Hasil untuk "Optics. Light"

Liang Tang, S. Kocabas, S. Latif et al.

P. Genevet, N. Yu, F. Aieta et al.

P. Tien, R. Ulrich

M. Sakakura, Y. Lei, L. Wang et al.

Polarization and geometric phase shaping via a space-variant anisotropy has attracted considerable interest for fabrication of flat optical elements and generation of vector beams with applications in various areas of science and technology. Among the methods for anisotropy patterning, imprinting of self-assembled nanograting structures in silica glass by femtosecond laser writing is promising for the fabrication of space-variant birefringent optics with high thermal and chemical durability and high optical damage threshold. However, a drawback is the optical loss due to the light scattering by nanograting structures, which has limited the application. Here, we report a new type of ultrafast laser-induced modification in silica glass, which consists of randomly distributed nanopores elongated in the direction perpendicular to the polarization, providing controllable birefringent structures with transmittance as high as 99% in the visible and near-infrared ranges and >90% in the UV range down to 330 nm. The observed anisotropic nanoporous silica structures are fundamentally different from the femtosecond laser-induced nanogratings and conventional nanoporous silica. A mechanism of nanocavitation via interstitial oxygen generation mediated by multiphoton and avanlanche defect ionization is proposed. We demonstrate ultralow-loss geometrical phase optical elements, including geometrical phase prism and lens, and a vector beam convertor in silica glass. The optical property of birefringence can be manipulated in silica glass using an ultrafast laser writing procedure, creating materials in which the phase and polarization of light can be controlled with significantly lower scattering losses than alternative techniques. Birefringence is the effect observed when the refractive index of a material varies depending on the polarization and direction of incident light. M. Sakakura, Y. Lei, L. Wang, Y.-H. Yu, and P. Kazansky at the University of Southampton, UK, used laser light with pulses in the femtosecond range to create elongated nanopores inside silica glass. When the nanopores are aligned perpendicular to incident polarized light they allow subtle control of the light’s properties with transmission as high as 99%. The ability of the materials to “shape” visible, near-infrared and ultra-violet light is expected to be beneficial in a variety of specialist optical applications.

Yang Chen, W. Du, Qing Zhang et al.

F. Mahmood, Ching-Kit Chan, Z. Alpichshev et al.

Time- and angle-resolved photoelectron spectroscopy experiments are used to monitor the transition between Floquet–Bloch and Volkov states in the topological insulator Bi2Se3. The coherent optical manipulation of solids is emerging as a promising way to engineer novel quantum states of matter1,2,3,4,5. The strong time-periodic potential of intense laser light can be used to generate hybrid photon–electron states. Interaction of light with Bloch states leads to Floquet–Bloch states, which are essential in realizing new photo-induced quantum phases6,7,8. Similarly, dressing of free-electron states near the surface of a solid generates Volkov states, which are used to study nonlinear optics in atoms and semiconductors9. The interaction of these two dynamic states with each other remains an open experimental problem. Here we use time- and angle-resolved photoemission spectroscopy (Tr-ARPES) to selectively study the transition between these two states on the surface of the topological insulator Bi2Se3. We find that the coupling between the two strongly depends on the electron momentum, providing a route to enhance or inhibit it. Moreover, by controlling the light polarization we can negate Volkov states to generate pure Floquet–Bloch states. This work establishes a systematic path for the coherent manipulation of solids via light–matter interaction.

Ryusuke Hisatomi, Alto Osada, Kotaro Taga et al.

Light possesses both spin and orbital angular momentum, which can spontaneously couple in spatially asymmetric optical fields. This phenomenon is referred to as optical spin-orbit coupling. This coupling is pivotal in modern optics due to its broad applications in communications, sensing, and quantum control. A central challenge is to elucidate how spatial asymmetries in optical fields facilitate this coupling. Previous research has primarily addressed spatial asymmetry using materials and devices such as lenses, interfaces, inhomogeneous media, and metasurfaces. However, Maxwell's equations indicate that matter can also introduce temporal asymmetry to optical fields. For instance, magnetic ordering can break time-reversal symmetry via the magneto-optical effect, resulting in nonreciprocal optical phenomena. Despite its importance, the combined effects of spatial and temporal asymmetries in optical fields remain unexplored. This study demonstrates that breaking time-reversal symmetry via magnons and spatial symmetry via light focusing enables the nonreciprocal transformation of a Gaussian beam into an optical vortex beam. This effect is attributed to the interplay between magnon-induced Brillouin light scattering and optical spin-orbit coupling. The results indicate that total angular momentum, including contributions from both magnons and photons, is conserved, suggesting that magnons can control both the spin and orbital angular momentum of light.

R. Khan, B. Gul, Shamim Khan et al.

Refractive index (RI) is a characteristic optical variable that controls the propagation of light in the medium (e.g., biological tissues). Basic research with the aim to investigate the RI of biological tissues is of paramount importance for biomedical optics and associated applications. Herein, we reviewed and summarized the RI data of biological tissues and the associated insights. Different techniques for the measurement of RI of biological tissues are also discussed. Moreover, several examples of the RI applications from basic research, clinics and optics industry are outlined. This study may provide a comprehensive reference for RI data of biological tissues for the biomedical research and beyond.

Daniel D. Hickstein, David R. Carlson, Zachary L. Newman et al.

All modern theories of gravitation, starting with Newton's, predict that gravity will affect the speed of light propagation. Einstein's theory of General Relativity famously predicted that the effect is twice the Newtonian value, a prediction that was verified during the 1919 solar eclipse. Recent theories of vector gravity can be interpreted to imply that gravity will have a different effect on pulsed light versus continuous-wave (CW) light propagating between the two mirrors of an optical cavity. Interestingly, we are not aware of any previous experiments to determine the relative effect of gravity on the propagation of pulsed versus CW light. In order to observe if there are small differences, we use a 6 GHz electro-optic frequency comb and low-noise CW laser to make careful measurements of the resonance frequencies of a high-finesse optical cavity. Once correcting for the effects of mirror dispersion, we determine that the cavity resonance frequencies for pulsed and CW light are the same to within our experimental error, which is on the order of $10^{-12}$ of the optical frequency, and one part in 700 of the expected gravitational shift.

Haishan Liu, Fei Wang, Ying Jin et al.

Abstract Imaging through dynamic scattering media is one of the most challenging yet fascinating problems in optics, with applications spanning from biological detection to remote sensing. In this study, we propose a comprehensive learning-based technique that facilitates real-time, non-invasive, incoherent imaging of real-world objects through dense and dynamic scattering media. We conduct extensive experiments, demonstrating the capability of our technique to see through turbid water and natural fog. The experimental results indicate that the proposed technique surpasses existing approaches in numerous aspects and holds significant potential for imaging applications across a broad spectrum of disciplines.

Laaya Sabri, Ranim El Ahdab, Frederic Nabki et al.

We present an interleaver using a Ring-Assisted Mach-Zehnder Interferometer (MZI) where the ring is coupled to one arm of the MZI through a linearly tapered multimode interferometer (MMI), harnessing the advantages of both the MMI coupler and ring assisted MZI to optimize performance. The tapered MMI coupler extends the operational bandwidth of the interleaver over more than 85 nm due to its wavelength-insensitive response and precisely tailored coupling ratio. Furthermore, it removes the need for thermal tuning of the coupling region, which reduces the power consumption and overall size of the device. The experimental performance of a silicon nitride based interleaver with a channel spacing of 0.8 nm in L-band is reported. The device shows a crosstalk level below 15 dB over a wavelength range of 85 nm.

Xiaoxi Xu, Feiyan Zhao, Jiayao Huang et al.

A new scheme for producing semidiscrete self-trapped vortices (\textquotedblleft swirling photon droplets\textquotedblright ) in photonic crystals with competing quadratic ($χ^{(2)}$) and self-defocusing cubic ($χ^{(3)}$) nonlinearities is proposed. The photonic crystal is designed with a striped structure, in the form of spatially periodic modulation of the $χ^{(2)}$ susceptibility, which is imposed by the quasi-phase-matching technique. Unlike previous realizations of semidiscrete optical modes in composite media, built as combinations of continuous and arrayed discrete waveguides, the semidiscrete vortex droplets are produced here in the fully continuous medium. This work reveals that the system supports two types of semidiscrete vortex droplets, \textit{viz}., onsite- and intersite-centered ones, which feature, respectively, odd and even numbers of stripes, $\mathcal{N}$. Stability areas for the states with different values of $\mathcal{N}$ are identified in the system's parameter space. Some stability areas overlap with each others, giving rise to multistability of states with different $\mathcal{N}$. The coexisting states are mutually degenerate, featuring equal values of the Hamiltonian and propagation constant. An experimental scheme to realize the droplets is outlined, suggesting new possibilities for the long-distance transmission of structured light carrying orbital angular momentum in nonlinear media.

Chenxia Liu, Tianwei Jiang, Hanyue Wang et al.

This paper proposes a stable radio frequency (RF) transfer scheme based on phase modulation. The passive compensation method is used to compensate the phase variations. The use of only one mixer reduces the power consumption during the frequency mixing process. By utilizing a phase modulator, the issue of bias drifting, encountered in RF transmission systems with intensity modulation method, is eliminated. A single-mode fiber (SMF) serves as a dispersive medium for phase modulation-to-intensity modulation (PM-to-IM) conversion. Our passive compensation system with phase modulation has the characteristics of robustness and low insertion loss at the modulation module. The RF signal with frequency of 2.4 GHz is transferred via a 125 km fiber optic link. The measured standard Allan deviation (ADEV) of our transmission system is 3.66 &#x00D7; <inline-formula><tex-math notation="LaTeX">$10^{-13}$</tex-math></inline-formula> at 1 s and 2.26 &#x00D7; <inline-formula><tex-math notation="LaTeX">$10^{-16}$</tex-math></inline-formula> at 10000 s, which is better than that of the reference atomic clock. The proposed system will be useful for further applications such as in square kilometer arrays and remote clock comparison.

Walker Peterson, Kotaro Hiramatsu, Keisuke Goda

Abstract Coherent Raman scattering microscopy can provide high-contrast tissue and single-cell images based on the inherent molecular vibrations of the sample. However, conventional techniques face a three-way trade-off between Raman spectral bandwidth, imaging speed, and image fidelity. Although currently challenging to address via optical design, this trade-off can be overcome via emerging computational tools such as compressive sensing and machine learning.

Hwi-Sung Park, Jeongju Jee, Hyuncheol Park

The unmanned aerial vehicle (UAV)-aided free-space optical/radio frequency (FSO/RF) technique has recently attracted significant attention, which offers new possibilities thanks to its dynamic deployment capability. However, many researchers have not considered the fading characteristic of both RF and FSO links and the limited UAVs&#x0027; size, weight, and power (SWAP) simultaneously. This paper focuses on a mixed FSO/RF system that facilitates the communication between a base station and mobile stations via a hovering UAV acting as a decode-and-forward relay. Considering the fading effects and the power amplifier (PA) non-linearity caused by the SWAP constraint, we mathematically analyze the closed-form and asymptotic outage probabilities. Especially in high transmit power regions, we present the destructive impact of nonlinear PAs on the outage probability and investigate modulation schemes to mitigate this degradation. The derived outage expressions match well with numerical results. Moreover, we propose a joint placement and transmit power optimization algorithm that minimizes the end-to-end outage probability with round-robin and absolute signal-to-noise ratio-based scheduling schemes. Finally, simulation results show that the performance of the proposed algorithm is comparable to that of the brute-force method.

Urban Mur, Miha Ravnik

Vector and vortex laser beams are desired in many applications and are usually created by manipulating the laser output or by inserting optical components in the laser cavity. Distinctly, inserting liquid crystals into the laser cavity allows for extensive control over the emitted light due to their high susceptibility to external fields and birefringent nature. In this work we demonstrate diverse optical modes for lasing as enabled and stablised by topological birefringent soft matter structures using numerical modelling. We show diverse structuring of light -- with different 3D intensity and polarization profiles -- as realised by topological soft matter structures in radial nematic droplet, in 2D nematic cavities of different geometry and including topological defects with different charges and winding numbers, in arbitrary varying birefringence fields with topological defects and in pixelated birefringent profiles. We use custom written FDFD code to calculate emergent electromagnetic eigenmodes. Control over lasing is of a particular interest aiming towards the creation of general intensity, polarization and topologically shaped laser beams.

Minsu Park, Yeonsang Park

Using meta-imagers, all-optical convolutional processing that arbitrarily reshapes the point spread function of an optical system can now be implemented.

E.Yu. Shchetinin

Early detection of patients with COVID-19 coronavirus infection is essential in ensuring an adequate treatment and reducing the burden on the health care system. An effective method of detecting COVID-19 is computer analysis of chest X-rays. The paper proposes a methodology that consists of stages of formatting X-ray images to the size (224, 224) size, their classification using deep convolutional neural networks, such as Xception, InceptionResnetV2, MobileNetV2, DenseNet121, ResNet50 and VGG16, which are pre-trained on the ImageNet dataset and then fine-tuned on a set of chest X-rays. The results of computer experiments showed that the VGG16 model with fine-tuning of parameters demonstrated the best performance in the COVID-19 classification with accuracy = 99.09 %, recall = 99.483 %, precision = 99.08 % and f1_score = 99.281 %.

Shangzhi Li, Juncheng Lu, Zhijin Shang et al.

A compact quartz-enhanced photoacoustic sensor for ppb-level ambient NO2 detection is demonstrated, in which a high-power blue laser diode module with a small divergence angle was employed to take advantages of the directly proportional relationship between sensitivity and power, hence improving the detection sensitivity. In order to extend the stability time, a custom grooved quartz tuning fork with 800-μm prong spacing is employed to avoid complex signal balance and/or optical spatial filter components. The sensor performance is optimized and assessed in terms of optical coupling, power, gas flow rate, pressure, signal linearity and stability. A minimum detectable concentration (1σ) of 7.3 ppb with an averaging time of 1 s is achieved, which can be further improved to be 0.31 ppb with an averaging time of 590 s. Continuous measurements covering a five-day period are performed to demonstrate the stability and robustness of the reported NO2 sensor system.

E. Collett