Hasil untuk "Optics. Light"

W. Knoll

Yuou Sun, Bailin Deng, Juyong Zhang

Precise simultaneous control of both angular and spatial light-field distributions remains a longstanding challenge in optical design, often requiring complex multi-element configurations. In this work, we propose a compact single-lens solution that achieves unified angular-spatial modulation through the co-optimization of double freeform surfaces. The problem is formulated as an extended caustic design that enforces prescribed irradiance patterns on two distinct receptive planes, where the dual-plane constraint implicitly defines the directional characteristics of the light field while preserving spatial accuracy. This framework eliminates the need for auxiliary optical components while delivering performance comparable to that of conventional multi-lens systems. Comprehensive numerical simulations verify the method's effectiveness, demonstrating accurate and stable control of both angular and spatial light-field properties. The proposed approach establishes a practical foundation for compact, high-performance optical systems and provides a promising route toward integrated angular-spatial light-field engineering.

Xuanjun Zhang, Wenjing Wang, Zhangjun Hu et al.

Zhujun Shi, A. Zhu, Zhaoyi Li et al.

Freeform metasurfaces couple the angle and polarization degrees of freedom, enabling new types of elliptical wave plates. Birefringence occurs when light with different polarizations sees different refractive indices during propagation. It plays an important role in optics and has enabled essential polarization elements such as wave plates. In bulk crystals, it is typically constrained to linear birefringence. In metamaterials with freeform meta-atoms, however, one can engineer the optical anisotropy such that light sees different indices for arbitrary—linear, circular, or elliptical—orthogonal eigen-polarization states. Using topology-optimized metasurfaces, we demonstrate this arbitrary birefringence. It has the unique feature that it can be continuously tuned from linear to elliptical birefringence, by changing the angle of incidence. In this way, a single metasurface can operate as many wave plates in parallel, implementing different polarization transformations. Angle-tunable arbitrary birefringence expands the scope of polarization optics, enables compact and versatile polarization operations that would otherwise require cascading multiple elements, and may find applications in polarization imaging, quantum optics, and other areas.

P. Stammer, J. Rivera-Dean, P. Tzallas et al.

Intense light-matter interaction largely relies on the use of high-power light sources, creating fields comparable to, or even stronger than, the field keeping the electrons bound in atoms. Under such conditions, the interaction induces highly nonlinear processes such as high harmonic generation, in which the low-frequency photons of a driving laser field are upconverted into higher-frequency photons. These processes have enabled numerous groundbreaking advances in atomic, molecular, and optical physics, and they form the foundation of attosecond science. Until recently, however, such processes were typically described using semi-classical approximations, since the quantum properties of the light field were not required to explain the observables. This has changed in the recent past. Ongoing theoretical and experimental advances show that fully quantized descriptions of intense light-matter interactions, which explicitly incorporate the quantum nature of the light field, open new avenues for both fundamental research and technological applications at the fully quantized level. These advances emerge from the convergence of quantum optics with strong-field physics and ultrafast science. Together, they have given rise to the field of quantum optics and quantum electrodynamics of strong-field processes.

Yujie Zhou, Jiazi Bu, Pengyang Ling et al.

Recent advancements in image relighting models, driven by large-scale datasets and pre-trained diffusion models, have enabled the imposition of consistent lighting. However, video relighting still lags, primarily due to the excessive training costs and the scarcity of diverse, high-quality video relighting datasets. A simple application of image relighting models on a frame-by-frame basis leads to several issues: lighting source inconsistency and relighted appearance inconsistency, resulting in flickers in the generated videos. In this work, we propose Light-A-Video, a training-free approach to achieve temporally smooth video relighting. Adapted from image relighting models, Light-A-Video introduces two key techniques to enhance lighting consistency. First, we design a Consistent Light Attention (CLA) module, which enhances cross-frame interactions within the self-attention layers of the image relight model to stabilize the generation of the background lighting source. Second, leveraging the physical principle of light transport independence, we apply linear blending between the source video's appearance and the relighted appearance, using a Progressive Light Fusion (PLF) strategy to ensure smooth temporal transitions in illumination. Experiments show that Light-A-Video improves the temporal consistency of relighted video while maintaining the relighted image quality, ensuring coherent lighting transitions across frames. Project page: https://bujiazi.github.io/light-a-video.github.io/.

Guojiong Li, Xiangyang Dai, Yuanhao Zhang et al.

A hybrid photonic integration scheme based on flip-chip bonding combined with vertical coupling is presented in this work, offering a novel solution for the integration of active and passive chips. An offset quantum-well laser is flipped and bonded into the pre-set cavity of the passive chip. The light emitted from the laser propagates through a taper into the passive chip. The proposed scheme utilizes only the existing processes, eliminating the need for additional process development. Furthermore, it preserves the performance of the laser while providing high tolerance. Simulations indicate that the coupling tolerance for 90% coupling efficiency is approximately ±1.5 μm in the lateral direction with the longitudinal tolerance exceeding 20 μm. The coupling efficiency remains stable across the O-band. This scheme is adaptable for integrating various photonic chips such as tunable lasers, high-speed modulators and detectors, and laser radar systems.

Arun Kumar, Nishant Gaur, Aziz Nanthaamornphong

One of the top candidates for an enhanced radio architecture is Optical Non-Orthogonal Multiple Access (O-NOMA), which is based on Multiple inputs and Multiple Outputs (MIMO). The identification of signals at the receiver terminal is more difficult due to the employment of a lot of antennas. For the identification of signals in the 8 × 8, 16 × 16, 64 × 64 and 256 × 256 O-NOMA frameworks, we provide a Maximum Likelihood (ML) and Successive Interference cancellation (SIC) method in this paper. Additionally, the suggested algorithms are compared with traditional ML, SIC, Zero Forcing (ZF), and Minimum Mean Square Error (MMSE) approaches, and rigorous estimations are made of metrics like Bit Error Rate (BER) and Power Spectral Density (PSD). The outcomes of the simulation show that the suggested SIC and ML outperform the traditional methods. It should be added that the 64 × 64 O-NOMA effectively increased the structure’s throughput and spectral efficiency.

Eliazar Elisha Audu, Akaa Agbaeze Eteng

Optical fiber is a cylindrical dielectric medium that transmits electromagnetic waves at optical frequency range, guiding them through the fiber core via constructive phase-shifted total internal reflection. Wave propagation in optical fibers can be modeled and described using Maxwell’s equations. This paper employs the parametric Nikiforov-Uvarov (NU) method, commonly used in quantum mechanics, to solve the Helmholtz equation derived by combining Maxwell’s equations. The NU method is less computationally cumbersome than traditional techniques such as Bessel functions or finite element methods. We derive the equation that describes the characteristics of the propagating electromagnetic wave with refractive index as an unnormalized radial wave function. We show that NU energy equation can be used to obtain the exact phase propagation constant condition for wave propagation in optical fibre. Additionally, we investigate the effects of wavelength, core radius, refractive index, and azimuthal index on wave propagation. Our results show that the phase propagation constant decreases as the wavelength increases. The radial function is found to be proportional to the degree of the Laguerre polynomial and the azimuthal index. We also report the effects of the azimuthal index, core radius, and refractive index on the radial function.

Long Jin, Yanhua Fu

In order to explore the transmission characteristics of linearly polarized chirped airy Gaussian beam array (LPCAGBA) in isotropic free space, we theoretically and numerically demonstrated the side view and intensity distribution of this beam array at several cross sections in paraxial and nonparaxial situations, respectively, based on the derived analytical electric expressions of x-, y-, and longitudinal components; the linearly polarized airy beam array (LPABA) and linearly polarized airy Gaussian beam array (LPAGBA) are deemed as two special cases in our model. These figures clearly show that both the chirp C and the refractive index n of the environments significantly impact the self-bending degree of LPCAGBA. However, the effects of these two factors on the trend of LPCAGBA are opposite. Additionally, the intensity appearances of the beam array on two axes are unaffected by the polarizing angle φ, but the LPCAGBA energy value in both x- and y-directions do vary with changes in φ. In the nonparaxial situation, the longitudinal component of LPCAGBA emerges even though the intensity of this direction in the initial plane is zero, but its magnitude is far less than that of the x- and y-components. Notably, unlike the paraxial components, the intensity pattern of the longitudinal component rotates counterclockwise around the origin as φ increases.

Yuxian Zhang, Guanyun Ding, Guanyu Liu

We numerically and experimentally demonstrate a phase-biased fiber oscillator with all-polarization-maintaining (all-PM) fibers. Through theoretical analysis, it is demonstrated that incorporating a non-reciprocal phase shifter improves the self-starting capability of the designed fiber laser. Moreover, the phase shifter in the all-PM laser configuration helps boost the repetition rate and further enhances the environmental stability. Numerical simulations are conducted for the proposed fiber laser operating in the normal-dispersion regime to investigate the spectral and temporal characteristics and the build-up dynamics. Experimentally, by manipulating the separation of the intra-cavity grating pair for dispersion compensation, this simple and novel Ytterbium-doped fiber laser delivers ultrashort pulses featuring a pulse duration of 1.81 ps, operating at a repetition rate of 44.4 MHz in the 1030 nm band. The delivered pulses are compressed externally using a grating pair, achieving a minimum pulse duration of 174 fs. We believe the proposed fiber oscillator provides a robust pulsed light source for numerous optical applications such as micromachining or optical frequency comb generation.

Zhijin Shang, Hongpeng Wu, Gang Wang et al.

Malte Plidschun, H. Ren, Jisoo Kim et al.

Strong focusing on diffraction-limited spots is essential for many photonic applications and is particularly relevant for optical trapping; however, all currently used approaches fail to simultaneously provide flexible transportation of light, straightforward implementation, compatibility with waveguide circuitry, and strong focusing. Here, we demonstrate the design and 3D nanoprinting of an ultrahigh numerical aperture meta-fibre for highly flexible optical trapping. Taking into account the peculiarities of the fibre environment, we implemented an ultrathin meta-lens on the facet of a modified single-mode optical fibre via direct laser writing, leading to a diffraction-limited focal spot with a record-high numerical aperture of up to NA ≈ 0.9. The unique capabilities of this flexible, cost-effective, bio- and fibre-circuitry-compatible meta-fibre device were demonstrated by optically trapping microbeads and bacteria for the first time with only one single-mode fibre in combination with diffractive optics. Our study highlights the relevance of the unexplored but exciting field of meta-fibre optics to a multitude of fields, such as bioanalytics, quantum technology and life sciences.

Ángel Solé Morillo, Joan Lambert Cause, Kevin De Pauw et al.

Photoplethysmography is a widely used optical technique to extract physiological information non-invasively. Despite its large use and adoption, multiple factors influence the signal shape and quality, including the instrumentation used. This work analyzes the variability of the DC component of the PPG signal at three source–detector distances (6 mm, 9 mm, and 12 mm) using green, red, and infrared light and four photodiodes per distance. The coefficient of variation (CV) is proposed as a new signal quality index (SQI) to evaluate signal variabilities. This study first characterizes the PPG system, which is then used to acquire PPG signals in the chest of 14 healthy participants. Results show a great DC variability at 6 mm, homogenizing at 9 and 12 mm. This suggests that PPG systems are also sensitive to the near- and far-field effects commonly reported and studied in optics, which can impact the accuracy of physiological parameters dependent on the DC component, such as oxygen saturation (SpO₂).

Sirazul Haque, Miguel Alexandre, António T. Vicente et al.

Hui Gao, Xuhao Fan, Yuxi Wang et al.

Multispectral and polarized focusing and imaging are key functions that are vitally important for a broad range of optical applications. Conventional techniques generally require multiple shots to unveil desired optical information and are implemented via bulky multi-pass systems or mechanically moving parts that are difficult to integrate into compact and integrated optical systems. Here, a design of ultra-compact transversely dispersive metalens capable of both spectrum and polarization ellipticity recognition and reconstruction in just a single shot is demonstrated with both coherent and incoherent light. Our design is well suited for integrated and high-speed optical information analysis and can significantly reduce the size and weight of conventional devices while simplifying the process of collecting optical information, thereby promising for various applications, including machine vision, minimized spectrometers, material characterization, remote sensing, and other areas which require comprehensive optical analysis.

Michael Rezac, Daniel Martinez, Amy Gleckl et al.

Annealing of amorphous optical coatings has been shown to generally reduce optical absorption, optical scattering, and mechanical loss, with higher temperature annealing giving better results. The achievable maximum temperatures are limited to the levels at which coating damage, such as crystallization, cracking, or bubbling will occur. Coating damage caused by heating is typically only observed statically, after annealing. An experimental method to dynamically observe how and over what temperature range such damage occurs during annealing is desirable as its results could inform manufacturing and annealing processes to ultimately achieve better coating performance. We developed a new instrument that features an industrial annealing oven with holes cut into its sides for viewports to illuminate optical samples and observe their coating scatter and eventual damage mechanisms in-situ and in real-time during annealing. We present results that demonstrate in-situ observation of changes to titania-doped tantala coatings on fused silica substrates. We obtain a spatial image (mapping) of the evolution of these changes during annealing, an advantage over x-ray diffraction, electron beam, or Raman methods. We infer, based on other experiments in the literature, these changes to be due to crystallization. We further discuss the utility of this apparatus for observing other forms of coating damage such as cracking and blisters.

Md Asif Hossain Bhuiyan, Shamima Akter Mitu, Sajid Muhaimin Choudhury

In this study, we present an all-optical reflection modulator for 2$μ$m communication band exploiting a nano-gear-array metasurface and a phase-change-material Ge$_2$Sb$_2$Te$_5$ (GST). The reflectance of the structure can be manipulated by altering the phase of GST by employing optical stimuli. The paper shows details on the optical and opto-thermal modeling techniques of GST. Numerical investigation reveals that the metastructure exhibits a conspicuous changeover from $\sim$ 99% absorption to very poor interaction with the operating light depending on the switching states of the GST, ending up with 85\% modulation depth and only 0.58 dB insertion loss. Due to noticeable differences in optical responses, we can demonstrate a high extinction ratio of 28 dB and a commendable FOM of 49, so far the best modulation performance in this wavelength window. In addition, real-time tracking of the reflectance during phase transition manifests high-speed switching expending low energy per cycle, on the order of sub-nJ. Hence, given its overall performance, the device will be a paradigm for the optical modulators for upcoming 2 $μ$m communication technology.

Xiaofeng Qian, Misagh Izadi

While optics and mechanics are two distinct branches of physics, they are connected. It is well known that geometrical/ray treatment of light has direct analogies to mechanical descriptions of particle motion. However, connections between coherence wave optics and classical mechanics are rarely reported. Here we explore links of the two for an arbitrary light field by performing a quantitative analysis of two optical coherence properties: polarization and entanglement (implied by a wave picture of light due to Huygens and Fresnel). A universal complementary identity relation is obtained. More surprisingly, optical polarization, entanglement, and their identity relation are shown to be quantitatively associated with mechanical concepts of center of mass and moment of inertia through the Huygens-Steiner theorem for rigid body rotation. The obtained result bridges coherence wave optics and classical mechanics through the two theories of Huygens.

Shiying Wu, Ying Liu, Yingna Chen et al.

Pathology is currently the gold standard for grading prostate cancer (PCa). However, pathology takes considerable time to provide a final result and is significantly dependent on subjective judgment. In this study, wavelet transform-based photoacoustic power spectrum analysis (WT-PASA) was used for grading PCa with different Gleason scores (GSs). The tumor region was accurately identified via wavelet transform time-frequency analysis. Then, a linear fitting was conducted on the photoacoustic power spectrum curve of the tumor region to obtain the quantified spectral parameter slope. The results showed that high GSs have small glandular cavity structures and higher heterogeneity, and consequently, the slopes at both 1210 nm and 1310 nm were high (p < 0.01). The classification accuracy of the PA time frequency spectrum (PA-TFS) of tumor region using ResNet-18 was 89% at 1210 nm and 92.7% at 1310 nm. Further, the testing time was less than 7 mins. The results demonstrated that identification of PCa can be rapidly and objectively realized using WT-PASA.