| In recent years,the whispering gallery mode optical resonator has attracted great attention from researchers at home and abroad due to its ultra-high optical quality factor and small size.At present,whispering gallery mode optical resonators have been applied to detect the magnetic field,the acceleration and the current.Among which magnetic field sensors are widely used in various regions.The DC magnetic field is demodulated with the wavelength shift of a single optical mode or light intensity change at specific wavelength based on whispering gallery mode optical resonator.Most researchers ignore the temperature drift effect when using the above two detection schemes,due to it is difficult to compensate the temperature drift effect in optical fiber system,which eventually leads to inaccurate demodulation results.To solve the existing problems,the solution in the existing research is to compensate the temperature drift effect by ways of dual cavity cascade,but this solution has some shortcomings such as difficult fabrication and high system complexity.Therefore,to solve this shortcoming,the magnetic field sensing characteristics of whispering gallery mode optical resonator are studied.The main contents include the following aspects:Firstly,this paper introduces the research status of magnetic field sensor based on optical methods at home and abroad.We propose two DC magnetic field sensing schemes to reduce the temperature drift effect and improve the magnetic field sensitivity.Secondly,this paper introduces the basic theory of whispering gallery mode optical resonator.By analyzing the commonly used coupling methods of resonator and the light field,we determined that the fiber taper coupling method is utilized in this paper.Then the performance indicators of whispering gallery mode optical resonator are briefly summarized.Thirdly,an externally driven capillary whispering gallery mode optical resonator structure is constructed,which makes the size of magnetostrictive medium increase as much as possible,improving the sensitivity of magnetic field.Based on the proposed resonator,the DC magnetic field is demodulated with the wavelength of the optical mode.We firstly tested the temperature response of optical modes in the externally driven capillary whispering gallery mode optical resonator and the wavelength of a single optical mode is used to demodulate the temperature variations.The test results show that the resonant wavelength of a single optical mode is sensitive to temperature fluctuation,and there is a significant temperature drift effect.Then,we use the single-wavelength demodulation scheme to detect the DC magnetic field in the open test environment.The experimental results show that the sensitivity of this direct sensing solution contains a large drift temperature effect,and the solution results are not accurate.To solve this problem,we propose a scheme of demodulating DC magnetic field with the wavelength difference between dual wavelengths.By testing the response of dual wavelengths difference to temperature,it is found that the offset of dual wavelength difference hardly changes with temperature.Finally,the DC magnetic field is detected by the dual wavelength difference method.The experimental results show that the dual wavelength difference demodulation scheme can not only detect the DC magnetic field,but also greatly reduce the influence of temperature drift effect.Fourthly,an AC magnetic field sensing system is built based on the externally driven capillary whispering gallery mode optical resonator,and its AC magnetic field sensing characteristics are studied.We use the AC magnetic field sensing system to detect the AC magnetic field signal,and give the related performance parameters of the AC magnetic field sensing system.Then,the temperature response of the AC magnetic field sensing system is tested,and the test results show that the AC magnetic field sensing system has low temperature dependence.Fifthly,DC magnetic field detection is realized with an AC magnetic field modulation signal.We use the externally driven capillary whispering gallery mode optical resonator to build a highsensitivity and low-temperature dependent AC magnetic field sensing system,and with the aid of AC magnetic field modulation signal,we can realize high-sensitivity detection of external DC magnetic field.Then,the influence of the amplitude and frequency of AC magnetic field modulation signal on the sensitivity of DC magnetic field sensing is studied.The two schemes proposed in this paper,the dual wavelength difference demodulation scheme and the change of signal to noise ratio of AC magnetic field modulated signal demodulation scheme,have the ability to compensate the temperature drift effect in optical fiber system and can detect DC magnetic field well.Among them,the sensitivity of the latter is 1.54 times higher than that of similar sensors.The research work in this paper provides a new idea and method to solve the cross-sensitivity problem in optical DC magnetic field sensors in the future. |
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