Low-loss Splicing Microfiber And Assembling Microfiber Devices Based On Polymer Coat

Microfiber is a kind of optical fiber which is fabricated by flame/laser-heated taper drawing method from standard singlemode fiber. It possesses apparent advantages in optical and mechanical applications over traditional optical fibers, including tight light confinement,intrinsic evanescent field and compactness. Photonic devices with compact sizes can be implemented by bending, twisting, coiling and assembling microfibers in free space.Furthermore, by connecting the microfiber devices, we could potentially promote the further development of integrated microphotonic platforms with complex optical structures. Hence, an important problem needed to be solved is low-loss splicing between microfibers and efficient assembling of microfiber devices, since the present methods have different limitations such as high splicing-loss, complicated operations and low mechanical strength. In this thesis, we propose a low-loss splicing method with high mechanical strength based on high-substituted hydroxypropyl cellulose(H-HPC), which is polymer material with a low refractive index, and we also apply it to manufacture different microfiber devices.The main content of the thesis is as follows:In the first part, the evanescent couplings between parallel microfibers are analyzed with weak and strong waveguide approximations, respectively. The H-HPC film coated on the surface of microfibers redistributes the mode fields propagating along the fiber when maintaining the index guidance, which means the evanescent fields between two parallel microfibers have been enhanced to increase the coupling efficiency to improve the coupling strength. This part of work provides the theory of low-loss splicing microfibers and assembling the microfiber devices.In the second part, we propose a low-loss splicing method base on high-substituted hydroxypropyl cellulose(H-HPC). By delicately choosing the material and optimizing the relevant parameters, we design a complete technique process. The minimal average loss is ~0.26 d B and the joint segment can stand an axial stress up to ~1 N.In the third part, the H-HPC-coating splicing method is employed to assemble microfiber devices including coil resonator, Sagnac interferometer, F-P resonator and Mach-Zehnder interferometer. All devices can maintain their geometric and functional structures. Measured result suggests that the devices can present good stability over 20 days. The devices can remain their characteristics of evanescent field as the H-HPC coating has a relative low refractive index than silica, thus, the functional performance of microfiber devices can be hardly affected. For example, the refractive index sensor based on Sagnac interferometer presents a sensitivity as high as ~2600nm/RIU。In the last part, we draw a conclusion of our work and give a further prospect of our research.The method we propose in this thesis can reduce the splicing loss while keeping a high mechanical strength, and maintain the functional and geometric structures of devices in both air and liquid environment. The whole system of the method is simple and the process is easy-operating, and the manipulation can be conducted in free space under real-time monitoring.This method will improve the development of integrated microphotonic devices.