Optical Review最新文献

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.

Optical resonators are particularly suitable for anaemia state detection due to small sample size, real-time detection and low power consumption. However, the quality factor and sensitivity of resonant cavity sensors are mutually constrained, so the single objective optimization algorithms proposed so far can only achieve a single optimization of sensitivity or quality factor, which limits chip performance. This article presents a multi-objective optimization design of the runway ring resonant cavity sensor based on the BP-NSGA II algorithm, which has achieved good performance improvement. The simultaneous incorporation of quality factor and sensitivity provides access to key structural design parameters to overcome the limitations of sensitivity and quality factor constraints on each other, thereby improving sensor performance. The results show that the optimized structure has a sensitivity of 439 nm/RIU, a quality factor of 938, a relative error of 1.37% and 3.9% for the sensitivity and quality factor, respectively, a linearity of 0.00004636% for the sensitivity, and a training time of 3 min. The method has the advantages of small errors and short learning time. A new optimization method is provided for the design of the resonant cavity of a runway ring.

The optical force exerted on a Rayleigh dielectric spherical particle by a photonic jet is investigated in the framework of the Rayleigh approximation. The photonic jet is generated by a plane wave illuminating a Generalized Luneburg Lens (GLLs). The electric field of the photonic jet is calculated using Discrete Dipole Approximation (DDA). The effects of wavelength of incident plane wave, focal length and radius of the GLLs on optical force are analyzed. Numerical results show that the stability of the captured particles can be controlled by changing the incident wavelength, focal length and radius of the GLLs.

Visibility high-precision measurement has a wide range of applications in the field of aviation and navigation. This paper proposes and designs a visibility measuring system based on a multi-reflection cell. In terms of the definition of the meteorological optical range (MOR), this system calculates the distance at which the beam is attenuated to 5% by means of multiple reflections with a long propagation distance, so as to obtain accurate atmospheric visibility. Different from the short-distance ring-down cavity with a length of 0.5 m, the length of the multi-reflection cell of this system can reach more than 10 m. Compared with the traditional transmissive method, the calculation results are more in line with the real situation of the atmospheric environment because the atmospheric non-uniformity and inversion parameters are considered. Experiments show that this method has better robustness and can stably measure atmospheric visibility under the condition of limited equipment space with an error of 5%.

In this paper, we propose a method to increase vection strength through video image processing in the periphery, rather than the center, of the visual field. Specifically, we propose two methods. One is an image stretching process in the visual periphery and the other is an alpha-blending process with an expanding circle grating in the periphery of the field. We clarified the relationship between the processing conditions and vection strength and found that stretching in the left–right direction increased vection strength while stretching in the downward direction did not. When adding expanding grating by alpha-blending, vection strength and duration were increased in almost all cases.

Abstract

We are researching a new display device that allows the public to experience augmented reality without wearable devices. In this paper, we implement an image processing system that improves the dynamically changing image quality deterioration, which is a problem unique to optical systems that project images on the real space, and specify the necessary system requirements from the results of verification of the effect. We quantify the characteristics of blur for each of the three primary colors defined as digital image data, and implement image processing that applies filter correction to the input image data during aerial imaging. Since the effect on image quality depends on what kind of imaging optical path is formed, we designed the device structure assuming that it will be applied to signage products, and built an experimental environment that can analyze the aerial image that the user actually sees. The image subjected to the correction process follows an optical path that forms an image in the air, and the user visually recognizes the image with emphasized edges. We compared the results of the actual aerial image and the simulation results, and clarified the system requirements for realizing an image processing system with higher correction accuracy.