A sensitivity-enhanced strain sensor constructed by a 7-mm-long thin-core fiber (TCF) splicing with a 10-mm-long tilted fiber Bragg grating (TFBG) was proposed. The modal interferometer formed by the TCF will interact with the spectrum of the TFBG to form an overlapped spectrum, which will extremely increase the axial strain sensitivity of the TFBG. Experimental results showed that the wavelength shifts of the resonant dip in the overlapped spectra for the applied axial strain have a high sensitivity of 0.67 pm/mu epsilon. Meanwhile, the proposed sensor has the temperature self-compensation function for the variation of the external temperature simply by measuring the relative wavelength shifts of the Bragg mode of the TFBC.

A polarization-dependent twist sensor based on an in-fiber Mach-Zehnder interferometer is proposed.The sensor is constructed by core-offset fusion splicing of a 15-mm-long polarization maintaining fiber (PMF) between two single mode fibers.With the increasing of the twist applied on the sensor,the intensity of the output light transmitting along the two orthogonal polarization states has changed,which leads to the intensity changes of the resonance peaks in the transmission spectrum.By measuring the slow axis resonance peak intensity changes in clockwise and counterclockwise directions with the distorted angle within 0-180°,the maximum sensitivity can reach 0.624 dB/° · m-1,which is almost 2 times of that of the existing similar strain sensor.Due to the intensity demodulation method,the proposed sensor has an application advantage in marked contrast compared with other twist optic fiber sensors which usually employ high-cost wavelength-shift means.

A transverse load fiber sensor based on Mach-Zehnder interferometer constructed by a Bowknot-type taper between a single mode fiber (SMF) and a polarization maintaining fiber (PMF) was proposed. Due to the polarization maintaining fiber's birefringence, intensities of the two peaks which are corresponding to the fast and slow axis modes changed with the transverse load applied on the PMF. The experimental results showed that the structure with a 2 cm-long PMF has the sensitivities of 104.52 and - 102.94 dB/(N/mm) for the fast and slow axis spectral dip wavelengths of 1485 and 1545 nm in the interference pattern, respectively, which are almost 7 times higher than that of the current similar existing transverse load sensor.

Optical hydrogen sensing based on surface plasmon resonance(SPR) has become a hot spot in hydrogen sensing technology.With advantages such as reliable safety,high sensitivity,real-time and multipoint detection,SPR sensor shows a wide application prospect in hydrogen leak detection.This review firstly introduced the detection principles and the typical structures and research progress of three main types of SPR hydrogen sensors:the prism coupling structure,the grating coupling structure and the optical fiber coupling structure.Then the present research situation and problems of hydrogen sensitive films in SPR hydrogen sensing technology were summerized.Finally,the direction of future research was discussed.We proposed to exploit new sensors based on optical fiber microstructures and nano materials and to extend the sensing principle to localized surface plasmon resonance and surface plasmon resonance imaging.

Abstract A polarization-dependent refractive index sensor based on the in-fiber Mach- Zehnder interferometer which is constructed by core-offset fusion splicing a tapered polarization maintaining fiber (PMF) with a length of 20 mm between the core-offset and the taper is proposed. Due to the introduced high environment-sensitivity of the two orthogonal polarization modes in the PMF and the enhancing effect of the tapered PMF, The sensitivity of the fast axis and the slow axis up to ∼-107.51 nm/RI and ∼-74.54 nm/RI in the RI range between 1.333 and 1.381 is obtained, respectively. Such kinds of low-cost and highly sensitive fiber-optic RI sensors would find applications in chemical or biochemical sensing fields.

Recently, we had reported some fiber sensing applications by using the tilted fiber Bragg grating (TFBG), such as twist sensor, polarization sensor, curve sensor and relative humidity sensor, and so on. Here, we summarized two kinds of TFBG-based sensors (humidity- and twist-sensing) for the conference of ICOCN 2016. An optical fiber humidity sensors based on a graphene oxide coated on a TFBG and a fiber twist sensor based on the surface plasmon resonance (SPR) effect of an Au-coated TFBG were presented. The sensitivity of 0.129 dB/%RH with a linear correlation coefficient of 99% under the RH range of 10%~80% was obtained. For the twist ranging from 0 to 180° in clockwise or anti-clockwise directions, the proposed sensor shows sensitivities of 0.037 dBm/°(S-polarized), 0.039 dBm/°(P-polarized), respectively.

An optical fiber humidity sensor based on Mach-Zehnder interferometer (MZI) was proposed. The MZI consists of two waist-enlarged tapers and a single mode fiber (SMF). The SMF between the two tapers was coated with a composite film of graphene oxide (GO) and polyvinyl alcohol (PVA). The finite element software called COMSOL Multiphysics was used to analyse the energy distribution in the sensor. The sensor was put inside a little chamber and a hygrometer was used to record the relative humidity (RH). The sensitivity of 0.193dB/% RH was obtained and the measurement range of relative humidity is between 25% and 80%.

A fiber optic relative humidity (RH) sensor based on the tilted fiber Bragg grating (TFBG) coated with graphene oxide (GO) film was presented. Amplitudes of the cladding mode resonances of the TFGB varies with the water sorption and desorption processes of the GO film, because of the strong interactions between the excited backward propagating cladding modes and the GO film. By detecting the transmission intensity changes of the cladding mode resonant dips at the wavelength of 1557 nm, the maximum sensitivity of 0.129 dB/%RH with a linear correlation coefficient of 99% under the RH range of 10–80% was obtained. The Bragg mode of TFBG can be used as power or wavelength references, since it is inherently insensitive to RH changes. In addition, the proposed humidity sensor shows a good performance in repeatability and stability.

A simple and low cost transverse load fiber sensor based on in-line Mach-Zehnder interferometer (MZI) is proposed. The sensor head is formed by a single mode fiber-polarization maintaining fiber-single mode fiber (SMF-PMF-SMF) structure through core-offset fusion splicing. With the increasing of transverse load on the PMF, the couple efficiency between the core mode and the cladding mode of PMF decreased, which further brings about a change of the interference fringe visibility. The experimental results show that the structure with a 1.3 cm-long PMF has the sensitivities of 12.85 dB/(N/mm) and 30.69 dB/(N/mm) for the fast and slow axes resonant wavelengths of 1517.1 nm and 1551.3 nm, respectively, which are about 2 times higher than that of the current similar existing transverse load sensor.

为实现手持测距望远镜的小型化和轻量化,利用ZEMAX光学软件设计了一款望远部分和接收部分共用的光学系统,其中望远系统的放大倍率6,物镜焦距82.5mm,物镜视场角达到6°,入瞳直径22mm,出瞳距离大于17mm,光学总长控制在90mm以内,系统二级光谱色差满足设计要求.接收部分与望远物镜共用,不仅能满足测距望远镜对其光学系统望远部分和接收部分的性能要求,而且会使光学系统结构简单、质量轻、体型小、较易加工组装.

Fiber optic humidity sensor based on an in-fiber Mach–Zehnder interferometer (MZI) coated with graphene oxide (GO)/PVA composite film was investigated. The MZI is constructed of two waist-enlarged tapers. The length between two waist-enlarged tapers is 20mm. By comparing the experiment results of MZI coated with different GO/PVA composite films, composite film formed by the ratio of 0.3g PVA mixed with 10ml GO dispersion shows a better performance of relative humidity sensing. By using the molecular structure model of the composited GO/PVA, the operation mechanism between GO/PVA composite film and water molecules was illustrated. The sensitivity of 0.193dB/%RH with a linear correlation coefficient of 99.1% and good stability under the relative humidity range of 25–80% was obtained. Temperature effect on the proposed fiber optic humidity sensor was also considered and analyzed. According to the repetitive experimental results, the proposed humidity sensor shows a good repeatability.

提出一种基于长周期光纤光栅(LPG)和蝶形锥(BTT)的光纤横向压力传感器.传感器是由LPG和一段单模光纤(SMF)熔接而成,其特点是在熔接处会形成一个BTT.实验中,横向压力作用在LPG上,干涉谱共振波长强度随横向压力的变化而变化.当横向压力从0.000增加到1.225 N/mm时,传感器的灵敏度达到-10.476 dB/(N/mm),是目前类似传感器灵敏度的2倍左右.本文传感器具有灵敏度高、成本低和结构简单的优点,具有广阔的应用前景.

A highly sensitive and compact fiber-optic strain sensor was presented and experimentally demonstrated. The sensor is based on an in-line fiber Mach–Zehnder interferometer (MZI), which is constructed by connecting a long-period fiber grating (LPG) with an up-taper. With the increasing of the axial strain on the sensor, both of the up-taper's diameter and the light coupling efficiency decreased. By measuring the transmission intensity changes of the resonant dips at wavelength ~1553.4nm under the fiber axial strain ranging from 0 to 590με, the sensitivity of 0.026dB/με was obtained, which is almost 2 times of the existing similar strain sensor. And the results were also confirmed by simulations.

提出了一种利用光纤Fabry-Perot(F-P)干涉结构的微位移传感器,该F-P干涉结构是由双倾斜光纤光栅(tilted fiber Bragg grating,TFBG)沿轴向错开一定距离构成空气腔形成的.入射光经双TFBG及其高反射端面往返传播,从而构成F-P干涉结构.光纤沿纵(z轴)向移动时,F-P腔的腔长发生变化,致使干涉光谱的自由光谱范围随之产生变化.实验验证,该传感器在0～115μm的测量范围内获得了高达0.475 nm/μm的灵敏度,较之前提出的光纤光栅型传感器灵敏度提高了近3倍.

The scatterings of P and S-polarized evanescent wave on the surface of a tilted fiber Bragg grating (TFBG) with a 50 nm thick gold coating were investigated experimentally by observing radiation patterns from discontinuities in the coating. The scattering intensity for P-polarized light is larger than for S-polarized light when the evanescent wave propagates from the coating towards the discontinuity. Using the characteristics of the polarization of the evanescent wave, the in-line polarimeter and twist sensors were designed.