1. The Simple Principle of Fiber Optic Image Bundle
1.1 Fiber optic and total reflection fiber optic generally refer to optical fibers composed of transparent media. Light enters from one end of the fiber optic, propagates along the fiber optic, and finally exits from the other end. A single fiber optic can only transmit light and cannot image. If many optical fibers are fixed together to form a fiber bundle, an image plane with a certain area can be passed through each fiber, and the image can be transmitted point by point from one end of the fiber bundle to the other end.
According to the different ways in which optical fibers transmit light, they can be divided into two categories. One is composed of uniform transparent media, and the light is transmitted through surface total reflection and linear propagation inside the fiber, known as total reflection fiber or stepped fiber; Another type of optical fiber is composed of non-uniform media, with high central refractive index and low edge refractive index. Light propagates along a curve inside the fiber, known as gradient index optical fiber. These two types of optical fibers propagate light in different ways and have different application ranges. Image transmission optical fibers are mainly composed of total reflection optical fibers.
1.2 Properties of Total Reflection Fiber
The simplest total reflection fiber is a cylindrical filament composed of a uniform transparent medium, known as a single fiber.
The light undergoes multiple total reflections on the inner surface of the optical fiber, propagating from one end of the fiber to the other. The disadvantage of this type of optical fiber is that the extremely small defects, dust, and dirt on the surface of the fiber will cause light to scatter and shoot out of the fiber, resulting in optical energy loss. Although these defects also exist on the reflective surface of a total reflection prism in general optical systems, they only have a few reflections in a prism system, so the impact is not significant. In optical fibers, light may undergo thousands of total reflections, and if a portion of the light energy is lost in each total reflection, the total loss is considerable. This type of single fiber is not suitable for image transmission fiber bundles because in fiber bundles, the fibers are in close contact, and light may pass through one fiber to another, which will affect the clarity of image transmission.
In order to overcome the above-mentioned drawbacks of single fiber optics, people wrap a layer of glass with a lower refractive index than the core material on the outside of the optical fiber, which is called an external fiber. In this type of optical fiber, light is fully reflected at the interface between the two types of glass inside and outside the fiber. In this way, the defects and dirt on the surface of the optical fiber will not affect total reflection. Currently, most of the optical fibers used are outsourced.
1.3 Principle of Fiber Optic Image Bundle
The optical fiber used for image transmission bundles must have a good outer layer. There are many special advantages to using image beams for image transmission, such as no strict limitations on length and space, large numerical apertures, and no aberrations. Its disadvantage is that a few fibers in the fiber bundle may be broken, causing blind spots on the output image plane; The arrangement shape of the input and output terminals may be deformed, causing deformation of the image; There is only one pair of common faces and the depth of field is very small; The resolution is limited by the diameter of the optical fiber.
Note: The image is floating on the end face of the image transmission bundle, which is one of the characteristics of fiber optic image transmission bundles.
If you want to make the image transmission clearer, you should choose fibers with smaller diameters as much as possible, because the finer the fiber, the more light beams can be accommodated in a certain image transmission bundle, which can transmit more pixels. Obviously, the more pixels there are, the clearer the image becomes.
Although fiber optic image bundles can be bent very flexibly, this does not mean that their internal fiber arrangement is irregular. On the contrary, all optical fibers are arranged neatly, and the positions and positions of the two ends correspond strictly. Assuming that the cross-section of the optical fiber image bundle is a rectangle, and one end of a certain optical fiber is in the 7th row and 2nd column of the rectangle, then the other end of the optical fiber must also be in the 7th row and 2nd column. The reason is very simple, it is to ensure that the transmitted image does not have misalignment on the surface, just like in a jigsaw puzzle game. If the two ends of the optical fiber are not in the same position, the transmitted image is like an image that has not been pieced together, giving people a feeling of misalignment.
2. Application of fiber optic image bundles
2.1 Boiler monitoring
Boiler flame monitoring is an important means to prevent boiler explosions caused by insufficient coal combustion. The signal anti-interference ability, sensitivity, and monitoring ability of traditional detectors are poor, which can easily lead to erroneous information. The use of fiber optic industrial endoscopes to monitor the combustion status of boiler flames has increased the information obtained by four orders of magnitude. It can not only judge the stability of flames, but also identify the shape of flames, ensuring the safe combustion of power plant boilers and improving their safety.
Fiber optic endoscopes are also effective in detecting damage or corrosion to electrical equipment such as boilers, steam turbines, transformers, and searching for falling objects.
2.2 Check the inner cylinder of the engine
Fiber optic endoscopes can be used to check the wear, carbon buildup, and blockage of engines, transmissions, mufflers, fuel pipes, etc., and have been widely used in the automotive repair industry. In terms of cleaning and maintenance of car engines, fiber optic endoscopes are also a good helper. Before cleaning the engine, observe the carbon deposits inside the engine using an endoscope and take photos. After cleaning the engine, observe and take photos. Then compare the images observed before and after cleaning, so that customers have a very intuitive understanding and comparison of the cleaning effect.
Endoscopy plays a crucial role in ensuring quality and reducing costs. For example, the quality of the engine is crucial for a car, as internal casting defects, burrs, etc. can have a significant impact on the quality of the car. In the past, automobile manufacturers used sampling methods to control the quality of engines. After a batch of engines are produced, a certain amount of engines are selected for dissection and inspection, and then the quality of the sampled products is evaluated based on the quality of the new production batch of engines. This method has two shortcomings: the quality of the sampled products may not necessarily represent the quality of every engine in the production batch, and the final engine quality cannot be fully guaranteed. The cost is high, and the sampled products are scrapped after dissection. By using an endoscope, every engine in this production batch can be inspected, ensuring quality. Due to non-destructive testing, the cost has been significantly reduced.
With the rapid expansion of China's opening-up to the outside world, the country has put forward higher requirements for public security criminal investigation. In order to effectively ensure social stability and the achievements of reform and opening up, and to crack down on criminals, the reconnaissance required by public security personnel is becoming increasingly high-tech. The transmission endoscope developed by Nanjing Fiberglass Institute has played a magical role in drug smuggling investigations, effectively detecting hidden blue kisses in enclosed cavities, completely replacing oral products
2.3 Medical diagnosis
Fiber optic endoscopy is an ideal medical diagnostic and therapeutic tool. In foreign countries, it has been clinically applied in cardiovascular and cerebrovascular surgery. Traditional angiography can cause allergic reactions in some populations, and this technique has a certain misdiagnosis rate. Endovascular endoscopy is an excellent supplement to traditional angiography, especially for those who are allergic to angiography, and its application undoubtedly brings them good news. In recent years, clinical doctors have shown great interest in the application of fiber optic endoscopes in various disease disciplines, and have achieved gratifying results. Osaka Labor Disaster Hospital in Japan uses an intracranial endoscope to perform brain tumor resection surgery, without the need for craniotomy. Only a small hole needs to be drilled in the skull. This device can also be used for diagnosis of the liver and kidneys. Kyoto Medical University uses pancreatic endoscopy to carry out early clinics of pancreatic cancer and pancreatic diseases, while it is extremely difficult to use ultrasonic CT or EPCR for early diagnosis. The Canadian College of Ophthalmology and Technology uses an endoscope to treat retinal detachment, which can also examine the cell membrane and surrounding conditions inside the eye, examine the oozing hole, and seal the oozing hole. It is also extremely useful in repairing damaged ocular fibrous tissue after trauma. Almost all human ducts and symptoms have corresponding endoscopes, such as bronchoscopy, choledochoscopy, hysteroscopy, laryngoscopy, and sinus endoscopy, and can also be used for open surgical treatment.
2.4 National Defense
The current various aiming equipment in the military is a rigid optical system composed of optical lenses and prisms. The prominent drawback of this type of equipment is its rigid structure and large size, especially with the increase of optical path length and instrument caliber, the weight increases sharply. At the same time, the rigid structure limits the position and posture of soldiers. Once the lens reflects light, they are easily attacked by enemy fire:
The machine guns and light weapons of the main battle tank have low accuracy due to continuous firing vibrations, making it difficult for the human eye to aim close. Taking photos of the high-speed dynamic process inside the shell poses difficulties in image transmission due to geometric obstacles. In order to overcome the above problems, it is necessary to develop new technologies that can meet the tactical requirements of modern warfare for aiming and periscope monitoring equipment. Large cross-section fiber optic image bundles have the advantages of good flexibility, small size, unrestricted image transmission process, easy image rotation and image stability, etc. They are an ideal and suitable image transmission tool for aiming and periscope monitoring in China.
3. Conclusion
The resolution of optical fiber image bundles is affected by their fiber diameter, and the depth of field is relatively small. If the fiber breaks, there will be blind spots in the output. However, it can be bent freely, with good durability and flexibility, high image quality transmission, high mechanical durability, high chemical stability, excellent optical transmission performance, and the ability to reproduce colors. It can be customized with longer length optical fibers, so it has a very wide range of application prospects. With the continuous improvement of fiber optic imaging technology, it will occupy an increasingly important position in non communication optical fibers.
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