Theory And Technology On Measuring Tapered Fiber Radius By Light Intensity Extremum Value Method

As a special fiber, tapered fiber is widely used in medicine, near-field optical microscopy and optical solution communication, and so on. Accurately measurement the size of tapered fibers is precondition and guarantee of researching it’s property and ensuring quality of the production. On the basis of domestic and international research on fiber radius measurements, this paper focusing on the scattered light intensity extreme value method which based on light scattering theory, Then improved the measurement solutions to improve the speed and accuracy of measurements. Three modules are established in this paper, which including the database of radius establishing, image processing and data matching.(1) Create a database based on scattering theory formula:starting from the basic wave equation, analyzing the complexity interference process when a Gaussian beam transmitted through a transparent dielectric tapered fiber medium, from can be understood as an interference of the diffracted and transmitter light. and then introducing the correlation function to solving the scattering formula approximate. Next, in the range of a given radius, obtaining each radius’s relationship figure between its scattered light intensity value and the corresponding scattering angles which based on the principle of the formula, then establishing the database by extracting the value of the scattering angles for each fiber radius from the map,(2) Set up the experimental platform to obtain the scattering image and performs the correlation processing:In this paper, we use the standard single-mode fiber cone which come from The 618th of Aviation Automatic Control Research Institute to measure its cone radius. The measurement system consist of a laser light shaping system, a cylindrical lens telescope system and an image acquisition system. Among them a detailed computational analysis are made in aspects such as the adjust of linear polarization direction, the preferences of cylindrical lens telescope system. After that, we use an industrial camera to capture the scattering fringe image and make the following image pre-processing scenarios:first, convert the image formats and capture it, and then respectively use the histogram equalization method, mean filtering method, low-pass filtering and median filtering method to execute the smoothing. Though comparing the results, we selected the histogram equalization and median filtering method for processing. Then use the smoothing algorithm to shape each single column of the extreme intensity image. And extract the scattering angle data of the corresponding fringe intensity extremes.(3) We design the data matching program which is mainly based on the theory of least squares. Then match the data of scattering angle obtained in experiment with which in self-built database. And then get the cone radius and output the result.After the laboratory tests,. It is show that the tapered fiber-radius measurement system can accurately and quickly measurement the diameter of the fiber, and the measurement accuracy meets the test requirements. We also made an assess about the actual measurement accuracy and its performance differences. Then proposes an improved direction to the performance of the algorithm and found deficiencies on algorithms, then proposed the improvement measures.