Search

The hyperspectral full polarization imaging system (HFPIS) based on spatial modulation and liquid crystal tunable filter (LCTF) can modulate the polarization information of the target into the interferogram by means of interference imaging. It has the advantage of rapid imaging of the hyperspectral full polarization information from the target, and has good real time imaging and practicality. Through the spectroscopic imaging mode of a Savart prism, the corresponding interference optical path and imaging system are designed, including a beam expander, spatial modulator, LCTF, focusing system, and imaging sensor. This system can extract the different information from the target and demodulate it so as to obtain the hyperspectral polarization image. The experiment shows that the HFPIS can reveal the texture, contour, and other details of the target in the fog, and has obvious advantages over the traditional intensity imaging methods.

Controlling dispersion of a whispering gallery mode resonator is of critical importance for many nonlinear applications, such as frequency comb generation, parametric oscillators, Raman lasers, stimulated Brillouin lasers, and ultrafast optics. Here, we show by numerical and theoretical modeling that dispersion can be strongly engineered in a three-layer-coated microsphere of high, low, and high refractive indices (RIs). We investigate the impact of the coating thickness, the gap between the two high-RI layers, the surrounding medium, and the coating materials on the group-velocity dispersion and discover that the dispersion is controllable over a broad range in both normal and anomalous dispersion regimes. Our approach provides dispersion engineering flexibility in any axisymmetric resonator with a three-layer-coating structure.

We investigate selective excitation of localized axial modes in a high-Q microcylindrical resonator experimentally, numerically, and theoretically. The resonator is fabricated using a standard fusion splicer, and the characteristic resonance spectra are acquired by using a tapered fiber coupled at different positions along the microcylinder. The spatial and spectral mode properties are analyzed with our numerical and theoretical model, which are in good agreement with the experimental results. Moreover, controlled and robust coupling is experimentally demonstrated by vertically moving the resonator while keeping it in contact with the tapered fiber. Our microcylindrical resonator combines clean and nearly equidistant spectra, a high quality factor up to 3.1×10(7), a large mode volume, and a more favorable frequency spacing of ∼3.91 GHz, offering unique potential in sensors, microlasers, optical filters, group delay lines, and especially some applied fields that require tuning.

A bicylinder-based geometric calibration and three-dimensional detecting method is developed for an artificial compound eye. The proposed method uses two coaxial cylinders as reference surfaces. This technique is more suitable for a wide field of view than the traditional two-plane method. A weighted multiple-line intersection algorithm is used to determine precisely the 3D intersecting point. To evaluate these methods, a number of known points that cover a 100°×90° field-of-view and different radial distances are measured. Experimental results indicate that the proposed methods are accurate and reliable, and satisfy the requirements of compound eye calibration.

A compound eye has the advantages of a large field of view, high sensitivity, and compact structure, showing that it can be applicable for 3D object detection. In this work, an artificial compound eye system is developed for 3D object detection, consisting of a layer of lenslets and a prism-like beam-steering lens. A calibration method is developed for this system, with which the correspondences between incident light rays and the relevant image points can be obtained precisely using an active calibration pattern at multiple positions. Theoretically, calibration patterns at two positions are sufficient for system calibration, although more positions will increase the accuracy of the result. 3D positions of point objects are calculated to evaluate the system, which are obtained by the intersection of multiple incident light rays in the least-squares sense. Experimental results show that the system can detect an object with angular accuracy of better than 1 mrad, demonstrating the feasibility of the proposed compound eye system. With a 2D scanning device, the system can be extended for general object detection in 3D space.

For conventional camera calibration methods, well-focused images are necessary to detect features accurately. However, this requirement causes practical inconveniences to image acquisition for long- and short-distance photogrammetry. In this study, three active phase-shift circular grating (PCG) arrays are used as calibration patterns. The PCGs' centers are regarded as feature points that can be accurately extracted by ellipse fitting of 2π-phase points even though patterns are substantially blurred. In the experiments, Gaussian filters are utilized to blur pattern images, and different standard deviations are set for different fuzzy degrees. Pattern images with different defocusing degrees are also captured. The period and number of PCGs and noise are considered. Experimental results indicate that our method is accurate, reliable, and insensitive to image defocusing.

We propose and realize a packaged structure for the microcylinder–taper coupling system by only gluing a glass tube and two glass plates together. Our package method avoids embedding the coupling system into the polymer, thus leaving the whispering gallery mode evanescent fields available for environmental sensing. The excitation of localized high-order axial modes in the cylindrical resonator fabricated by using a fusion splicer is demonstrated and a quality factor (Q) up to 1.4×107 is obtained. The Q maintenance and stable spectrum are realized by sealing the packaged device in a clean box. Moreover, the robustness of the packaged structure is also tested, demonstrating its remarkable antivibration ability. The portability and robustness of the device make it attractive in practical applications such as sensors, lasers, and especially some applied areas in strong vibration environments.

A novel packaged microsphere-taper coupling system which consists of a glass tube and two glass plates is proposed and demonstrated in this paper. We analyze the impact of the microsphere distortion on the resonant spectrum and it is observed that a very high quality factor (Q) up to 1.08×10(8) can be achieved by optimizing the microsphere position and orientation relative to the fiber taper. The maintenance of Q and a stable spectrum are realized by placing the packaged structure in a sealed organic glass box. Furthermore, to verify the practicability of the sealed device, thermal sensing experiments are carried out, which indicates the excellent convenience of the device with a resolution of 1.12×10(-4)°C. The portability and robustness of the packaged structure make it strikingly attractive and illustrate its potential in practical microcavity sensors and lasers.

Rotating point spread function (PSF) provides a novel approach to detect three-dimensional position. As the optical aberration of a system can hardly be removed completely, effects of aberration on the PSF were studied both analytically and numerically. Results show that the intensity pattern is robust to both astigmatism and coma, while astigmatism affects the rotating angle of the PSF, and coma affects the lateral position of the PSF.

An aspherical lens is fabricated from an ultraviolet (UV) curable polymer and is characterized by measuring its focal spot. Electrostatic force is employed to manipulate the shape of the liquid polymer lens. Experiment results show that a liquid lens in a strong electrostatic field can be distorted from initial spherical shape to parabolic to even near cone shape. With in situ measurement of the surface profile and focal spot, an aspherical liquid lens with good performance can be cured to a solid aspherical lens by UV light. A probe scanning microscope is employed to accurately measure the focal spot of the aspherical lens, and the modulation transfer function (MTF) of the aspherical lens is calculated to characterize it. A focal spot of 1.825 microm diameter, an MTF of 800 line pairs/mm cutoff spatial frequency, and a Strehl ratio of 0.742 are achieved. These demonstrate the feasibility of fabricating an aspherical lens with small aberrations by using this method.