Perfect Optical Vortex Research Articles

Performance evaluation of perfect optical vortices transmission in an underwater optical communication system: publisher's note.

This publisher's note identifies an error in the paper title of Appl. Opt.57, 9148 (2018)APOPAI0003-693510.1364/AO.57.009148.

High order perfect optical vortex shaping

Abstract We proposed a method based on high-order Bessel–Gaussian beam to improve quality and intensity profile of high-order perfect optical vortex (POV) array under tight focusing condition. By using this method, parameters of POV could be controlled such as uniform ring width, adjustable ring diameter as well as controllable position, numbers and topological charges. A quality factor was proposed for assessing POV with different ring diameter and different topological charge. Comparing with the conventional method for generating POV, the optimal high-order POV carry uniform intensity distribution and the same ring width and diameter, which may enlarge the application on optical manipulation of multiple particles, large capacity optical storage and multiplexing optical vortex communication.

Non-ring perfect optical vortices with p-th order symmetry generated using composite diffractive optical elements

A “perfect” optical vortex (POV), a ring-shaped singular beam whose diameter does not scale with its topological charge, is now being extensively studied owing to its important practical applications ranging from optical trapping and manipulation of microscale objects to laser material processing with structured beams. At the same time, the ability to shape the intensity distribution of the POV in a controlled manner is of crucial importance for the mentioned applications; however, only circular- or elliptical-shaped POVs were demonstrated so far. Here, we propose and design pure phase diffractive optical elements (DOEs) with an optimized composite transmission function allowing high-efficient generation of non-ring-shaped POVs with p-th order symmetry. We demonstrate the generation of POVs with the desired topological charge, transverse size, and variable “polygon-like” lateral intensity distribution. Our experimental results are in good agreement with theoretical and simulation predictions. The proposed DOEs can be characterized by high conversion efficiency (more than 60%), thus substantiating their applicability for high-performing optical manipulation and advanced laser nanopatterning.

Performance evaluation of perfect optical vortices transmission in an underwater optical communication system.

In this paper, we experimentally evaluated the performance of underwater optical communications using 1Mbit/s on-off keying signals of perfect optical vortices. Perfect optical vortices generated by Fourier transformation of the Bessel-Gaussian beam are propagated through a 2.6m underwater medium and affected by various water conditions such as stagnant water, water flow, temperature difference, and air bubbles, so beam wander and fluctuation of the signal are studied. Air bubbles have the maximum effect on signal fluctuations and beam wanders. Measurement of the system bit error rate (BER) based on the signal-to-noise ratio (SNR) for these situations matches the results of wandering and fluctuations. The system BER is studied for different values of SNR, and its value is more degraded due to the air bubbles.

Generation of elliptic perfect optical vortex and elliptic perfect vector beam by modulating the dynamic and geometric phase

We propose a method for generating an elliptic perfect vector beam (EPVB) by modulating the dynamic and geometric phases. It is theoretically demonstrated that the shape of the beam can be changed from circle to ellipse by setting the scale factor m of the dynamic phase, but the diameter of it is independent on the topological charge and the polarization order. Since the geometric phases provided by the dialectic Q-plate vary with the polarization state of the illumination beam, EPVB can be converted to the elliptic perfect optical vortex (EPOV) beam by changing the polarization state of the illuminating beam. Therefore, we also provide an alternative method to generate the EPOV beam. The experimental results agree well with the theoretical expectations.

Two-dimensional multiplexing scheme both with ring radius and topological charge of perfect optical vortex beam

ABSTRACTPerfect optical vortex (POV) beam is a special kind of vortex beam, whose radius is independent of its topological charge. In this paper, we propose a two-dimensional multiplexing scheme with a ring radius and topological charge of POV beam. A communication system using the proposed multiplexing scheme with a two-step detection method is presented, and on–off keying modulation is applied to demonstrate the bit error rate (BER) performance under atmospheric turbulence. The numerical results show that the BER performance of the proposed scheme is better than that when only topological charge is multiplexed with the same conditions. The two-dimensional multiplexing scheme has an anti-interference capability since the ring radius is only concerned in magnitude. At the same time, the capacity and the spectral efficiency of the system are improved since both ring radial and topological charge of POV beam are used.

Free-space optical communication with perfect optical vortex beams multiplexing

We demonstrate a 2-channel orbital angular momentum (OAM) multiplexed free space optical communication (FSO) link using perfect optical vortex (POV) beams. POV beams are able to be transmitted coaxially over than 1m with the assistance of a microscope objective and normal lens. 16QAM-OFDM signals are used to measure the performance, which is also compared with the FSO link based on Laguerre–Gaussian (LG) vortex beams multiplexing in the same experimental environment. The results show that, the FSO link employing POVs multiplexing can bring a better performance to the system, which can always obtain a lower BER under the same received power; The using of POVs as carriers greatly reduces the systems’ sensitivity to the change of OAM topological charge numbers; And the constant diameter of POVs is also improve the versatility of the optical devices of different channels in the system.

Radiation characteristics of nanoscopic structures driven by perfect optical vortex pulse

The generation of tightly focused light beams carrying orbital angular momentum (OAM) offers new opportunities for applications in photonics, optoelectronics and optical communications. These spatially inhomogeneous light fields render possible the coupling of the photon field to the angular momentum characteristics of the sample. In this study we exploit this fact and consider nanostructured quantum rings (QRs) irradiated by OAM beams with the aim of inducing swiftly local magnetic moments as well as harmonic generation. Based on a time-dependent quantum simulation we investigate different laser setups for efficient magnetic moment generation during and after the pulse application. In particular, we study the role of the winding number of the optical vortex in enhancing the magnetic moment at a fixed laser intensity. Further, we analyze the emitted radiation associated with the photoinduced charge oscillations and the non-equilibrium current circulation. Irreversible relaxation processes due to the interaction of charged carriers with acoustic phonons are included using a density matrix formalism.

Adjustable Elliptic Annular Optical Vortex Array

We present an elliptic annular optical vortex array (EOVA), whose annular eccentricity can be freely adjusted. The EOVA is generated by coherent superposition of two elliptic perfect optical vortices (EPOVs) with the same eccentricity. The vortex number and sign of the EOVA are determined by the difference of the topological charges (TCs) of these two EPOVs. Continuously increasing the initial phase difference between the EPOVs, each vortex of the EOVA can be rotated on the elliptic ring. Moreover, the birth process of a vortex is visualized by changing the TC of one of the EPOVs from an integer to the adjacent integer in steps of 0.1. This letter demonstrates a different spatial-structured optical vortex array, which is of significance in applications such as optical tweezers and micro-particle manipulation.

Controllable mode transformation in perfect optical vortices.

We report a novel method to freely transform the modes of a perfect optical vortex (POV). By adjusting the scaling factor of the Bessel-Gauss beam at the object plane, the POV mode transformation can be easily controlled from circle to ellipse with a high mode purity. Combined with the modulation of the cone angle of an axicon, the ellipse mode can be freely adjusted along the two orthogonal directions. The properties of the "perfect vortex" are experimentally verified. Moreover, fractional elliptic POVs with versatile modes are presented, where the number and position of the gaps are controllable. These findings are significant for applications that require the complex structured optical field of the POV.

Elliptic perfect optical vortices

We generalize the concept of perfect optical vortices, studying the elliptic perfect optical vortices (EPOVs), which also have diameters independent on the topological charge. A pure-phase diffractive optical element is proposed for efficient generation of such EPOV. Intensity of EPOV generated by this element is order of magnitude higher than that of the EPOV generated by the Fraunhofer diffraction of an elliptic Bessel beam. It is also higher than that of the EPOV, generated approximately by an elliptical axicon. We obtain exact analytical expressions for the orbital angular momentum (OAM) density and for the total OAM of the EPOV. These expressions show that the normalized OAM of the EPOV is fractional and it always exceeds the OAM of the conventional circular perfect optical vortex, which equals the topological charge. It allows continuous controlling of the OAM by changing the ellipticity. We show analytically that the OAM density is maximal on the smaller side of the EPOV and is minimal on its larger side. The ratio between the maximal and minimal OAM density equals the squared ratio between the ellipse diameters. Using the proposed element, EPOVs of several topological charges are generated experimentally using a spatial light modulator. We experimentally confirm the independence of their size on the topological charge, which is determined interferometrically. Such EPOVs can be used for movement of microscopic particles along an ellipse with acceleration, as well as for generation of OAM-entangled photons.

Generation of Circular Optical Vortex Array

AbstractWe report on a novel optical vortex array named circular optical vortex array, which is generated by the superposition of two concentric perfect optical vortices. The circular optical vortex array has a constant topological charge of +1 or −1, the number and sign of which are determined by the topological charges of the two perfect optical vortices. Moreover, the radius of the circular optical vortex array is easily adjusted by using the cone angle of an axicon. Furthermore, the circular optical vortex array and multiple circular optical vortex array can be rotated by changing the initial phase difference of the perfect optical vortices on demand. This work demonstrates a complex structured optical field, which is of significance for applications such as optical tweezers, micro‐particle manipulation, and optical imaging.

Comment on “Generating a perfect quantum optical vortex”

In a recent article, Banerji et al. introduced a novel quantum state of light, coined as the perfect quantum optical vortex state [Phys. Rev. A 94, 053838 (2016)] due to its mathematical similarity with the classical perfect vortex beam. This state is obtained by means of the Fourier transform of a Bessel-Gaussian vortex state, and the authors claim that this can be accomplished by means of a simple lens. Here, we will show that this statement is wrong since a lens cannot modify the quantum noise distribution related to the input optical quantum state and this has to be exchanged by an "effective lens".

Generation of perfect optical vortices using a Bessel-Gaussian beam diffracted by curved fork grating.

Perfect optical vortices (POVs) are beams whose topological charges are independent of radius, unlike conventional optical vortices. POVs are the Fourier transformation of Bessel-Gaussian (BG) beams and can be seen in the far-field diffraction of BG beams. In this paper, we present the generation of POVs of arbitrary charge using curved fork grating (CFG) illuminated by BG beam. For this purpose, first, a theoretical study of the Fresnel-Kirchhoff integral for diffraction of a BG beam by CFG is completed. The analytical results show the presence of vortex beams with various topological charges in diffraction orders. Then, diffraction of the BG beam with the order (l) by CFG with a topological charge (p) is numerically simulated. Additionally, experimental results prove the generation of POVs in diffraction orders. Also, experimental interference patterns obtained by interfering a POV and Gaussian beam confirm the ability of analytical solutions to determine the topological charges of vortex beams. Comparison of the results reveals the validity of the analytical, simulation, and experimental results.

A highly efficient element for generating elliptic perfect optical vortices

We generalize the concept of perfect optical vortices, studying the elliptic perfect optical vortices (EPOVs), which also have diameters independent of the topological charge. A phase-only diffractive optical element is proposed for the efficient generation of such EPOV. The intensity of the EPOV generated by this element is higher than that of the EPOV generated approximately by an elliptical axicon. We obtain exact analytical expressions for the orbital angular momentum (OAM) density and for the total OAM of the EPOV. These expressions show that the normalized OAM of the EPOV is fractional and it exceeds the OAM of the conventional circular perfect optical vortex, which equals the topological charge. It allows continuous controlling of the OAM by changing the ellipticity. We show analytically that the OAM density is maximal on the smaller side of the EPOV. The ratio of the maximal to the minimal OAM density equals the squared ratio of the ellipse dimensions. Using the proposed element, EPOVs that carry different topological charges are generated experimentally with the aid of a spatial light modulator. We experimentally confirm the independence of their size from the topological charge, which is determined interferometrically. Such EPOVs can be used for moving microscopic particles along an ellipse with acceleration, as well as for the generation of OAM-entangled photons.

Concentric Perfect Optical Vortex Beam Generated by a Digital Micromirrors Device

We propose a kind of perfect optical vortex beam (POV) generated via Fourier transformation of Bessel-Gauss (BG) beams through encoding of the amplitude of the optical field with binary amplitude digital micromirrors device. We call them concentric POVs which consist of several POVs and where every POV has the same center and independent characters, and we confirm the correct phase patterns of the concentric POVs with the method of Mach–Zehnder interference and self-interference. This special property could be considered as a potential of implement to increase the orbital angular momentum communication capacity vastly.

Generation of Perfect Optical Vortices by Using a Transmission Liquid Crystal Spatial Light Modulator

We have experimentally created perfect optical vortices by the Fourier transformation of holographic masks with combination of axicons and spiral functions, which are displayed on a transmission liquid crystal spatial light modulator. We showed theoretically that the size of the annular vortex in the Fourier plane is independent of the spiral phase topological charge but it is dependent on the axicon. We also studied numerically and experimentally the free space diffraction of a perfect optical vortex after the Fourier back plane and we found that the size of the intensity pattern of a perfect optical vortex depends on the topological charge and the propagation distance.

Generating a perfect quantum optical vortex

In this article we introduce a novel quantum state, the perfect quantum optical vortex state which exhibits a highly localised distribution along a ring in the quadrature space. We examine its nonclassical properties using the Wigner function and the negativity volume. Such a quantum state can be a useful resource for quantum information processing and communication.

Optimal phase element for generating a perfect optical vortex.

We derived exact analytical relationships to describe the complex amplitude of a perfect optical vortex generated by means of three different optical elements, namely, (i) an amplitude-phase element with a transmission function proportional to a Bessel function, (ii) an optimal phase element with a transmission equal to the sign function of a Bessel function, and (iii) a spiral axicon. The doughnut intensity was shown to be highest when using an optimal phase element. The spiral-axicon-aided diffraction ring was found to be twice as wide as when generated using two other elements. Thus, the optimal filter was shown to be best suited for generating a perfect optical vortex. The simulation results were shown to corroborate theoretical predictions, with the experiment being in agreement with theory and simulation.

Refractive index mapping of single cells with a graphene-based optical sensor

Graphene-based optical sensors exhibit good performance in cell refractive index (RI) measurements, with high resolution and large detection depths. In this manuscript, we report an RI mapping method based on the polarization-sensitive light absorption of graphene, in focused scanning mode. Several RI mapping images of normal and cancerous human colonic cells have been obtained. A high-numerical-aperture microscope objective is used to minimize the focusing spot size. Under optimized conditions, the experimental spatial resolution reaches 2.34μm. A ring-shaped perfect optical vortex beam with a tunable diameter is generated to control the incident angles, and the experimental RI resolution is 9.3×10−4 refractive index units. The large longitudinal penetration depth of the graphene evanescent field allows the recognition of RI difference between two individual cancer cells. The RI distribution and morphology of the cells can be determined, and different carcinogenesis stages can also be concluded from the image. This method has potential in biomedical sciences, especially in cell imaging, differentiation, and sorting.