| Intensity-modulated optical fiber sensor?IM-OFS?is an important type of optical fiber sensors.For its simple structure,easy demodulation,anti-interference and low cost,it has been widely studied and first entered the commercial market in the early stage of optical fiber sensing technology development.However,less research has been made in the fields of structural design and signal processing for traditional IM-OFS.Light power fluctuations and spurious intensity modulation seriously affect its measurement accuracy and stability.Therefore,intensity-modulated optical fiber sensing has long been considered as a low-precision sensing technology,which affects its further application.Based on the analysis of the existing intensity compensation technologies of IM-OFS,this dissertation proposes a pulse reference-based compensation technique,which can theoretically completely suppress the intensity fluctuation of light source,the variation of the optical path transmission loss,the change of the coupling ratio and photodetector responsibility.Based on this compensation technology,a high-precision intensity-modulated optical fiber sensing scheme is designed and the corresponding experimental research is carried out.By testing and optimizing intensity compensation capability,noise and stability of this sensing scheme,accurate measurement to physical quantities can be made.On this basis,in order to expand its application fields and verify its ability to achieve high-precision sensing,several sensing experiments have been made,including refractive index sensing based on Fresnel reflection,temperature sensing based on coating materials-covered microfiber probe and temperature sensing based on semiconductor-coated fiber end face.The main findings and innovations of this dissertation are as follows:1.Pulse reference-based compensation technique for IM-OFS is proposed and analyzed in detail.The impact of non-ideal factors on the system in this technology is discussed.2.The intensity compensation capability,noise and stability of proposed high-precision intensity-modulated optical fiber sensing scheme are tested and optimized.After eliminated the influence of polarization state and additive noise,the system noise is suppressed,and the long-term stability as well as startup repeatability are improved.The effective noise relative change?reaches 0.00039d B,and the30-minute long-term stability fluctuation?is 0.00012dB.3.Based on the proposed high-precision intensity-modulated optical fiber sensing scheme,a refractive index sensor based on Fresnel reflection of fiber end face is developed.The minimum refractive index resolution can reach 1.6×10-6RIU.A temperature sensor based on coating materials-covered microfiber probe is proposed,with its temperature sensitivity of-0.063dB/?and temperature resolution of0.008?.Another temperature sensor based on semiconductor-coated fiber end face is also developed,reaching a temperature resolution of 0.2?when the temperature sensitivity is only-0.063dB/?. |
PDF Full Text Request