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.

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.

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.

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.

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.