Propagation Properties Of Beams Research Articles

Performance analysis of the OAM based optical wireless communication systems with partially coherent elegant Laguerre–Gaussian beams in oceanic turbulence

The transmission model of partially coherent elegant Laguerre–Gaussian (ELG) beams in oceanic turbulence is established by employing the spatial power spectrum of the refractive index of sea-water and the optics approximation. The mathematical expressions of mode probability, energy content, and orbital angular momentum (OAM) state detection probability for partially coherent ELG beams are obtained. The influences of beam and turbulence parameters on the propagation properties of light beam are illustrated in detail with numerical simulations. Results indicate that partially coherent ELG beams with smaller azimuthal mode, smaller OAM state difference, longer blue–green incident wavelength, and appropriate beam waist are less affected by turbulent ocean. Moreover, the evolution characteristics of laser beam may be able to keep a better quality under the condition of lower rate of dissipation of mean-square temperature, higher rate of dissipation of turbulent kinetic energy per unit mass of fluid, and smaller ratio of temperature to salinity for maritime environment. In addition, the partially coherent ELG beams exhibit more robust resistance to turbulence than the partially coherent standard Laguerre–Gaussian beams. These results are expected to be potential helpful in understanding the optical transmission process in turbulent media and designing the optical vortex communication systems.

Propagation of a Bessel-Gaussian beam in a gradient-index medium.

Based on the ABCD matrix method and Collins diffraction integral formula, analytical expression for Bessel-Gaussian beam propagation in a gradient-index medium is derived. The propagation trajectory, intensity, and phase distributions of the zeroth-order, second-order, and superposition cases are numerically investigated. The effect of beam waist radius w0 on the properties of beam propagation in a gradient-index medium is discussed in detail. The result shows that the beam is focused at z/L=N/2 (N=0,1,2,…) and propagates periodically in the medium. Evolution of the vortical structure of the superposed Bessel-Gaussian beam is investigated, showing that the superposed beam forms new singularities, and the rotation of the beam occurs mainly near the singularities.

有偏压光伏光折变晶体中艾里高斯光束的传输特性

有偏压光伏光折变晶体中艾里高斯光束的传输特性

Twisted vortex Gaussian Schell-model beams.

We introduce a new class of partially coherent vortex beams in which the angular momentum of the beam is provided from two different sources: the underlying vortex of the random beam and the "twist" given to the ensemble of beams. The statistical and propagation properties of such beams are investigated, and their orbital angular momentum properties are analyzed. The combination of distinct orbital angular momentum sources allows unusual behaviors that were previously unobserved.

Influence of oceanic turbulence on propagation of Airy vortex beam carrying orbital angular momentum

With Rytov approximation theory, we derive the analytic expression of detection probability of Airy vortex beam carrying orbital angular momentum (OAM) through an anisotropic weak oceanic turbulence. We investigate the influences of turbulence parameters and beam parameters on the propagation properties of Airy-OAM beam. The numerical simulation results show that the anisotropic oceanic turbulence with a lower dissipation rate of temperature variance, smaller ratio of temperature and salinity contributions to the refractive index spectrum, larger dissipation rate of kinetic energy per unit mass of fluid, bigger inner scale factor, higher anisotropic coefficient causes the larger detection probability of Airy-OAM beam. Moreover, the Airy-OAM beam with a smaller topological charge, larger main ring radius and longer wavelength, has strong resistance to oceanic turbulent interference. Additionally, the detection probability decreases with the increase of receiving aperture size. In comparison with Laguerre-Gaussian-OAM beam, Airy-OAM beam has more anti-interference to turbulence when its topological charge is larger than 5 due to its non-diffraction and self-healing characteristics. The results are useful for underwater optical communication link using Airy-OAM beam.

Propagation properties of Airy Gaussian vortex beams in strongly nonlocal nonlinear media

Abstract By solving the normalized dimensionless Snyder–Mitchell model, the analytical expression of the Airy Gaussian vortex (AiGV) beams propagating in strongly nonlocal nonlinear media (SNNM) is specifically derived for the first time. We analytically and numerically study the AiGV beams propagating in SNNM. The influence of the changes in the input energy parameter and decay factor on the wave nodes of the propagation trajectory of the AiGV beams is described in detail. The difference in the effect of the wave nodes on the Poynting vector and the angular momentum is shown. The input energy parameter and distribution factor are discussed for the influence of the diffraction of the AiGV beams, the distribution area of Poynting vector, angular momentum, and gradient force, the peak value of the maximum scattering force, and the period of fluctuation. Our research results provide many interesting properties related to the AiGV beams in SNNM and also broaden the research areas of the AiGV beams and may promote the potential application of the AiGV beams in unique SNNM in physics or other related fields.

Parabolic-Gaussian Schell-model sources and their propagations.

In this work, a new class of partially coherent Schell-type sources is introduced by modifying its degree of coherence, which is a product of a parabolic function and a Gaussian function. Such sources are confirmed to be physically genuine and may be called parabolic-Gaussian Schell-model (PGSM) sources. The propagating expression of the cross-spectral density function of such PGSM sources is derived in a general linear optical system. In particular, the propagation properties of such PGSM beams in both free space and lens systems are discussed. The results show that such PGSM sources can produce dark-hollow intensity profiles in the regions of free space very near as well as far away from the source plane, or in the focal region of the lens system.

Propagation properties of hypergeometric-Gaussian type-II beams through the quadratic-index medium.

The analytical expressions of hypergeometric-Gaussian type-II (HyGG-II) beams propagating in the quadratic-index medium are deduced based on the ABCD optical transformation matrix method. The propagation properties of HyGG-II beams in the quadratic-index medium are numerically and theoretically analyzed in detail. The intensity distribution and the second-order moment-based beam width vary periodically when the HyGG-II beams pass through the quadratic-index medium. The interactions of two HyGG-II beams are also discussed graphically.

Properties of nonparaxial partially coherent flat-topped vortex hollow beam

The propagation equations of nonparaxial partially coherent flat-topped vortex hollow beam have been derived, and the nonparaxial propagation properties of beam are analyzed using the numerical examples. The results show that the nonparaxial partially coherent flat-topped vortex hollow beam will evolve into flat-topped beam as the propagation distance increases, and the far field results are the special case of the nonparaxial propagation. It is also found that the partially coherent flat-topped vortex hollow beam with smaller coherence length will lose its dark hollow centre more rapidly.

Analytic expression and propagation properties of hollow Gaussian beams for the off-waist incident case in strongly nonlocal media

Abstract In this paper, the propagation properties of hollow Gaussian beams (HGBs) are discussed in detail when they are off-waist incident in strongly nonlocal media. A set of mathematic expressions are given to describe the evolutions of the beam intensity, the beam width, and the real beam radius. Numerical simulations are carried out to illustrate these propagation properties depended on the off-waist incidence. It is found that a HGB always periodically transforms its transverse patterns during propagation. Accordingly, the beam width and the real beam radius are also periodic during propagation.

Fractional Fourier transform of double-half inverse Gaussian hollow beams

In this paper, we study an appropriate mathematical model of dark-hollow beam by concerning double-half inverse Gaussian hollow (DHIGH) beams passing through fractional Fourier transform (FRFT) optical systems. Based on Collins integral formula and using the expression of the hard-edged aperture function into a finite sum of complex Gaussian functions, analytical expressions for the propagation properties of DHIGH beams through the FRFT optical systems without and with apertures have been derived in detail. Some numerical simulations are given to illustrate the normalized intensity distribution of DHIGH beams in a FRFT system by studying the important factors of both incident beams order and the FRFT order. Our results obtained by using an approximate analytical formula, are in a good agreement with those obtained by using numerical integral method. The results show that the FRFT optical system is a convenient way for DHIGH beams shaping.

Skew line ray model of nonparaxial Gaussian beam.

Many ray-optics models have been proposed to describe the propagation of paraxial Gaussian beam. However, those paraxial ray-optics models are inapplicable to the beams that violate the paraxial condition. In this paper, we present a skew line ray (SLR) based model to represent the propagation properties of nonparaxial Gaussian beam under the oblate spheroidal coordinates. The free-space evolution of complex wavefront of the light beam including amplitude and phase is derived via this model. Our analysis demonstrates that the SLR model is available for both nonparaxial and paraxial conditions, and can be used to precisely describe the propagation of complex wavefront. Furthermore, this model changes the transverse density of rays while propagating. The behavior influences the transverse intensity distribution and makes the optical rays become concentrated towards the center. We believe that this ray-optics model can be further developed to describe other kind of structured beams such as Laguerre-Gauss and Bessel-Gauss beams.

Optical coherence grids and their propagation characteristics.

A novel class of partially coherent light sources termed optical coherence grids (OCGs) are introduced that can yield stable optical grids in the far field. The optical grids, of which the light distributes in a network of straight lines crossing each other to form a series of hollow cages, can be seen as a better controlled optical lattice. Propagation properties of OCG beams in free space, including spectral density, transverse coherence, and M2 factor, are investigated in detail. It is interesting that a periodic grid pattern is produced at a distance and remains stable on further propagation, and we stress that the structure of far-field optical grids can be flexibly tuned by modulating the correlation parameters of the source. In addition, by performing convolution of degree of coherence, we also propose perfect optical coherence grids (POCG). The far-field grid pattern of POCG is in a fully controllable fashion. This work is expected to find applications in cooling atoms, trapping microscopic particles, or assembling cells, etc.

基于高斯光束传播性质的激光相位恢复

基于高斯光束传播性质的激光相位恢复

Propagation Properties of Airy Beam through Periodic Slab System with Negative Index Materials

Based on light transfer matrix and electric field vector equation, the evolution of Airy beam propagating in periodic slab system with three negative index materials (NIMs) and its transmission mechanism are investigated. The intensity profiles on emergent surface of periodic slab system and side view of Airy beam propagating in each right handed material (RHM) and double negative material (DNM) unit including lossless and losses DNMs are discussed. It is revealed that the self-recovery Airy beam can be achieved in long distance by using lossless periodic slab system as long as the negative refractive index nl=-nr and each unit length L=Z. As to losses slab system contained DNMs, the smaller the collision frequencies are, the better the Airy beam quality is formed. It is expected that the proposed manner of beam transmission and corresponding conclusions can be useful for extension applications of optical control, especially for optical communication and optical encryption technique.

相位屏法模拟高斯阵列光束海洋湍流传输特性

相位屏法模拟高斯阵列光束海洋湍流传输特性

Propagation dynamics of ring Airy Gaussian beams with cosine modulated optical vortices

We numerically investigate the propagation properties of ring Airy Gaussian beams (RAGBs) with cosine modulated optical vortices (CMOV). In comparison to the common RAGBs without any modulation, the dynamic propagation of RAGBs with CMOV exhibits a unique feature: the rings of RAGBs with CMOV will gradually shrink into several main lobes with the increase of the propagation distance. The number of lobes and the peak intensity of each lobe are determined by the factors of cosine modulated function. By designing the initial phase, we can easily change the transversal location of the peak intensity. Our results may find potential applications in optical manipulations.

Microtube fabrication based on femtosecond Bessel beam and its flexible driving with external magnetic field

Microtube, with simple and uniform geometry, is one of the basic structures in micro/nano field. We present a method for the fabrication of magnetic drivable microtubes, by direct femtosecond laser writing combined with magnetron sputtering with metal layer. Femtosecond laser beam is modulated into Bessel beam with spatial light modulator (SLM), and then Bessel beam is focused with a high numerical aperture objective. Microtubes are fabricated by scanning focused femtosecond Bessel beam in a sample anchored on a three dimension stage. Followed by magnetron sputtering a nickel layer, the microtubes exhibit supermagnetic property and can be flexibly driven by external magnetic field. In this study, the propagation and high numerical aperture focusing properties of femtosecond Bessel beams are investigated. Microtubes, with well controlled diameter, length and distribution are efficiently fabricated. Rapid steering of nickel coated microtubes along specific route in fluid environment with external magnetic field has been realized. The steering of microtubes can be realized in various fluid environments. This method is flexible, controllable and efficient and the fabricated drivable microtubes have a promising applications in noninvasive surgery, targeted drug delivery, bioimaging or biosensing and microenvironment cleaning.

Propagation properties of cosh-Airy beams

We theoretically investigate the propagation properties of cosh-Airy beams, which can be considered as a superposition of two Airy beams with different decay factors. We find that the field distribution of cosh-Airy beams is the same as that of Airy beams. Moreover, we find that the evolution of cosh-Airy beams is determined by the parameters of the cosh modulation function, in addition to the transverse scale factor and decay factor of the Airy beams. Our results demonstrate a possible method of manipulating Airy beams in free space. They can also be extended to the study of the propagation properties of cosine-Airy beams (or sine-Airy beams).

Propagation characteristics of ring Airy beams modeled by fractional Schrödinger equation

We have numerically investigated the propagation properties of ring Airy beams modeled by a fractional Schrodinger equation (FSE). Beam splitting is exhibited and clarified from the view of group delay. Compared with the case of the condition in free space, the focal intensity is greatly enhanced and presents a trend from increasing to decreasing with the decrement of the Levy index, while the focal length largely increases; in addition, the parabolic trajectory is distorted with the Bessel pattern gradually disappearing. However, both the focal intensity and its length get decreased due to the absence of the initial phase of ring Airy beams; simultaneously, the size of the focal spot decreases for a larger Levy index. The changes of focusing properties are clearly clarified. Moreover, without initial phase, the ratio of focal intensity under the Levy index to the condition in free space is given to show the faster growth of focal intensity when the Levy index is lower than 1.25; otherwise, the trend gets reversed. The autofocusing properties of ring Airy beams modeled by FSE can find applications in optical trapping and manipulation.