| Fiber-optic micro-cavity interferometers,as the competitive candidate of lab-on-a-chip,have been widely used in strain and curvature sensing applications,and tapered fibers have high potential for strain sensing applications due to their structural properties compared to other types of fibers.Based on the large offset splicing method,this paper designs a tapered fiber micro-open-cavity（T-MOC）strain sensor for testing strain and bending sensing characteristics and designs a fiber optic sensing system for wearable devices,which can quickly respond to changes in physical quantities and monitor high-speed dynamic measurements in real time.The main contents are as follows:（1）Based on modal interference,the sensing principle of the open cavity structure is analyzed under the influence of temperature,strain,and bending.The energy distribution of optical field of the T-MOC structure with variable parameters is simulated and analyzed using the beam propagation method,and the optimal fabrication parameters are determined,with the offset of 62.5μm and the minimum diameter of 30μm.The T-MOC structures with different parameters are then prepared experimentally,and the output characteristics of interference fringes are investigated.According to experimental results,the temperature responses of the T-MOC structure are independent on the air-cavity length,and the temperature sensitivity decreases as the waist diameter decreases,the minimum temperature sensitivity is 30.25 pm/°C when dt=39.76μm.（2）Further,the strain characteristics of the T-MOC structure are verified by simulation analysis and experiments.The results show that the axial-strain sensitivity is inversely proportional to the cavity length and waist diameter,and the maximum sensitivity is-16.91 pm/μεwhen La=1200μm and dt=30μm.Moreover,the intensity modulation can be realized when a large bias length is adopted,and the sensitivity reaches0.043 d B/μεwith the accuracy of 0.22με.Being the state of small bias length,the Vernier effect improves the sensitivity to 313.14 pm/με,and the detection accuracy of 0.19μεis gained in wavelength modulation scheme.（3）The bending characteristics of T-MOC structure are experimentally tested,and the wavelength sensitivity is witnessed to be inversely proportional to the waist diameter.When dt is decreased to 31.12μm,the maximum sensitivity reaches 7.92 pm/m-1.Additionally,to enhance the mechanical strength,the structure is well packaged by using PDMS.And a intensity-based demodulation system is then built for monitoring human body movements,such as breathing,pulse and leg bending.The results show that the rapid and real-time monitoring can be realized by our sensor. |
