The Processing Of Microstructure Fiber With A CO₂ Laser And Sensor Application

Microstructure Optical Fiber?MOF?refers to optical fibers with micrometer or nanometer scale structures,and generally includes Photonic Crystal Fiber?PCF?and other optical fibers with special structures such as grapefruit optical fiber,Bragg optical fiber,multi-core fiber and so on.Since the PCF has been proposed,its novel optical properties allow people to have a new understanding of optical fiber,which makes a variety of new kind optical fiber have been put forward to achieve.At the same time,the microstructure fiber greatly enriched the application of special optical fiber for many fields,such as the communications,Laser,sensor and so on.Because of MOF's the special structure and material,the MOF has some compatibility problems to be used in original system directly.Moreover,some kinds of MOF can show better performance after it is processed into a fiber optic device.So the post-processing for MOF is very important for the application of MOFs.The way of research in this paper is:1 Designing and fabricating MOF based on the requirements of fiber devices or sensing applications.2 Improving the splicing of MOFs makes them more compatible.3 Exploring the MOFs'post-processing technology and fabricating fiber devices.4 Testing the MOF's device and confirming whether the fiber or device is applicable.At first,this paper introduces the classification and theory of the micro-structure fiber.Then the paper introduces some application of MOF or MOF's devices which are proposed by other researchers.Then this paper introduces a new type fiber splicer with CO2 laser and its basic functions.Based on this splicer we develop some methods for processing of fiber devices.1.The splicing of special fiber:the splicing between two kinds of fiber which have different diameters;the splicing between fiber and endcap of fiber;the splicing between single mode fiber?SMF?and PCF.Particularly,the paper introduces a method for the splicing between highly nonlinear PCF and single mode fiber which is stable and high repeatability.2.The method for fabricating long period grating?LPG?with a CO₂ laser splicer.Then some researches on the application of the long-period grating on special fiber in our group have been introduced.This part is the foundation of next research.We have demonstrated a helical long-period grating?HLPG?manufactured from multicore fiber?MCF?combined with twist and CO2-laser heating technology.The coupling between MCF's small cores is so strong,so MCF behaves as a kind of single mode fiber which makes all of the small cores as a whole.The nineteen cores of MCF are distributed hexagonally which make the helical structure only exist in core area after heating and twisting.The external structure has little changing after HLPG been fabricated.There are several strong couplings between the core and cladding modes at different wavelengths when the grating pitch was 900?m.The extinction ratio of the main coupling reached 20 dB at1550 nm.We have investigated the sensor characteristics of the HLPG.It is found that the grating presents clear sensitivity to refractive-index while exhibiting smaller cross-sensitivity to environmental temperature than conventional long-period gratings.The HLPG also shows great potential as a twist sensor,which has a sensitivity up to 0.198 nm/?rad/m?and can apply for measuring twist directions.We have demonstrated a new type of long-period grating?LPG?manufactured with a thermal diffusion treatment.The LPG was inscribed on an ultrahigh-numerical-aperture?UHNA?fiber highly doped with Ge and P elements,which can easily diffuse at high temperatures within few seconds.We have analyzed how the elements diffused at a high temperature over 1300? in UHNA fiber.Then we developed a periodically heated technology with a CO2 laser which can make the diffusing of elements constitute the modulations of an LPG.By this technology,there is little damage to the outer structure of the fiber,which is different from the traditional LPG with being periodically tapered.Since the LPG itself was manufactured under high temperature,it can stand higher temperatures than traditional LPGs.Furthermore,The LPG presents a higher sensitivity to high temperature due to a large amount of Ge-doping which is approximately 100 pm/?.In addition,the LPG shows insensitive to the changing of environment refractive index and strain.We have demonstrated a refractive index fiber sensor worked as a Mach-Zehnder interferometer with a piece of etched microstructure fiber.The interferometer can be formed by fusing single mode fiber on the each end on the MOF without any extra processing.When part of MOF is etched,the interferometer can show the sensitive to the changing of environment refractive index.The interference spectrum does not change much after the microstructure fiber etched.When the temperature of environment rises from 26? to 100?,the shifting wavelength is within 0.7nm which means it can be seen as a temperature-insensitive sensor.