Bessel Gaussian Research Articles

Research on spatial multiplexing using BGSM beam in FSO communication

We propose a spatial division multiplexing scheme based on the Bessel–Gaussian​ Schell-mode beam. Sucha communication scheme can enhance the capacity of free-space optical communication (FSO) in turbulence. This multiplexing utilizes the relationship between the characteristics of coherence degree distribution and the distant facula, realizing the separation of several BGSM beams with different Bessel parameter from each other, which makes the multiplexing technique deploying coherence modulation possible. The advantage of this scheme is its resistance to the atmospheric influence which exists widely in the optical wireless communication’s application environment. According to the simulation, for the transmission length of about 1300 m, under the weak turbulence environment (Cn2=10−16 m2/3), the BGSM-SDM scheme can support about 5 times more capacity compared with the traditional optical wireless communication scheme with Gaussian beam, and while the turbulence becomes strong (Cn2=10−13 m2/3), the SDM scheme degenerates to single channel because of the beam expansion, but it can still support more than 2 times more capacity. The scheme is proved work stable for each channel, and applicable in strong turbulent environment by measuring the signal and noise in the experiment. I believe it provides a promising choice for the future 6G ultrahigh-speed wireless communication.

Propagation properties of the superimposed chirped Bessel–Gaussian vortex beams in strongly nonlocal nonlinear medium

In this paper, by applying the Collins integral formula, we obtain the analytical solution of the superimposed chirped Bessel–Gaussian vortex beam (SCBGVB) in strongly nonlocal nonlinear medium (SNNM). We investigate the SCBGVB’s propagation behaviors as well as the distribution of the intensity and the phase of the periodic self-focusing light field generated by the SNNM. And we can modulate its focusing times and the depth of the focus by choosing the appropriate factors. In this way, we can achieve a one-dimensional flat-topped light field with controllable length. In addition, we can manipulate the pattern of beam transmission, change its centroid position and regulate its focal intensity by choosing different components of SCBGVB’s vortex structure. What important is, we can also adjust its autofocusing position and control the ratio of two focal light intensity to form a series of high and low fluctuations without changing input power.

Tightly focusing properties of chirped phase modulate Bessel-Gaussian beam

This research is to explore the focusing characteristics of chirped phase modulating the Bessel-Gaussian (BG) beam. It can be observed that the focal spot of mixed chirped phase of BG beam will split along the optical axis under different beam parameters β. Simultaneously, the spot length, the spot position and the peak intensity is tunable by modulating the light distribution factor b and chirped factor c1 and c2. In addition, the evolution of longitudinal field and transverse field is also explored in detail. With the introduction of the special chirped phase, the focusing pattern obtains a series of observable evolution characteristics. These results will be potentially applied to many optical frontier areas, such as optical information transmission, optical capture and modern medical treatment.

Attenuation characteristics of Bessel Gaussian vortex beam by a wet dust particle

The potential applications of complex optical fields for environmental detection have attracted a lot of attention. In this study, dusty medium is equivalent to a uniformly charged sphere and a non-uniform concentric layered sphere that satisfying the single scattering condition, respectively. The interaction between a high-order polarized Bessel Gaussian beam and a spherical particle is investigated using the generalized Lorenz–Mie theory and the angular spectrum decomposition method. The location of incident beam is considered for the first time. The extinction efficiency results of a wet charged particle are compared with those of a wet neutral particle. Simulations show that the difference in extinction between these two kinds of particles mentioned above is more evident in the smaller size parameter range, which is similar to the case of plane wave incidence. In addition, the influence of complex refractive index and size proportion of heterogeneous medium on the extinction effect is analyzed. The characteristic parameters of the incident beam are considered and find out that how they affect the differences in extinction is independent of the illuminated particle. This study lays the foundation for analyzing the transmission capacity of a Bessel Gaussian vortex beam with various parameters in a dust particle cluster.

Non-iterative multifold strip segmentation phase method for six-dimensional optical field modulation.

In this Letter, we propose a non-iterative multifold strip segmentation phase method for a spatial light modulator (SLM) to generate multifocal spots of diverse beams (Airy, spiral, perfect vortex, and Bessel-Gaussian beams) in a high-numerical-aperture system, with up to 6D controllability. The method is further validated by an inverted fluorescence microscope. By adjusting the bright and dark voltage parameters of the SLM, zero-order light caused by the pixelation effect of the SLM has been successfully eliminated. We hope this research provides a more flexible and powerful approach for the rapid modulation of multi-focus light fields in the development of biomedicine and lithography.

Focusing of radially polarized bessel gaussian and hollow gaussian beam of high NA to achieve super resolution

To achieve super-resolution, a radially polarized Bessel Gaussian and a Hollow Gaussian Beam with high NA are focused. For both Bessel Gaussian and Hollow Gaussian Beams with high numerical aperture NA, the radially polarized component with two equal-intensity peaks covers 25% of the total intensity, while the longitudinally polarized component covers the rest. By focusing radially polarized Bessel and Hollow Gaussian beams, it is possible to generate various focal spots with different dimensions that are applicable for various applications in optical trapping, data storage, biomedical imaging, laser cutting, material processing, and microscopy. The effects of various Bessel beam characteristics are investigated. It was found that the beam radius reaches a minimum at a specified starting beam radius for all propagation distances and that the optimum starting beam radius is also large at long propagation distances. This findings are of great significance in optical trapping, data storage, biomedical imaging, and laser cutting.

Free Space Realization of the Symmetrical Tunable Auto‐Focusing Lommel Gaussian Vortex Beam

AbstractAn auto‐focusing beam with adjustable symmetry is proposed numerically and experimentally. The initial field of the auto‐focusing Lommel Gaussian vortex beam (ALoGVB) consists of the Lommel function and the Gaussian term. When the asymmetry factor ε of the beam approaches zero, the ALoGVB will degenerate into a circular Bessel Gaussian vortex beam (CBGVB). Compared with the CBGVB, the ALoGVB is more diverse. The shape, symmetry, normalized focusing intensity, and focus distance of the ALoGVB can be controlled by flexibly adjusting the asymmetry factor ε and the topological charge n. In addition, the effect of off‐axis vortices on the propagating characteristics of the beam is also discussed. The experiment is in good agreement with the numerical simulation. The results could be beneficial for potential applications in optical trapping or micromachining.

Probability property of orbital angular momentum distortion in turbulence

The probability property of the orbital angular momentum (OAM) distortion of the Bessel Gaussian beam propagating through the turbulence is investigated in this study. The mean and variance of the beam harmonic intensity are derived from the Rytov theory with a bias of less than 6% when compared with the data calculated by the phase-screen method. Based on these statistics, the probability density function (PDF) of the harmonic intensity fluctuation is proposed to characterize the randomness property of the beam OAM distortion, which agrees well with the result obtained from the phase-screen method. The PDF of the intensity difference between the fundamental and its adjacent crosstalk modes is derived. Furthermore, the probability of the OAM decoding error is also provided. This study not only facilitates beam OAM crosstalk characterization, but also provides the applicable condition of beam multiplexing for the beam parameter selection and the communication link design.

Modified Bessel–Gaussian Vortex Beam with an Adjustable Broken Opening

AbstractIn this study, an open‐ring controllable Bessel vortex beam is theoretically and experimentally constructed with a power‐exponent‐phase vortex. Its distribution in the far field after being blocked with obstacles is subsequently investigated. In the far field, the beam exhibits different degrees of the open‐loop effect following adjustments in the phase term of the power exponent. For an obstructed beam, the direction of the open loop is offset by a certain value, and different open‐loop angles can be achieved for different blocking angles. The developed beam can be used to guide particles and avoid obstacles.

Received probability of perfect optical vortex in absorbent and weak turbulent seawater links.

We investigated the effects of absorbent and weak turbulent seawater channels on the orbital angular momentum (OAM) mode carried by perfect optical vortex (POV) based on the Rytov approximation. After deriving the received probability of OAM modes, some numerical results are worked out to show that the receiving probability of OAM modes decreases linearly with the increase of virtual refractive index of the water body. An underwater communication link with POV as the signal carrier can obtain high receiving probability by adopting long signal wavelength in intervals of "seawater window wavelength," low OAM quantum number, a POV with a larger ring radius, and a transmitter as well as receiver with a smaller aperture. The transmission distance of OAM mode carried by POV in four kinds of seawater is better than that of a Bessel-Gaussian beam.

Generation of Perfect Vortex Beams by Dielectric Geometric Metasurface for Visible Light

AbstractA perfect vortex beam (PVB) is a propagating optical field carrying orbital angular momentum (OAM) with a radial intensity profile that is independent of topological charge. PVBs can be generated through the Fourier transform of a Bessel–Gaussian beam, which typically requires a well‐aligned optical setup consisting of a spiral phase plate, an axion, and a lens. Here, based on a single‐layer dielectric metasurface, the broadband generation of PVBs across the entire visible spectrum is demonstrated. The metasurface is composed of TiO2 nanopillars acting as deep‐subwavelength half‐waveplates, and able to provide the desired geometric phase profile to an incident circularly polarized light for the generation of PVBs. Through rigorous optimization of the nanopillars’ structural parameters, the authors experimentally generate vortex beams carrying OAM with different topological charges that exhibit constant radial intensity profiles, verifying their “perfect” characteristics. Furthermore, it is also demonstrated that the ellipticity and diameter of a PVB can be simultaneously controlled by adjusting the structural parameters of the metasurface, which further increases the flexibility in their design. These results open a new route towards creating ultra‐compact, flat, multifunctional nanophotonic platforms for efficient generation of structured light beams.

Focusing properties of power order space-variant phase modulate Bessel-Gaussian vortex beam

The purpose of this paper is to study the focusing properties of power order space-variant phase modulate the Bessel-Gaussian (BG) vortex beam, which is based on vector diffraction theory. Results show that under different power order of space-variant phase, the modulation of topological charge number and phase parameter have different evolution rules. Specifically, when power order n = 1, the position of the focal pattern will be arbitrarily adjusted on the X-axis by modulating the phase parameter C. Under the condition of n = 2, the focal spot will be expanded along y = -x with the increase of topological charge l. Meanwhile, by modulating C, two opposite phenomena of focal spot separation will be obtained. When n = 3, the increase of l will make the focal spot expand along the positive and negative directions of the Y-axis. Besides, increasing the value of C, the original focal spot intensity will converge to the X-axis, and a new intensity peak will be formed on the X-axis. A series of focal properties have been obtained as the power order space-variant phase introduced. These novel properties have potential applications in many fields such as particle trapping, particle movement and optical modulation related fields.

Structural stability of open vortex beams

Normally, intensity patterns of vortex beams are closed rings such as Laguerre–Gaussian beams and Bessel–Gaussian beams. Recent studies showed that the vortex beams with open ring structures, namely, open vortex beams (OVBs), have non-trivial orbital angular momentum (OAM) spectra and optical forces and can be employed in many applications such as metrology and quantum information. However, the structural stability of OVBs, including the topological charge conservation and the intensity invariance, has not been studied yet. Here, we theoretically propose a generalized model of OVBs, using both geometrical ray-like trajectories and coherent wave-packets, and the structural stability of OVBs is validated by the geometrical envelope of ray bundles. Moreover, we experimentally demonstrated that such OVBs can be generated by a partial fork-grating (PFG). Our study reveals structural characteristics of OVBs, which lays a foundation for the OVB's potential applications in optical manipulation, optical metrology, etc.

Size-invariant twisted optical modes for the efficient generation of higher-dimensional quantum states

Optical vortex beams are profiled as helical wavefronts with a phase singularity carrying an orbital angular momentum (OAM) associated with their spatial distribution. The transverse intensity distribution of a conventional optical vortex has a strong dependence on the carried topological charge. However, perfect optical vortex (POV) beams have their transverse intensity distribution independent of their charge. Such “size-invariant” POV beams have found exciting applications in optical manipulation, imaging, and communication. In this paper, we investigate the use of POV modes in the efficient generation of high-dimensional quantum states of light. We generate heralded single photons carrying OAM using spontaneous parametric downconversion (SPDC) of POV beams. We show that the heralding efficiency of the SPDC single photons generated with a POV pump is greater than that with normal optical vortex beams. The dimensionality of the two-photon OAM states is increased with POV modes in the pump and projective measurements using Bessel–Gaussian vortex modes that give POV, instead of Laguerre–Gaussian modes.

Improving the demultiplexing performances of the multiple Bessel Gaussian beams (mBGBs)

As approximate non-diffracted beams, Bessel Gaussian (BG) beams are more suitable to be used in free-space optical (FSO) communication system than Laguerre Gaussian (LG) vortex beams because of its self-recovering property. However, due to the limitation of its detection method, the multiplexing communication based on multiple Bessel Gaussian beams (mBGBs) has not been investigated deeply. In this paper, we propose a method for simultaneous demodulation of 36-mBGBs using 6 × 6 multiplexing phase hologram (MPH). To solve the problem that the energy of some BG beams are too low at the demodulation end, a method is proposed to optimize the pinhole size of the pinhole plate at the demodulation end. Compared with the traditional decomposition method, the proposed method not only improves the decoding efficiency greatly, but also has better robustness. In addition, the communication performance of 32-mBGBs encoded with four ASCII codes has been constructed and investigated numerically. The results show that the transmitted information can be clearly decoded by setting a reasonable threshold value, which is beneficial to the practical application of mBGBs in FSO communications.

Reducing orbital angular momentum modes crosstalk of Bessel Gaussian beams in anisotropic atmospheric turbulence with Localized Wave

Rytov theory is employed to analyze the spiral spectrum and orbital angular momentum (OAM) crosstalk effects of partially coherent Bessel Gaussian localized wave (BGLW) in the completely weak to strong anisotropic atmospheric turbulence channel. Propagation quality of OAM mode carried by BGLW is superior to that of the traditional Bessel Gaussian (BG) beam in the turbulence, which provide a good choice for OAM based optical communication. Atmospheric turbulence grows up with the increase of Reynolds number, the effects of the atmospheric turbulence parameters (anisotropy parameters, power spectrum index and refractive index structure constant) on the OAM modal detection probability also enhance. The influence of atmospheric turbulence can be reduced by increasing the half pulse width of the input pulse and wavelength of BGLW. The research results provide a theoretical basis for the performance evaluations and parameters optimization of practical OAM based optical communication technology.

Weak turbulence effects on different beams carrying orbital angular momentum.

The study of beams carrying orbital angular momentum (OAM) has been of interest for its use in free-space optical communications (FSOC), directed energy applications, and remote sensing (RS). For FSOC and RS, it is necessary to measure the wavefront of the beam to recover transmitted or environmental information, respectively. In this computational study, common OAM beams such as the Laguerre-Gaussian (LG), Bessel-Gaussian (BG), and Bessel beams are propagated through atmospheric turbulence and compared to their Gaussian beam counterpart. The turbulence is simulated using multiple phase screens within the framework of a split-step method. Beam metrics used to quantify beam propagation will include the spatial coherence radius, OAM spectrum, on-axis intensity, spot size, divergence, and on-axis scintillation. Atmospheric turbulence along the path is limited to the weak scintillation limit, where beam parameters can be predicted analytically using the Rytov approximation. The results show that BG beams and multiplexed BG beams retain more OAM information than their LG and Bessel beam counterparts. The LG beam on-axis intensity and on-axis scintillation are seen to be independent of OAM mode. The scintillation of the LG beam is less than a BG, Bessel, and Gaussian beam across low- and high-order OAM modes. Insight into these results is discussed through studying the beam divergence, while the initial spot sizes of the Gaussian, LG, and BG beams are limited to the same spatial extent.

Conservation of the half-integer topological charge on propagation of a superposition of two Bessel-Gaussian beams

We theoretically show that by continuously varying the amplitude of a constituent beam in the superposition of two Bessel-Gaussian (BG) beams with topological charges (TCs) $m$ and $n$ the TC of the entire superposition can be controlled. Between the constituent beams, there is a topological competition. For some parameters of the BG beams, TC of the superposition equals $n$, while for other parameters, it is equal to $m$. In the center of such a superposition (on the optical axis), there is an $m$-fold degenerate intensity null (optical vortex with the TC of $m<n$), whereas $n--m$ optical vortices with the unitary TC are in the beam periphery. We demonstrate that when the amplitudes of the constituent beams tend to be equal, peripheral vortices ``move'' to infinity. In this case, superposition of two BG beams has a half-integer TC, and this TC is conserved on propagation in space. The fractional part of the TC is, however, ``hidden'' in the infinity (``hidden'' phase). Conservation of the half-integer TC of an optical vortex on propagation is shown.

Splitting, generation, and annihilation of phase singularities in non-coaxial interference of Bessel–Gaussian beams

Based on the non-coaxial interference of Bessel–Gaussian (BG) beams, a new complex-structured light field is formed. By varying the off-axis distance, phase difference, separation angle, and topological charges (TCs) of the component beams, we observed the splitting, generation, and annihilation of phase singularities. The net TCs of the composite light field is not always equal the sum of the TCs of the original beams. Different from the general single-ringed vortex beams, because BG beams have infinitely many rings, alternately positive and negative unit vortex chains arise in the interference region. Furthermore, the edge dislocations are unstable, by modulating the phase difference and separation angle, we observe controllable transitions between edge dislocations and vortex singularities. Beyond providing an effective method for studying composite vortex beam interference, our results are significant for laser calibration and complex particle manipulation.

Propagation dynamics and radiation forces of autofocusing circle Bessel Gaussian vortex beams in a harmonic potential.

In this paper, the circle Bessel Gaussian vortex beams (CBGVBs) are introduced in a harmonic potential for the first time, whose autofocusing properties are explored by theoretical analysis as well as numerical simulation. According to the dimensionless linear (2+1)D Schrödinger equation, we numerically simulate the transmission trajectories of different topological charges of the off-axis vortices and the positions, the intensity and the phase distributions, the maximum transmission intensity, the center of mass, the energy flow, and the angular momentum. The simulation results show that the periodically autofocusing CBGVBs can flexibly adjust the position, the intensity, and the focus points by controlling the parameters. By increasing the number of off-axis vortices and adjusting the position of off-axis vortices, the transmission trajectory and the intensity of the CBGVBs can be controlled. Furthermore, we notice that the larger the slope of the curve where the combined force of the scattering force and the gradient force is 0, the particles are more likely to be trapped.