Theoretical analysis of the optical rotational Doppler effect under atmospheric turbulence by mode decomposition

The optical rotational Doppler effect associated with orbital angular momentum provides a new means for rotational velocity detection.In this paper,we investigate the influence of atmospheric turbulence on the rotational Doppler effect.First,we deduce the generalized formula of the rotational Doppler shift in atmospheric turbulence by mode decomposition.It is found that the rotational Doppler signal frequency spectrum will be broadened,and the bandwidth is related to the turbulence intensity.In addition,as the propagation distance increases,the bandwidth also increases.And when C_(n)^(2)≤5×10^(-15)m^(-2/3)and 2z≤2 km,the rotational Doppler signal frequency spectrum width d and the spiral spectrum width d_(0)satisfy the relationship d=2d_(0-1).Finally,we analyze the influence of mode crosstalk on the rotational Doppler effect,and the results show that it destroys the symmetrical distribution of the rotational Doppler spectrum about 2l·Ω/2π.This theoretical model enables us to better understand the generation of the rotational Doppler frequency and may help us better analyze the influence of the complex atmospheric environment on the rotational Doppler frequency.

Method for compensating translational motion of rotationally symmetric target based on local symmetry cancellation

The micro-Doppler effect of moving targets may suffer from aliasing and Doppler migration due to the translational motion, which affects the application in real-time target identification. A new compensating method for the rotationally symmetric target is proposed and demonstrated. By utilizing the micro-Doppler symmetry cancellation effect, the method can accurately compensate the translation effect, meanwhile, it behaves well in noise restraint. Computer simulations verify the high accuracy and efficiency of this method.

Dual-point noncoaxial rotational Doppler effect towards synthetic OAM light fields for real-time rotating axis detection

Probing the axis of a rotator is important in astrophysics,aerospace,manufacturing,machinery,automation,and virtual reality,etc.Existing optical solutions commonly require multiple sequential measurements via symmetry-broken light fields,which make them time-consuming,inefficient,and prone to accumulated errors.Herein,we propose the concept of a dual-point noncoaxial rotational Doppler effect(DNRDE)and demonstrate a one-shot detection technique to solve this problem.An on-demand synthetic orbital angular momentum(OAM)light beam impinges on a rotating scatterer surface,supporting dual-point rotational Doppler shifts,in which the information of the rotating axis is acquired by comparing these two frequency shifts with a prescribed threshold.The existence of arbitrary dual-point Doppler shifts enables the one-time direct identification of rotating axis orientations,which is fundamentally inaccessible in single-point detection.This robust detection technique is compatible with generalised synthetic OAM light fields by utilising optical modal filters.Compared with traditional approaches,our DNRDE-driven detection approach exhibits a four-fold enhancement in measurement speed,higher energy efficiency,and superior accuracy with a maximal absolute measurement error of 2.23°.The proposed dual-point detection method holds great promise for detecting rotating bodies in various applications,such as astronomical surveys and industrial manufacturing.

Implementation of integrated nonlocal sensing for object shape and rotational speed

The expeditious acquisition of information pertaining to objects through the utilization of quantum technology has been a perennial issue of concern.So far,the efficient utilization of information from dynamic objects with limited resources remains a significant challenge.Here,we realize a nonlocal integrated sensing of the object's amplitude and phase information by combining digital spiral imaging with the correlated orbital angular momentum states.The amplitude information is utilized for object identification,while the phase information enables us to determine the rotational speed.We demonstrate the nonlocal identification of a rotating object's shape,irrespective of its rotational symmetry,and introduce the concept of the correlated rotational Doppler effect,establishing a fundamental connection between this effect and the classical rotational Doppler effect,i.e.,that both rely on extracting crucial information from the spiral spectrum of objects.The present study highlights a promising pathway towards the realization of quantum remote sensing and imaging.

点迹-曲线关联算法的旋转对称群目标分辨

基于微多普勒效应分析的弹道目标识别得到了广泛研究,然而传统的微多普勒特征提取技术大都难以解决空间群目标的分辨与识别。针对这一问题,提出了一种基于点迹-曲线关联算法的空间群目标分辨方法。在以旋转对称群目标为研究对象的前提下,建立了具有滑动散射特性的目标模型并分析推导了散射点的微动表达式,利用点迹凝聚处理抑制了一维距离像旁瓣,在此基础上,提出了点迹-曲线关联算法分离出混叠的群目标微多普勒曲线,通过各曲线的极值包络特性差异实现了旋转对称群目标分辨。实验仿真验证了本方法的正确性和可行性。

Orbital angular momentum complex spectrum analyzer for vortex light based on the rotational Doppler effect

The ability to measure the orbital angular momentum(OAM)distribution of vortex light is essential for OAM applications.Although there have been many studies on the measurement of OAM modes,it is difficult to quantitatively and instantaneously measure the power distribution among different OAM modes,let alone measure the phase distribution among them.In this work,we propose an OAM complex spectrum analyzer that enables simultaneous measurements of the power and phase distributions of OAM modes by employing the rotational Doppler effect.The original OAM mode distribution is mapped to an electrical spectrum of beat signals using a photodetector.The power and phase distributions of superimposed OAM beams are successfully retrieved by analyzing the electrical spectrum.We also extend the measurement technique to other spatial modes,such as linear polarization modes.These results represent a new landmark in spatial mode analysis and show great potential for applications in OAM-based systems and optical communication systems with mode-division multiplexing.

Symmetry detection of rotating patterns based on rotational Doppler effect of light

We propose a method for detecting the symmetry of rotating patterns based on the rotational Doppler effect(RDE)of light.The basic mechanisms of the RDE are introduced,and the spiral harmonic distribution of rotating patterns is analyzed.By irradiating the rotating pattern using a superimposed optical vortex and analyzing the amplitude of the RDE signal,the spiral harmonic distribution of the pattern can be measured,and then its symmetry can be detected.We demonstrate this method experimentally by using patterns with different symmetries and shapes.As the method does not need to receive the scattered light completely and accurately,it promises potential application in detecting symmetrical rotating objects at a long distance.

旋转对称目标滑动型散射中心的微Doppler特性

微动特征是当前学术界公认的弹道中段目标雷达识别的有效特征之一,目前的特征提取与识别研究通常假定散射中心与目标自身的微动规律一致,其微Doppler效应为正弦调频信号.但这种假设忽视了随着观测视角的改变,散射中心将在目标体上滑动这一事实.文中对弹体不同位置散射中心的微运动特性进行了完整建模,首次得到了滑动型散射中心微Doppler的数学表达式,并针对导弹攻防对抗条件导出其Taylor近似,指出并非文献上通常假定的正弦规律.设计了进动目标暗室动态测量实验,生动揭示了散射中心的这种滑动特性,实验现象与文中的理论分析结果相一致.文中揭示的微Doppler机理为弹头类目标微动特性模拟及特征反演等应用领域提供了更为准确的物理基础和数学模型.

Integrated terahertz vortex beam emitter for rotating target detection

We propose a terahertz(THz)vortex emitter that utilizes a high-resistance silicon resonator to generate vortex beams with various topological charges.Addressing the challenge of double circular polarization superposition resulting from the high refractive index contrast,we regulate the transverse spin state through a newly designed second-order grating partially etched on the waveguide’s top side.The reflected wave can be received directly by a linearly polarized antenna,simplifying the process.Benefiting from the tuning feature,a joint detection method involving positive and negative topological charges identifies and detects rotational Doppler effects amid robust micro-Doppler interference signals.This emitter can be used for the rotational velocity measurement of an on-axis spinning object,achieving an impressive maximum speed error rate of∼2%.This approach holds promise for the future development of THz vortex beam applications in radar target detection and countermeasure systems,given its low cost and potential for mass production.