ABSTRACT
We demonstrate an all-fiber structure that can realize LP01-LP11 mode conversion and twist measurement. It is a thin-core fiber (TCF) grating at a wavelength of 1310 nm cascaded to a short segment of a TCF of a different core size. It is found that the different core size of the TCF between the fiber and the grating has an impact on the excitation of a higher-order mode and mode conversion efficiency. The fiber structure exhibits a good linear response to twisting, strain, and temperature. Depending on the associated mode, the mode intensity and the wavelength for exciting the peaks of the grating have different sensitivities to twisting angle, applied strain, and temperature. These properties can be exploited for simultaneous measurement.
ABSTRACT
An optical fiber humidity sensor based on an optical Fabry-Perot interferometer is proposed and experimentally demonstrated. The sensor is constructed by a short section of hollow-core fiber coated with a polyimide (PI) film. Taking advantage of the direct response of the PI film, a sensitivity of up to 1.309 nm/%RH can be achieved in the humidity change range from 40% RH to 80% RH. The temperature sensitivity is measured to be 43.57 pm/°C when the temperature changes from 25°C to 55°C. Because of its simple structure, fast response time, convenient production, and good reproducibility, the proposed sensor will be competitive in the field of cultural relic humidity monitoring and pharmaceutical storage.
ABSTRACT
An integrated ultrasonic detection system that consists of emission and detection has been proposed and demonstrated experimentally. The proposed emission source is based on plastic optical fiber (POF). In order to promote the coupling of ultrasound-to-POF, and the end of the POF is heated to form a circular pedestal. A homemade fiber Fabry-Perot interferometer is employed to evaluate the coupling efficiency of ultrasound-to-POF. The sensing head is spliced with a short section of hollow-core fiber and single-mode fiber, resulting in an air microbubble formation by discharging. The experimental results show that ultrasound can be transmitted effectively in a narrow space using the coupling method, and the compact sensor also presents a considered sensitivity for ultrasonic detection. This all-fiber ultrasonic interrogation can be integrated as a system for the application in the bioimaging field, especially the organism body.
ABSTRACT
A micro-fiber-optic Fabry-Perot interferometer (FPI) is proposed and demonstrated experimentally for ultrasonic imaging of seismic physical models. The device consists of a micro-bubble followed by the end of a single-mode fiber (SMF). The micro-structure is formed by the discharging operation on a short segment of hollow-core fiber (HCF) that is spliced to the SMF. This micro FPI is sensitive to ultrasonic waves (UWs), especially to the high-frequency (up to 10 MHz) UW, thanks to its ultra-thin cavity wall and micro-diameter. A side-band filter technology is employed for the UW interrogation, and then the high signal-to-noise ratio (SNR) UW signal is achieved. Eventually the sensor is used for lateral imaging of the physical model by scanning UW detection and two-dimensional signal reconstruction.
