In this work, a blue gallium nitride (GaN) micro-light-emitting-diode (micro-LED)-based underwater wireless optical communication (UWOC) system was built, and UWOCs with varied Maalox, chlorophyll, and sea salt concentrations were studied. Data transmission performance of the UWOC and the influence of light attenuation were investigated systematically. Maximum data transmission rates at the distance of 2.3 m were 933, 800, 910, and 790 Mbps for experimental conditions with no impurity, 200.48 mg/m³ Maalox, 12.07 mg/m³ chlorophyll, and 5 kg/m³ sea salt, respectively, much higher than previously reported systems with commercial LEDs. It was found that increasing chlorophyll, Maalox, and sea salt concentrations in water resulted in an increase of light attenuation, which led to the performance degradation of the UWOC. Further analysis suggests two light attenuation mechanisms, e.g., absorption by chlorophyll and scattering by Maalox, are responsible for the decrease of maximum data rates and the increase of bit error rates. Based on the absorption and scattering models, excellent fitting to the experimental attenuation coefficient can be achieved, and light attenuation by absorption and scattering at different wavelengths was also investigated. We believe this work is instructive apply UWOC for practical applications.

The scattering properties of ZnO nanospheres with four different particle diameters of 10, 50, 100, and 200 nm suspended in water are investigated theoretical and experimentally in the spectral range of the entire visible range and part of the near-infrared region. The scattering properties of ZnO nanospheres suspended in water are described by employing three main parameters: the angular distribution of the scattering intensity I, the scattering extinction coefficient αscat, and the scattering cross section σscat. The results indicate that (i) at a certain wavelength, the angular distribution of the scattering intensity appears as an obviously forward-propagating feature, and the forward-scattering intensity is dominant gradually when the particle diameter increases from 10 to 200 nm, and (ii) the scattering extinction coefficient and cross section can be determined by using the measured transmittance changes of a pure water sample and a given ZnO sample; they all are shown to be dependent on the particle size and incident wavelength. The experimental results of four different scattering samples agree well with the theoretical predictions within the given wavelength range.

We demonstrate a size sensing technique for nano-particles using optical differential phase measurement by a dual fiber interferometer through phase-generated carrier (PGC) demodulation. Nano-particle diameters are obtained from the differential phase shift as a result of adding an optical scattering perturbation into two-beam interference. Polystyrene nano-particles with diameters from 200 to 900 nm in a microfluidic channel are detected using this technique to acquire real-time particle diameters. Compared with amplitude sensing with over 10 mW of laser irradiance, particle sizing by PGC phase sensing can be achieved at a laser power as low as 1.18 mW. We further analyze major sources of noise in order to improve the limits of detection. This sensing technique may find a broad range of applications from the real-time selection of biological cell samples to rare cell detection in blood samples for early cancer screening.

In order to improve the inversion precision of aerosol mass concentrations based on the particle group light scattering method, the concept that particles through a laser beam are equivalent to an aggregate is proposed. A fractal model for aerosol mass concentration using the signal amplitude distribution of aggregates is presented, and then the subsection calibration method is given. The experimental results show that the mass concentrations inversed by this model agree well with those measured by the norm-referenced instrument. The average relative errors of the two experiments are 5.6% and 6.0%, respectively, which are less than those obtained by the conventional inversion model.

A method of chromatic polarization imaging is presented for the online detection of colorless plastic contaminants from ginned cotton in an industrial setting. To understand the experimental results, we consider a realistic microscopic model, including the multiple scattering of anisotropic fibers and the light propagation in anisotropic slabs. A Monte Carlo code, based on the extended Jones matrix, is developed to simulate photon migration with polarization states, and phase information followed. Using simulations and experiments, we analyze the underlying mechanisms and evaluate the performance of this method with different layer thicknesses. Our approaches proposed in this Letter also have the potential to be applied in tissue imaging, remote sensing, and other scenarios.

The far-zone scattered spectral density of a light wave on the scattering from a collection of particles is investigated, and the relationship between the character of the collection and the distribution of the scattered spectral density is discussed. It is shown that both the number of particles and their locations in the collection play roles in the distribution of the far-zone scattered spectral density. This phenomenon may provide a potential method to reconstruct the structure character of a collection of particles from measurements of the far-zone scattered spectral density.

Research on light scattering from a large chiral sphere shows that the rainbow phenomenon is different from that of an isotropic sphere. A chiral sphere with certain chirality generates three first-order rainbows. In this Letter, we present a geometric optics interpretation for the phenomenon and make a calculation of the rainbow angles. The ray traces inside the sphere are determined by the reflection and refraction laws of light at the achiral–chiral interface and the chiral–achiral interface. The calculated rainbow angles achieve good agreements with those obtained by the analytical solutions. The effects of chirality and the refractive index of the sphere on rainbow angles are analyzed.