Simulation Of Measuring The Optical Fiber Refractive Index Profiles By Refraction Near-Field Method

Measurement of fiber refractive index profiles by refracted near-field method was firstlyproposed and demonstrated before about30years. As a high-precision method of measuringoptical fiber refractive index profiles, it has become a benchmark method specified by CCITTnow. Refracted near-field method has many advantages, such as the test data dose not need tocorrect leakage mode, and after an align of the test system it can measure many kinds of fibersabsolute refractive index profiles directly and accurately, whose spatial resolution is small andwith high accuracy. As the development of optical fiber communications, fiber-optic imagebundles, astronomical telescope system, optic gyroscope and optical fiber sensing technology,new requirements of the times are put forward, such as the measurement accuracy and methodof the optical fiber refractive index profiles and geometric parameters, which are suitable formeasuring different kinds of novel fibers refractive index profiles.In this subject I correct the refracted near-field formula of the original linear one by thestudy of refraction near field technique, establish the square root relation between refractiveindex difference and power distribution, simulate the experimental device, process anddisplay data based on the LabVIEW platform. I get end images and relative and absoluterefractive index profiles of single-mode fiber, multimode fiber, polarization maintaining fiber,multi-core fiber, photonic crystal fiber and a large core optical fiber.First of all, I derivate the linear formula of refraction near-field method, correct thismodel and obtain a complete and new formula, which describes the precise relationshipbetween the intensity distribution and the optical refractive index profiles.Secondly, I use the software of Zemax to simulate measuring fiber refractive indexprofiles by the refracted near-field method, and prove that the measurement simulation isfeasible and accurate. Simulation based on the refracted near-field method is established tomeasure single-mode fiber, multimode fiber, multi-core optical fiber, polarization maintainingfiber and a large core fiber. The measurement of photonic crystal fiber is discussed. However,an expanded scan of the region around the core is found in the measurement simulation ofrefractive index profile large-core fiber, as it does not guide modes. It impacts on test resultsgreatly. In this paper, the simulating optimization of traditional measuring device is necessary. The experimental device needs to be improved. Good test results have been obtained insimulation and experiment.Finally, the data of the collected light intensity distribution is processed based on theLabVIEW platform. The refractive index profile of any straight line in fiber cross-section isobtained by calculation. Image processing tool is powerful in LabVIEW. Photonic crystalfiber gray-scale image is turned to pseudo-color image by the tool. We can clearly see thefiber end details.