An in-line fiber Mach-Zehnder interferometer (MZI) based on twin-hole fiber for humidity sensing was proposed and experimentally demonstrated. The twin-hole fiber was filled in black phosphorus (BP) by capillary absorption method, and then was sandwiched in between two single mode fibers (SMFs) to form intermodal interference. Utilizing the sensitivity of BP to ambient humidity, the MI could realize humidity measurement. Experiment results reveal that the interference intensity changes in the RH range of 20-80%RH, and the sensitivity was -0.028 dB/%RH. This sensor has great potential for application in chemical and biology fields.
Resonance frequency calculation of accelerometer based on equal strength cantilever beam by Rayleigh method has been proposed and experimentally demonstrated. The accelerometer is with a compact structure in which a short section of fiber stubs containing a fiber Bragg grating (FBG) is attached on the bisector of a equal strength cantilever beam. By comprehensive considering the mass of beam and the mass of the block together, resonance frequency of different accelerometer can be calculated more precisely, compared with the experimental results the maximum relative error is 7.2% over the low frequency range from 20 to 45 Hz.
An in-fiber Michelson interferometer based on core mismatching for liquid refractive index sensing is proposed and demonstrated. The sensor can be simply fabricated by fusion splicing a section of thinned core fiber (TCF) to a standard single mode fiber (SMF) without any reflection coating. The experimental results show that the sensor possesses RI sensitivity of -111.58 dB/RIU in the RI range of 1.333-1.380 RIU. The liquid temperature cross-sensitivity is experimentally analyzed and reveals that the measurement error of the liquid RI caused by temperature is -0.89×10-6 RIU/℃ in water temperature range of 25℃-80℃. The advantages of easy fabrication, high sensitivity, working on reflective intensity detection and compact size make the proposed sensor can offer promising applications in chemical, biomedical and petrochemical fields.
A humidity sensor based on microfiber Bragg grating is proposed and demonstrated. The microfiber Bragg grating is obtained through chemical etching commercial fiber Bragg grating. The experimental results show that the central wavelength of the microfiber Bragg grating has red shift with humidity increasing, while the power decreases. The relative humidity sensitivity of the microfiber Bragg grating with diameter of 8.9um is 3pm/%RH in the range of 55%-80%RH. Furthermore, the sensor has a linear response to humidity with linear fitting of 0.991. The sensor possesses advantages of easy fabrication and low cost.
A novel strain sensor based on in-fiber Mach-Zehnder interferometer (MZI) is proposed in this paper. The sensor is with the structure of single mode-thin core-multimode-thin core-single mode (STMTS) fiber structures fabricated by splicing two short sections of thin core fiber (TCF) among lead-in single mode fiber (SMF), multi-mode fiber (MMF) and lead-out SMF. The first section of TCF excites the core mode and high-order modes in the core of MMF and the second section of TCF couples the core mode and high-order modes into lead-out SMF to procedure inter-modes interferences. The sensor with MMF length of 20mm and TCFs length of 1mm is fabricated. The transmission spectrum of the sensor with respect to external strain has been studied by experiment. The result shows that the central wavelength respects to external strain with a good linearity. The strain sensitivity of the sensor is -2 pm/ue; over a strain range of 0 to 4500ue;. The temperature response of the sensor is also studied by experiment. The results indicate that the central wavelength of the transmission spectrum is insensitive to external temperature change. The proposed sensor features the advantages of easy fabrication, low cost and high sensitivity, and it exhibits great potential in single parameter measurement.