We derive the probabilities of the signal OAM state and crosstalk OAM state for a Laguerre-Gaussian (LG) beam propagating through Kolmogorov and Non-Kolmogorov turbulence, and derive the accurate analytical function of the probability for the received OAM state modulated by an arbitrary receiver aperture. The probability of the detected OAM state with a receiver aperture for different values of the radius is demonstrated numerically. Our numerical results show that the probability of the signal OAM state remains almost invariant when the radius of the receiver aperture varies. The probability of the crosstalk OAM state decreases with the decrease of the radius of the receiver aperture, thus it can be optimized by choosing a suitable value of the radius of the receiver aperture. Our results will be useful in free-space optical communications.

We propose a principal scheme to generate the cylindrical and the elliptical symmetrical vector beam based on a modified Mach-Zehnder interferometer. The modified Mach-Zehnder interferometer, the wave plates, the Polarizing Beam Splitter (PBS) and the Dove prism are used in this optical system. Two different order polarized beams can be generated and combined by this system and the arbitrary-order cylindrical and elliptical vector beams can be obtained. With the help of this simple optical system, the various profile vector beams can be generated flexibly.

A general form of twisted Hermite Gaussian Schell-model (THGSM) beams is introduced; analytical expressionsare obtained for cross-spectral density and M²-factor using the extended Huygens–Fresnel principle and Wigner function. The evolution of THGSM beams during propagation in non-Kolmogorov turbulence is shown numerically; the beams exhibit self-splitting and twist into two lobes. The intensity distribution evolves into a Gaussian shape and beam quality worsens with increasing distance; the intensity distribution and M²-factor are determined by the twist factor, beam orders, and other beam parameters. THGSM beams provide more degrees of freedom to regulate beam parameters, thereby enriching the types of partially coherent beams.

Optical fiber sensors are used for partial discharge detection in many applications due their advantage of strong anti-electromagnetic interference capability. Multi-point distributed partial discharge detection and location are important for electrical equipment. In this paper, a distributed partial discharge location and detection scheme based on optical fiber Rayleigh backscattering light interference is experimentally demonstrated. At the same time, the location and extraction algorithm is used to demodulate the partial discharge signal; furthermore, the high-pass filter is used to reduce the system low-frequency noise and environment noise. It is clear that the proposed system can detect a partial discharge signal generated by metal needle sensitivity, and the detectable frequency range is 0–2.5 kHz. We carried out 10 locating tests for two sensing units, the experimental results show that the maximum location error is 1.0 m, and the maximum standard deviation is 0.3795. At same time, the signal-to-noise ratio (SNR) of sensing unit 1 and sensing unit 2 are greatly improved after demodulation, which are 39.7 and 38.8, respectively. This provides a new method for a multipoint-distributed optical fiber sensor used for detecting and locating a long-distance electrical equipment partial discharge signal.

Based on the extended Huygens–Fresnel principle, the analytical expressions for the intensity distribution, effective radius of curvature, beam wander, Strehl ratio, and the power in the bucket of a partially coherent crescent-like (PCCL) beam under the maritime environment are derived. The propagation properties of the PCCL beams through the maritime environment are investigated in detail. Numerical results indicate that, for the maritime environment, the propagation properties and beam quality of a PCCL beam are closely related to its initial beam parameters and the turbulence parameters. Comparative analyses are performed for the new models under the marine turbulence and the terrestrial turbulence. It turns out that the marine turbulence influences the beam width and the beam wander more than the terrestrial turbulence does. Also, the beam quality of the PCCL beams in marine turbulence can be improved by choosing a large beam width, high coherence length, or short wavelength. The PCCL beams have a range-dependent tilt, which can be useful for some practical applications, such as traveling around an obstacle. The results are of significance for over-the-sea communication systems.