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

Abstract

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.

Using a complex optical orbital-angular-momentum spectrum to measure object parameters

“…Then, the relative phase difference between the two OAM modes is given by (See Methods section for details) 29,36,40 : Δφ = atan I -− I Q-I OP − I =RP (2) We note that reports have shown the complex OAM spectrum measurement using an interferometer 34,35 , which might be sensitive to the setup vibration since its two branches usually have different optical paths. However, the approach in this work is based on non-interference 29,36,40 and may provide a more stable phase measurement.…”

“…The use of structured beams has recently been investigated in imaging 4,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] , sensing 4,11,[26][27][28][29][30][31][32][33][34][35][36] , and communications 4,11,37,38 and other applications 4,11,39 , including using OAM basis for single-frequency imaging and sensing in the radio frequency domain 24 and the quantum domain 20 . It may be desirable to design a complex OAM spectrum analyzer in the classical optical domain and explore its potential to provide information that could not be readily obtained using the traditional approach.…”

Single-shot measurement of the orbital-angular-momentum spectrum of light

“…However, this method also requires a series of measurements and since in this method only a very small portion of the incident field is used for detection, it is not suitable for very low-intensity fields such as the fields produced by parametric down-conversion (PDC). The other approaches to measuring the OAM spectrum include techniques based on rotational Doppler frequency shift 35,36 and concatenated Mach-Zehnder interferometers 37 . However, due to several experimental challenges, these approaches [35][36][37] have so far been demonstrated only for fields consisting of just a few modes.…”

“…The other approaches to measuring the OAM spectrum include techniques based on rotational Doppler frequency shift 35,36 and concatenated Mach-Zehnder interferometers 37 . However, due to several experimental challenges, these approaches [35][36][37] have so far been demonstrated only for fields consisting of just a few modes. Thus the existing methods for measuring the OAM spectrum information suffer from either poor efficiency 28,35 or strict interferometric stability requirements 31,32,37 or too much loss 33,34 .…”

“…One of the major challenges faced in the implementation of OAM-based high-dimensional protocols is the efficient detection of OAM spectrum, and it is currently an active research area [28][29][30][31][32][33][34][35][36][37] . There are several approaches to measuring the OAM spectrum of a field.…”