ABSTRACT
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.
ABSTRACT
Based on the Snyder-Mitchell linear model and the cross-spectral density (CSD) function, the analytical propagation formula of twisted Gaussian Schell-model (TGSM) beams in strongly nonlocal nonlinear medium (SNNM) is derived. Then the propagation characteristics of TGSM beam are studied. It is found that the soliton radius is jointly determined by the initial power, coherence length, and twist factor; the degree of spatial coherence is adjusted by changing the twist factor without affecting the soliton intensity. In the case of non-soliton properties, there is a threshold of coherence length which makes partially coherent beams have the same evolution law as completely coherent beams. Furthermore, increasing the twist factor, decreasing the coherence length and initial power can improve the beam quality of the beam propagating in SNNM.
ABSTRACT
We first introduce a class of a superimposed Hermite-Gaussian-correlated Schell model with a multiple off-axis vortices beam, with the side lobe of the beam carrying one to four vortex singularities at the source plane. Subsequently, the variation laws of this beam after being focused by a thin lens are studied theoretically to obtain the optimal beam parameters. The numerical simulation results show that the beam possesses a unique multiple vortex structure, phase structure, and orbital angular momentum. Its intensity resembles a spiral staircase rotating around the axes. The rotational symmetry property of the transverse energy flow along the z axis was broken by the vortices. The hot spot position can be adjusted flexibly by changing the off-axis distance of vortices. This study is of great significance for nondestructive capture and manipulation of multiple particles or cells.
ABSTRACT
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.
ABSTRACT
A 2.8-dB polarization squeezing of the Stokes operatorS^2for the rubidium D1 line (795 nm) is achieved, with the lowest squeezing band at an audio frequency of 2.6 kHz. It is synthetized by a bright coherent beam and a squeezed vacuum, which are orthogonally polarized and share same frequency. Two methods are applied to support the optical parametric oscillator: an orthogonally-polarized locking beam that precludes residual unwanted interference and quantum noise locking method that locks the squeezing phase. Besides, the usage of low noise balanced detector, mode cleaner and the optical isolator helped to improve the audio frequency detection. The squeezing level is limited by absorption-induced losses at short wavelengths, which is 397.5 nm. The generated polarization squeezed light can be used in a quantum enhanced magnetometer to increase the measurement sensitivity.
ABSTRACT
We report on efficient generation of second harmonic laser and single-mode vacuum squeezed light of 795 nm with periodically poled KTiOPO4 (PPKTP) crystals. We achieved 111 mW of ultra-violet (UV) light at 397.5 nm from 191 mW of fundamental light with a PPKTP crystal in a doubling cavity, corresponding to a conversion efficiency of 58.1%. Using the UV light to pump an optical parametric oscillator with a PPKTP crystal, we realized -5.6 dB of a maximum squeezing. We analyzed the pump power dependence of the squeezing level and concluded that the UV light induced losses limit the improvement of the squeezing level. The generated squeezed light has huge potential application in quantum memory and ultra-precise measurement.
ABSTRACT
We demonstrate a simple, compact and cost-efficient diode laser pumped frequency doubling system at 795 nm in the low power regime. In two configurations, a bow-tie four-mirror ring enhancement cavity with a PPKTP crystal inside and a semi-monolithic PPKTP enhancement cavity, we obtain 397.5nm ultra-violet coherent radiation of 35mW and 47mW respectively with a mode-matched fundamental power of about 110mW, corresponding to a conversion efficiency of 32% and 41%. The low loss semi-monolithic cavity leads to the better results. The constructed ultra-violet coherent radiation has good power stability and beam quality, and the system has huge potential in quantum optics and cold atom physics.
