Vector Modes Research Articles

Polymer negative curvature ring-core fiber for OAM modes guidance.

In this paper, a novel, to the best of our knowledge, polymer-based negative curvature ring-core fiber (NC-RCF) is proposed and investigated. The hollow-core NC-RCF is composed of TOPAS as background material. The inner and outer negative curvature structure layers are connected to the annular area, and the orbital angular momentum (OAM) modes can propagate in the annular core. In the frequency region of 1.0-1.5THz, the designed NC-RCF can stably transmit 82 OAM modes. Investigation results indicate that the effective refractive index differences between the corresponding HE and EH modes are above 10-4. The confinement losses of EH or HE modes are smaller than 10-8 d B/m, and the dispersion variations are lower than 0.31ps/THz/cm. Effective mode areas are larger than 5.14m m 2. Additionally, the highest mode purity of all vector modes is 99.78%. In addition, modal birefringence, also known as the walk-off length, has also been discussed. All these operation performances indicate that the designed NC-RCF make contributions to the optical communication systems.

Extending the degree of polarization concept to higher-order and orbital angular momentum Poincaré spheres

In this work, the density matrix formalism that describes any standard polarization state (fully or partially polarized) is applied to describe vector beams and spatial modes with orbital angular momentum (OAM). Within this framework, we provide a comprehensive description of the mapping between the corresponding Poincaré spheres (PSs); namely: the polarization PS, the higher-order PS (HOPS) and the orbital angular momentum PS (OAMPS). Whereas previous works focus on states located on the surface of these spheres, here we study vector and scalar modes lying inside the corresponding PS. We show that they can be obtained as the incoherent superposition of two orthogonal vector (or scalar) modes lying on the corresponding sphere surface. The degree of polarization (DoP) of a classical polarization state is thus extended to vector beams and OAM modes. Experimental results validate the theoretical physical interpretation, where we used a q-plate to map any state in the polarization PS onto the HOPS, and a linear polarizer to finally project onto the OAMPS. Three input states to such q-plate-polarizer system are considered: totally unpolarized, partially polarized, and fully polarized light. For that purpose, we design a new polarization state generator, based on two geometric phase gratings and a randomly polarized laser, which generates partially polarized light in an efficient and controlled way. We believe that the extension of the DoP concept to vector and OAM beams introduces a degree of freedom to describe spatially polarization and phase variant light beams.

Experimental generation of arbitrary abruptly autofusing Circular Airy Gaussian vortex vector beams

Complex vector modes represent a general state of light nonseparable in their spatial and polarization degrees of freedom, which have inspired a wide variety of novel applications and phenomena, such as their unexpected propagation behaviour. For example, they can propagate describing periodic polarization transitions, changing from one vector beam to another. Here, we put forward a novel class of vector modes with the capability to experience an abruptly autofocusing behaviour. To achieve such beams, we encode the spatial degree of freedom in the Circular Airy Gaussian vortex (CAGV) beams. We demonstrate the experimental generation of arbitrary CAGV vector beams and evince some of their properties, such as a rotation of intermodal phase. We anticipate that the fascinating properties of theses modes will prompt the development of novel applications associated to their autofocusing behaviour and polarization distribution.

Broadband vector mode converters based on cascaded long-period fiber gratings written in slightly elliptical ring-core fiber

A broadband vector mode converter is proposed based on cascaded long-period fiber gratings(LPFGs) written in slightly elliptical ring-core fiber. In order to realize the phase shift between the cascaded LPFGs, an unirradiated optical fiber is introduced. The mode converter can directly convert fundamental mode into first-order vector modes (TE01, HE21even, HE21odd and TM01 modes) with high efficiency without using assistive devices. The effect of cascaded grating period and the unirradiated optical fiber length on the performance of the mode converter is investigated. Through optimizing the structure parameters, the designed broadband vector mode converters provide a 20-dB bandwidth of 104 nm, 97.5 nm, 101 nm and 97 nm for respectively generating TE01, HE21even, HE21odd and TM01 modes covering C+L band, which could be applied in broadband mode division multiplexing (MDM) transmission systems based on vector modes.

The cosmological vector modes from a monochromatic primordial power spectrum

The cosmological background of higher order vector modes can be generated by the first order scalar perturbations. We investigate the second order and the third order vector modes in a radiation-dominated era systematically. The explicit expressions of two point functions 〈V (n),λ V (n),λ' 〉(n = 2,3) and corresponding power spectra are presented. In the case of a monochromatic primordial power spectrum, the second order vector modes do not exist. However, the third order vector modes can be generated by a monochromatic primordial power spectrum. And it is found that the third order vector modes sourced by the second order scalar perturbations dominate the two point function 〈V (3),λ V (3),λ' 〉 and corresponding power spectra.

GeO2-doped ring-core photonic crystal fiber for supporting robust orbital angular momentum modes.

Orbital angular momentum (OAM)-mode-supported photonic crystal fibers (PCFs) have inspired intensive research in modern fiber optics due to the robust propagation and theoretically unlimited signal-carried channels. In this paper, a dual-cladding GeO2-doped ring-core PCF is designed, and a strategy for optimizing OAM mode properties is analyzed by structure parameters and GeO2-doping concentration. Numeric results show that high structural degrees of freedom are available to improve the effective refractive index separation (within the vector modes), chromatic dispersion, effective mode field area, nonlinear coefficient, and OAM mode purity in terms of inner cladding, outer cladding, and ring-core. In particular, the effective refractive index separation and chromatic dispersion can exhibit a high order magnitude of 10-3 and a low value in the broad band from 1.3 µm to 1.7 µm, respectively. In addition to structural optimization, doping high index material into the ring-core is another way to regulate the fiber performance by controlling the doping concentration. A systematic investigation shows that as the doping concentration increases, the effective refractive index separation and mode purity increase obviously, while the dispersion and mode field area gradually decrease. This flexible manipulation offers a method for customizing the optical properties of OAM-supported PCFs in communication and sensor systems.

Numerical analysis of a photonic crystal fiber with elliptical air hole for supporting 80 orbital angular momentum modes

• We design photonic crystal fiber with elliptical air holes, which has good orbital angular momentum transmission performance. • The influence of elliptic air hole eccentricity on photonic crystal fiber transmission performance is analyzed. • This paper provides some ideas for new photonic crystal fiber design and air hole shape error analysis. In this paper, a new photonic crystal fiber with elliptical air hole (EAH-PCF) is designed, which can support stable transmission of 80 orbital angular momentum (OAM) modes at 1550 nm. The effective refractive index differences between vector modes are all above 0.002. Most of the modes have a confinement loss between 10 −10 dB/m and 10 −8 dB/m. The effective mode area of the vector modes are all greater than 70 μm 2 and the nonlinear coefficients are all less than 1.8 W −1 /km. These properties guarantee high quality OAM. Finally, we discuss the effect of EAH’s eccentricity on the PCF. Simulations show that increasing the EAH’s eccentricity will increase the degree of separation between the vector modes, but causes a slight decrease in the quality of OAM.

On the Reconstruction of the Scalar Mode of GW170817 in Scalar‐Tensor Gravity Theory

AbstractIn general metric theory of gravity, a gravitational wave is allowed to have up to six polarizations: two scalar and two vector modes in addition to tensor modes. In case the number of laser‐interferometric gravitational wave telescopes is larger than the number of polarizations of a gravitational wave, all the polarizations can be individually reconstructed. Since it depends on theories of gravity which polarizations the gravitational waves have, the investigation of polarizations is important for the test of theories of gravity. In order to test the scalar–tensor gravity theory, one of important alternative theories of gravity, the scalar mode of GW170817 observed by LIGO Livingstone, Hanford and Virgo is reconstructed without prior information about any tensor–scalar gravity theories. The upper limit of the scalar mode in term of the band‐limited root‐sum‐square of the amplitude is with the time window of 2 [s] and frequency window of ≈60–120 [Hz]. It is also studied how much the tensor modes are leaked into the reconstructed scalar mode, and it is found that the reconstructed scalar mode contains roughly 30% of energy leaked from the tensor modes.

Few-mode fiber design for multiple-input-multiple-output-less mode division multiplexing by machine learning

Neural networks (NNs), random forests (RF), and extreme gradient boosting (XGBoost) are applied separately to inversely design the ring-core few-mode fiber (FMF) with a desired weakly coupled performance. We demonstrate the procedure of inverse designing of FMF via machine learning (ML) algorithms and evaluate the prediction accuracy of the above ML algorithms. Compared with RF and XGBoost, the NN performs the highest prediction accuracy. For the NN, RF, and XGBoost, the correlation coefficients of the mode effective index difference are 0.99993, 0.99857, and 0.99937, respectively. Subsequently, by utilizing the method of permuting feature importance ranking, we obtain the high-correlation fiber structural features with the mode effective index difference. Moreover, we analyze the effect of the minimum index difference between two adjacent modes ( Δ n e f f , m i n ) on the structural parameters and get consistent feature attribution via permuting feature importance ranking above. Finally, we design a weakly coupled ring-core fiber that supports four modes ( H E 11 , T E 01 , H E 21 , T M 01 ) based on the NN algorithm, which could be successfully applied in vector mode division multiplexing.

Mode-locked laser with flat-top beam output based on all polarization-maintaining fiber structure

By reason of the special intensity profile, the flat-top beam is applied in numerous fields. Utilizing fiber laser to generate the flat-top beam with excellent beam quality is gradually becoming a hot research topic in recent years. In this work, we propose a novel fiber laser that emits mode-locked pulse flat-top beam by the incoherent superposition of cylindrical vector modes (TM01) and fundamental modes (LP01). The beam obtained in our laser has a normalized root mean square (NRMS) of 0.127 and a steep degree Ω of 0.87 meaning the favorable effect of the experiment result. As far as we know, this laser is the first mode-locked pulse flat-top beam laser based on all polarization-maintaining fiber structure.

Highly-stable generation of vector beams through a common-path interferometer and a DMD

Complex vector modes of light, non-separable in their spatial and polarisation degrees of freedom, are revolutionising a wide variety of research fields. It is therefore not surprising that the generation techniques have evolved quite dramatically since their inception. At present it is common to use computer-controlled devices, among which digital micromirror devices have become popular. Some of the reason for this are their low-cost, their polarisation-insensitive and their high-refresh rates. As such, in this manuscript we put forward a novel technique characterised by its high stability, which is achieved through a common-path interferometer. We demonstrate the capabilities of this technique experimentally, first by generating arbitrary vector modes on a higher-order Poincaré sphere, secondly, by generating vector modes in different coordinates systems and finally, by generating various vector modes simultaneously. Our technique will find applications in fields such as optical manipulations, optical communications, optical metrology, among others.

Angular Displacement Control for Timoshenko Beam by Optimized Traveling Wave Method

The vibration of flexible structures in spacecraft, such as large space deployable reflectors, solar panels and large antenna structure, has a great impact on the normal operation of spacecraft. Accurate vibration control is necessary, and the control of angular displacement is a difficulty of accurate control. In the traditional control method, the mode space control has a good effect on suppressing low-order modes, but there is control overflow. The effect of traveling wave control on low-order modes is worse than the former, but it has the characteristics of broadband control. It can better control high-order modes and reduce control overflow. In view of the advantages and disadvantages of the two control methods, based on Timoshenko beam theory, this paper uses vector mode function to analyze the modal of spacecraft cantilever beam structure, establishes the system dynamic equation, and puts forward an optimized traveling wave control method. As a numerical example, three strategies of independent mode space control, traditional traveling wave control and optimized traveling wave control are used to control the active vibration of beam angle. By comparing the numerical results of the three methods, it can be seen that the optimal control method proposed in this paper not only effectively suppresses the vibration, but also improves the robustness of the system, reflecting good control performance. An innovation of this paper is that the Timoshenko beam model is adopted, which considers the influence of transverse shear deformation and moment of inertia on displacement and improves the accuracy of calculation, which is important for spacecraft accessory structures with high requirements for angle control. Another innovation is that the optimized traveling wave control method is exquisite in mathematical processing and has good results in global and local vibration control, which is not available in other methods.

Series expansion of the overlap reduction function for scalar and vector polarizations for gravitational wave search with pulsar timing arrays

In our previous work [Phys. Rev. D 103, 064044 (2021)] we calculated the overlap reduction function for the tensor polarization without employing the short wavelength approximation, this was done by obtaining a power series of nested sums which is valid for all gravitational wave frequencies and pulsar distances. In this work we generalize the power-series expansion method to vector and scalar polarizations. We have compared our expression for the breathing and vector modes with previous literature. We present for the first time analytic expressions for the overlap reduction function of the longitudinal mode for all angles between the pulsar pairs.

Study on vector mode conversion based on tilted asymmetric fiber Bragg grating in vortex fiber

A vector mode conversion approach based on tilted asymmetric fiber Bragg grating (TAFBG) written in vortex fiber is investigated. The mode coupling properties of TAFBG are numerically analyzed. In contrast to step index fiber, the large mode separation in vortex fiber is advantageous to extracting the desired vector mode at specific wavelength. Under the constraint of phase matching, the vector modes could be achieved at separated wavelengths for TAFBG in vortex fiber. The high order vector mode conversion could be realized effectively in two methods by adjusting tilt angle and attenuation coefficient of index change distribution. In addition, the coupling coefficients have an important guiding significance to vector mode conversion. The TAFBG has the advantages of simple structure, multiple flexible operation for vector mode conversion, and it has great potential for optical fiber communication system and fiber lasers with vortex beams output.

Design of ultra-flattened dispersion weakly coupled few-mode photonic crystal fiber with low confinement loss

We present a unique design of weakly coupled few-mode photonic crystal fiber (FM-PCF), which can support six vector modes (HE11a,HE11b,TM01,HE21a,HE21b, and TE01) with ultra-flattened chromatic dispersion over the C wavelength band. We investigate the impact of fiber parameters on chromatic dispersion, minimum effective refractive index difference (minΔneff), confinement loss, bending loss, and differential mode delay using the finite element method. To achieve ultra-flattened chromatic dispersion and large minΔneff, an extra small elliptical defected hole is introduced in the fiber core. The circular holes in the first ring are replaced by elliptical holes to further obtain flattened-chromatic dispersion. The simulated results show that the designed weakly coupled FM-PCF can obtain an ultra-flattened average dispersion of 0.011 ns/nm/km with a small dispersion slope (<1.5 × 10 − 5 ns / km / nm2) in the wavelength range of 1520 to 1570 nm. And the proposed weakly coupled FM-PCF has large minΔneff (>1 × 10 − 3), low confinement loss (<10 − 4 dB / km), and good bending resistance. In summary, the proposed weakly coupled FM-PCF has potential applications for large-capacity MDM communication systems.

Polarization modes of gravitational waves in Palatini-Horndeski theory

In this paper, the polarization modes of gravitational waves in Horndeski gravity are studied under the Palatini formalism. After obtaining the linearized equation of perturbations in Minkowski background, we find that the polarization modes of gravitational waves depend on the selection of the theoretical parameters. The polarization modes can be divided into quite rich cases by parameters. In all cases of parameter selection, there are $+$ and $\times$ modes propagating at the speed of light but no vector modes. The only difference from general relativity is scalar modes, especially the scalar degrees of freedom can be 0, 1 or 2 in different cases. The appropriate parameter cases can be expected to be selected in the detection of gravitational wave polarization modes by Lisa, Taiji and TianQin in the future.

Sensitivity of third-generation interferometers to extra polarizations in the stochastic gravitational wave background

When modified theories of gravity are considered, at most six gravitational wave polarization modes are allowed and classified in tensor modes, the only ones predicted by General Relativity (GR), along with additional vector and scalar modes. Therefore, gravitational waves represent a powerful tool to test alternative theories of gravitation. In this paper, we forecast the sensitivity of third-generation ground-based interferometers, Einstein Telescope and Cosmic Explorer, to non-GR polarization modes focusing on the stochastic gravitational wave background. We consider the latest technical specifications of the two independent detectors and the full network in order to estimate both the optimal signal-to-noise ratio and the detectable energy density limits relative to all polarization modes in the stochastic background for several locations on Earth and orientations of the two observatories. By considering optimal detector configurations, we find that in 5 years of observation the detection limit for tensor and extra polarization modes could reach $h_0^2\Omega^{T,V,S}_{GW} \approx 10^{-12}-10^{-11}$, depending on the network configuration and the stochastic background (i.e., if only one among vector and scalar modes exists or both are present). This means that the network sensitivity to different polarization modes can be approximately improved by a factor $10^3$ with respect to second-generation interferometers. We finally discuss the possibility of breaking the scalar modes degeneracy by considering both detectors angular responses to sufficiently high gravitational wave frequencies.

Development of epoxy resin-based microfluidic devices using CO2 laser ablation for DNA amplification point-of-care (POC) applications

Microfluidic devices are a rising technology to automatize chemical and biological operations. In this context, laser ablation has significant potential for polymer-based microfluidic platforms’ fast and economical manufacturing. Nevertheless, the manufacturing of epoxy-based microfluidic chips is considered highly cost full due to the demand for cleanroom facilities that utilize expensive equipment and lengthy processes. Therefore, this study targeted investigating the feasibility of epoxy resins to be fabricated as a lab-on-chip using carbon dioxide laser ablation. The chemical structural properties and thermal stability of the plain epoxy resins were characterized by Fourier transform infrared spectral analysis (FT-IR) and thermogravimetric analysis (TGA). Moreover, a specific migration test was performed to quantify potential migrants by gas chromatography coupled to mass spectrometry (GC–MS) to prove that the cured epoxy resin would not release unreacted monomers to the biological solution test, which caused inhibition of the sensitive biological reactions. By investigating the impact of this process on microchannels’ dimensions and quality, a laser technique using CO2 laser was used in vector mode to engrave into a transparent epoxy resin chip. The resulting microchannels were characterized using 3D laser microscopy. The outcomes of this study showed considerable potential for laser ablation in machining the epoxy-based chips, whereas the microchannels machined by laser processing at an input power of 1.8 W and scanning speed of 5 mm/s have an aspect ratio of about 1.19 and a reasonable surface roughness (Ra) of ~ 15 µm. Meanwhile, the bulge height was 0.027 µm with no clogging, and HAZ was ~ 18 µm. This study validated the feasibility of quick and cost-effective CO2 laser microfabrication to develop epoxy resin-based microfluidic chips without the need for cleanroom facilities that require expensive equipment and lengthy process.

Ultra-broadband mid-infrared TE01 vector mode selector based on ring-core few-mode photonic crystal fiber

A mid-infrared TE01 vector mode selector based on chalcogenide ring-core few-mode fiber is proposed and investigated numerically by the finite element method (FEM). By embedding metal composite nanowire in the PCF core to generate surface plasmon resonance, TE01 vector mode could propagate due to low loss transmission, whereas the fundamental mode, TM01 and HE21 modes could hardly be maintained due to high loss. The effects of structural parameters on mode transmission characteristics and mode loss in photonic crystal fibers in the mid-infrared wavelength range are investigated. Under the optimal structural parameters, the loss ratios of each mode to TE01 mode are more than 50 in the waveband range from 2 to 3 μm, which means the TE01 single-mode transmission can be maintained in ultra-wide mid-infrared band. The designed fiber can be connected with the mid-infrared laser as a vector mode selection device to efficiently output pure TE01 mode cylindrical vector beam, which makes preferable application in mid-infrared optical communication, optical capture, super-resolution imaging, biochemical sensing and other fields.

A vectorization of iterative computational processes and time acceleration estimates

O b j e c t i v e s. The problem of efficient organization of the execution of sequential computational processes in the vector mode is solved, taking into account the capabilities of modern high-performance vector-pipeline computers. The relevance of the problem under consideration is due to the fact that processes that occur during cyclic data processing and in iterative algorithms are the most difficult to parallelize. In solving the problem, three main objectives were set. Construction of a mathematical model that takes into account the main architectural and computational features of modern vector-conveyor computers. Calculation of the optimal total execution time of vector operations. Evaluation of the time gain compared to the sequential mode of data processing.M e t h o d s. To achieve the objectives and to prove the main and auxiliary statements, an original method was used, including establishing the validity of the inductive assumptions in the cases under consideration, as well as an illustrative method of scheduling theory using Gantt charts.R e s u l t s . A vector model for the implementation of sequential calculations is proposed, which takes into account the main features of vector-conveyor computers. The optimal total execution time of sequential calculations in the vector mode is determined, and a lower estimate of the time gain is obtained in comparison with the sequential mode of their execution.C o n c l u s i o n. It has been established that when processing scalar input data in the sequential mode by vector operations with a pipeline length k, acceleration is possible by at least a factor nN (nk+N) , where N is the size of the input, n is the number of vector and corresponding scalar operations. The estimation of the time acceleration in the vectorization of calculations is compared with the sequential mode of their execution.