Investigation On Selectively Liquid-infiltrated Photonic Crystal Fibers And Based Applications

As a typical application of two-dimensional photonic crystals, photonic crystal fiber (PCF) with its flexible design and unique light guiding properties has gradually become a research hotspot in the field of fiber optics in recent years, which is widely used in optical fiber communication and optical fiber sensing systems. With the development of post-processing technologies for PCF, the research on the functional materials-filled PCF can combine the comprehensive merit of fiber optics and materials science, which derives out a large number of photonic devices with exquisite micro-nano structures and excellent optical properties. Aim at the current research status of the functional devices based on material filling, this paper puts forward some new research ideas from the viewpoint of structural design. By utilizing the numerical simulation method and selectively infiltrating technique for PCF, we design and fabricate three different types of fiber optic devices, and the corresponding theoretical mechanism, fabrication method, spectral characteristics and sensing properties of the devices are systematically investigated in the paper. The main research work and obtained achievement are listed as following:1. We proposed and demonstrated a tunable dual-band optical fiber filter based on selectively infiltrating liquids with different refractive indexes into two air holes in the cladding of PCF. The full-vector finite-element method (FEM) is used to compute and analyze the excited modes and mode coupling in solid core and liquid rod. Theoretical simulation and experimental results show that the filter has a good performance in terms of tuning sensitivity and linearity. Experimentally, as the temperature rises from27.0℃to30.6℃, the tuning range of the filter can reach145nm and125nm in different wavebands, meanwhile, two communication windows including1310nm and1550nm are covered in the range.2. A liquid-infiltrated-PCF-based dual-parameter sensor with high sensitivities and low insertion loss is proposed and demonstrated by selective filling liquids with high refractive indexes into the PCF. Two liquid rod waveguides can be effectively formed after two air holes in the cladding are filled with1.466and1.500refractive index liquids, respectively. Based on index-matching coupling, in a certain temperature the fundamental core mode could be simultaneously coupled to different local cladding modes of the adjacent liquid rod waveguide, resulting in the emergence of multiple resonance peaks with different sensing characteristics, which can be used to resolve the temperature-force cross-sensitivity issue that is commonly encountered in most practically deployed sensing components.3. A novel fiber optic Mach-Zehnder interferometer (MZI) based on near-elliptic core PCF is fabricated by selectively filling specific index-matching liquid into one air hole of the innermost layer of the PCF. The refractive index of the liquid is so close to that of the background silica in the wavelength range of1300-1600nm that the solid core of the PCF will be greatly influenced by the liquid rod and a modified elliptically shaped core is effectively formed to support a certain number of modes. Due to the overlap of mode fields and different propagation constants, the stable intermodal interference can be easily obtained. Theoretical simulation and experimental results show that the interference mainly occurs between the fundamental mode and the first-order higher mode of the liquid-filled PCF, moreover, such a device can be employed as a high-sensitivity temperature and strain sensor with advantages of high visibility and wide dynamic range.