Measurement Of Topological Charge Research Articles

Measurement of the fractional topological charge of an optical vortex beam through interference fringe dislocation.

An optical vortex beam carrying fractional topological charge (TC) has become an immerging field of interest due to its unique intensity distribution and fractional phase front in a transverse plane. Potential applications include micro-particle manipulation, optical communication, quantum information processing, optical encryption, and optical imaging. In these applications, it is necessary to know the correct information of the orbital angular momentum, which is related to the fractional TC of the beam. Therefore, the accurate measurement of fractional TC is an important issue. In this study, we demonstrate a simple technique to measure the fractional TC of an optical vortex with a resolution of 0.05 using a spiral interferometer and fork-shaped interference patterns. We further show that the proposed technique provides satisfactory results in cases of low to moderate atmospheric turbulences, which has relevance in free-space optical communications.

Measurement of Topological Charge of Obstructed Wandering Vortex Beams

Measurement of Topological Charge of Obstructed Wandering Vortex Beams

Constraints on the detection of topological charge of optical vortices using self-reference interferometry

In this paper we investigate the self-reference interferometry of optical vortices using a Michelson interferometer. It is found that the detection of topological charge (TC) for optical vortices is constrained by some physical conditions. We present these conditions through theoretical analyses, numerical simulation and experimental results. The maximal detectable TCs are different for different parameters, which is helpful for the measurement of TC in practical applications. Within the range allowed by the constrained conditions, we also study the detection of TC using the interference pattern of a two-way optical vortex, by changing the inclined angle of one mirror of the Michelson interferometer.

Measure the arbitrary topological charge of perfect optical vortex beams by using the dynamic angular double slits.

Perfect optical vortex beams (POV) have attracted considerable attention in many novel applications because they have the advantage of a radial profile that is independent of the topological charge (TC). Nowadays, there are few effective methods to measure both the integer and the fractional TCs of the POV. In this paper, we achieve the precise measurement of arbitrary TCs through the approach of dynamic angular double slits (ADS), which performs the transformation from the POV to the interference intensity patterns at the angular bisector direction of the ADS. The information of the TC can be obtained from the periodically changing interference pattern. The deviation is less than 2% by comparing the theoretical values with the fitting results, therefore the detection method is effective and reasonable.

Measuring the topological charge and ellipticity of elliptic vortex

The intensities and phase profiles of the elliptic optics vortex beam both are determined by the topological charge (TC) and ellipticity. This paper presents an efficient and simple method for measuring the TC and ellipticity of elliptic vortex. By observing the diffraction patterns, the TC modulus and ellipticity can be probed with the suitable rectangular aperture, and the TC sign can be detected with the suitable right triangular aperture. The scheme works well even for high-order elliptic vortex with topological charge value as high as ± 18, and ellipticity range from 0.5 to 2 at least. Obviously, the measurement of TC and ellipticity have important research value for promoting the application of elliptical vortex.

Settled fast measurement of topological charge by direct extraction of plane wave from vortex beam* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61975015, 61575022, and 61421001) and the Beijing Natural Science Foundation, China (Grant No. L191004).

A method of measuring the vortex beam topological charge (TC) is proposed based on a device that can directly extract the plane wave form from the vortex beam in which the different propagation angles of the plane waves are uniquely related to the different TCs. Then the TC can be obtained by simply comparing the energy values perceived by two fixed sensors in the detection location with the help of twin omnidirectional energy absorbers (OEAs). Because the settled detection relies only on the simple quantitative value at two fixed positions, neither pattern recognition nor field analysis procedure is applied, thus allowing faster measurement. Some features of the methodology are investigated, and the numerical simulations verify the feasibility and robustness of the system.

A composite beam of radiation with orbital angular momentum allows effective local, single-shot measurement of topological charge

We introduce and report experimental realization of a method to measure the topological charge of radiation carrying orbital angular momentum by accessing a small portion of the wavefront. The method exploits the superposition of matched-curvature beams in separated frequency bands to achieve a differential measure realized by a pair of phase-sensitive detectors. The method is suitable for long-distance communications.

Phase detection of coherence singularities and determination of the topological charge of a partially coherent vortex beam

In the theory of partial coherence, coherence singularities can occur in the spectral degree of coherence (SDOC): in case the fields at two different points are completely uncorrelated, the phase of the SDOC is undefined. For a partially coherent vortex beam, the detection of coherence singularities is linked to the measurement of topological charge, whose magnitude equals the number of ring dislocations in its far field amplitude. However, the phase distribution of coherence singularities is rarely mentioned in the literature and the amplitude distribution can hardly reflect the sign of topological charge. In this letter, we present a phase-analysis method for measuring the coherence singularities by introducing a movable perturbation at a certain point in an illumination window of a finite size. Using the proposed method, we measure experimentally the coherence singularities of a partially coherent vortex beam in the focal plane. From the results, the magnitude and sign of the topological charge can be determined simultaneously from the phase distribution of the coherence singularities. Our results can find application in information transmission.

Ultrafast vortices generation at low pump power and shearing interferometer-based vortex topological detection

A single mode fiber coupled laser diode was employed to generate a low threshold femtosecond vortex by using an off-axis pumping technique and mode converter with a pair of cylindrical lenses. In this way, the pump threshold of a laser system can be decreased and the slope efficiency can be increased. Two lateral interferometric techniques for optical vortex detection were improved using the circular common-path (CCP) geometry configuration. In the CCP interferometer, the object optical vortex was divided into two beams that transmit oppositely along the interferometer and interfere with themselves in the beam splitter. The two beams traveled along the same path through the same optical elements. These new designs omit delicate adjustment of two interference arms, and can easily manipulate the optical path difference between the two beams. The results show that the experimental results are in good agreement with the numerical simulation. These CCP interferometers are insensitive to the environment and are suitable for the measurement of topological charge of a laser source with a short coherence length, including white lasers.

拉盖尔高斯光束拓扑荷复用测量的仿真

拉盖尔高斯光束拓扑荷复用测量的仿真

Topological Blockade and Measurement of Topological Charge

The fractionally charged quasiparticles appearing in the 5/2 fractional quantum Hall plateau are predicted to have an extra nonlocal degree of freedom, known as topological charge. We show how this topological charge can block the tunneling of these particles, and how such topological blockade can be used to read out their topological charge. We argue that the short time scale required for this measurement is favorable for the detection of the non-Abelian anyonic statistics of the quasiparticles. We also show how topological blockade can be used to measure braiding statistics, and to couple a topological qubit with a conventional one.

Propagation of helical beams through amplitude diffractive optical elements and the measurement of topological charge

A new method is proposed to generate amplitude diffractive optical elements such as Young's double-slits and triangular apertures from a spatial light modulator (SLM). With the help of plane wave angular spectrum diffraction formula and Collins formula, the propagation property of helical beams passing through those two amplitude optical elements is studied, and the measurement of topological charge of helical beams is also achieved with those two amplitude diffractive optical elements. Due to the fact that the SLM can flexibly and accurately change the configurations and locations of optical elements, the measurements can be conveniently achieved.

Measurement-only topological quantum computation via anyonic interferometry

We describe measurement-only topological quantum computation using both projective and interferometrical measurement of topological charge. We demonstrate how anyonic teleportation can be achieved using “forced measurement” protocols for both types of measurement. Using this, it is shown how topological charge measurements can be used to generate the braiding transformations used in topological quantum computation, and hence that the physical transportation of computational anyons is unnecessary. We give a detailed discussion of the anyonics for implementation of topological quantum computation (particularly, using the measurement-only approach) in fractional quantum Hall systems.