Fuxing Zhu

A highly sensitive hybrid structure sensor based on suspended-core fiber (SCF) is proposed for vector curvature and temperature measurement. The sensor is prepared by self-assembly of SCF-based cascaded Fabry-Perot interferometer (cFPI), single-mode fiber (SMF), and fiber Bragg grating (FBG). In view of the asymmetry of the cFPI, theoretical analysis of the beam transmission and spectral characteristics is implemented when the beam is incident from different directions. The two sensing fibers in the triangular distribution sensor will not be located on the neutral plane at the same time, which makes it possible to measure bending in any orientation. The Vernier effect formed by the cFPI enlarges the curvature and temperature sensitivity to −1064.5 pm/m ⁻¹ and 50.7 pm/°C, respectively, without affecting the measurement range. The spectrum shows the opposite spectral response when the sensor bending direction difference is 180°. The sensor overcomes the bottleneck of bending sensitive blind spots in dual-fiber sensing. In addition, the sensor maintains a smaller size and more flexible preparation, which is conducive to its application in artificial intelligence, medical detection.

A novel fiber Fabry-Perot interferometer (FPI) vector curvature sensor based on Vernier effect is proposed and demonstrated. The triangular-distributed sensing structure is fabricated by self-assembly of FPI and single-mode fiber (SMF). When the device is bent in any orientation, a direction-dependent wavelength shift of the interference pattern is produced because the sensing fiber always deviates from the neutral plane. In order to overcome the trade-off between high sensitivity and large dynamic range, we connect the reference fiber and the sensing fiber to produce the Vernier effect. Without affecting the measurement range of the sensing structure, the sensitivity of the self-assembled sensor based on Vernier effect is amplified by 5 times and 3.6 times respectively by using different FPIs as sensing arm. The experimental results show that the sensing structure has good stability and repeatability. Compared with the substrate packaging, the fiber FPI sensing structure based on self-assembly can realize miniaturization, which is conducive to the application of the sensor in medical detection and artificial intelligence.

We present the design and experimental demonstration of a 3rd-order-reflective hybrid interleaver based on Fabry-Perot (FP) cavity assisted Michelson interferometer (FPA-MI), in which the FP cavity consists of two cascade Sagnac loop reflectors (SLRs). Through comparison, it can be seen that the flatness and rectangularity of interleaver are increased with the increase of order. When the transmission coefficient of the variable SLR is 0.1975 or 0.98, the performance of the interleaver is the best under the lossless condition. The influence of loss and transmission coefficient on the flatness of the interleaver can be evaluated by the dispersion model when the loss is considered, and when the dispersion range is 0.911, the flatness of the interleaver is the best. The reflective FPA-MI interleaver, due to its superior performance, will provide a more promising application in dense wavelength division multiplexing optical communication systems.

A polarization-controlled strain fiber sensorwith a low detection limit and high sensitivity is proposed and demonstrated using a helical birefringence fiber loop mirror (HBFLM). The HBFLM is consists of a micro-helix region, a macro-helix region, and a fiber ring mirror (FLM). The two standard single-mode fibers (SMFs) are pre-surrounded by each other and use hydrogen flame heating and stretching techniques to prepare the micro-helix region (MIHR). The pre- rotation turns of the MIHR determine the coupling length. The MIHR is influenced by a twisting force. The purpose of the macro-helix region (MAHR) is to regulate the x- and y-polarizationstates in the fiber (applying stress inducesdouble refraction). At the same time, the envelope of the transmission spectrum is modulated to ultimately control the strain sensor. The polarization control of the strain sensor is realized by using the principle of stress birefringence of the SMF. The reasons for the polarization control spectrum are analyzed theoretically. The strain and temperature characteristics were indicated in the experiment. Polarization-controlled strain sensors are expected to be used in high-precision and varying strain range measurements.

We demonstrate a switchable and flexible comb filter/interleaver based on ring-resonator (RR) in which the directional couplers are replaced by tunable couplers. The tunable coupler is composed of an even-arm-length Mach-Zehnder interferometer (MZI) with a micro-heater embedded in one of the arms. For the sake of discussion, we convert the heating power of the micro-heater into a pure phase shift value independent of the waveguide material and size. By changing the phase shift value, the filter can be switched between comb filter and interleaver. Meanwhile, the insertion loss (IL), full width at half maximum (FWHM), extinction ratio (ER), and the shape of the response spectrum can also be reconfigured. The switchable and flexible comb filter/interleaver may provide a potential application in dense wavelength division multiplexing (DWDM) optical communication systems.