Research On New Type Optical Device With Cascade Conical Structure

With the increasing demand for optical communication capacity,communication distance and transmission rate,fiber post-processing technology and optoelectronic devices have been developed.Fiber optic filter as one of the key components in the modern optical fiber system plays an important role,in which fiber ring mirror filter is the most practical.The main principle of the filter is a beam of light through the 3dB coupling device which is divided into two beams of light and along the opposite direction in the fiber ring mirror cavity propagation,and finally meet in the coupler and interference.The output characteristics of the filter can be improved by placing high birefringence fiber,different mutation cone structure fiber and cascade cone structure Mach-Zehnder(M-Z)interferometer.Conventional optical fiber in the conical area,changing the physical parameters of the fiber itself,making the optical power redistribution,part of the core light energy in the form of evanescent field excitation to the cladding in the form of high-order form of propagation,which is modulated light field foundation.Based on the analysis of the mode field characteristics of the cone zone,two kinds of tapered optical fibers with different mutation cone structures were developed by means of fiber optic taper and fiber splicing machine.The Mach-Zehnder(MZ)interferometer based on thin cone and thick cone,to improve its performance controllability.As a sensor to achieve the refractive index and temperature measurement,put it into the fiber ring mirror filter to achieve stable and adjustable output spectrum that can also be used as a wavelength selector for tuning the output of the laser.The main work of the paper is as follows:1.Analyzed the basic structure and transmission characteristics of the single-mode tapered fiber.Introduced the precautions and key techniques of the production and production process of the torsion cone and the fusion box.Analyzed the mode excitation coupling of the cone structure based on theoretically principle to get the relationship between the mold field radius and the core radius.2.Based on the fine cone and the rough cone,two kinds of cascade symmetrical optical fibers with different conical structures were fabricated,and get the output spectrum by connecting the broadband light source(BBS)and the optic spectral analyzer(OSA).By comparing the performance of single cone's transmission spectrum and cascade cone's transmission spectrum under different cone interval,the cascade cone structure parameters corresponding to the best transmission spectrum are obtained: the thin fiber cone's waist diameter is 25 um,the transition zone is about 5mm,cone interval L is 13.1cm,the thick fiber cone's waist radius is 165 um,length of cone is 450 um,cone interval L is 10 cm.The cone interval is inversely proportional to the peak of the transmission spectrum and the change in the effective refractive index of the cladding mode results in an interference spectral wavelength shift,which can be used for the measurement of external refractive index and temperature.3.The M-Z interferometer was used to carry out the sensing experiment of refractive index and temperature respectively.By fitting the experimental data with different concentration of alcohol the sensitivity of the optical fiber M-Z sensor based on the thin cone and the thick cone is-120 nm / RIU and-152 nm / RIU.Put the sensor into the temperature control box,adjust the temperature and track the transmission spectrum of the two peak points 1,2.The experiment of thin cone fiber M-Z sensor ambient temperature changes between 25 ~ 40 ?,the peak 1,2 corresponding of the temperature response sensitivity is 0.04 nm / ? and 0.023 nm / ? respectively.When the ambient temperature changes between 40 ~ 55 ?,the corresponding temperature response sensitivity at the peak 1,2 is 0.247 nm / ? and 0.117 nm / ?,respectively.Based on the thick cone fiber the corresponding temperature response of the M-Z sensor at the peak 1,2 is 0.096 nm / ? and 0.070 nm / ?,respectively.4.The high-birefringence fiber,single-cone fiber and cascade tapered fiber are placed in the fiber ring mirror filter to analyze the output spectrum characteristic change.Theoretical and experimental studies have found that the single cone fiber placed into the fiber ring mirror filter and its quality factor increased by about 2 times.Adjusting the polarization controller to achieve modulation depth from 11 d B to 37 dB.Placed the cascaded optical fiber M-Z interferometer into the fiber ring mirror filter and obtained the output transmission spectrum which is the result of the non-coherent superposition of the interference spectra of the two filters.In the free spectrum range 1425 ~ 1550 nm the modulation depth of the new type of optical fiber filter is from 5dB to 10 dB respectively,and the transmission envelope will change with the rotation control rotation angle.In a certain wavelength range to achieve tunable filter,tuning range of more than 60 nm.