With the development of LLL night vision technology from the second and third generation to 4G, the specifications of imaging have been significantly improved. In particular, the contrast of imaging, which determines the clarity, even resolution of the image. The contrast of imaging also refers to the Stray Light Crosstalk (SLC) among optical fibers. How to characterize the contrast of Optical Fiber Imaging Elements (OFIE) by detecting the SLC has become an important problem that must be solved. At present, the contrast performance is often characterized by the Knife-edge Response Value (KERV), which is the transmittance value of light passing through the knife edge through optical fiber imaging element. However, KRV has some disadvantages, such as inaccurate measurement value, harsh test conditions, complex sample preparation and great influence on the measurement result. The most important disadvantage is that KRV is an indirect detection, which needs to slice and grind the tested sample, and the slice position often cannot represent the overall contrast performance of the tested OFIE. In this paper, the digital imaging equipment (high-precision CMOS camera + high-resolution microscope) is used to take photo of the end face of the OPIE placed on the black-and-white boundary of the USAF resolution target. The process of light passing through the black-and-white edge provides accurate information for the contrast change. Through the computer analysis and processing of the digital image, the SLC in different positions of the OPIEs is obtained. The SLC can be used to analyze the degree of crosstalk, or contrast. The digital imaging equipment mainly includes light source system, precision transmission system, CCD camera system, software analysis system and control system. The equipment has the advantages of direct detection, simple operation, high precision, good repeatability and reliability, convenient maintenance, and can be used to test and analyze the imaging contrast of all optical fiber imaging elements. It has been proved that the device is effective in detecting the SLC, and completely replaces the KRV method.
Microchannel plate (MCP) is an important compact signal multiplier. The dynamic range of MCP is the key index influencing the detection quality of high flux, high energy and wide output linearity signals, but limited on the bulk resistance of MCP multiplier. Therefore, the problem of the bulk resistance-dependent of dynamic range transition in these devices needs to further continues to be investigated. In this paper, lead silicate glass microchannel plates in three different bismuth contents (0at%, 1at%, 2at%) were present. The bulk resistance decreased exponentially (from 6000MΩ into 15MΩ) with the increase of the content of bismuth in the lead silicate glass from 0at% to 2at%, meanwhile, the dynamic range was increased from 3.3×102 to 2.3×103 . As the bulk resistance of MCP multipliers dropped from 150MΩ into 15 MΩ (dropped about 90%), while the dynamic range of that just extended by seven times, meanwhile, the dark current of that boosted almost ten times (from 1pA to 10pA). It implicated that the dynamic range of MCP multiplier was influenced not only by the charge replenishment abilities involved in the bulk resistance, but also by the joule heating effect-depended dark current variation concerned with the bulk resistance.
The research object of surface defects in optical glass processing is mainly focused on the surface of homogeneous monomers, but there are few reports on the surface polishing defects of composite materials with a variety of monomers with different physical and chemical properties. In this paper, the defect samples with different characteristics are obtained by changing the types of optical fiber image transmission elements, adjusting different polishing processes and parameters. The structure and morphology of the defects on the surface of optical fiber image transmission components are observed by white light interferometer and atomic force microscope. The composition at different positions and the combination of chemical elements are determined by Energy Dispersive Spectrometer (EDS). The specific reasons for the defects are analyzed, the optimal polishing process and corresponding parameters are obtained, and the mechanism of the formation of defects on the polished surface of optical fiber image transmission elements is clarified. The results of the study have a certain guiding significance for the control of polishing defects on the surface of composite materials composed of various monomers, and provide data and theoretical support for improving the polishing quality and efficiency of optical fiber image transmission components.
Fiber optic imaging elements is a general term for optical fiber products including fiber optic plate (FOP), fiber optic inverter (FOI), and fiber optic taper (FOT), which is a light and image transmission array made of optical glass fibers that are drawn, regularly arranged, vacuum melted-pressed, secondary thermal processed and optically processed. They are mainly used in photomultiplier devices for low-light-level night vision and particle detection equipment. Its devices have been widely used in many fields such as low-light night vision, electronics, aerospace, nuclear diagnostics, high-speed photography, etc., especially in the field of military operations at night combat, guidance, early warning, and electro-optical countermeasures. With the continuous development of glass fiber material, preparation technology and performance requirements, the optical fiber imaging element has been significantly improved, and its application field has been continuously expanded. This paper reviews the materials, structures, principles, characteristics, preparation processes and detection technologies of optic fiber imaging elements. It mainly summarizes the development situation, latest technological progress, and several major devices in optical applications. And the bottlenecks in the preparation and detection of fiber-optic imaging elements at present are analyzed. Furthermore, the development trend and challenges of fiber-optic imaging elements evolving to larger size with smaller diameter of fiber, higher contrast, higher resolution, lower distortion, ultra-short and ultra-light are prospected.
The existence of blemishes deteriorates the imaging quality of fiber-optic imaging elements and reduces the yield of finished products in factories. The effective detection of blemishes is a prerequisite for analyzing the causes of blemishes and preventing their generation. An independently developed detection device for fiber-optic imaging elements based on machine vision is implemented to detect blemishes automatically and accurately. The blemish distributions of three typical fiber-optic imaging elements, including a fiber-optic plate (FOP), a fiber-optic inverter (FOI), and a fiber-optic taper (FOT), are compared with each other, and the causes of blemishes in fiber-optic imaging elements are analyzed. The distribution of blemishes in the FOP is random, and the average number (AN) of blemishes in the first zone (central zone) and the second zone (outer zone) with the same area is similar. The AN of blemishes for the FOI prepared by twisting the FOP at high-temperature increases from 272.8 (FOP) to 2125.0, and the AN in the outer zone is 1542.5, higher than that in the central zone. More blemishes are generated by the twisting process, and the distribution of these blemishes is close to the outer zone. A significant amount of chicken wires is found in the outer zone, but the majority of blemishes are still spots. The AN of blemishes for the FOT prepared by stretching the FOP increases from 383.0 (FOP) to 515.0, which is attributed to the increase of the number of blemishes in the first zone from 190.8 to 427.0, but the AN of blemishes in the second zone decreases from 192.3 to 88.0. The stretching process stimulates the formation of blemishes with a distribution that is close to the central ring. These blemishes are randomly distributed inside or at the boundary of the multifiber. Most of the blemishes are still spots.
A novel imaging sensor which is made of image optical-fiber bundle and industrial camera is proposed. All of the image optical fiber component are custom made and the diameters of the mono fibers are only 1 or 2 μm. In order to match the resolution of image optical-fiber bundle, the pixel size of the sensor chip are also smaller than 2 μm. After removing the protective glass window that cover the sensor chip of camera, the high-resolution imaging can be realized by bonding the optical fiber component and the sensor. The theoretical analysis and experimental result show that the resolution of the sensor is larger than 250 lp/mm, which can improve the imaging quality of industrial detection and monitoring. In particular, the proposed imaging sensor is suited for the oil mist or dust detection environment.
Micro-channel plate is an electronic multiplier element with two-dimensional hollow glass tube array structure, which has been widely used in low-light-level night vision imaging, particle detection and other devices. Bulk resistance of microchannel plate is an important performance index, which affects the electronic multiplication performance, dynamic response range and time resolution of micro-channel plate. There are many literatures about the influence of the preparation process of microchannel plate on bulk resistance, but few reports about the influence of the working conditions of microchannel plate on bulk resistance. In this paper, we mainly study the influence of micro-channel plate voltage and ambient temperature on bulk resistance, and analyze the mechanism of the change by tunneling. The results show that: 1) The change of working conditions leads to the change of the bulk resistance of the micro-channel plate. The higher the temperature and the voltage of the micro-channel plate, the lower the bulk resistance of micro-channel plate. The larger the original bulk resistance, the smaller the change rate of the micro-channel plate is. 2) The phenomenon that the resistance of micro-channel plate varies with the use conditions conforms to the mechanism of tunneling conduction.
The corrosion of optical glass has become the main factor affecting the qualified rate of products, so it is urgent to solve the corrosion of products. It has been found that under the same cleaning conditions, corrosion mostly occurs on the small side, that is, the first side of polishing, while the other side is not corroded. This indicates that cleaning has little effect on the corrosion of fiberboard. Corrosion occurs in polishing and the process of upper and lower discs. According to the different conditions of two-sided processing, the causes and influencing factors of corrosion were analyzed. By refining the processing technology and adjusting the proportions of protective paint, turning temperature and water stain and other process parameters to achieve the goal of effective controlling the corrosion within 2%.
Optic fiber imaging elements are used in weak visible light, X-ray imaging and high-energy particle detection imaging devices. They play an important role as input and output window materials of image intensifiers. Optic fiber imaging elements are arrays of tens of millions of micron-scale single optical fibers arranged regularly. The fabrication process requires several times of fiber drawing and secondary thermal processing such as hot melting pressure, torsion, and stretching. After these processes, there may be spots and linear chicken filaments that are called defects existed on the interface among the fibers and multi-fibers. Due to these defects, the quality of imaging is seriously reduced, and even the misjudgment or omission of image signal recognition can are caused. How to detect such defects has no an ideal solution. Currently, non-quantitative microscopic observation is generally used. This method, however, is high in misjudgment and low in detection efficiency. In this paper, a device for automatic detection of optical fiber image defects based on machine vision algorithms, including its working principle, structure, detection steps and characteristics are introduced. The device not only can automatically measure the size of each defect, but also can count the defect distribution according to the quality zones. The test results are stable and accurate. It is especially suitable for batch detection and research of optic fiber imaging elements.
Based on the high-resolution imaging property of the products of optical fiber material, a novel imaging system is proposed. The prototype of the system is made by coupling CCD chip(CMOS) and a large-scale optical fiber faceplate together. Firstly, the working principle and manufacturing process of large-scale optical fiber faceplate is described. Secondly, the effectiveness and practicability of the prototype of the system is verified by experiment. Finally, the potential application prospect of the imaging system is discussed. The theoretical analysis and experimental result show that the prototype works perfectly under high temperature and pressure condition and the resolution of the image that obtained by the imaging system is larger than 70 lp/mm, which can satisfy the basic imaging requirements in the research fields such as medical diagnosis, industrial detection and monitoring. Further, the novel imaging system provides a new approach for the application of optical fiber product in scientific research.