonic metamaterial. The non-zero off-diagonal permeability tensor element causes the transverse magneto-optical Kerr effect under s-polarized incidence that otherwise vanishes if the permeability tensor is not gyromagnetic. By retrieving the permeability tensor elements from reflection, transmission, and transverse magneto-optical Kerr effect spectra, we show that the effective off-diagonal permeability tensor elements reach 10−3 level at the resonance wavelength (~900 nm) of the split-ring resonators, which is at least two orders of magnitude higher than magneto-optical materials at the same wavelength. The artificial gyromagnetic permeability is attributed to the change in the local electric field direction modulated by the split-ring resonators. Our study demonstrates the possibility of engineering the permeability and permittivity tensors in metamaterials at arbitrary frequencies, thereby promising a variety of applications of next-generation nonreciprocal photonic devices, magneto-plasmonic sensors, and active metamaterials.

Single‐Photon Nonreciprocity with an Integrated Magneto‐Optical Isolator

AbstractNonreciprocal photonic devices are essential components of classical optical information processing. It is interesting and important to investigate their feasibility in the quantum world. In this work, a single‐photon non‐reciprocal dynamical transmission experiment has been performed with an on‐chip silicon nitride (SiN)‐based magneto‐optical (MO) isolator. The measured isolation ratio for single photons achieved is 12.33 dB, consistent with the result of the classical test, which proves the functionality of our on‐chip isolator. The quantum coherence of the passing single photons is further verified using high‐visibility quantum interference. This work will promote on‐chip nonreciprocal photonic devices within the integrated quantum circuits and help introduce novel phenomena in quantum information processes.

Dysprosium Substituted Ce:YIG Thin Films for Temperature Insensitive Integrated Optical Isolator Applications.

Magneto-optical isolators are key components in photonic systems. Despite the progress of silicon-integrated optical isolators, the Faraday rotation of silicon-integrated magneto-optical materials, such as cerium-doped yttrium iron garnet (Ce:YIG), show a strong temperature dependence, limiting the temperature range for integrated nonreciprocal photonic device applications. In this work, we report dysprosium substituted Ce:YIG thin films (Dy2Ce1Fe5O12, Dy:CeIG) showing a low temperature coefficient of Faraday rotation. A temperature insensitive range of the Faraday rotation is observed in between 25 °C to 70 °C for this material, compared to 20% variation of the Faraday rotation in Ce:YIG thin films. A Dy:CeIG based temperature insensitive silicon-integrated optical isolator operating in the temperature range of 23 °C to 70 °C is experimentally demonstrated.

Optical nonreciprocity and nonreciprocal photonic devices with directional four-wave mixing effect.

A scheme for magnetic-free optical nonreciprocity in an ensemble of four-level cold atoms is proposed by exploiting the directional four-wave mixing effect. Using experimentally achievable parameters, the nonreciprocal optical responses of the system can be observed and the conversion on nonreciprocal transmission and nonreciprocal phase shift can be implemented. These nonreciprocal phenomena originate from the directional phase matching, which breaks the time-reversal symmetry and dynamic reciprocity of the cold atomic system. Moreover, by embedding the cold atoms into a Mach-Zehnder interferometer and choosing proper parameters, a two-port optical isolator with an isolation ratio of 79.70 dB and an insertion loss of 0.35 dB and a four-port optical circulator with a fidelity of 0.9985 and a photon survival probability of 0.9278 can be realized, which shows the high performance of isolation and circulation. The proposal may enable a new class of optically controllable cavity-free nonreciprocal devices in optical signal processing at the low light level.

Nonreciprocal magneto-optic beam splitting

We report an unexplored magneto-optic effect, triple circular reflection/refraction, for the manufacture of nonreciprocal beam splitters. Such beam splitters split up linearly polarized light into opposite-helicity plus linearly polarized beams all traveling in different directions. We present a mathematical description of the effect and its experimental verification in the visible and near-infrared in bismuth-substituted iron garnets. The phenomenon also provides the existence of quadruple and higher order reflection/refraction modes. The effect in question could produce nonreciprocal photonic devices that operate in classical or quantum regimes such as beam steerers, isolators, and routers.