Phase Of Optical Wave Research Articles

Nanoscale plasmonic logic gates design by using an elliptical resonator.

This study implemented AND, NAND, OR, XOR, NOR, XNOR, and NOT plasmonic logic gates using the finite element method. The all-optical nanoscale logic gates were designed using a single structure based on the technology of insulator-metal-insulator nanoscale plasmonic waveguides. The phase of optical waves and the position of the control and input ports are the most important factors for attaining the optimal transmission value based on interference between the input and control ports. The transmission threshold is 35%, and 850 nm is the operating wavelength. This design creates nanoscale logic gates with a structure dimension of 250nm×250nm. The transmission threshold, modulation depth, contrast ratio, and insertion loss criteria were proposed to evaluate the efficacy of the all-optical gates.

A Survey of Structure of Atmospheric Turbulence in Atmosphere and Related Turbulent Effects

The Earth’s atmosphere is the living environment in which we live and cannot escape. Atmospheric turbulence is a typical random inhomogeneous medium, which causes random fluctuations of both the amplitude and phase of optical wave propagating through it. Currently, it is widely accepted that there exists two kinds of turbulence in the aerosphere: one is Kolmogorov turbulence, and the other is non-Kolmogorov turbulence, which have been confirmed by both increasing experimental evidence and theoretical investigations. The results of atmospheric measurements have shown that the structure of atmospheric turbulence in the Earth’s atmosphere is composed of Kolmogorov turbulence at lower levels and non-Kolmogorov turbulence at higher levels. Since the time of Newton, people began to study optical wave propagation in atmospheric turbulence. In the early stage, optical wave propagation in Kolmogorov atmospheric turbulence was mainly studied and then optical wave propagation in non-Kolmogorov atmospheric turbulence was also studied. After more than half a century of efforts, the study of optical wave propagation in atmospheric turbulence has made great progress, and the theoretical results are also used to guide practical applications. On this basis, we summarize the development status and latest progress of propagation theory in atmospheric turbulence, mainly including propagation theory in conventional Kolmogorov turbulence and one in non-Kolmogorov atmospheric turbulence. In addition, the combined influence of Kolmogorov and non-Kolmogorov turbulence in Earth’s atmosphere on optical wave propagation is also summarized. This timely summary is very necessary and is of great significance for various applications and development in the aerospace field, where the Earth’s atmosphere is one part of many links.

Express Wavenet: A lower parameter optical neural network with random shift wavelet pattern

Compared with other optical diffractive neural networks, the express wavenet (ExWave) is an improved and efficient network which adopts much fewer parameters. For advantages of the ExWave, firstly, the wavelet-like pattern is used to modulate the phase of optical waves; secondly, the number of parameters can be reduced from O(n2) to O(n), for the input image with n2 pixels; thirdly, the accuracy can be still high with only 1% of total parameters of the famous D2 NN. Besides, in the modified national institute of standards and technology (MNIST) dataset, 93.5% accuracy can be achieved with only 2457 parameters, nevertheless, 250880 parameters are required to meet a similar accuracy for the standard optical network. Moreover, the random shift wavelets exhibit characteristics of optical network vividly, especially for the vanishing gradient phenomenon in the training process. We present the modified expressway structure for solving this problem. Afterward, simulation have been carried out to validate effects of both random shift wavelet and expressway structure. Finally, it can be shown that the optical diffractive network in this work utilizes much fewer parameters than other neural networks. The detailed source code can be available in the following link: https://github.com/closest-git/ONNet.

Optical differentiation wavefront sensing with binary pixelated transmission filters.

Sensors measuring the spatial phase of optical waves are widely used in optics. The optical differentiation wavefront sensor (ODWS) reconstructs the wavefront of an optical wave from wavefront slope measurements obtained by inducing linear field-transmission gradients in the far-field. Its dynamic range and sensitivity can be adjusted simply by changing the gradient slope. We numerically and experimentally demonstrate the possibility of implementing the spatially varying transmission gradient using distributions of small pixels that are either transparent or opaque. Binary pixelated filters are achromatic and can be fabricated with high accuracy at relatively low cost using commercial lithography techniques. We study the impact of the noise resulting from pixelation and binarization of the far-field filter for various test wavefronts and sensor parameters. The induced wavefront error is approximately inversely proportional to the pixel size. For an ODWS with dynamic range of 100 rad/mm over a 1-cm pupil, the error is smaller than λ/15 for a wide range of test wavefronts when using 2.5-μm pixels. We experimentally demonstrate the accuracy and consistency of a first-generation ODWS based on binary pixelated filters.

Phase Retrieval with Application to Optical Imaging: A contemporary overview

i»?The problem of phase retrieval, i.e., the recovery of a function given the magnitude of its Fourier transform, arises in various fields of science and engineering, including electron microscopy, crystallography, astronomy, and optical imaging. Exploring phase retrieval in optical settings, specifically when the light originates from a laser, is natural since optical detection devices [e.g., charge-coupled device (CCD) cameras, photosensitive films, and the human eye] cannot measure the phase of a light wave. This is because, generally, optical measurement devices that rely on converting photons to electrons (current) do not allow for direct recording of the phase: the electromagnetic field oscillates at rates of ~1015 Hz, which no electronic measurement device can follow. Indeed, optical measurement/detection systems measure the photon flux, which is proportional to the magnitude squared of the field, not the phase. Consequently, measuring the phase of optical waves (electromagnetic fields oscillating at 1015 Hz and higher) involves additional complexity, typically by requiring interference with another known field, in the process of holography.

Free space millimeter wave-coupled electro-optic high speed nonlinear polymer phase modulator with in-plane slotted patch antennas.

We report in-plane slotted patch antenna-coupled electro-optic phase modulators with a carrier-to-sideband ratio (CSR) of 22 dB under an RF power density of 120 W/m(2) and a figure of merit of 2.0 W(-1/2) at the millimeter wave frequencies of 36-37 GHz based on guest-host type of second-order nonlinear polymer SEO125. CSR was improved more than 20 dB by using a SiO(2) protection layer. We demonstrate detection of 3 GHz modulation of the RF carrier. We also derive closed-form expressions for the modulated phase of optical wave and carrier-to-sideband ratio. Design, simulation, fabrication, and experimental results are discussed.

Scintillation resistant wavefront sensing based on multi-aperture phase reconstruction technique

A scintillation resistant sensor that allows retrieval of an input optical wave phase using a multi-aperture phase reconstruction (MAPR) technique is introduced and analyzed. The MAPR sensor is based on a low-resolution lenslet array in the classical Shack-Hartmann arrangement and two high-resolution photo-arrays for simultaneous measurements of pupil- and focal-plane intensity distributions, which are used for retrieval of the wavefront phase in a two stage process: (a) phase reconstruction inside the sensor pupil subregions corresponding to lenslet subapertures and (b) recovery of subaperture averaged phase components (piston phases). Numerical simulations demonstrate the efficiency of the MAPR technique in conditions of strong intensity scintillations and the presence of wavefront branch points.

Observation of optical wave phase and wave-front-correction in photorefractive two-wave mixing

The coupling effect between coupled optical wave phase and intensity is observed in photorefractive Bi 12GeO 20 crystal. The dependence of coupled optical wave phase variations on applied field, light beams ratio and grating spacing in two-wave mixing with Bi 12GeO 20 crystal is studied in theory and the comparison between the theoretical and experimental results is made. A way to correct wave-front-distortion is demonstrated.

Digital Image Processing in Flow Visualization

Flow visualization results from the interaction between light and matter. Classical methods such as shadowgraphy, schlieren photography, and interferometry visualize variation in the index of refraction induced by changes in density, pressure, or temperature. Nonuniformities of these physical observables modify the phase of optical waves, rendered visible by free-space propagation (shadowgraphy), optical processing in the back focal plane of a lens (schlieren photography), or interference with a ref­ erence wave (interferometry). The classical methods visualize variations of the index of refraction or spatial derivatives thereof integrated along the light path through the fluid. Three-dimensional space is projected onto a plane with the corresponding reduction in degrees of freedom. Except for axial symmetric or two-dimensional flows, spatial structures cannot be recovered from a single image. Interior detail may be visualized by illuminating the flow with a sheet of light and imaging scattered radiation from variations in particle density or physical observables. Mie scattering is widely used because particles scatter more efficiently than molecules. Rayleighand Raman-scattering cross sections are small, necessitating intense laser sources for flow visu­ alization. Excellent reviews of classical flow-visualization methods have been pub­ lished, for example, by Merzkirch (1974) and Lauterborn & Vogel (1984) and a beautiful and inspiring collection of pictures by Van Dyke (1982).

Theoretical model for optical-wave phase fluctuations

A model is developed for the probability density function of the phase of an optical wave propagating through atmospheric turbulence. The field of the optical wave is modeled as the coherent sum of a constant-amplitude component and a random component whose amplitude is governed by the K distribution. Under the same conditions, it was previously shown that the intensity of the field is approximately governed by the I–K distribution. Two functional forms of the phase distribution are derived, and special cases of each are discussed.

Optical wave phase fluctuations

This paper presents a series of studies on the effect of low-frequency fluctuations of the atmospheric refractive index on phase fluctuations of space-limited optical beams. Theoretical calculations have been made in the approximation of a smooth perturbation method. Numerous experimental data on statistical characteristics of optical wave phase fluctuations are given. These are used to verify the theoretical conclusions and to solve an inverse problem on the determination of the atmospheric turbulence characteristics.