Biomedical subjects
Publications and source records attributed to Guiyun Kai.
We present a new method of the fiber grating sensing interrogation technique by utilizing an indium gallium arsenide photodiode linear array and blazed fiber Bragg gratings. An interrogation system based on an InGaAs photodiode linear array is designed, and the system performance is analyzed. The interrogation system shows a good prospect for smart sensing.
The germanium-doped photonic crystal fiber (PCF) has some characteristics that differentiate it from pure-silica PCF for a germanium element being doped in the core, such as the intensified nonlinearity, the enhanced photosensitivity, and so on. To pave the way for the application of the Ge-doped PCF successfully, it is necessary to study its properties. We investigated the modal cutoff properties of Ge-doped PCF quantitatively by using the beam propagation method. The numerical results show that the effective refractive indices and the normalized frequency V of Ge-doped PCF not only depend on the normalized pitch delta/lambda but also depend on the normalized hole size d/delta, the modal cutoff boundary for the single mode-multimode of the Ge-doped PCF shift to the low d/delta side in contrast to the pure-silica PCF.
A novel tunable highly birefringent photonic bandgap fiber (PBGF) is designed theoretically by filling its air holes with high-index material. The transmission band can be continuously tuned by changing the refractive index of the filling material. Accordingly, the tunable modal birefringence and polarization mode dispersion of the PBGFs are investigated by adjusting the refractive index of the filling material. Furthermore, we have also analyzed the effect of surface modes in the photonic bandgap on the characteristics of the tunable PBGFs. The simulation results show the feasibility of constructing birefringence-tunable photonic crystal fibers and related fiber devices in practical applications.
Coupling characteristics of dual-core photonic bandgap fibers with triangular photonic crystal cladding are investigated by use of a vector plane-wave expansion method and a vector finite-element method. We demonstrate the eigenmodes and the coupling length for two orthogonal polarizations. A decoupling phenomenon is found at a certain wavelength in this fiber configuration. The decoupling effect is attributed to the effect of surface modes on the eigenmodes. The decoupling wavelength decreases as the ratio of core radius to cladding air-hole pitch increases from 1.05 to 1.15.
Transformation of an optical transmission mechanism was achieved when the holes of normal silica-guiding microstructure fiber (MF) were filled with nematic liquid crystal (NLC). Moreover, two photonic bandgaps (PBGs) were obtained by using a plane-wave method to create the pattern. The wavelength dependence of the effective mode area, leakage loss, and group velocity dispersion (GVD) has been theoretically investigated by using a full-vector finite-element method with anisotropic perfectly matched layers. The results reveal that the characteristics of the NLC-filled PBG-MFs are particularly wavelength dependent. This research gives a physical insight into the propagation mechanism in MFs and is crucial for future transmission applications.
The reflection and transmission characteristics of a high-birefringence fiber loop mirror (HiBi-FLM), which is composed of a standard fiber coupler and one-section or multisection high-birefringence fibers (HBFs), are analyzed and discussed in detail. Theoretical reflectivity and transmissivity expressions for HiBi-FLMs with one-, two-, and three-section HBFs were obtained. The procedure for calculating reflectivity and transmissivity for HiBi-FLMs with n-section HBFs is given. Experimental results have verified the theoretical model. The basic characteristics of the one-section HiBi-FLM when strain and high temperature are applied to HBFs were analyzed and investigated theoretically and experimentally. The experimental results are in good agreement with the theoretical analysis. Furthermore, a strain--temperature sensor that makes use of those characteristics, which is new for applications of HiBi-FLMs, has been proposed and demonstrated.
An actively mode-locked fiber laser with two overlapping cavities is proposed and successfully demonstrated to generate switchable quadruple-wavelength picosecond pulses. The wavelengths are specified by two Bragg gratings in polarization-maintaining and absorption-reducing fiber. By simple adjustment of two polarization controllers, the proposed laser can be made to operate at quadruple wavelength or to switch between wavelengths at room temperature. For wavelength switching, four single-wavelength, six dual-wavelength, and four triple-wavelength operations were performed without changing the repetition rate of the output pulses.