Antimony sesquisulfide Sb2S3, an emerging low-loss phase change material, has attracted great interest for its unique properties, enabling its huge potential applications in programmable integrated optics. A reconfigurable mode converter is proposed and demonstrated numerically assisted by a rectangle Sb2S3 inlaid in a slab 4H-SiC waveguide. A threedimension finite-difference time-domain (3D FDTD) method is employed to simulate and optimize the proposed structure. The TM0-to-TM1 mode conversion is realized with transmittances (T) of 0.91 and mode purity (MP) of 93% at the wavelength of 1550 nm in the crystalline Sb2S3 state. When the Sb2S3 is switched to the amorphous state, the mode-conversion effect disappears, and the incident TM0 mode propagates unimpededly with T > 0.99 and MP > 97.64% within the waveband from 1500 nm to 1600 nm. The nonvolatile reconfigurable mode converter can contribute to programmable photonic integrated circuits and neuromorphic optical computing.
KEYWORDS: Phase measurement, Imaging systems, Reflection, Microlens, Light sources and illumination, Microlens array, Collimation, Phase distribution, LED lighting, Chemical elements
We present a reflection quantitative phase measurement system via transport of intensity equation (TIE). The proposed system includes an illumination collimation module and a microscopic imaging module. LED illumination is used in illumination module to avoid the effect of speckle noise. In imaging module, the 4f imaging system is formed by a long working distance objective and a lens. The constructed system was calibrated and the actual magnification of the system was 5x for 10x objective imaging. By moving the camera, two images at different defocused distances can be recorded and used for solving TIE to retrieve the phase of tested sample. Finally, the characterization of microlenses demonstrate the effectiveness of the proposed system.
Average speckle size is an important statistical parameter representing the lateral profile feature of laser speckle, which has an impact on the measurement of in-plane displacement of scattering object. In this experiment, a measurement system of in-plane displacement through scattering object has been setup. By varying propagation distance and scattering surface diameter, laser speckles are collected by CCD camera and autocorrelated to obtain the estimation values of average speckle size, and then the in-plane displacements are measured by digital image correlation method. Afterward, the influence of average speckle size on in-plane displacement measurement is discussed, and the result shows that the larger the average speckle size is, the greater the measurement error is, and the smaller the measurement limit is, which has a certain reference value for practical applications in the displacement and deformation measurement of objects.
A reconfigurable polarization rotator is proposed and demonstrated numerically assisted by a right-angle Sb2S3 inlaid in a slab SiC waveguide. The crystalline Sb2S3 enables a 90° polarization rotation with transmittances (T) of -0.22 dB and polarization conversion efficiency (PCE) of 98.36% at the wavelength of 1500 nm. This rotation effect disappears with T > -0.014 dB and PCE < 3.16% within the waveband from 1500 nm to 1600 nm when the Sb2S3 is switched to the amorphous state. The reconfigurable polarization rotator can contribute to the programmable photonic integrated circuits and neuromorphic optical computing.
The liquid refractive index is one of the important optical parameters reflecting the properties of solution. A simple scheme based on shading effect for measuring liquid refractive index is presented. When a light beam passes through the liquid, the total reflection occurs at the interface with the air to produce a shading effect, forming a circular shading pattern, and its radius is related to the refractive index of the liquid. Based on this principle, a liquid refractive index measurement system based on smartphone is built. A rectangle colorimetric dish with tested liquid is illuminated by He-Ne laser. A white stickable label paper is attached to one side of colorimetric dish. Then the circular shading pattern displayed on label paper can be recorded by smartphone. A smartphone data processing program was developed to calculate the liquid refractive index from the image taken by smartphone. System calibration and smartphone shooting parameters are discussed in detail. The refractive index measurement experiments of sucrose solution and sodium chloride solution with different concentrations demonstrate the feasibility and effectiveness of the proposed method.
We present a simple and stable liquid refractive index measurement technique via electrically tunable lens (ETL). A focal point is produced when the parallel light passes through a convex lens. If a parallel plate with tested liquid is placed behind the lens, the position of focal point will be changed, which reflect the change of liquid refractive index. The axial displacement of focus point can be obtained by moving the camera and used to calculate the liquid refractive index. To avoid the mechanical movement of system, the convex lens is replaced by an electrically tunable lens. By exactly controlling the external currents of the ETL, the position of focal point can remain unchanged after placing the parallel plate with tested liquid. The change of focal length can be obtained by the change of external currents, which equal to the axial displacement of focus point. Thus, the liquid refractive index can be measured with the change of focal length. Some experiments of water, blend oil and 75% alcohol for measuring the liquid refractive index demonstrate the feasibility and effectiveness of the proposed method.
KEYWORDS: 3D modeling, 3D metrology, Ceramics, 3D scanning, Data modeling, 3D applications, Reverse modeling, Process modeling, Calibration, Design and modelling
Digitization is the inevitable trend of cultural heritage protection and research, and the structural measurement of cultural relics is an important basis for three-dimensional (3D) digitization, and it is also a necessary prerequisite for other digital derivative work. Taking ceramic artifacts as an example, this paper explores the comprehensive, accurate and efficient measurement of the size of cultural relics and realizes the comprehensive 3D digitization. The 3D data model of cultural relics was obtained by 3D scanner, and the model was processed and measured by Geomagic series software, so as to obtain the one-dimensional size parameters, overall and local area and volume information of cultural relics. The experimental results show that this method was convenient, fast and accurate, which was of great significance for understanding the structure of cultural relics and provides a reliable basis for the comprehensive digital display and subsequent protection research of cultural relics.
Based on the refraction characteristic of uniform and transparent liquid, the measurement error of the liquid refractive index using the internal standard method is analyzed, and an improved laser speckle method is proposed. This method designs a double-cell structure composed of two identical rectangular parallelepiped glass cells with one cell containing the liquid to be measured and the other one being empty. This double-cell structure is placed in the built optical system based on laser speckle, and then the refractive indices of sodium chloride solution and sucrose solution with various concentrations are measured by the improved method. Compared with the measurement values of the Abbe refractometer and the internal standard method, the results show that the improved method can significantly reduce the measurement error and improve the measurement accuracy.
We present a simple and stable quantitative phase imaging technique via Fresnel biprism-based digital holographic microscopy. A Fresnel biprism is used to divide the incoming beam and generate self-referencing common-path configuration. So, high contrast hologram is produced in overlapping area. To evaluate the performance of Fresnel biprism with different refringence angles, the system magnification and length are discussed in detail. In addition, different sources of illumination, such as laser and LED, are used in proposed system for studying the feasibility of quantitative phase imaging. The temporal stability of system is also illustrated by comparing with the Mach-Zehnder-based off-axis digital holographic setup. It is shown that the proposed scheme has sub-nanometer temporal stability (~0.109𝑛𝑚) due to the common-path geometry. The experiments on micro-lens array, biological cell and water droplet are reported demonstrating its application both for static and dynamic samples. The refractive index measurement results of polyester fiber also further demonstrate the effectiveness of the proposed system.
We present a simple and effective method for dual-wavelength phase imaging in Lensless Reflection Digital Holographic Microscopy (LRDHM). A filter is inserted between beam splitter and mirror in LRDHM. By adjusting the filter and mirror, the propagation directions of two reference beams of different wavelengths can be separated, and thus two off axis holograms with different fringe directions are simultaneously captured by a monochrome camera. Our scheme is available for real-time dual-wavelength phase imaging but requires minimum optical element and system modification for LRDHM. A series of simulations on wavefront interference analysis for using a filter is discussed in detail. We demonstrate the validity of proposed method with a step target.
A single-shot dual-wavelength lensless digital holography based on a dichroic mirror is presented to achieve quantitative phase imaging. The lensless digital holography is designed by a wavefront division transmission configuration with only a plane mirror and a beam splitter. By merely adding a dichroic mirror between plane mirror and beam splitter in lensless transmission digital holography, the propagation direction of two reference waves for different wavelengths can be adjusted separately by dichroic mirror and plane mirror. Therefore, a multiplexed hologram with different fringe directions for two wavelengths can be simultaneously obtained. Our technique is capable of real-time wavelength-multiplexing with minimum optical element and system modification.
Digital holographic microscopy is a well-known powerful technique for quantitative phase measurement. However, the object phase is always embedded in aberrations. Here, a simple numerical compensation method based on rotation and transpose is reported. At first, we can obtain transpose phase by doing transpose transformation for original unwrapped phase. After subtracting transpose phase from original unwrapped phase, the subtraction phase is obtained and parts of aberrations also can be compensated. Subsequently, the rotation phase is obtained by doing rotation transformation with 180° for subtraction phase. Then, the residual phase aberrations are eliminated by subtracting rotation phase from subtraction phase. Not only off-axis tilt and parabolic phase aberration but also high order aberrations are removed without fitting operation or prior parameter of the specimen. The great performance makes our scheme available for single-shot quantitative phase imaging. The simulation results demonstrate the feasibility of our proposal.
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