Omnidirectional Optical System Research Articles

MEMS mirror based omnidirectional scanning for lidar optical systems

Lidar 3D vision system is currently one of the most effective technical means for high-precision perception of three-dimensional image information of the surrounding environment. Microelectron-mechanical systems (MEMS) micromirror lidar has advantages of miniaturization, fast scanning speed, and relatively low price. The MEMS micromirror scanning method has become the best choice for laser scanning 3D image sensors. However, due to the small size of the MEMS micromirror, it can only scan a small angle range, which limits its industrial applications. In this paper, combined with MEMS micro-mirror spiral scanning form, we design a new type of omnidirectional optical system that can realize MEMS lidar omnidirectional scanning imaging. The overall optical system is composed of the catadioptric prism, the MEMS micromirror, and the compensation prism. The overall system can achieve 360° omnidirectional scanning imaging with a horizontal resolution of 0.1°; a vertical field view with a 0.5° resolution. The design results are analyzed by the optical design software (Zemax). The point diagram shows that the emitted light spots are circular and evenly distributed. The divergence angle is less than 1mrad, which can well meet the actual needs and solve the problems of solid-state, miniaturization, and omnidirectional scanning imaging of lidar.

A Novel Focal Length Measurement Method for Center-Obstructed Omni-Directional Reflective Optical Systems

An omni-directional optical system can be used as a surveillance camera owing to its wide field angle. In cases in which a system is designed with a central screen obscuring structure to increase the resolution of the off-axis field, however, the conventional methods cannot be used to measure the effective focal length (EFL). We assumed the actual and theoretical distortion values of the fabricated optical system to be the same and determined the system’s EFL by finding the minimum deviation point of the measured and theoretical distortions. The feasibility of the determined EFL was verified through a tolerance analysis of the system. For these precise measurements we also analyzed the sources of error. To verify our proposed measurement method, we measured the focal length of a center-obstructed omni-directional reflective optical system with an 80–135° field of view (FOV). The EFL from the measurement was 0.3739 mm and was only approximately 11 µm different from the EFL calculated using the design software. Thus, the reliability of focal length measurements in omni-directional optical systems was improved.

A Bezel-Less Tetrahedral Image Sensor Formed by Solvent-Assisted Plasticization and Transformation of an Acrylonitrile Butadiene Styrene Framework.

A method for transforming planar electronic devices into 3D structures under mechanically mild and stable conditions is demonstrated. This strategy involves diffusion control of acetone as a plasticizer into a spatially designed acrylonitrile butadiene styrene (ABS) framework to both laminate membrane-type electronic devices and transform them into a desired 3D shape. Optical, mechanical, and electrical analysis reveals that the plasticized region serves as a damper and even reflows to release the stress of fragile elements, for example, an Au interconnect electrode in this study, below the ultimate stress point. This method also gives considerable freedom in aligning electronic devices not only in the neutral mechanical plane of the ABS framework, which is the general approach in flexible electronics, but also to the top surface, without inducing electrical failure. Finally, to develop a prototype omnidirectional optical system with minimal aberrations, this method is used to produce a bezel-less tetrahedral image sensor.

Development of an Omnidirectional Optical System Based Photoacoustic Instrumentation

Development of an Omnidirectional Optical System Based Photoacoustic Instrumentation

Design on omnidirectional optical system of lidar based on 2D MEMS mirror

In order to satisfy the omnidirectional laser detection, a structure of lidar based on 2D micro-electro-mechanical systems (MEMS) mirror scanning was proposed. The laser provides light signals to 6 scanning subsystems through a 1×6 high speed optical switch and it realizes 360° horizontal scanning by adding the field of view of 6 scanning subsystems together. The scanning range of each scanning subsystem can reach 60° × 30°, including a transmitting optical antenna that expands the MEMS mirror scanning angle and a large field of view(FOV) receiving optical antenna with gain. The transmitting optical antenna extends the scanning angle of the MEMS mirror from ±10° to ±30°, and the divergence is less than 0.2 mrad. The half image height of the laser echo in the receiving field angle passing through the receiving antenna on the detector is less than 1 mm and the gain of the receiving optical antenna is 3.65. By calculating the corrected lidar equation, the laser beam with a transmitting power of 20 W can achieve an echo power of ≥1 nW within a working distance of 100 m, and the result shows that the optical system can be applied to lidar system.

광선추적을 사용한 나사산 표면결함 검사용 환형 광학계 개발

This study aims to develop a vision inspection system for screw threads. To inspect external defects in screw threads, the vision inspection system was developed using front light illumination from which bright images can be obtained. The front light system, however, requires multiple side images for inspection of the entire thread surface, which can be performed by omnidirectional optics. In this study, an omnidirectional optical system was designed to obtain annular images of screw threads using an image sensor and two reflection mirrors; one large concave mirror and one small convex mirror. Optical simulations using backward and forward ray tracing were performed to determine the dimensional parameters of the proposed optical system, so that an annular image of the screw threads could be obtained with high quality and resolution. Microscale surface defects on the screw threads could be successfully detected using the developed annular inspection system.

중심 구멍이 있는 구면거울과 평면거울을 이용한 가시광용 반사굴절식 전방위 광학계

전방위 광학계는 360도의 방위각과 지평선 위와 아래의 수직화각에 대한 상을 동시에 결상이 가능한 광학계이다. 본 논문에서는 제작을 쉽게 하면서 크기가 작아지도록 하기 위해서 가운데에 구멍이 뚫려있는 옵스큐레이션(obscuration)을 갖는 구면거울 1장과 평면거울 1장으로 이루어진 거울계 및 이 거울계에서 반사하여 구면거울의 옵스큐레이션을 통과한 시야각 범위 안의 광을 결상하는 구면렌즈 3개와 하나의 구면 이중렌즈로 구성된 결상렌즈계를 사용하는 가시광용 반사굴절식 전방위 광학계를 설계하고 제작하여 전방위 영상을 실제로 결상하였다. 그리고 자동차 앞, 뒷번호판의 영상을 보고 이 전방위 광학계의 통과 공간주파수를 측정하고, ISO 12233 차트의 영상으로부터 전방위 광학계의 수직화각을 측정하여 광학계의 성능을 평가하였다. 이 결과 전방위 광학계의 수직화각은 <TEX>$+53^{\circ}{\sim}-17^{\circ}$</TEX>이며, 방위각은 <TEX>$360^{\circ}$</TEX>이고, 3 m 거리에서 자동차 앞번호판의 숫자를 구별할 수 있었는데, 이는 135 lp/mm의 통과 공간주파수에 해당한다. An omnidirectional optical system can be described as a special optical system that images in real time a panoramic image with an azimuthal angle of <TEX>$360^{\circ}$</TEX> and the altitude angle corresponding to the upper and lower fields of view from the horizon line. In this paper, for easy fabrication and compact size, we designed and fabricated a catadioptric omnidirectional optical system consisting of the mirror part of a spherical mirror with a central hole (that is, obscuration), a plane mirror, the imaging lens part of 3 single spherical lenses, and a spherical doublet in the visible light spectrum. We evaluated its image performance by measuring the cut-off spatial frequency using automobile license plates, and the vertical field of view using an ISO 12233 chart. We achieved a catadioptric omnidirectional optical system with vertical field of view from <TEX>$+53^{\circ}$</TEX> to <TEX>$-17^{\circ}$</TEX> and an azimuthal angle of <TEX>$360^{\circ}$</TEX>. This optical system cleaniy imaged letters on a car's front license plate at the object distance of 3 meters, which corresponds to a cut-off spatial frequency of 135 lp/mm.

Transformation algorithm for images obtained by omnidirectional cameras

Omnidirectional optoelectronic systems find their application in areas where a wide viewing angle is critical. However, omnidirectional optoelectronic systems have a large distortion that makes their application more difficult. The paper compares the projection functions of traditional perspective lenses and omnidirectional wide angle fish-eye lenses with a viewing angle not less than 180°. This comparison proves that distortion models of omnidirectional cameras cannot be described as a deviation from the classic model of pinhole camera. To solve this problem, an algorithm for transforming omnidirectional images has been developed. The paper provides a brief comparison of the four calibration methods available in open source toolkits for omnidirectional optoelectronic systems. Geometrical projection model is given used for calibration of omnidirectional optical system. The algorithm consists of three basic steps. At the first step, we calculate he field of view of a virtual pinhole PTZ camera. This field of view is characterized by an array of 3D points in the object space. At the second step the array of corresponding pixels for these three-dimensional points is calculated. Then we make a calculation of the projection function that expresses the relation between a given 3D point in the object space and a corresponding pixel point. In this paper we use calibration procedure providing the projection function for calibrated instance of the camera. At the last step final image is formed pixel-by-pixel from the original omnidirectional image using calculated array of 3D points and projection function. The developed algorithm gives the possibility for obtaining an image for a part of the field of view of an omnidirectional optoelectronic system with the corrected distortion from the original omnidirectional image. The algorithm is designed for operation with the omnidirectional optoelectronic systems with both catadioptric and fish-eye lenses. Experimental results are presented.

双谱段全景电晕探测光学系统

In order to achieve the wide angle,large relative aperture and uniform illumination of corona detectors,a novel catadioptric omnidirectional optical system applied in the corona detector is presented which operates in the region of Solar Blind UV/visible.Operating principle of the dual spectral panoramic corona detector is introduced.And,the structure of the dual spectral panoramic imaging system is determined by assigning optical parameters of the primary(panoramic shell)and secondary(relay optics)groups.After investigating the origin and characters of the aberrations in the panoramic imaging system,methods for balancing aberration between the two groups and improving illumination uniformity are proposed.Finally,dual spectral panoramic imaging systems satisfying specifications are obtained.The field of view of the system achieves 360°×(45°~90°)and relative aperture extends to 1:2,the diameter of 80% encicled energy of SBUV panoramic imaging system is 20μm,smaller than the pixel size of ICCD,the MTF value of visible panoramic imaging system is higher than 0.5@83lp/mm over all fields,and the illumination uniformity on the images of SBUV /visible detectors is superior to 99.8%.The present results show that application of panoramic annular lens to the corona detector can satisfy the design requirements.