Compared with conventional optical elements, 2D photonic metasurfaces, consisting of arrays of antennas with subwavelength thickness (the ‘meta-atoms’), enable the manipulation of light–matter interactions on more compact platforms. The use of metasurfaces with spatially varying arrangements of meta-atoms that have subwavelength lateral resolution allows control of the polarization, phase and amplitude of light. Many exotic phenomena have been successfully demonstrated in linear optics; however, to meet the growing demand for the integration of more functionalities into a single optoelectronic circuit, the tailorable nonlinear optical properties of metasurfaces will also need to be exploited. In this Review, we discuss the design of nonlinear photonic metasurfaces — in particular, the criteria for choosing the materials and symmetries of the meta-atoms — for the realization of nonlinear optical chirality, nonlinear geometric Berry phase and nonlinear wavefront engineering. Finally, we survey the application of nonlinear photonic metasurfaces in optical switching and modulation, and we conclude with an outlook on their use for terahertz nonlinear optics and quantum information processing. Photonic metasurfaces can be used to control the polarization, phase and amplitude of light. Nonlinear metasurfaces enable giant nonlinear optical chirality, realization of the geometric Berry phase, wavefront engineering, and optical switching and modulation, and hold potential for on-chip applications.
Nanophotonics, the field that merges photonics and nanotechnology, has in recent years revolutionized the field of optics by enabling the manipulation of light–matter interactions with subwavelength structures. However, despite the many advances in this field, the design, fabrication and characterization has remained widely an iterative process in which the designer guesses a structure and solves the Maxwell’s equations for it. In contrast, the inverse problem, i.e., obtaining a geometry for a desired electromagnetic response, remains a challenging and time-consuming task within the boundaries of very specific assumptions. Here, we experimentally demonstrate that a novel Deep Neural Network trained with thousands of synthetic experiments is not only able to retrieve subwavelength dimensions from solely far-field measurements but is also capable of directly addressing the inverse problem. Our approach allows the rapid design and characterization of metasurface-based optical elements as well as optimal nanostructures for targeted chemicals and biomolecules, which are critical for sensing, imaging and integrated spectroscopy applications. Scientists have used the power of computing to design tiny structures capable of controlling light at the nanoscale, opening the door for new applications in sensing, imaging and spectroscopy. The emerging field of nano-photonics, which enables the manipulation of light-matter interactions using nanostructures, has revolutionized the field of optics. However, designing a nanostructure that produces a desired optical response is very challenging. Rising to the challenge, Haim Suchowski and colleagues from Tel Aviv University in Israel have developed an innovative technique that uses Deep Neural Networks to model the complex relationships between light-matter interactions, allowing them to characterise nanostructures based on their far-field optical responses. Their approach provides a rapid and efficient method for the designing the optical responses of nanostructures, and could be used in a range of applications, including sensing and imaging.
Rapidly growing demands for fast information processing have launched a race for creating compact and highly efficient optical devices that can reliably transmit signals without losses. Recently discovered topological phases of light provide novel opportunities for photonic devices robust against scattering losses and disorder. Combining these topological photonic structures with nonlinear effects will unlock advanced functionalities such as magnet-free nonreciprocity and active tunability. Here, we introduce the emerging field of nonlinear topological photonics and highlight the recent developments in bridging the physics of topological phases with nonlinear optics. This includes the design of novel photonic platforms which combine topological phases of light with appreciable nonlinear response, self-interaction effects leading to edge solitons in topological photonic lattices, frequency conversion, active photonic structures exhibiting lasing from topologically protected modes, and many-body quantum topological phases of light. We also chart future research directions discussing device applications such as mode stabilization in lasers, parametric amplifiers protected against feedback, and ultrafast optical switches employing topological waveguides.
This chapter examines solutions to the Maxwell equations in a vacuum: monochromatic plane waves and their polarizations, plane waves, and the motion of a charge in the field of a wave (which is the principle upon which particle detection is based). A plane wave is a solution of the vacuum Maxwell equations which depends on only one of the Cartesian spatial coordinates. The monochromatic plane waves form a basis (in the sense of distributions, because they are not square-integrable) in which any solution of the vacuum Maxwell equations can be expanded. The chapter concludes by giving the conditions for the geometrical optics limit. It also establishes the connection between electromagnetic waves and the kinematic description of light discussed in Book 1.
Since the invention of optical tweezers, optical manipulation has advanced significantly in scientific areas such as atomic physics, optics and biological science. Especially in the past decade, numerous optical beams and nanoscale devices have been proposed to mechanically act on nanoparticles in increasingly precise, stable and flexible ways. Both the linear and angular momenta of light can be exploited to produce optical tractor beams, tweezers and optical torque from the microscale to the nanoscale. Research on optical forces helps to reveal the nature of light–matter interactions and to resolve the fundamental aspects, which require an appropriate description of momenta and the forces on objects in matter. In this review, starting from basic theories and computational approaches, we highlight the latest optical trapping configurations and their applications in bioscience, as well as recent advances down to the nanoscale. Finally, we discuss the future prospects of nanomanipulation, which has considerable potential applications in a variety of scientific fields and everyday life. A review of the latest advances in optical manipulation predicts the emergence of new and exciting applications. Optical manipulation, which utilizes light to trap and move small objects, has become a vital tool in many fields. The development of optical tweezers together with advances in nanotechnology has opened the door to new applications. By first considering the fundamental properties of the optical forces and approaches for calculating them, Cheng-Wei Qiu and colleagues from the National University of Singapore, and co-workers, appraise recent developments and emerging technologies in optical manipulation. They predict that more sophisticated methods for manipulating the electromagnetic field will lead to the emergence of new beams for optical manipulation. They also consider that subnanoscale structures may be used in the future, which will require accounting for quantum effects.
Recent experimental developments in diverse areas—ranging from cold atomic gases to light-driven semiconductors to microcavity arrays—move systems into the focus which are located on the interface of quantum optics, many-body physics and statistical mechanics. They share in common that coherent and driven–dissipative quantum dynamics occur on an equal footing, creating genuine non-equilibrium scenarios without immediate counterpart in equilibrium condensed matter physics. This concerns both their non-thermal stationary states and their many-body time evolution. It is a challenge to theory to identify novel instances of universal emergent macroscopic phenomena, which are tied unambiguously and in an observable way to the microscopic drive conditions. In this review, we discuss some recent results in this direction. Moreover, we provide a systematic introduction to the open system Keldysh functional integral approach, which is the proper technical tool to accomplish a merger of quantum optics and many-body physics, and leverages the power of modern quantum field theory to driven open quantum systems.
We study light propagation in the picture of semiclassical space-time that emerges in canonical quantum gravity in the loop representation. In such a picture, where space-time exhibits a polymerlike structure at microscales, it is natural to expect departures from the perfect nondispersiveness of an ordinary vacuum. We evaluate these departures, computing the modifications to Maxwell's equations due to quantum gravity and showing that under certain circumstances nonvanishing corrections appear that depend on the helicity of propagating waves. These effects could lead to observable cosmological predictions of the discrete nature of quantum space-time. In particular, recent observations of nondispersiveness in the spectra of gamma-ray bursts at various energies could be used to constrain the type of semiclassical state that describes the universe.
Chirality is fundamental in many aspects of life, from chemical reactions to biological processes. In medicine, it is central to the diagnosis of diseases such as Parkinson's and Alzheimer's, whose biomarkers are chiral and can appear in blood before symptoms emerge. In pharmaceuticals, chirality is critical: while one enantiomer of a drug may provide therapeutic benefit, its mirror image can be ineffective or toxic. Despite this importance, detecting and discriminating chiral molecules at low concentrations remains a challenge, largely due to the intrinsically weak nature of chiroptical signals. Recent advances in nanophotonics have opened promising pathways to overcome these limitations by engineering light‐matter interactions at the nanoscale. This article summarizes recent progress in chiral nanophotonic biosensing, spanning plasmonic nanoparticles, metasurfaces, magnetophotonic nanostructures, and emerging quantum‐enabled schemes. How engineered near‐fields, extrinsic and substrate‐induced chirality, and magneto‐chiroptical effects enable ultrasensitive detection of enantiomers and biologically relevant aggregates are discussed. Particular emphasis is given to quantum plasmonic biosensing, where nonclassical light and quantum tunneling effects can act together to push sensitivity toward the single‐molecule limit with unprecedented enantiomeric discrimination. With the integration of these developments, nanophotonics is poised to deliver a new generation of label‐free, highly selective chiral biosensors with far‐reaching implications for drug discovery, diagnostics, and personalized medicine.
Thin films composed of titanium dioxide (TiO2) are renowned for their exceptional optical and surface characteristics, making them crucial in various applications including solar cells, LEDs, and self-cleaning surfaces. Nevertheless, fine-tuning these properties through precise manipulation of coating layers remains problematic. This research examines the effects of single, double, and triple TiO2 coatings on photonic and wetting properties, utilizing an economical sol–gel spin-coating technique. The findings demonstrated that increasing the number of layers led to enhanced surface roughness, with measurements rising from 11 nm for a single layer to 26 nm for a triple layer, as determined by atomic force microscopy (AFM). Field emission scanning electron microscopy (FESEM) cross-sectional analysis verified thicknesses of 182 nm, 201/230 nm, and 203/180/225 nm for single, double, and triple coatings, respectively. UV–VIS spectroscopy showed improved optical transmittance and a red shift in the stop band with additional layers, which is advantageous for anti-reflective applications. Water contact angle measurements revealed a transition from hydrophobic (110° for a single layer) to hydrophilic (55° for a triple layer) behavior, attributed to increased roughness and surface irregularities. These results establish a clear correlation between the number of layers and improved photonic and self-cleaning properties, underscoring the potential of TiO2 multilayers for advanced solar cell coatings and optical devices.
Talenti Francesco Rinaldo, Lovisolo Luca, Gerini Andrea
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While frequency comb generation in passive nonlinear optical cavities has been demonstrated in purely quadratic and Kerr platforms, the interplay between χ(2) and χ(3) effects is yet to be fully understood. In this work, we propose a doubly resonant AlGaAs microring design for second-harmonic Kerr-comb generation. We compute the full dispersion profile of the guided modes to describe the resulting dynamics. The doubly resonant condition implies the use of a double envelope mean-field model, and the confined field owns spectral components around both the pump and second harmonic wavelengths. The fabrication of such devices is discussed, and preliminary experimental results are presented. Due to its record nonlinear performance, we address AlGaAs as a promising platform for the generation of such novel microcomb sources.
Martina Hentschel, Samuel Schlötzer, Lukas Seemann
Mesoscopic billiard systems for electrons and light, realized as quantum dots or optical microcavities, have enriched the fields of quantum chaos and nonlinear dynamics not only by enlarging the class of model systems, but also by providing access to their experimental realization. Here, we add yet another system class, two-dimensional billiards with anisotropies. One example is the anisotropic dispersion relation relevant in bilayer graphene known as trigonal warping, and another is the birefringent closed optical disk cavity. We demonstrate that the established concept of ray–wave correspondence also provides useful insight for anisotropic billiard systems. First, we approach the dynamics of the anisotropic disk from the ray-tracing side that takes the anisotropy in momentum space into account, based on the non-spherical index ellipsoid. Second, we use transformation optics to solve the wave problem and find the resonances to be those of the isotropic elliptical cavity. We illustrate ray–wave correspondence and mark differences in the description of optical and electronic anisotropic systems.
Structured illumination microscopy (SIM) is one of the most widely applied wide field super resolution imaging techniques with high temporal resolution and low phototoxicity. The spatial resolution of SIM is typically limited to two times of the diffraction limit and the depth of field is small. In this work, we propose and experimentally demonstrate a low cost, easy to implement, novel technique called speckle structured illumination endoscopy (SSIE) to enhance the resolution of a wide field endoscope with large depth of field. Here, speckle patterns are used to excite objects on the sample which is then followed by a blind-SIM algorithm for super resolution image reconstruction. Our approach is insensitive to the 3D morphology of the specimen, or the deformation of illuminations used. It greatly simplifies the experimental setup as there are no calibration protocols and no stringent control of illumination patterns nor focusing optics. We demonstrate that the SSIE can enhance the resolution 2–4.5 times that of a standard white light endoscopic (WLE) system. The SSIE presents a unique route to super resolution in endoscopic imaging at wide field of view and depth of field, which might be beneficial to the practice of clinical endoscopy.