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Dynamic topological photonics is a novel research field, combining the time-domain optics and topological physics. In this review, the recent progress and realization platforms of dynamic topological photonics have been well introduced. The definition, measurement methods and the evolution process of the dynamic topological photonics are demonstrated to better understand the physical diagram. This review is meant to bring the readers a different perspective on topological photonics, grasp the advanced progress of dynamic topology, and inspire ideas about future prospects. [ABSTRACT FROM AUTHOR]

This article presents second- and third-generation photonics-electronics convergence devices developed at NTT Device Innovation Center. The target applications and technical requirements for each generation of the devices are described. The advantages that can be obtained from photonics-electronics convergence devices and the technical points to achieve such advantages are also explained. [ABSTRACT FROM AUTHOR]

[Display omitted] Optical metasurfaces, i.e., subwavelength planar nanostructures, have attracted increasing attention due to their unprecedented capabilities of molding classical light and revolutionized conventional optics by replacing bulky optical components with ultrathin, lightweight, and ultracompact meta -optics. In addition to controlling classical light, meta -optics demonstrate the potential to efficiently manipulate nonclassical light and start to enter the realm of quantum photonics. Here, we briefly overview recent advances in quantum meta -optics for generation and manipulation of nonclassical light, highlighting innovative approaches, and discuss future opportunities in this burgeoning area, ranging from fundamental research to practical applications. [ABSTRACT FROM AUTHOR]

Several recent business reports have described the global growth in demand for optical and photonic components, paralleled by technical reports on the growing shortage of skilled manufacturing staff to meet this demand. It is remarkable that producing ultraprecision surfaces remains so dependent on people, in contrast to other sectors of the economy, e.g., car manufacturing. Clearly, training can play some role, but ultimately, only process automation can provide the solution. This paper explores why automation is a challenge and summarizes multidisciplinary work aiming to assemble the building blocks required to realize automation.Highlights: Capturing polishing craft-expertise was academically successful, but commercially unviable due to personal privacy issues. Automating software communication between optical-design and manufacturing can minimise manufacturing cost and risk. Computational fluid dynamics of abrasive-slurries, plus real-time process-sensing, promises improved rocessconvergence. [ABSTRACT FROM AUTHOR]

[Display omitted] Interest in 3D (3- dimensional) printed optics and photonics by both industry and academic researchers is burgeoning, due to the unique features availed by 3D printing not achievable by traditional manufacturing techniques. 3D printing offers tremendous opportunities for developing new integrated systems in optics and photonics. Although a variety of manufacturing approaches have been developed, no single method can satisfy the requirement of small features, low roughness, and high speed simultaneously, thus opening up vast opportunities for innovations in 3D printed photonics. Besides the availability of state-of-the-art 3D printing technology, printable materials for the fabrication of 3D printed optics and photonics devices are also crucial. In this comprehensive review, we highlight the latest developments in 3D printing techniques, as well as developments in innovative practical technologies used for optics and photonics. In addition, we cover the latest progress in the materials used for 3D printed optics and photonics and future prospects in applications of 3D printed optics and photonics. The purpose of this review is to discuss technological and material advances, and potential future opportunities in the field of 3D printed optics and photonics. [ABSTRACT FROM AUTHOR]

The rapid development of additive manufacturing has fueled a revolution in various research fields and industrial applications. Among the myriad of advanced 3D printing techniques, two‐photon polymerization lithography (TPL) uniquely offers a significant advantage in nanoscale print resolution, and has been widely employed in diverse fields, for example, life sciences, materials sciences, mechanics, and microfluidics. More recently, by virtue of the optical transparency of most of the resins used, TPL is finding new applications in optics and photonics, with nanometer to millimeter feature dimensions. It enables the minimization of optical elements and systems, and exploration of light‐matter interactions with new degrees of freedom, never possible before. To review the recent progress in the TPL related optical research, it starts with the fundamentals of TPL and material formulation, then discusses novel fabrication methods, and a wide range of optical applications. These applications notably include diffractive, topological, quantum, and color optics. With a panoramic view of the development, it is concluded with insights and perspectives of the future development of TPL and related potential optical applications. [ABSTRACT FROM AUTHOR]

Gender biases play a very significant role in areas related to science, technology, engineering, and mathematics (STEM). The association of gender with certain attributes, behaviors or professions leads to a lower proportion of women in STEM. In the field of Optics and Photonics, we can identify a gender disparity between technical or bio-clinical approaches within the same area when examining the authorship of the defended thesis. In this work, we quantify the impact of implicit gender bias in the Ph.D. programs related to Optics and Photonics in Spain. Here we present an exhaustive study about the UNESCO descriptors of the theses defended within 2015-2020 through the open-access repository TESEO, where all the doctoral theses of Spanish universities are compiled. The doctorate program of each thesis is considered and classified into a technical or bio-clinical category. With this classification, we quantify the number of male and female authors within each category, and the results show up a clear unbalance in most of the evaluated descriptors: men are more likely to choose technical doctorate programs, while women are mostly present in clinical or biological programs. This difference is seen even in descriptors where both genders are equally represented. On one side, women's underrepresentation is higher in "Physics", "Astronomy and Astrophysics", "Earth and Space Sciences", and "Technological Sciences". Oppositely, the areas of "Chemistry", "Life Sciences", and "Medical Sciences" show a greater gender-balanced distribution for most of the descriptors. [ABSTRACT FROM AUTHOR]

The classic Grangier et al. (1996) experiment is revisited to suggest an alternative model of a single photon. Photon-counting experiments using spontaneous parametric down conversion (SPDC) show that not every single-photon incident on a detector triggers it, and that coincident triggering of detectors can occur during a single gate. The latter is usually interpreted as being caused by spurious photons entering the gate from different SPDC events. However, a pseudo-classical-type model is suggested which dispenses with these intruder photons. Here, a single-photon manifests as a transversely-iterated front of non-rotating screw threads. Each advancing thread has the potential to trigger a detector, and each allows the transfer of spin angular momentum (SAM). On exiting a beam splitter, a single-photon front can produce multiple triggering of detectors on different parts of the front with a probability of at most 5. 0 2 × 1 0 − 5 − 3. 5 4 × 1 0 − 4 for the experiments presented. [ABSTRACT FROM AUTHOR]

Microscale functional materials permit advanced applications in optics and photonics. This work presents the additive manufacturing of three-dimensional structured phosphors emitting red, green, blue, and white. The development is a step forward to realizing additive colour synthesis within complex architectures of relevance in integrated optics or light-emitting sources. [ABSTRACT FROM AUTHOR]

During its fifty-five years of history, the flagship journal of the scientific society SEDOPTICA has, together with its members, witnessed the transformation of a country. In this article we analyse how values such as equality between men and women have been reflected in the magazine over this time. [ABSTRACT FROM AUTHOR]

Optics means a general area of physics that covers a broad range of topics relevant to the study of light. Optics has subfields they are quantum optics, geometrical optics, and physical optics. Photonics refers to a subset of the optics discipline. The simplicity, high efficiency, reliability, transparency, and robust feature of PID controllers were few factors behind the reasons for its acceptance and more popularity for control in processing industries globally. All the conventional techniques for PID controller design and tuning offer early workable values for reaching favorable performances. The manual tuning of the PID controller variables becomes a difficult role that needs comprehensive knowledge and expertise in that field. Certain meta-heuristic techniques are explored to design PID controllers with the main aims of attaining minimum overshoot in lesser settling time and steady state response. For accomplishing enhanced robustness, minimization of disturbance elimination, operating, and physical restraints are treated as multi-optics functions. Therefore, this article presents a modified honey badger optimization (MoHBO) algorithm-based parameter tuning of the PID controller for optics and photonics. The tuning of the PID controller with constraints on the relative delay margin was considered an optimum disturbance rejection issue and summarized the tuning process. The presented MoHBO algorithm is derived by the inclusion of oppositional based learning (OBL) with standard HBO algorithm. In addition, the MoHBO algorithm is tested using the Magnetic Levitation System (MLS) and Phase Locked Loop system (PLL) to assure the enhanced robust nature of the PID controller. A wide ranging comparison study with other metaheuristic optimization algorithms demonstrates the better performance of the MoHBO algorithm over recent algorithms. [ABSTRACT FROM AUTHOR]

Here we present a detailed analysis of a new concept for beam propulsion that extends the propagation range through space by circumventing fundamental limitations on the beam divergence. Using a combination of spatially overlapped continuous laser and neutral particle beams, opto-mechanical forces and light refraction are simultaneously exploited to produce self-guided modes. The aim of the present work is to elucidate the relevant physical phenomena, their relation to the conditions for self-guiding, and practical considerations for the design parameters of such a propulsion system. Methods for computing the lowest order axisymmetric self-guided modes are presented along with the resulting spatial mode structure. Key non-dimensional parameters are derived, including the use of linear stability analysis to determine features of the dynamic interaction. Based on these findings, a beam parameter optimization framework is proposed and applied to a 100-year interstellar flyby mission to Proxima b. With 200 GW of combined laser and particle beam power, we find that a 0.3 kg spacecraft could be accelerated to 0. 044 c over a distance of 4. 37 × 1 0 6 km (0.029 AU) using a small 1 m 2 beam cross-section. Compared to an equivalent particle beam with no self-guiding, this represents an over 50 × increase in payload. Similar payload mass would be possible by laser propulsion with an approximately 1 0 4 m 2 area laser array. These results suggest that self-guided beam propulsion possesses unique attributes that could enable the acceleration of larger spacecraft to relativistic velocities and enhance scientific capabilities for future interstellar and interstellar-precursor missions. [ABSTRACT FROM AUTHOR]

The article titled "Light Engineering and Silicon Diffractive Optics Assisted Nonparaxial Terahertz Imaging" explores the use of structured terahertz light in nonparaxial lensless imaging systems. The study focuses on the application of silicon diffractive optics to create Airy beams, which resemble a "THz sun," and illuminate Fresnel, Fibonacci, and Bessel shaped THz beams. The article, authored by Sergej Orlov, Rusnė Ivaškevičiūtė‐Povilauskienė, and their colleagues, provides a comprehensive analysis of the modulation transfer map dependencies on the distance between the imaged object and the optical element. [Extracted from the article]

A universal cluster model (UCM) of a defect (cluster) structure was developed on examples of nanostructured nonstoichiometric crystals (NNCs) M1−xRxF2+x (M = Ca, Sr, Ba; R = La–Lu, Y) of the fluorite type (CaF2). This family of NNCs consists of 48 phases of different elemental (M, R) compositions. Their RF3 content reaches 50 ± 3 mol%. Crystal matrices MF2 and RF3 control the cluster structure and properties of the NNCs. They are components of MF2–RF3 systems in which these NNCs are formed. The UCM was created on the basis of the studied structures of the ordered phases M4R3F17 (M = Sr, Ba) and M2RF7 (M = Ca) and the mineral tveitite Ca14Y5F43 with a structure derived from the CaF2 type. Clusters [M8R6F68–70] are the structural units in them. The M4R3F17 architecture was first presented as an assembly of blocks of MF2 matrix structure and blocks of both types of structures of the second system components: LaF3 [R6F44] and β-YF3 [R6F40]. Rare-earth clusters in MF2 matrices are treated as nanoscale blocks (R-enriched "nanophases"). The model is based on the octa-cubic cluster [M14−xRxF64+x] with the cuboctahedral anionic core {F12}. The new model describes the structure of M1−xRxF2+x with all M and R and any x. The UCM is of fundamental interest for the most common nonstoichiometry in inorganic fluorides of the CaF2 structural type. The properties of fluorite-type NNCs are controlled by a defect structure, which allows them to be used in quantum electronics, optics, solid state ionics, photonics, in vivo deep-tissue bioimaging NaRF4:(R' + R′′) and other fields. [ABSTRACT FROM AUTHOR]

Neuromorphic photonics has relied so far either solely on coherent or Wavelength-Division-Multiplexing (WDM) designs for enabling dot-product or vector-by-matrix multiplication, which has led to an impressive variety of architectures. Here, we go a step further and employ WDM for enriching the layout with parallelization capabilities across fan-in and/or weighting stages instead of serving the computational purpose and present, for the first time, a neuron architecture that combines coherent optics with WDM towards a multifunctional programmable neural network platform. Our reconfigurable platform accommodates four different operational modes over the same photonic hardware, supporting multi-layer, convolutional, fully-connected and power-saving layers. We validate mathematically the successful performance along all four operational modes, taking into account crosstalk, channel spacing and spectral dependence of the critical optical elements, concluding to a reliable operation with MAC relative error < 2 % . [ABSTRACT FROM AUTHOR]

We propose obtaining TiO2 films by ICPCVD for the fabrication of low-loss waveguides. The challenge is to produce a dense and homogeneous layer with a high refractive index and low absorption in the visible range. Crystallized layers with features such as grains and amorphous layers have a rather low index for the application targeted, so we aimed for an intermediate state. We investigated the influence of plasma power, pressure, deposition time and annealing temperature on the structural, crystalline, and optical properties in order to tailor them. We showed that crystallization into rutile at the nanoscale occurred during deposition and under wisely chosen conditions, we reached a refractive index of 2.5 at 630 nm without creating interfaces or inhomogeneity in the layer depth. Annealing permits one to further increase the index, up to 2.6. TEM analysis on one sample before and after annealing confirmed the nano-polycrystallization and presence of both anatase and rutile phases and we considered that this intermediate state of crystallization was the best compromise for guided optics. [ABSTRACT FROM AUTHOR]

Tailoring light properties using metasurfaces made of optically thin and subwavelength structure arrays has led to a variety of innovative optical components with intriguing functionalities. Transmitted/reflected light field distribution with exquisite nanoscale resolution achievable with metasurfaces has been utilized to encode holographic complex amplitude, leading to arbitrary holographic intensity profile in the plane of interest. Vectorial metasurface holography, which not only controls the intensity profile, but also modifies the polarization distributions of the light field, has recently attracted enormous attention due to their promising applications in photonics and optics. Here, we review the recent progresses of the vectorial metasurface holography, from the basic concept to the practical implementation. Moreover, vectorial metasurfaces can also be multiplexed with other degrees of freedom, such as wavelength and nonlinearity, enriching and broadening its applications in both civil and military field. [ABSTRACT FROM AUTHOR]

Radiative cooling with eco-friendly and zero-energy advantages is considered one of the most viable solutions to address the conflict between traditional energy-intensive cooling systems and global decarbonization. Despite significant advances, the development of radiative cooling still faces many challenges, such as fine-engineering of materials and structures to enhance solar reflection and mid-infrared emission, solar absorption caused by coloring for colorful radiative cooling, and spectral modulation for environmental-adaptative dynamic radiative cooling. Over millions of years of natural selection, utilizing a limited set of biomaterial palettes, optimized strategies, and micro-nano structural design, natural organisms have demonstrated fine control over light-matter interactions at different wavelength scales. Including broadband reflection of the sunlight to prevent solar heating, narrowband reflection of visible light to display brilliant colors, strong emission of mid-infrared wave to complete its cooling, and environmental-adaptative spectral modulation to achieve camouflage or thermal regulation. These biological structures and strategies provide extremely valuable inspiration for the development of advanced radiative cooling techniques. In this review, we systematically summarized the research progress of bioinspired radiative cooling technologies. Emphatically introducing the mechanism of key biological structures to achieve several optical functions, and discussing the various bioinspired radiative coolers and their application potential in different fields. Finally, we present the remaining challenges and outlook on the possible research directions in the future. It is hoped that this review will contribute to further research on bioinspired radiative cooling technology and make exciting progress. [ABSTRACT FROM AUTHOR]

Symmetry underpins our understanding of physical law. Open systems, those in contact with their environment, can provide a platform to explore parity-time symmetry. While classical parity-time symmetric systems have received a lot of attention, especially because of the associated advances in the generation and control of light, there is much more to be discovered about their quantum counterparts. Here we provide a quantum theory which describes the non-Hermitian physics of chains of coupled modes, which has applications across optics and photonics. We elucidate the origin of the exceptional points which govern the parity-time symmetry, survey their signatures in quantum transport, study their influence for correlations, and account for long-range interactions. We also find how the locations of the exceptional points evolve as a function of the chain length and chain parity, capturing how an arbitrary oligomer chain transitions from its unbroken to broken symmetric phase. Our general results provide perspectives for the experimental detection of parity-time symmetric phases in one-dimensional arrays of quantum objects, with consequences for light transport and its degree of coherence. Open quantum systems governed by non-Hermitian dynamics provide a platform to explore PT symmetric phases. Here, a general theory is derived to describe the location of exceptional points in a 1D oligomer chain of arbitrary length. [ABSTRACT FROM AUTHOR]

The notion of non-Hermitian optics and photonics rooted in quantum mechanics and photonic systems has recently attracted considerable attention ushering in tremendous progress on theoretical foundations and photonic applications, benefiting from the flexibility of photonic platforms. In this review, we first introduce the non-Hermitian topological physics from the symmetry of matrices and complex energy spectra to the characteristics of Jordan normal forms, exceptional points, biorthogonal eigenvectors, Bloch/non-Bloch band theories, topological invariants and topological classifications. We further review diverse non-Hermitian system branches ranging from classical optics, quantum photonics to disordered systems, nonlinear dynamics and optomechanics according to various physical equivalences and experimental implementations. In particular, we include cold atoms in optical lattices in quantum photonics due to their operability at quantum regimes. Finally, we summarize recent progress and limitations in this emerging field, giving an outlook on possible future research directions in theoretical frameworks and engineering aspects. [ABSTRACT FROM AUTHOR]

Geometric phase is a unifying and central concept in physics, including optics. As a matter of fact, optics played a pivotal role from the inception of this new paradigm, as some of the first experimental demonstrations have been carried out in optics. A specific type of geometric phase was first introduced by Pancharatnam while investigating interference effects between different polarizations. This specific type of geometric phase, nowadays called the Pancharatnam–Berry phase, is related to the variation of light polarization, encompassing exotic properties when compared with the dynamic phase associated with the optical path. The most widespread manifestation of the Pancharatnam–Berry phase occurs in the presence of a twisted anisotropic material, yielding a point‐wise phase modulation proportional to the local rotation angle of the material. Here the basic mechanism behind the Pancharatnam–Berry phase is discussed. The various applications of this relatively original concept in photonics are then reviewed, presenting both the most important results and manufactured devices reported in literature. The interplay between geometric phase and diffraction occurring in bulk structures is discussed in detail. In the latter case it is shown how geometric phase can be harnessed to generate a new kind of optical waveguide without the necessity of any index gradient. [ABSTRACT FROM AUTHOR]

Organic photonic materials have high refractive index, fast transfer speed, low heat generation, and so on; and therefore, have great potential in optoelectronics and optical micro/nanocircuits. Herein, a new strategy using fluorescence–phosphorescence dual emission and disparity of optical loss in a smooth needle‐like organic crystal is reported to realize color tuning of the optical waveguide (OWG). Especially, a warm white‐light OWG emission is achieved by appropriately adjusting the excitation position, presenting the first report of single‐component organic waveguide with white light emission. Based on this, the as‐prepared 1D organic crystal has been demonstrated as a microscale optical correspondence device with multiple input and output responses, which offers potential applications in modern optics and photonics fields. [ABSTRACT FROM AUTHOR]

The research carried out in the field of optics and photonics with an idea to design and develop the all optical logic devices in the fascinating material known as photonic crystals (PhCs). The structural investigation reveals that the two dimensional (2-D) PhCs is more suitable for fabrication of optoelectronic components. In this article we have designed basic logic gates in 2-D PhCs as they are the building blocks for the construction of optical devices and in these, refractive index is periodically modulated with the wavelength. The understanding of light behaviour in complex PhCs helps in creating photonic band gap (PBG) that can prevent light of certain wavelength propagating in crystal lattice structure. For the selected geometry structure, three PBG bands will exists out of which two of them are transverse electric (TE) and one is transverse magnetic (TM) mode. The PBG bands in the TE mode ranges from 0.31(α/λ) to 0.46(α/λ), 0.61(α/λ) to 0.63(α/λ) and TM mode ranges from 0.86(α/λ) to 0.93(α/λ). The free space wavelength of 1550 nm is set for the finite difference time domain (FDTD) simulation of the structure. The response time and computational overhead required for the proposed OR gate is 0.128ps and 4.4MB is obtained. Also we calculated the extinction ratio for AND gate and NOT gate as 6.19 dB and 10.21 dB respectively. [ABSTRACT FROM AUTHOR]

Contribution: A hybrid approach involving reduced lecture content with project-based learning (PBL) was introduced to a standalone course in optics at an engineering school not specialized in this area, with promising results. Background: At most schools, optics is an elective “niche” area involving a single senior course. This presents challenges, since the topic has breadth and depth, leaving little time for application projects. Yet, seniors want future applicability. After many years, the instructor questioned his “broad-brush” approach involving many topics with limited application, especially given the role of optics and photonics in technology leadership. A literature search uncovered recent use of project-based methods for optics in K–12 and community colleges but little use in U.S. universities, suggesting an opportunity. Intended Outcomes: The authors intended that achievement and valuation by students would be greater with authentic projects and less content. Application Design: Therefore, an approach that concentrated content and project work on light’s dualistic nature in a mathematically rigorous manner was taken. With reduced content, class time was available for PBL, whereby the problem motivated the content. For light’s wave nature, five lecture weeks were followed by a project simulating the propagation of light. For the particle nature, a circuit design project to implement analog electronic circuits during class occurred after five lecture weeks. Findings: Student interviews and instructor perspectives on impacts of learning, career preparation, graduate school interest, and in-class engagement uncovered encouraging results. A direct assessment showed significantly higher homework scores with the course changes. [ABSTRACT FROM AUTHOR]

The controllability of photonic setups is strongly related to how coherently their outputs react to changes in their inputs; such a generic concept is treated in the case of films comprising multilayers of tilted optical axes, under visible light. The optimized designs incorporate ordinary metals or semiconductors while being able to achieve practically all the combinations of reflected, transmitted and absorbed power within the passivity limits. Importantly, most of the proposed structures exhibit substantial robustness to manufacturing defects and are fabricable with various methods. Therefore, they can make indispensable pieces of integrated photonic systems by improving their light-controlling operation for applications ranging from steering and electrodynamic switching to filtering and optical signal processing. [ABSTRACT FROM AUTHOR]

The study and applications of in vivo skin optics have been openly documented as early as the year 1954, or possibly earlier. To date, challenges in analyzing the complexities of this field remain, with wide scopes requiring more scrutiny. Recent advances in spectroscopic research and multivariate analytics allow a closer look into applications potentially for detecting or monitoring diseases. One of the challenges in this field is in establishing a reference for applications which correspond to certain bandwidths. This article reviews the scope on past research on skin spectroscopy, and the clinical aspects which have or may have applications on disease detection or enhancing diagnostics. A summary is supplied on the technicalities surrounding the measurements reported in literature, focused towards the wavelength-dependent applications in themes central to the respective research. Analytics on the topology of the papers' data cited in this work is also provided for a statistical perspective. In short, this paper strives to immediately inform the reader with possible applications via the spectroscopic devices at hand. Graphical Abstract . [ABSTRACT FROM AUTHOR]

Optics, playing an ever‐important role in life, is developing toward miniaturization and integration. Particularly, the field programming of integrated optics will benefit its functionality and durability, thus is highly pursued. Here, through precisely controlling the space‐variant orientations of anisotropic liquid crystals (LCs), various graded‐index waveguides are demonstrated in a homogeneous medium. Straight/bending waveguides and ring resonators are fabricated via LC photopatterning. They exhibit pronounced polychromatic light‐guiding performance. Thanks to their intrinsic external‐stimuli responsivity, the thermal switchability and polarization tunability are verified. By selectively polymerizing, robust functional components and active connecting waveguides can be realized on the same chip. It provides a practical and universal solution to programmable integrated optics, and extends the applications of microstructured soft matter even in wearable photonics. [ABSTRACT FROM AUTHOR]

The outreach activities related to Optics and Photonics carried out by the non-profit association Physics League are presented. Physics League is located at the Science Faculty of the University of Valladolid, and is formed by young scientists and bachelor students. The key features of the activity carried out by the association are: 1) the interaction of the public with the experiments, in contrast with mere demonstration; 2) the setting of the experiments in a universe or story, real or fictional, which the public might feel identified with or attracted to; and 3) the use of uncommon staging such as theatrical plays or escape rooms. The great impact of its activities, with almost 20,000 participants in just five years, and the positive feedback obtained make the results from the small-scale outreach carried out by the association useful to motivate future scientists and to bring science (especially Physics) closer to society. [ABSTRACT FROM AUTHOR]

Using numerical simulations, we investigate the realization of self-focusing media using two-dimensional graded photonic crystals and their applications for imaging and non-imaging purposes. The two-dimensional graded photonic crystals consist of spatially varying cylindrical holes drilled in a dielectric host. By controlling the gradient of the refractive index and the thickness of the self-focusing medium, it is possible to obtain either a focusing lens with Fourier transforming capabilities or an imaging lens, which produces inverted images. Non-imaging applications include a simple antenna for directive emission obtained from the focusing lens, whereas a directional cloak is obtained by modifying the imaging lens. Graded photonic crystal based devices work well up to the Bragg frequencies. They are compact, made from lossless dielectrics, and compatible with planar lithographic techniques, so they can find applications in a broad frequency range, even at the optical frequencies. [ABSTRACT FROM AUTHOR]

By means of area-transformation method, the material parameters of the invisible cloaks in elliptic-cylindrical and spherical coordinates were obtained. The material parameters of the invisible cloaks are nonsingular and the cloaks can operate in a wide bandwidth due to the area-transformation rather than the point-transformation. The invisible properties of the cloaks are nearly perfect when the original area is small enough compared with its counterpart in the transformed space. Full wave simulations based on finite element method verified the designed cloaks. [ABSTRACT FROM AUTHOR]

Photonic crystal fiber (PCF) modal interferometer is studied for sensing applications. There is a trade-off between high sensitivity and wide sensing range due to the intrinsic two-beam interference. We propose and experimentally demonstrate a three-beam path reflective interferometer by exciting mode conversion at the end surface of a dual-mode PCF. Approximately 5% mode conversion is taken place at the PCF end surface according to our model. In comparison with the normal dual-mode interference in a PCF, the mode conversion induced three-beam interference generates sharper spectrum and expanded sensing range. Gas sensing experiment is implemented with a sensitivity of 3019 nm/RIU. The advantage of expanded sensing range is also experimentally demonstrated. [ABSTRACT FROM AUTHOR]

The acousto-optic (AO) effects of photonic crystals (PCs) were studied. Both the PCs’ periodicity and their index distribution could be modulated instantly by the propagating acoustic wave. As a consequence, the PCs’ band structure becomes tunable. In addition to band gap shift in an ideal PC, AO frequency modulation was observed in a PC with single defect, which is quite different from normal AO tunable filters and gives rise to some interesting applications. Furthermore, in dual-defect situation, synchronized and desynchronized modulations were realized at different acoustic wavelengths. Interesting phenomena such as dual frequency sweeping and dual frequency Q-switching were demonstrated. [ABSTRACT FROM AUTHOR]

Imaging effects in metallic photonic crystals (PCs) are examined theoretically based on the finite difference time-domain method. The analysis shows that, in metallic PC-based systems, far-field images do form at the opposite side of the PC “lens” and more importantly, follow the rule of geometric optics with respect to the changes in the source position as a direct proof of negative refraction. However, the comparison of ideal left-handed media with a metallic PC suggests that the focusing effect in the PC based system is different from that of the ideal left-handed media in many aspects, due to the inhomogeneous nature of the PC. Particularly, strong dependence on the individual geometry as well as the frequency in the PC-based system renders the effective index sensitive to the variations and potentially limits its application as a superlens. [ABSTRACT FROM AUTHOR]

We report the properties of one-dimensional heteroepitaxial all-garnet magneto-optical (MO) photonic crystals (MOPCs) composed of alternating MO-active Bi3Fe5O12 (BIG) and transparent Sm3Ga5O12 (SGG) quarter-wavelength layers grown by rf-magnetron sputtering on Ca,Mg,Zr:Gd3Ga5O12(111) and Gd3Sc2Ga3O12(001) crystals. MOPCs’ spectra, as designed, exhibit a stop band structure and a band gap with the transmittance central peak at 750 nm caused by light localization in the half-wavelength BIG cavity. A series of MOPCs with different numbers of [BIG/SSG]m reflectors (m=4, 5, and 6) has been fabricated to optimize the specific Faraday rotation θF (deg/μm) and MO-quality factor Q(deg)=2|θF|/absorption coefficient. A close BIG-to-SGG lattice match enabled significant improvement of [Bi3Fe5O12/Sm3Ga5O12]m properties compared to previously reported [Bi3Fe5O12/Y3Fe5O12]m [S. Kahl and A. M. Grishin, Appl. Phys. Lett. 84, 1438 (2004)] and [Bi3Fe5O12/Gd3Ga5O12]m [S. I. Khartsev and A. M. Grishin, Appl. Phys. Lett. 87, 122504 (2005)] pulsed laser deposited photonic crystals. At the resonance wavelength λ=750 nm, θF=-20.5 deg/μm and Q=66 deg represent the highest MOPC performance achieved so far. Respectively, these are 470% and 31% enhancements compared to a single layer Bi3Fe5O12 film Faraday rotator with equivalent thickness. [ABSTRACT FROM AUTHOR]

Reactive ion etching (RIE) using a CH4–H2 plasma is investigated for the fabrication of a GaN one-dimensional (1D) photonic crystal (PhC) slab. The dominant control parameter for the etch rate and the sidewall profile is the dc bias. The influence of operating pressure, CH4/H2 ratio, and total gas flow rate on the etching characteristics is also presented. An etch rate as high as 85 nm/min and an overcut angle as low as 5° obtained in this work are among the best values reported for conventional RIE technique. The CH4–H2 process is used to etch 1D PhCs with a lattice parameter ranging from 700 to 350 nm and an air filling factor of 0.30 into a 600-nm-thick GaN/sapphire slab. Sharp peaks corresponding to the resonant modes of the nanopatterned structures are observed in the experimental reflection spectra for all the lattice periods. Furthermore, the good optical quality of the nanostructures is evidenced by a resonantly enhanced second-harmonic generation experiment around 400 nm. A second-harmonic generation enhancement factor as high as 105 is obtained, compared with the unpatterned GaN reference slab. These results demonstrate that the CH4–H2 conventional RIE technique is well adapted to the etching of GaN PhC for the fabrication of next generation photonic devices exploiting nonlinear processes. [ABSTRACT FROM AUTHOR]