Band 14, Heft 7

We propose a scheme to create and unidirectionally transport thermal squeezed states and random-phase coherent states in a system of two interacting levitated nanoparticles. In this coupled levitated system, we create a thermal squeezed state of motion in one of the nanoparticles by parametrically driving it and then transporting the state to the other nanoparticle by making use of a unidirectional transport mechanism. This mechanism is based on inducing a nonreciprocal type of coupling in the system by suitably modulating the phases of the trapping lasers and the interparticle distance between the levitated nanoparticles. A nonreciprocal coupling creates a unidirectional channel where energy flows from one nanoparticle to the other nanoparticle but not vice versa, thereby allowing for the transport of mechanical states between the nanoparticles. We also affirm this unidirectional transport mechanism by creating and efficiently transporting a random-phase coherent state in the coupled levitated system. In both instances of mechanical state transport, the final nanoparticle showed similar characteristics to the original nanoparticle, depicting a high-fidelity unidirectional transport mechanism. Further, we make use of the feedback nonlinearity and parametric driving to create simultaneous bistability in the coupled levitated system also via this unidirectional mechanism. Our results may have potential applications in tunable sensing, metrology, quantum networks, and in exploring many-body physics under a controlled environment.

This work aims to advance the room-temperature manipulation of photonic qubits and enhance coherence preservation in and for quantum applications via tailored spatio-spectral localized (SSL) systems. We focus on an innovative all-plasmonic SSL system consisting of a gold bowtie array on a gold substrate. This design produces a high-Q spectral-localized mode through the lattice array, emerging from the collective lattice response of localized surface plasmon resonance (LSPR), particularly the surface lattice resonance (SLR). The SSL system enables tunable modal coupling between the LSPR and SLR, allowing precise alignment with quantum emitters to form quasi-bound states across an energy range of 1.45–1.91 eV. This flexibility allows us to investigate how innovative configurations – such as three-body coupling symmetry and modal-coupling strength – affect coherence protection. These insights pave the way for optimizing SSL systems, setting the stage for significant advancements in nanophotonic qubit manipulation at ambient conditions and the future of photonic quantum systems.

Optical bound states in the continuum (BICs) provide a unique mechanism of light confinement that holds great potential for fundamental research and applications. Of particular interest are merging BICs realized in planar periodic structures by merging accidental and symmetry-protected BICs. Topological nature of merging BICs renders their Q factors exceptionally high and robust. However, the existence of accidental BICs with the radiation loss canceled in both the upward and downward directions relies on the up-down mirror symmetry of the structure. If this symmetry is broken, e.g., by a substrate, the Q factor of the mode drops down. Consequently, ultrahigh- Q merging BICs cannot be achieved in substrate-supported structures. Here, by studying the case of a one-dimensional periodic dielectric grating, we discover a simple method to fully compensate for the detrimental effect of breaking the up-down mirror symmetry. The method makes use of a thin layer of a high-refractive-index dielectric material on one side of the structure, allowing one to restore the diverging Q factor of the accidental BIC and fully recover the merged BIC. As an application example, we show that the proposed structures can be used as ultrahigh-performance optical sensors.

Unprecedented atomic-scale measurement resolution has recently been demonstrated in single-shot optical localization measurements based on deep-learning analyses of diffraction patterns of topologically structured light scattered from objects. Here, we show that variations in the diffraction patterns caused by positional changes of an object depend upon the spatial derivatives of the amplitude and phase of the incident field, most strongly around phase singularities. Despite lower intensity near the singularity, an orders-of-magnitude increase in Fisher information contained in the diffraction patterns can be achieved when a nano-object is illuminated by light containing phase singularities, rather than a plane wave. Our work provides a fundamental explanation and motivation for singularity-based metrology with deeply subwavelength precision.

Artificial intelligence algorithms based on deep neural network (DNN) have become an effective tool for conceiving metasurfaces recently. However, the complex and sharp resonances of metasurfaces will tremendously increase the training difficulty of DNNs with non-negligible prediction errors, which hinders their development in designing multifunctional metasurfaces. To overcome the obstacles, the interaction mechanisms between meta-atoms and terahertz (THz) waves via multipole decomposition are investigated to establish a high-quality dataset, which can decrease the complexity of DNN and improve the prediction accuracy. Meanwhile, transfer learning is also employed to reduce the large quantity of training data required by the DNN. Accordingly, two broadband and transmission-reflection-integrated reconfigurable metasurfaces for focused vortex beam generation are inversely designed by counter propagating the DNN with fraction error less than 10 −4 . The results indicate that transmission-reflection-integrated achromatic performances are well achieved in the frequency range of 0.7–1.3 THz, which have the average focusing efficiency and mode purity higher than 48 % and 92 %, respectively. Moreover, transmission-reflection-integrated achromatic THz imaging and edge detection can also be realized by the metasurfaces. This work provides a high accuracy inverse design method for conceiving multifunctional meta-devices, which may promise further progress for the on-chip THz imaging systems.

This study introduces fiber-assisted nanoparticle tracking analysis (FaNTA) as a platform for nanorheology that utilizes an advanced antiresonant optical fiber to analyze the viscoelastic properties of fluids at the nanoscale. The platform confines colloidal nanotracers within a fiber-integrated microchannel, significantly extending observation times and improving statistical accuracy. The FaNTA system consists of a custom-designed microstructured antiresonant fiber, a dedicated optical setup, and sophisticated data processing including image analysis and statistical filtering, enabling precise determination of the hydrodynamic diameter and thus the local viscosity. The study demonstrates the capabilities of the FaNTA concept in the context of rheology by measuring the viscosity of glycerol-water solutions at different concentrations using 50 nm gold nanospheres as nanoprobes. By analyzing their individual diffusive motion, the platform accurately determines fluid viscosities with results that closely match literature values, validating the efficacy of FaNTA for nanorheological applications. FaNTA’s high accuracy and performance in nano- and microrheological measurements highlight its broad potential in nanoscale materials science, dynamic process studies, life and environmental sciences, and nanochemistry. This innovative approach provides a valuable extension to current microrheological methods and offers precise nanoscale fluid characterization for a wide range of applications.

Light waves possess multiple degrees of freedom besides intensity, including phase and polarization, that often contain important information but require complex and bulky systems for their measurement. Here we report a pair of compact multifunctional photodetectors that can selectively measure the local phase gradient of, respectively, the right and left circular-polarization component of any incident wave. These devices employ a chiral pair of integrated plasmonic metasurfaces to introduce a sharp dependence of responsivity on local direction of propagation of the desired polarization component. An order-of-magnitude polarization selectivity with respect to phase gradient is demonstrated with both devices. Using the measured device characteristics, we also describe computationally a pixel array that allows for the simultaneous separate mapping of the right and left circularly-polarized incident wavefronts in a particularly simple imaging setup. These unique capabilities may be exploited to enable new functionalities for applications in chemical sensing, biomedical microscopy, and machine vision.

Metasurface can accurately control and manipulate electromagnetic (EM) waves with high degree of freedom, which is mainly due to their subwavelength structures and functional arrangements. However, most reconfigurable metasurfaces are currently limited to modulating EM waves in a single band. In order to further expand the application scenarios of metasurface, a stimulator-multiplexing framework of microwave-infrared compatible reconfigurable metasurface integrated with LED array is proposed. In this framework, a photoresistor is fully embedded into the meta-atom as an active device. Its resistance value can be adjusted through controlling the luminous intensity of the LED array. The LED array generates excitation light source, along with infrared characteristics. Therefore, it is not only the controller in the microwave band, but also the basic pixel in the infrared band. The framework adopts the way of stimulator-multiplexing, and the reconfigurable characteristics in the microwave and infrared bands can be realized through a single meta-atom structure. This work greatly enriches the metasurface design, which has a wide application prospect in many fields such as information transmission, and adaptive intelligent perception.

Optical phased arrays (OPAs) hold significant promise for low-cost, solid-state beam steering in LiDAR and free-space optical (FSO) communications. The field of view (FOV) is one of the key performance metrics in OPA for both optical beam transmitting (Tx) and receiving (Rx). Currently, people tend to use the same design for both the Tx and Rx parts under the hypothesis of reciprocity. In fact, Tx antennas typically generate well-controlled near-field profiles, whereas Rx apertures encounter randomly distributed incident waves due to uncontrolled reflection and propagation. This work demonstrates that leveraging mode diversity can effectively expand the FOV and enhance the receiving efficiency of Rx OPAs, irrespective of the antenna type. To efficiently utilize collected photons for coherent detection in LiDAR and FSO systems, we introduce an inversely designed mode splitter-converter and a coherent combination architecture. Unlike traditional methods, our approach effectively handles beams with varying amplitudes. As proof of concept, we designed and fabricated an 8-channel edge-emitting OPA receiver operating in TE 0 and TE 1 modes, employing a sparse array to suppress grating lobes within the ±90° range. Experimental results reveal an FOV of 133° for our multimode receiver, surpassing the 49° FOV of a single-mode counterpart with the same antenna array. Our approach, encompassing both mode diversity and coherent combination, introduces a new degree of freedom – higher-order spatial modes – with the potential to significantly advance OPA receiver design.

Human vital-sign sensing using electromagnetic wave has emerged as a promising technology for the noninvasive monitoring of individuals’ health status. Here, a modular reprogrammable metasurface system is presented to suppress noise in noninvasive human respiration sensing. The proposed reprogrammable Biological Metasurface ( BioMeta ) provides three-dimensional dynamic control over wavefront shaping and thus can reduce interference from human limb motions. This capability allows the system to acquire health data accurately and reliably and is particularly beneficial in real-world environments where human subjects may change posture or location frequently. Furthermore, the meta-atom in BioMeta is modular and detachable, thereby resulting in reusable properties and promoting environmental sustainability. Meanwhile, the characteristics of mechanical control enable BioMeta to operate without continuous power supply, thus saving energy to a certain extent. A contactless human respiration sensing prototype based on the proposed BioMeta is demonstrated. Experimental results validate that the BioMeta system can accurately monitor the breathing of multiple individuals with limb movements by means of time multiplexing, with an average estimation error of 0.5 respiration per minute. The proposed system enhances sensing accuracy and reliability for noninvasive human respiration monitoring, presenting a versatile and environmentally friendly solution for applications like elderly care and disease monitoring.

The photonic spin Hall effect can engender transverse spatial and angular displacements in both transmission and reflection, with significant applications in optical imaging, edge detection, and the development of spin-based nanophotonic devices. While previous research has focused on enhancing the photonic spin Hall effect, suppression can be beneficial for photonic spin-switching, offering advantages such as increased speed and sensitivity in nanophotonic devices. In this study, we establish a quantitative correlation between the reflection coefficient and the transverse spatial and angular displacements of reflected light, as induced by the photonic spin Hall effect, grounded in electromagnetic theory. We find that the transverse spatial displacement of reflected light can be eliminated under the condition r pp = − r ss , where r denotes the reflection coefficient, and the first (second) superscript denotes the polarization of the reflected (incident) light. This condition applies to light with arbitrary polarization states, at arbitrary incident angles, and is independent of wavelength and beam waist. A similar outcome is obtained for the transverse angular displacement of the reflected light. Such distinctive displacements are attainable through the use of an electromagnetic interface that satisfies the reflected condition r pp = − r ss . Additionally, we provide a succinct overview of the methodologies for constructing reflective spin switches.

The manipulation of nonlinear spin–orbit interaction at the nanoscale is crucial for advancing information processing in integrated nanophotonics. However, the weak spin–orbit interaction (SOI) in conventional waveguide materials significantly limits the efficiency of nonlinear optical processes. In this work, we design a hybrid plasmonic waveguide composed of a gold film and a Y-branch CdSe nanowire, which addresses the aforementioned limitations. The designed hybrid structure enables efficient directional emission of second-harmonic generation (SHG) via control of the polarization of the excitation light. The transversely emitted SHG can be visualized for directly imaging the SOI. Our work not only provides a way to enhances the efficiency of the nonlinear SOI but also a promising platform for further advances in integrated photonics and nonlinear optics.

We report ring resonators on a silicon germanium on silicon platform operating in the mid-infrared wavelength range around 3.5–4.6 µm with quality factors reaching up to one million. Advances in fabrication technology enable us to demonstrate such high Q -factors, which put silicon germanium at the forefront of mid-infrared integrated photonic platforms. The achievement of high Q is attested by the observation of degeneracy lifting between clockwise (CW) and counter-clockwise (CCW) resonances, as well as optical bistability due to an efficient power buildup in the rings.