Ke Tian

A Curvature Sensor Based on Twisted Single-Mode–Multimode–Single-Mode Hybrid Optical Fiber Structure

An optical fiber curvature sensor based on a twisted multimode fiber (MMF) sandwiched between two single-mode fibers (SMF) is proposed and investigated theoretically and experimentally. The measured transmission spectrum exhibits good agreement with theoretical predictions. Compared with a traditional single-mode–multimode–single-mode fiber structure sensor, the proposed configuration offers a higher average curvature sensitivity of –2.42 nm/m^–1 over a curvature measurement range of 0–1.7390 m^–1 and –7.09 dB/m^–1 at an operating wavelength of 1537 nm. The temperature sensitivity of this sensor has been determined as 0.01 nm/°C over a wavelength range of 1535–1550 nm and circa 0.007 dB/°C at the wavelength of 1537 nm, over a measured temperature range of 21–121 °C.

A Humidity Sensor Based on a Singlemode-Side Polished Multimode–Singlemode Optical Fibre Structure Coated with Gelatin

A novel relative humidity sensor based on a singlemode-side polished multimode-singlemode fibre structure coated with gelatin material is reported. The sensing principle and fabrication method of the proposed sensor are presented. The experimental method is demonstrated to provide the optimum thickness of coating layers in order to achieve the highest sensitivity of 0.14 dB/%RH and a fast response time of 1000 ms for a given relative humidity sensing range. The developed humidity fibre optic sensor based on a gelatin coating shows great potential for many applications such as industrial production, food processing, and environmental monitoring.

Investigation of a novel SMS fiber based planar multimode waveguide and its sensing performance

A novel, MMI-based all-fiber structure, which consists of two single-mode fibers and a multimode fiber polished on both sides, is described. The light propagation characteristics of this fiber structure, as well as its superior sensing performance, are analyzed theoretically by using the beam propagation method (BPM). This fiber structure demonstrates a significant spectral response to changes of the surrounding refractive index (RI), and the measured results exhibit good agreement with the predicted data. The measured average RI sensitivity is as high as 151.29 nm/RIU over an RI range from 1.3450 to 1.4050, when the polished depth is 30 µm on both sides of the multimode fiber. This fiber structure can be an advantageous platform for various applications, especially for a lab-on-fiber type sensing application.