Study On Theoretical Modeling And Applications Of Hybrid Microfiber Devices

The feature size of integrated circuits is decreasing day by day that makes the feature size of process develop from the initial millimeter scale to the nanometer scale today,which is closer to the limited size of electrical physics.The traditional optimization space for electrical information processing has encountered bottlenecks.At the same time,people's demand for large bandwidth and high-speed communication has risen to a new level with the advent of the"Internet of Things"era.Therefore,how to break through the bottleneck of the development of traditional electronic information processing technology as soon as possible has become the primary problem needed to be solved by scientific researchers.As the most basic transmission unit in micro-nano photonic devices,microfibers have potential applications in the fields of generation,coupling,transmission,resonance,amplification,modulation and sensing for optical signals at micro-nano scale due to their excellent characteristics such as tight optical confinement,large scale evanescent field transmission,large waveguide dispersion and small bending radius.However,due to the limitation of material and structure,it is more and more difficult to meet the increasing demand for micro/nano photonic devices relying solely on silica microfibers.Therefore,it is important to solve the problem of single structure and material of microfibers to make them have more diverse functional characteristics and meet the practical requirements of more micro-nano photonic devices.In this paper,a series of hybrid microfiber devices with different functions are proposed,which combine the structure functionalization with the material functionalization of microfibers.These devices are applied to all-optical tuning technology of microfibers and temperature sensing field of microfibers.The main researches include:1.The basic theory of microfiber transmission is studied.The basic transmission of microfibers is theoretically analyzed and deduced solving Maxwell equations.The surface evanescent field distribution of microfibers with different diameters is studied.Based on the coupled mode theory and beam propagation method,the coupling mechanism of microfibers is analyzed.The lateral coupling characteristics under different coupling conditions are mainly studied,which provides a theoretical basis for the fabrication of microfiber coupling structure devices.The mode transmission in the tapered transition region of microfibers is analyzed.The guided mode equation,adiabatic conditions and the structure of tapered transition region are analyzed and discussed in detail.The loss of microfibers is summarized in detail which provides theoretical guidance for the design and fabrication of microfiber devices with good optical performance.2.All-optical tunable device based on hybrid graphene-microfiber is studied.Firstly,the preparation methods of low loss microfibers are introduced in detail and the effect of graphene on the evanescent field of microfibers is studied.Then,the different methods of graphene transferred to microfibers are compared.Finally,an all-optical tunable Mach-Zehnder interferometer based on hybrid graphene-microfiber structure is proposed and experimentally demonstrated.In order to optimize the manufacturing process and improve the tuning efficiency,sandwich hybrid graphene-microfibers were used.Ohmic heating of graphene can effectively change the refractive index of microfibers when the pumped light irradiates the modulation region of the device.The final modulation efficiency of the resonant wavelength shift is 0.856 pm/mW.The modulation efficiency of the resonant wavelength shift of the proposed structure is improved by six times comparing with the microfiber Mach-Zehnder interferometer with bottom graphene film only.It is noteworthy that the red shift range of the resonant wavelength can exceed a free spectral range which means that the resonant wavelength of the device can be tuned to any wavelength within the transparent window.Simultaneously,the effective size of the device is about 7.31×8.66 mm~2,which is several orders of magnitude smaller than other reported all-optical tunable Mach-Zehnder interferometers based on optical fiber system.3.Hybrid polydimethylsiloxane(PDMS)-microfiber temperature sensors are studied.Some basic characteristics and preparation methods of PDMS are introduced,and its performance is analyzed.Then,a temperature sensor based on covered hybrid PDMS-microfiber ring resonator is introduced.The basic sensing unit of the sensor is microfiber ring resonator.Therefore,the relationship between transmission and important parameters of microfiber ring resonator is analyzed using scattering matrix model.The sensing region of the device combines two PDMS thin films with microfibers to form a sandwich covered hybrid PDMS-microfiber.The high negative thermo-optical coefficient of PDMS ensures that the temperature sensor has high sensitivity(-75.78 pm/~oC).Finally,we experimentally demonstrate a compact temperature sensor using microfiber-based Mach-Zehnder interferometer with a micro-ring resonator.The straight arm of the device is completely wrapped in PDMS to form the sensing area of the device.The effective area of the device is about12.59×3.01 mm~2.The theoretical model of the device is established using scattering matrix method,and the relationship between the parameters and the performance of the device is analyzed.Because of the high thermo-optical coefficient of PDMS,there is a blue shift with the transmission spectrum of the device increasing the ambient temperature.At the same time,the device can effectively monitor temperature in two different environments(air and liquid).In addition,PDMS can not only be used as a thermal sensitive material,but also prevent the sensing area from being polluted by surrounding materials such as dust,humidity and scratches so that the service life of the device is prolonged.4.The research of hybrid microfiber temperature sensing technology based on liquid packaging is discussed.The transmission of microfiber mode interferometer is introduced.The sensing characteristics of microfiber mode interferometer are further studied by analyzing the influence of device parameters on its transmission.On the basis of theoretical analysis,the temperature sensing characteristics of the hybrid liquid-encapsulated microfiber mode interferometer are experimentally verified.Because of the high negative thermal-optical coefficient of deionized water,the temperature sensor has high sensitivity(-258.73 pm/~oC).At the same time,the existence of liquid packaging has played a protective role in the device,so that it can avoid the deformation caused by changes in the external environment,and greatly improve the mechanical stability of the device.