Theoretical And Experimental Study On Fiber Interferometer Sensor And Wavelength Interrogation System

Optical sensor has played a critical role in the development of the new generation Internet of Things(IOT)and intelligent sensor technology due to their intrinsic advantages of fast responsibility,simple configuration,flexible design and resistance to electromagnetic interference.In turn,the development of these emerging technology also promoted the progress of sensing technology.In this thesis,three sensors have been proposed to improve the sensing performance,and two wavelength interrogation systems are proposed to explore new wavelength interrogation technology,the five systems involving new sensing mechanism and wavelength interrogation methods,and they are respectively based on high birefringence fiber loop mirror(HiBi-FLM)with three section high birefringence fibers(HBFs),HiBi-FLM incorporating with FBG,cascaded HiBiFLMs with vernier effect,pulse light source incorporating with crossed HiBi-FLMs and pulse light source incorporating with jammed-array wideband sawtooth(JAWS)filter,Every chapter in this thesis revolves around a kind of sensing system or wavelength interrogation system,and introduce the system principle,the design and realization of key elements,and the system performance parameters from both theoretical and experimental aspects.The main achievements and innovations are summarized as follows:1.Sensing system based on HiBi-FLM with three section HBFs has been proposed and experimentally demonstrated.The sensor of HiBi-FLM with three section HBFs has been designed and made.The transmission spectrum of HiBi-FLM with arbitrary section HBFs has been derived using Jones matrix.Differentiate the transmission spectrum of HiBi-FLM with respect to temperature and strain,we can get the temperature and strain sensitivity for the resonance dips in the transmission spectrum.We simulated the transmission spectrum of HiBi-FLM with three section HBFs,simulated result match the measured transmission spectrum well.We measured the temperature and strain response characteristics of the proposed sensor,the temperature and strain resolution of the proposed sensor are measured to be ±0.3 ?and ±12 ??,respectively.2.The sensing system of HiBi-FLM with one section of HBF and a piece of FBG has been proposed and experimentally demonstrated.The temperature and strain sensitivities of the resonance wavelengths of HiBi-FLM and FBG are different with each other,therefore,the four measured sensing parameters can be formed into a sensor coefficient matrix.Incorporate the coefficient matrix with the measured wavelength shifts of the HiBi-FLM resonant dip and FBG resonant peak,the environment temperature and strain changes can be simultaneously determined.The temperature and strain resolutions of the proposed sensor are measured to be ±0.5 ?and ±22 ??,respectively.3.A cascaded HiBi-FLMs sensing system with vernier effect has been proposed and experimentally demonstrated.Since the transmission spectrum of HiBi-FLM with a section of HBF is periodic,it can be regarded as an optical vernier caliper.And the optical vernier effect can be produced by cascade two HiBi-FLMs with slightly different FSRs.When the transmission spectrum of single HiBi-FLM shift with a small amount,then the vernier spectrum will shift to the corresponding direction by a magnification factor,result in a magnification of the measure sensitivity and resolution of single HiBi-FLM.The realization process of the optical vernier effect for two cascaded HiBi-FLMs is theoretically described and simulated,the enhancement factor for vernier effect and the equation of the transmission spectrum of the cascaded configuration are derived.Gauss fitting algorithm and Lorentz fitting algorithm have been proposed to fit the vernier spectrum envelope,so as to recover the envelope peak and precisely determine the vernier spectral shift.We made the cascaded HiBi-FLMs sensor and measured its temperature characteristic,experimental result shows the temperature sensitivity and resolution of the cascaded configuration are both M times of those for single HiBi-FLM,which agree well with the theoretical predication.The magnification factor for the sensitivity and resolution of the cascaded configuration can be further enlarged by reducing the difference of the two HiBi-FLM FSRs.We made the cascaded HiBi-FLMs sensor with a smaller FSR difference and measured its temperature characteristic,a greater magnification factor for temperature sensitivity and resolution are obtained as expected.4.A FBG wavelength interrogation system based on crossed HiBi-FLMs is proposed and experimentally demonstrated.The advantages of edge filter-based wavelength interrogation system are analyzed,the periodic rising edge(or falling edge)of the transmission spectrums of the two HiBi-FLM can be used as edge filter to interrogate the FBG resonance wavelength.Taking the logarithm of the demodulation results of the two channels(i.e.,two HiBi-FLM branches),and then make the difference,the result is a linear function of the FBG resonance wavelength,so as to realize the linear mapping of the FBG environmental parameters.We made the two HiBi-FLMs with specific FSRs,both wavelength division multiplexing(WDM)and time division multiplexing(TDM)are used in the wavelength interrogation system to interrogate multiple sensing signal at the same time,so as to monitor the state of multiple targets.Owing to the advantages of fast interrogation,simple configuration,low cost and flexible design,we expect the proposed interrogation technique find widespread application in the field of ultrafast dynamic phenomenon monitoring and ultrahighresolution sensing.5.The jammed-array wideband sawtooth(JAWS)filter based FBG wavelength interrogation system is proposed and experimentally demonstrated.Based on paraxial wave theory,the spectral dispersion law for finite reflection virtually imaged phased array(FRVIA)is derived using Fresnel diffraction analysis.The optical spectrum for FRVIA based JAWS filter is simulated,and we made the FRVIA based JAWS filter,the measured filter spectrum agrees well with the simulated result.The customed JAWS filter is used to interrogate three FBG signal,and the real-time dynamic variation of vibration amplitude of iron pipe is monitored.The velocity of the strain-wave in the iron pipe is calculated using correlation algoritnm.Besides,the mapping relationship between the collected voltages and the vibration amplitude of the iron pipe is derived.The proposed wavelength interrogation system can detect and interrogate the signal whose frequency is less than 200 k Hz.Due to the advantages of fast interrogation,resistance to electromagnetic interference,flexible using and low cost,we expect the proposed technique can find widespread application in ultra-fast dynamic phenomenon monitoring(such as molecular dynamic sensing and aerospace diagnosis),highspeed communication,ultrafast and ultrahigh resolution sensing,structural health monitoring,medical treatment and other fields.