Kaicheng Zhu

Flattened multi-Gaussian light beams with an axial shadow generated through superposing Gaussian beams

Abstract Making use of combining 2( N − L +1) off-axial Gaussian beams, the beams with nearly flattened top profiles and an on-axial shadow are introduced. An analytical expression of the beams propagating through a first-order ABCD system is derived. The closed form of the beam propagation factor ( M 2 -factor) is presented to characterize the quality of the beams. Additionally, it is showed that the beam is yet a special solution of the paraxial wave equation and the scheme to generate such a light beam is also proposed.

Study on the propagation parameters of Bessel–Gaussian beams carrying optical vortices through atmospheric turbulence

Based on the integral representation of Bessel function and the extended Huygens-Fresnel principle, an integral expression of the Wigner distribution function (WDF) for partially coherent Bessel-Gaussian beams (PBGBs) propagating through turbulent atmosphere has been obtained. Also, the analytical formulas of the M2-factor for PBGB propagation in such a medium have been derived, which can be applied to cases of different spatial power spectra of the refractive index fluctuations. The performed numerical results reveal that the M2-factor of a PBGB in turbulent atmosphere depends on the beam parameters of the initial input beam, the structure constants of the turbulent atmosphere, and the propagation distance. These results may be useful in long-distance optical communications in free space or in turbulent atmosphere.

Flattened light beams with an axial shadow generated through superposing cosh-Gaussian beams

Summary Making use of combining N — L + 1 cosh-Gaussian beams, the beams with nearly flattened top profiles and an on-axial shadow are introduced. An analytical expression of the beams propagating through a first-order ABCD system is derived. The closed expression of the beam propagation factor (M2-factor) is presented to characterize the quality of the beams, and the kurtosis parameter is employed to describe the sharpness of such beams. Additionally, the scheme to generate such a light beam is also proposed.

Peak-to-average power ratio reduction in orthogonal frequency division multiplexing visible light communications system using a combination of a genetic algorithm and a hill-climbing algorithm

Abstract. The orthogonal frequency division multiplexing (OFDM) modulation technique has been used widely in visible light communications (VLC) systems to combat intersymbol interference. At the same time, the inherent drawback of OFDM with a high peak-to-average power ratio (PAPR) is brought into OFDM visible light communications (VLC-OFDM). Furthermore, considering the limited dynamic range characteristics of light-emitting diodes, the performance degradation caused by a high PAPR is more serious in VLC-OFDM. In this paper, we propose a partial transmit sequence (PTS) technique based on the combination of a genetic algorithm (GA) and a hill-climbing algorithm (GH-PTS) to solve the problem of high PAPR. GH-PTS is a modified PTS technique based on GA-PTS. Essentially, GH-PTS is a local optimization of GA-PTS. Simulation results show that the optimized technique is able to reduce PAPR more effectively without any loss of bit error rate performance than the GA-PTS technique in VLC-OFDM system.

Two-mode superposition coherent states with spatial vortex structure for the quantized radiation field

Through superposing M two-mode coherent state a two-mode superposition coherent state with a spatial vortex structure in configuration space is constructed. Such quantum vortex state is an eigenstate of sum of squared two-mode annihilation operators and is always entangled. In the limiting condition of large M the quantum vortex state has a modified Bessel–Gaussian vortex structure with topological charge index n. Experimentally, such two-mode vortex states may be prepared by virtue of a multimode coherent state with currently available technology.

Non-Gaussian state with vortex structure of quantized radiation field

A new kind of quantum non-Gaussian state with vortex structure termed as a modified Bessel–Gaussian vortex state is constructed, and it is an eigenstate of sum of squared annihilation operator a2+b2. The quantum vortex state exhibits a rich variety of nonclassical signatures and is always entangled. The dependence of its statistical properties on state parameters is analyzed, and the non-Gaussianity is investigated in detail. It is found that, for sufficient small values of α, the properties clearly depend on the topological charge index n. Moreover, a scheme for generating such quantized vortex states is proposed.

Propagation of multi-cosine-Laguerre-Gaussian correlated Schell-model beams in free space and atmospheric turbulence

We introduce a class of random stationary, scalar source named as multi-cosine-Laguerre-Gaussian-correlated Schell-model (McLGCSM) source whose spectral degree of coherence (SDOC) is a combination of the Laguerre-Gaussian correlated Schell-model (LGCSM) and multi-cosine-Gaussian correlated Schell-model (McGCSM) sources. The analytical expressions for the spectral density function and the propagation factor of a McLGCSM beam propagating in turbulent atmosphere are derived. The statistical properties, such as the spectral intensity and the propagation factor, of a McLGCSM beam are illustrated numerically. It is shown that a McLGCSM beam exhibits a robust ring-shaped beam array with adjustable number and positions in the far field by directly modulating the spatial structure of its SDOC in the source plane. Moreover, we provide a detailed insight into the theoretical origin and characteristics of such a ring-shaped beam array. It is demonstrated that these peculiar shaping properties are the concentrated manifestation of the individual merits respectively associated with the Laguerre- and multi-cosine-related factors of the whole SDOC. Our results provide a novel scheme to generate robust and controllable ring-shaped beam arrays over large distances, and will widen the potentials for manipulation of multiple particles, free-space optical communications and imaging in the atmosphere.

Paraxial propagation of Gaussian beam through curved transverse parabolic graded-index waveguides

Based on the unitary transformation and the Lie algebra decomposition technology widely used in quantum mechanics, we obtain the analytical propagation kernel of a light field through curved transverse parabolic graded-index (GRIN) waveguides. The results show that, unlike in a straight parabolic graded-index waveguide, the curve of a transverse parabolic GRIN waveguide can result in two new effects during a Gaussian beam propagation: one is a phase shift including a global one and a local one, which result in the direction change of the light beam propagating through such a curved transverse parabolic GRIN waveguide. The other is to transform an on-axis Gaussian beam into a off-axis Gaussian one. In addition, the deviation of the Gaussian beam distribution center from the center of the curved transverse parabolic GRIN waveguide is also calculated.

Vortex and entanglement occurring in propagating states through coupled lossy waveguides

A separable input state consisting of an