| In recent years,micro structured optical fiber has been widely used in the design and manufacture of optical fiber sensors because of its rich internal structure and various novel optical properties.There are four types of sensors based on micro structure fiber: grating type,interferometer type,SPR type and material filling type.Material filled micro structure optical fiber sensor allow integrates kinds of new functional materials into the micro holes of the optical fiber by means of full filling or selective filling,which facilitates the strong interaction between functional materials and the light transmitted in the optical fiber.Meanwhile,the high sensitivity of functional materials to the external environment endows the sensor with better sensing performance.In this paper,based on the current research progress of microstructural optical fiber sensor technology filled with functional materials,several new microstructural optical fiber sensors are designed and studied:1.A fiber-optic sensor based on self-imaging effect in hollow-core fiber is demonstrated for sensing applications.The device is mainly composed of a section of hollow-core fiber that sandwiched between two single-mode fibers.The self-imaging effect is investigated with different fiber lengths and arc-fusion parameters.The sensing performance of the sensor is experimentally investigated with a liquid-infiltrated structure and an un-filled one.The temperature sensitivity of the device can be improved significantly with the infiltrated structure and reaches-0.49 nm/? when temperature is increased from 25 ? to 75 ?.Both the un-filled and liquid-filled device exhibit approximately the same RI sensitivity of ~12000 nm/RIU in the RI range of 1.448–1.450.The proposed sensor is simple,highly sensitive and cost effective,which may find potential applications in physical and chemical sensing.2.An ultra-sensitive optical fiber temperature sensor based on a photonic crystal fiber(PCF)coupler is proposed and demonstrated.With the method of the offset splicing technology-assisted selective liquid-filled,the PCF coupler is fabricated by selectively filling liquid mixed by glycerol and water into one air hole in the PCF.As the liquid filled air hole is adjacent to the core of PCF,the fundamental modes of the core and the liquid rod waveguide can effectively couple with each other at the resonant wavelength,and then we can get the transmission spectrum with a wavelength dip.By filling different refractive index liquids,the PCF couplers with different resonant wavelengths are obtained,and the corresponding temperature responses are experimentally investigated.The achieved temperature sensitivity is up to 543.05 nm/°C,which is the highest temperature sensitivity ever reported,as far as we know.Such device may have great potential applications in biomedical related highly accurate temperature sensing.3.An electric field sensor based on a liquid crystal-filled PCF is proposed.The E7 liquid crystal is precisely filled in one of the innermost air holes of the PCF and forms an in-fiber optical coupler,and the resonance wavelength can be tuned with a sensitivity of 0.70 nm/(Vrms/mm)when an external electric field is applied.The device can operate as an electro-optical switch/modulator and exhibits response and recovery times of approximately 47 ms and 24 ms,respectively.The proposed structure is expected to have potential applications in electric field sensing and wavelength-tunable electro-optical devices.4.A high-sensitivity sensor based on liquid-crystal-filled side-hole fiber is proposed,which has the advantages of a simple structure,being easy to fabricate,and having low cost.This device can be used for high-sensitivity temperature or electric field sensing.Experimental results show that the device can realize low-threshold electric field sensing.The temperature and electric field sensitivity of the device are-1.50 nm/? and 1.20 nm/(Vrms/mm),respectively,and the device response to external temperature or electric field has good repeatability,these significant advantages make it promising for sensing applications. |
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