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Hofstadter's butterfly spectrum, which characterizes the energy bands of electrons in a 2D lattice under a perpendicular magnetic field, has been emulated and experimentally characterized in periodic bandgap structures at microwave and acoustic frequencies. However, measurement of the complete spectrum at optical frequencies has yet to be demonstrated. Here, we propose a simple topological photonic structure based on a circular array of microrings with periodic resonant frequency detunings that can be implemented on an integrated optics platform. We show that this ring-of-rings structure exactly emulates the Harper equation and propose an experimental approach for measuring Hofstadter's butterfly spectrum at optical frequencies.The quasi-steady-state (QSS) self-focusing of partially coherent light pulses (PCLPs) in nonlinear media is studied. The analytical formulas of the QSS self-focusing of PCLPs in nonlinear media (e.g., the beam width, spatial coherence width, and focal length) are presented. The effect of spatial coherence on the focal length and focus moving is investigated in detail. In particular, it is found that a PCLP has more advantages to avoid the optical damage of materials than a fully coherent light pulse.Mueller polarimetry is a powerful optical technique in the analysis of micro-structural properties of optical samples. However, there is no explicit relationship between individual Mueller matrix elements and the physical properties of the sample. Several matrix decomposition algorithms corresponding to specific optical models have been proposed, which extract the physical information from measured Mueller matrices. Nevertheless, we still need a prior assessment method to decide which model is more suitable for the experimental data. In this Letter, we propose a set of characteristic Mueller matrices that allows us to obtain information about the breaking of rotation, mirror, and reciprocal symmetry properties in the sample by direct inspection of several elements of the Mueller matrix. [https://www.selleckchem.com/products/oul232.html find more] By further analyzing the possible origin of symmetry breaking, we can learn the type and mixing status of anisotropies in the measured sample. We have verified our theory with Monte Carlo simulations of polarized light scattering in an isotropic or anisotropic medium containing different configurations of spherical and cylindrical scatterers. This study may help experimenters choose more suitable Mueller matrix decomposition methods.We experimentally demonstrate simultaneous turbulence mitigation and channel demultiplexing in a 200 Gbit/s orbital-angular-momentum (OAM) multiplexed link by adaptive wavefront shaping and diffusing (WSD) the light beams. Different realizations of two emulated turbulence strengths (the Fried parameter $r_0 = 0.4,\,1.0\;\rm mm$r0=0.4,1.0mm) are mitigated. The experimental results show the following. (1) Crosstalk between OAM $l = + 1$l=+1 and $l = - 1$l=-1 modes can be reduced by $ \gt 10.0$&gt;10.0 and $ \gt 5.8\;\rm dB$&gt;5.8dB, respectively, under the weaker turbulence ($r_0 = 1.0\;\rm mm$r0=1.0mm); crosstalk is further improved by $ \gt 17.7$&gt;17.7 and $ \gt 19.4\;\rm dB$&gt;19.4dB, respectively, under most realizations in the stronger turbulence ($r_0 = 0.4\;\rm mm$r0=0.4mm). (2) The optical signal-to-noise ratio penalties for the bit error rate performance are measured to be $\sim0.7$∼0.7 and $\sim1.6\;\rm dB$∼1.6dB under weaker turbulence, while measured to be $\sim3.2$∼3.2 and $\sim1.8\;\rm dB$∼1.8dB under stronger turbulence for OAM $l = + 1$l=+1 and $l = - 1$l=-1 mode, respectively.We demonstrate theoretically that the average spatial intensity profile of any partially coherent optical beam, composed of a finite-power bright intensity bump atop a fluctuating background, evolves into a universal self-similar Gaussian shape upon long-term propagation in a statistically homogeneous, isotropic linear random medium. The result depends neither on the degree of the background spatial coherence nor on the strength of the medium turbulence. To our knowledge, this is the first demonstration of universal self-similar asymptotics in linear random media.Retinal optical coherence tomography (OCT) and OCT angiography (OCTA) suffer from the degeneration of image quality due to speckle noise and bulk-motion noise, respectively. Because the cross-sectional retina has distinct features in OCT and OCTA B-scans, existing digital filters that can denoise OCT efficiently are unable to handle the bulk-motion noise in OCTA. In this Letter, we propose a universal digital filtering approach that is capable of minimizing both types of noise. Considering that the retinal capillaries in OCTA are hard to differentiate in B-scans while having distinct curvilinear structures in 3D volumes, we decompose the volumetric OCT and OCTA data with 3D shearlets, thus efficiently separating the retinal tissue and vessels from the noise in this transform domain. Compared with wavelets and curvelets, the shearlets provide better representation of the layer edges in OCT and the vasculature in OCTA. Qualitative and quantitative results show the proposed method outperforms the state-of-the-art OCT and OCTA denoising methods. Also, the superiority of 3D denoising is demonstrated by comparing the 3D shearlet filtering with its 2D counterpart.A chirped anti-resonant reflecting optical waveguide (ARROW) for the simultaneous measurement of pressure intensity and spatial localization has been proposed and experimentally demonstrated. An etched chirped ARROW was fabricated, which shows a chirped spectral characteristic. Additionally, an in-line Mach-Zehnder interferometer is also formed with the core mode and higher-order modes. The pressure intensity and the spatial localization can be detected by interrogating the wavelength shift of the in-line Mach-Zehnder interferometer and the chirped ARROW, respectively. The experimental results show that the pressure sensitivity of $ - 4.42\;\rm nm/MPa$-4.42nm/MPa and the spatial sensitivity of 0.86 nm/cm can be achieved. The proposed fiber optic sensor can be used for multipoint pressure detection in the fields of security, structure monitoring, and oil exploration, etc.