Hasil untuk "Optics. Light"

Agostino Di Francescantonio, Alessandra Sabatti, Eleni Prountzou et al.

We report the experimental realization of a LiNbO3 metasurface for electro-optic modulation of light polarization in the telecommunication band. High-Q quasi-bound states in the continuum are emploied to enhance the modulation of amplitude and phase of an impinging beam by a driving electric field, leading to efficient polarization rotation and conversion. We quantified modulation effects under a CMOS-compatible bias at 1 MHz frequency, achieving a variation of 5% in the Stokes parameters and a variation of the polarization ellipse angles of about 3° for the transmitted light. These results demonstrate that dynamic polarization and phase modulation can be attained in a compact platform, highlighting the potential of high-Q resonant LiNbO3 metasurfaces for enhanced light-matter interaction in subwavelength electro-optic devices.

Thien Duc Ngo, Hai Dang Ngo, Toan Phuoc Tran et al.

Ni–Al intermetallic compounds are highly stable, heat‐resistant superalloys that have been studied as possible materials for automotive and aerospace applications. However, no reports of their thermophotonic applications, such as high‐temperature IR emitters, have been reported. Herein, an integrated approach that combines a theoretical investigation of the optical properties of Ni–Al compounds with an optimized geometrical microdevice design is reported. Benchmarking of the optical properties and device performance revealed that NiAl exhibited the best optical properties among the surveyed families of Ni–Al intermetallic compounds, comparable to those of conventional plasmonic materials in the IR region. Additionally, the NiAl‐based microdevices exhibited an excellent quality of 692, making them promising high‐temperature plasmonic superalloys for IR thermophotonic applications. In addition, the experimental dielectric function in the IR region was consistent with the simulated value. Simultaneously, various designs of plasmonic metamaterial structures are modeled successfully based on NiAl, demonstrating the good performance of this material as a perfect spectroscopic absorber and emitter operating in the IR region.

V.A. Gladkikh, V.D. Vlasenko

For a weakly guiding, single-mode, graded-index circular optical fiber, the general form of the dependence of the propagation constant on the waveguide parameter is obtained. From Maxwell's equations, an equation for the field in a light guide with a gradient refractive index profile is derived. Using a power-law refractive index profile for the first three powers and a Gaussian index profile as examples, dependences of the propagation constant, phase and group velocities on the waveguide parameter are obtained. For the ratio of the power transferred by the mode to the total stored energy per unit length of the waveguide, a dependence on the waveguide parameter is plotted. It is shown that as the waveguide parameter increases and the degree of the power-law profile increases, the fraction of transferred power decreases and approaches the fraction of transmitted power for the Gaussian profile. The results obtained can be used to create waveguides for specific applications.

Mohamed S. Abdelkhalik, Xavier Garcia-Santiago, Thomas-Jan van Raaij et al.

Abstract Micro light-emitting diode devices (microLEDs) have the potential to lead the next generation of displays. However, their integration for achieving high brightness is severely limited by the challenge of their low external quantum efficiency (EQE). Another limiting factor of such devices is their Lambertian emission, which requires secondary optics to beam the emitted light in defined directions. To address these limitations, we introduce metallic and dielectric metasurfaces to improve light outcoupling efficiency and control the emission directionality of blue LEDs with micrometer size. The proposed mechanism relies on the interaction between light emitted by multiple quantum wells (MQWs) and metasurfaces supporting collective resonances that result from the coupling of localized resonances in nanoparticles throughout the array. We implemented a hexagonal diffraction lattice of resonant Al and SiO2 nanoparticles in LED devices to achieve reshaping of the far-field electroluminescence, thus demonstrating light beam control capabilities on these emitters. To expand and validate the proposed approach for small LED devices (even at the sub-micrometer scale), we integrate a subdiffraction lattice of Al nanoparticles into the device’s architecture. Implementing the proposed design allows us to control the generated light and achieve enhanced far-field emission.

Chia-Chih Huang

A polarization beam splitter (PBS) is key for building polarization-diversity systems in optical communication networks. Here, we propose a compact and easy-to-fabricate PBS based on a dual subwavelength-grating (DSWG) structure positioned between two Si waveguides on a silicon-on-insulator platform. The coupling strengths of the transverse-electric (TE) and transverse-magnetic (TM) modes were selectively modified, with TE mode suppression and TM mode enhancement. By optimizing the duty cycles along transverse and longitudinal directions of the DSWG structure, the device length is reduced by approximately 40%, and the polarization extinction ratio (PER) of the TM mode is improved by ∼5 dB at a wavelength of 1.55 μ m, compared to a single subwavelength grating structure. Numerical simulations revealed high PERs and low insertion losses (ILs) of 26.7 dB (0.1 dB) for TE mode and 23.2 dB (0.28 dB) for TM mode, with a compact footprint of 1.34 × 2.86 μ m ^2 . Across a bandwidth of ∼90 nm within the C-band (1.53–1.56 μ m), the proposed PBS achieves a TM mode PER of ∼20 dB, a TE mode PER greater than 25 dB, and ILs below 0.25 dB for both modes. This approach, utilizing biaxial anisotropic metamaterials, offers a flexible method for integrating PBSs into photonic integrated circuits using standard semiconductor fabrication processes.

Wei‐Si Qiu, Li‐Li Yang, Dan‐Dan Lian et al.

For light, its spin can be independent of the spatial distribution of its wave function, whereas its intrinsic orbital angular momentum does depend on this distribution. This difference suggests that the spin Hall effect may differ from the orbital Hall effect as light propagates through optical materials. Herein, optical materials are modeled as curved spacetime and light propagation in two specific materials by solving the covariant Maxwell equations is investigated. It is found that the trajectory of light with spin σ and intrinsic orbital angular momentum ℓ deviates from that of light without angular momentum (σ=0 and ℓ=0) by an angle θσ,ℓ∝2σ+ℓ. In particular, the contribution of spin σ to angle θσ,ℓ is twice that of the intrinsic orbital angular momentum ℓ, highlighting their differing effects on light propagation in optical materials. Furthermore, angle θσ,ℓ can potentially be observed experimentally, enhancing the understanding of the role of angular momentum in light propagation.

Minyang Zhang, Dong-Xu Chen, Pengxiang Ruan et al.

The rich structure of transverse spatial modes of structured light has facilitated their extensive applications in quantum information and optical communication. The Laguerre-Gaussian (LG) modes, which carry a well-defined orbital angular momentum (OAM), consist of a complete orthogonal basis describing the transverse spatial modes of light. The application of OAM in free-space optical communication is restricted due to the experimentally limited OAM numbers and the complex OAM recognition methods. Here, we present a novel method that uses the advanced deep learning technique for LG modes recognition. By discretizing the spatial modes of structured light, we turn the OAM state regression into classification. A proof-of-principle experiment is also performed, showing that our method effectively categorizes OAM states with small training samples and high accuracy. By assigning each category a classical information, we further apply our approach to an image transmission task, demonstrating the ability to encode large data with low OAM number. This work opens up a new avenue for achieving high-capacity optical communication with low OAM number based on structured light.

Igor Garcia-Atutxa, Ekaitz Dudagoitia Barrio, Francisca Villanueva-Flores

Skepticism and critical inquiry play crucial roles in the scientific process, acting as safeguards against the "ad verecundiam" fallacy, where claims are accepted solely based on authority endorsement. This study thoroughly investigates Augustin-Jean Fresnel's challenge to Newton's corpuscular theory with his innovative wave theory of light. Supported by precise measurements and the "Fresnel integrals," Fresnel earned the Paris Academy of Sciences Prize in 1819. Despite staunch opposition from corpuscular theory proponents, his theory's validity was confirmed with Poisson's point paradox, where light waves from two sources interfere to create a bright spot in the center of a shadow, providing compelling evidence for the wave nature of light. This successful resolution of the paradox confirmed the validity of Fresnel's wave theory and contributed significantly to the acceptance of wave optics over the corpuscular theory. This conflict transcended a mere clash of explanatory models in the physics of light, prompting reflections on the nature of light, reality, and epistemological issues. Examining how Fresnel overcame challenges offers lessons on constructing scientific knowledge, emphasizing the importance of avoiding theory acceptance based solely on authority and focusing on empirical evidence and theoretical coherence. The case of Fresnel serves as a valuable example for teaching the history of science and understanding complex scientific evolution. Analyzing how Fresnel navigated challenges and opposition provides valuable insights into the development of scientific knowledge, emphasizing the intricate nature of scientific progress characterized by debates and efforts to gain acceptance. This study on Fresnel's groundbreaking wave theory of light not only illuminates the historical clash between competing scientific paradigms but also aims to contribute to modern science by emphasizing the enduring significance of empirical evidence and theoretical coherence in knowledge construction. Through an insightful exploration of Fresnel's triumph over challenges, we anticipate offering valuable insights that resonate with contemporary scientific methodologies, fostering a deeper understanding of the dynamic evolution of scientific thought.

Chenglong Wang, Xiang Guo, Xidong Wu

Abstract Controlling the nonlinear relationship between surface plasmon polariton (SPP) mode index and chemical potential of graphene can be used in the field of active transformation optics. Here, we propose an electrically tunable 2D Graded Photonic Crystal (GPC) lens based on graphene SPP platform. Our platform comprises a graphene monolayer integrated into a back-gated structure with nano-patterned gate insulators. When the chemical potential of the graphene surface is designed to operate in the nonlinear region, the designed GPC lens can be continuously transformed between a Maxwell’s fish-eye lens and a Luneburg lens by tuning the gate voltage. The range of the lens background chemical potential for allowing this transformation is systematically studied. To compensate for the significant errors inherent in the conventional effective medium theory (EMT) during the homogenization of photonic crystals (PCs), we propose a generalized effective medium theory (GEMT). The validity and accuracy of this approach are verified through comparisons with true values (based on rigorous eigenvalue solutions) and EMT values. Due to its advantages of on-site controls and easy fabrication characteristics, the proposed graphene GPC provides a new way for practical on-chip light manipulation.

E. P. Mattos, A. Vidiella-Barranco

In this letter, we present a simple and versatile scheme for enhancing the nonclassical properties of light states using only linear optics and photodetectors. By combining a coherent state $|α\rangle$ and an arbitrary pure state of light $|φ\rangle$ (excluding coherent states) at two beam splitters, we show that the amplitude $α$ of the coherent state can be tuned to filter out specific Fock components and generate states of light with enhanced nonclassical features. We provide two examples of input states and demonstrate the effectiveness of our scheme in enhancing the sub-Poissonian statistics or the quadrature squeezing of the output states.

Zheyuan Zhu, Joe H. Doerr, Guifang Li et al.

Multi-plane light converter (MPLC) designs supporting hundreds of modes are attractive in high-throughput optical communications. These photonic structures typically comprise >10 phase masks in free space, with millions of independent design parameters. Conventional MPLC design using wavefront matching updates one mask at a time while fixing the rest. Here we construct a physical neural network (PNN) to model the light propagation and phase modulation in MPLC, providing access to the entire parameter set for optimization, including not only profiles of the phase masks and the distances between them. PNN training supports flexible optimization sequences and is a superset of existing MPLC design methods. In addition, our method allows tuning of hyperparameters of PNN training such as learning rate and batch size. Because PNN-based MPLC is found to be insensitive to the number of input and target modes in each training step, we have demonstrated a high-order MPLC design (45 modes) using mini batches that fit into the available computing resources.

Avner Peleg, Toan T. Huynh

We investigate fast collisions between pulsed optical beams in a linear medium with weak cubic loss that arises due to nondegenerate two-photon absorption. We introduce a perturbation method with two small parameters and use it to obtain general formulas for the collision-induced changes in the pulsed-beam's shape and amplitude. Moreover, we use the method to design and characterize collision setups that lead to strong localized and nonlocalized intensity reduction effects. The values of the collision-induced changes in the pulsed-beam's shape in both setups are larger by one to two orders of magnitude compared with the values obtained in previous studies of fast two-pulse collisions. Furthermore, we show that for nonlocalized setups, the graph of the collision-induced amplitude shift vs the difference between the first-order dispersion coefficients for the two pulsed-beams has two local minima. This finding represents the first observation of a deviation of the graph from the common funnel shape that was obtained in all previous studies of fast two-pulse collisions in the presence of weak nonlinear loss. The predictions of our perturbation theory are in good agreement with results of numerical simulations with the perturbed linear propagation model, despite the strong collision-induced effects. Our results can be useful for multisequence optical communication links and for reshaping of pulsed optical beams.

Junxiang Zhang, Quan Sheng, Lu Zhang et al.

The saturable absorption effect of unpumped, rare earth‐doped fiber can be used as a method of achieving single‐frequency operation in fiber lasers. This effect in thulium‐doped fiber is used to achieve single‐frequency operation from an all‐fiber oscillator centered at 1720 nm. The characteristics of the saturable absorption effect are carefully studied and numerous operating regimes are identified wherein the oscillating state and frequency output characteristics of the laser can be manipulated via the injection of auxiliary pump light to the saturable absorber. A record single‐frequency output power of 2.56 W at 1720 nm is obtained; the slope efficiency is 44% and the laser linewidth is 3.3 kHz. The power scaling of the laser is only limited by the available power of the single‐mode 1570 nm pump source. Herein, new insights into methods of generating high‐power, single‐frequency emission from all‐fiber oscillators are offered.

T. Lu, M. Fanto, Hyeongrak Choi et al.

We demonstrate a wide-bandgap semiconductor photonics platform based on nanocrystalline aluminum nitride (AlN) on sapphire. This photonics platform guides light at low loss from the ultraviolet (UV) to the visible spectrum. We measure ring resonators with intrinsic quality factor (Q) exceeding 170,000 at 638 nm and Q >20,000 down to 369.5 nm, which shows a promising path for low-loss integrated photonics in UV and visible spectrum. This platform opens up new possibilities in integrated quantum optics with trapped ions or atom-like color centers in solids, as well as classical applications including nonlinear optics and on-chip UV-spectroscopy.

Saman Jahani, Joong Hwan Bahng, Arkadev Roy et al.

High-index dielectrics can confine light into nano-scale leading to enhanced nonlinear response. However, increased momentum in these media can deteriorate the overlap between different harmonics which hinders efficient nonlinear interaction in wavelength-scale resonators in the absence of momentum matching. Here, we propose an alternative approach for light confinement in anisotropic particles. The extra degree of freedom in anisotropic media allows us to control the evanescent waves near the center and the radial momentum away from the center, independently. This can lead to a strong light confinement as well as an excellent field overlap between different harmonics which is ideal for nonlinear wavelength conversion. Controlling the evanescent fields can also help to surpass the constrains on the radiation bandwidth of isotropic dielectric antennas. This can improve the light coupling into these particles, which is crucial for nano-scale nonlinear optics. We estimate the second-harmonic generation efficiency as well as optical parametric oscillation threshold in these particles to show the strong nonlinear response in these particles even away from the center of resonances. Our approach is promising to be realized experimentally and can be used for many applications, such as large-scale parallel sensing and computing.

Albrecht Steinkopff, Cesar Jauregui, Christopher Aleshire et al.

In this work we analyze the power scaling potential of amplifying multicore fibers (MCFs) used in coherently-combined systems. In particular, in this study we exemplarily consider rod-type MCFs with 2x2 up to 10x10 Ytterbium doped cores arranged in a squared pattern. We will show that, even though increasing the number of active cores will lead to higher output powers, particular attention has to be paid to arising thermal effects, which potentially degrade the performance of these systems. Additionally, we analyze the influence of the core dimensions on the extractable and combinable output power and pulse energy. This includes a detailed study on the thermal effects that influence the propagating transverse modes and, in turn, the amplification efficiency, the combining efficiency, the onset of nonlinear effect, as well as differences in the optical path lengths between the cores. Considering all these effects under rather extreme conditions, the study predicts that average output powers higher than 10 kW from a single 1 m long Ytterbium-doped MCF are feasible and femtosecond pulses with energies higher than 400 mJ can be extracted and efficiently recombined in a filled-aperture scheme.

Cizhe Fang, Qiyu Yang, Qingchen Yuan et al.

The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protected bound in the continuum (BIC) and the magnetic dipole dominates these peculiar states. A smaller size of the defect in the broken-symmetry block gives rise to the resonance with a larger Q factor. Importantly, this relationship can be tuned by changing the structural parameter, resulting from the modulation of the topological configuration of BICs. Consequently, a Q factor of more than 3,000 can be easily achieved by optimizing dimensions of the nanostructure. At this sharp resonance, the intensity of the third harmonic generation signal in the patterned structure can be 368 times larger than that of the flat silicon film. The proposed strategy and underlying theory can open up new avenues to realize ultrasharp resonances, which may promote the development of the potential meta-devices for nonlinearity, lasing action, and sensing.

Soha Yousuf, Jongmin Kim, Ajymurat Orozaliev et al.

In this study, deoxyribonucleic acid (DNA) hybridization was demonstrated using a suspended silicon photonics micro-ring resonator with a 90 nm-thick slab and morpholino as the capture probe. Complementary DNA of various concentrations were tested achieving a surface sensitivity of 2.12 nm/nM, a detection limit of 250 pM, and an intrinsic detection limit of 36.9 pM. A bulk sensitivity of 98 nm/RIU and an intrinsic detection limit of <inline-formula><tex-math notation="LaTeX">$1.03\times 10^{-3}$</tex-math></inline-formula> RIU was also measured upon exposure to isopropanol/deionized water solutions. With these characteristics, the suspended 90 nm slab ring sensor proved as a promising candidate for lab-on-a-chip bio-sensing applications.

Shailendra K. Chaubey, Gokul M. A, Diptabrata Paul et al.

Influencing spectral and directional features of exciton emission characteristics from 2D transition metal dichalcogenides by coupling it to plasmonic nanocavities has emerged as an important prospect in nanophotonics of 2D materials. Herein, the directional photoluminescence emission from a tungsten disulfide (WS2) monolayer sandwiched between a single‐crystalline plasmonic silver nanowire (AgNW) waveguide and a gold (Au) mirror is experimentally studied, thus forming a AgNW–WS2–Au cavity. Using polarization‐resolved Fourier‐plane optical microscopy, the directional emission characteristics from the distal end of the AgNW–WS2–Au cavity are quantified. Given that the geometry simultaneously facilitates local field enhancement and waveguiding capability, its utility in 2D material‐based, on‐chip nanophotonic signal processing is envisaged, including nonlinear and quantum optical regimes.