Fast mode decomposition in few-mode fibers

Retrieval of the optical phase information from measurement of intensity is of a high interest because this would facilitate simple and cost-efficient techniques and devices. In scientific and industrial applications that exploit multi-mode fibers, a prior knowledge of spatial mode structure of the fiber, in principle, makes it possible to recover phases using measured intensity distribution. However, current mode decomposition algorithms based on the analysis of the intensity distribution at the output of a few-mode fiber, such as optimization methods or neural networks, still have high computational costs and high latency that is a serious impediment for applications, such as telecommunications. Speed of signal processing is one of the key challenges in this approach. We present a high-performance mode decomposition algorithm with a processing time of tens of microseconds. The proposed mathematical algorithm that does not use any machine learning techniques, is several orders of magnitude faster than the state-of-the-art deep-learning-based methods. We anticipate that our results can stimulate further research on algorithms beyond popular machine learning methods and they can lead to the development of low-cost phase retrieval receivers for various applications of few-mode fibers ranging from imaging to telecommunications

Efficient and mode selective spatial mode multiplexer based on multi-plane light conversion.

International audienc

Rotational Doppler effect on reflection upon an ideal rotating propeller

International audienceThe rotational Doppler shift is the counterpart of the usual linear Doppler effect for rotating bodies. We study by an experimental approach coupled with theoretical considerations the rotational shift of a fundamental laser light reflected on an ideal rotating propeller. We decompose the reflected light on a Laguerre–Gaussian basis and show that only modes having the same rotational symmetry as the propeller are involved in the decomposition. The latter experience a frequency shift proportional to the rotation frequency of the propeller and the topological charge of the beam. Extensions of this work in the microwave domain are then considered. © 2022 Optica Publishing Grou

Combined third-harmonic generation and four-wave mixing microscopy of tissues and embryos

Nonlinear microscopy can be used to probe the intrinsic optical properties of biological tissues. Using femtosecond pulses, third-harmonic generation (THG) and four-wave mixing (FWM) signals can be efficiently produced and detected simultaneously. Both signals probe a similar parameter, i.e. the real part of the third-order nonlinear susceptibility χ((3)). However THG and FWM images result from different phase matching conditions and provide complementary information. We analyze this complementarity using calculations, z-scan measurements on water and oils, and THG-FWM imaging of cell divisions in live zebrafish embryos. The two signals exhibit different sensitivity to sample size and clustering in the half-wavelength regime. Far from resonance, THG images reveal spatial variations |Δχ((3))(-3ω;ω,ω,ω)| with remarkable sensitivity while FWM directly reflects the distribution of χ((3))(-2ω(1) + ω(2);ω(1), -ω(2), ω(1)). We show that FWM images provide χ((3)) maps useful for proper interpretation of cellular THG signals, and that combined imaging carries additional structural information. Finally we present simultaneous imaging of intrinsic THG, FWM, second-harmonic (SHG) and two-photon-excited fluorescence (2PEF) signals in live Caenorhabditis elegans worms illustrating the information provided by multimodal nonlinear imaging of unstained tissue

Weakly-Coupled 6-LP-Mode Fiber with Low Differential Mode Attenuation

International audienc