Optical Review最新文献

We have derived formulation and evaluation of polarization-modulated triple-view information display with three TN-LCD layers. The proposed display is composed of three liquid–crystal display (LCD) panels that are placed at a certain gap between polarizers. The viewed image is generated after polarization modulations by the three LCD panels. The polarization modulated results depend on the view directions. Thus, information of three binary images is shared between the displayed images on the three LCD panels.

Magnesium fluoride (MgF₂) thin films deposited using atomic layer deposition (ALD) were studied for use as optical coatings, meta-surface anti-reflection layer, and chemically resistive passivation. The deposition was performed in a commercially available Picosun® R-200 Advanced ALD reactor. Characterization of composition, density, optical property, chemical resistivity and coverage were performed. ALD-deposited films showed high R + T at wavelength down to 350 nm, excellent 3D coverage, and high chemical resistivity. This technology enables unique properties to improve 3D structured optics such as metasurface.

We present an efficient construction method for object recognition based on speckle learning using the optical memory effect. An object classifier based on speckle learning without the process of reducing or eliminating scattering and with a simple optical setup has been previously reported, but it requires a large number of training images to improve the performance of the classifier. This method is not applicable for bioimaging because of the difficulty of collecting training images caused by position control and phototoxicity of target cells. In our method, a wide variety of training images are augmented by a computer from a few speckle intensity images in the working range of the optical memory effect. We experimentally demonstrated our method with a 4f-optical system implementing the optical memory effect. As a result, the constructed binary classifier showed high accuracy under various scattering conditions and resolutions of the test image.

Femtosecond pulsed lasers are widely used in applied technologies, such as laser processing, nonlinear optical microscopy, and time-of-flight measurement, wherein narrowing the pulse duration is particularly important for improving the processing efficiency and signal-to-noise ratio of measurement systems. This paper proposes a method for shortening temporal pulse waveforms using spectral intensity filtering. Symmetrical spectral filtering was specifically applied at the central wavelength of the femtosecond pulsed laser spectrum. To investigate the pulse-narrowing effect, we numerically simulated the pulse duration as a function of the filtering width and cut-off wavelength position. The results of these simulations showed that the pulse duration decreased as the filter wavelength approached the central wavelength of the light. Furthermore, increasing the filter width reduced the pulse duration. Additionally, we implemented a spatial light modulator-based pulse-shaping system to realize a spectral intensity filter. We experimentally demonstrated that the duration of a telecom-band pulse was reduced by 9.8% when using a spectral intensity filter with a width of 1 nm.

In a flow channel, generally, microorganisms derived from bacteria contained in water first attach to a surface, form colonies and then become a pollutant known as biofilm. It is important to control the generation and growth of this pollutant, because it has the disadvantage of causing insanitary conditions inside tubes employed in medical and food processing, resulting in various infections. In the present study, we estimate the process of formation of biofilm inside a glass tube by means of binarization and fractal dimension of light scattering patterns obtained under illumination of a white light source and a laser diode. Experiments are conducted for glass tubes filled with bacteria-containing water without flow and with flow to confirm the feasibility of the present method for monitoring biofilm adhering to their inner surfaces.

Acetone is a reliable index to evaluate the aging state of oil paper insulation. It is of great significance to study a fast, highly sensitive and accurate method of detecting acetone in oil to ensure the safe and stable operation of oil-immersed transformers. In this paper, a method based on surface enhanced Raman spectroscopy for the detection of acetone in oil is investigated. Based on the mechanism of surface-enhanced Raman spectroscopy (SERS), a simulation model of surface-enhanced substrate was constructed using COMSOL software, and it was determined that the enhancement effect was better when silver nanowires/zinc oxide nanorods (Ag/ZnO) composite structure was selected. Ag/ZnO substrates were prepared by solvothermal method and experimentally tuned and characterized to obtain SERS substrates with high enhancement properties. The substrate coupled partial least square (PLS) model was used to establish a method for the detection of acetone in insulating oils, and its limit of quantification for acetone was 0.003 mg/g, which meets the requirements for engineering testing.

Intensity modulation/direct detection (IM/DD) optical interconnect systems are susceptible to waveform distortion caused by complex nonlinearities. To reduce the effect of waveform distortion on signal transmission accuracy, in this paper, a random forest (RF) equalization algorithm based on decision tree (DT) integration is proposed for cost-sensitive IM/DD systems, which has the characteristics of nonlinear classification and regression. The performance of the RF equalizer is verified by simulation experiments on a 120 Gbps 8-level pulse amplitude modulation (PAM8) transmission system using an electro-absorption-modulated laser (EML). Simulation studies show that whether it is a back-to-back (B2B) transmission system or a 10 km optical fiber transmission system, the RF equalization scheme can achieve much better bit error rate (BER) performance than the traditional equalization scheme. In addition, in both transmission cases, the RF equalization scheme enables efficient classification of signals and is much less simpler than the artificial neural network (ANN) equalization scheme.

Abstract

Imaging of phase objects behind scattering media is a challenging task. Intensity imaging through diffusers can be achieved based on digital holography by obtaining the complex amplitude of the diffuser in advance. As described in this paper, we experimentally demonstrate the reconstructed images of phase objects behind diffusers with different diffusion angles by digital holography. Using the complex amplitude information of the diffuser to correct the complex amplitude information of the object through the diffuser, the phase distribution of the object is obtainable behind the diffuser. Imaging of phase objects behind diffusers has been verified through experiments using a plano-convex lens and a wedge substrate as phase objects with various scattering angles. Quantitative analyses of the phase objects are performed. The lens shape can be visualized from the known refractive index. Moreover, the curvature radius can be estimated.

The structure of the disordered gain media for a two-dimensional random laser was designed to achieve the specified emission spectrum by treating the scattering medium as deterministic cavities. A checkerboard distribution of scattering elements allows structural optimization of the scatterer array using a direct binary search method. Simulation results show that the emitted light can be concentrated in the specified wavelength bands. The effects of scatterer size and fabrication errors on the optimized emission spectrum were also investigated.

A biosensor based on 2-D photonic crystals is presented and considered. The proposed structure is made of 24 × 23 Si rods in the air background. The presented biosensor would be considered for detection of Cholesterol concentrations in blood samples, which can aid physicians in diagnosis of Hypercholesterolemia and heart diseases in early stages. To facilitate the designation and fabrication processes and overcome the gain and nonlinearity problems, only linear rods would be utilized. The presented structure operates based on the interference and scattering effects of Si defect rods positioned in the structure (black rods operate as the confining sensing media and dark green rods function as the coupling rods). The PANDA (the proposed structure indicates a PANDA face)-shaped waveguides can filter the resonant wavelengths. For studying the functionality of the proposed biosensor, photonic band gap (by the plane wave expansion (PWE) method) and field distribution (by the finite-difference-time-domain (FDTD) method) spectra should be considered. The appropriate dimension of the proposed biosensor (111.78 μm²) makes it a considerable option for utilization in bio-optical integrated circuits. Finally, for the Cholesterol concentrations in blood samples, the remarkable sensitivity (595.74 nm/RIU “RIU stands for refractive index unit”), quality factor (35–46), detection limit (6.1e−3–6.7e−3) RIU and figure of merit (14.89–16.3) RIU⁻¹ were achieved.