Design And Simulation Of Spectrum Focusing System In Multi-wavelength Pyrometry

Every object in nature with a temperature higher than absolute zero will radiateenergy in the form of electromagnetic wave. The radiated infrared wave has a strongtemperature effect, that is, we could measure the temperature of the object bymeasuring the infrared light intensity radiated by the object. That’s the basic theoryof measuring temperature using radiation method. The traditional radiation methodsare single-wavelength measuring temperature， double-wavelength andmulti-wavelength measuring temperature. And using the method of multiplewavelengths can we get a more accurate temperature theoretically. Generallyspeaking, the multi-wavelength pyrometry uses filter, prism or grating as the tool toseparate light with different wavelengths. The optical system of filter-basedpyrometry is rather complex and difficult to maintain. In addition, the filter is easy tobreak; therefore, the filter is not the best spectroelements. For the prism-basedpyrometry, the material of the prism needs to be chosen strictly so that the prism hasa better transmittance to all wavelengths within the spectrum range. Thegrating-based pyrometry generally uses fibers to realize the output and input of theradiation. But the size of the fiber core will limit the energy extracted. Thus thesensitiveness and total property of the equipment are affected. So adopting someeffective method to improve the number of the extracted energy will improve thesensitiveness and detecting property. To solve the questions stated above, this article proposed to adopt the method ofmicrolen-fiber coupling. More energy can be focused by the microlens and coupledinto the fiber, and thus more energy can be extracted. The detectors are used tomeasure the light intensity of different wavelength. After the careful analysis of thedata, we can get the accurate temperature of the object. In the research ofmultiwavelength pytrometry, enhancing the light intensity received by the detector isof great importance. This thesis is dedicated to enhance the intensity receiving by thedetectors. In this thesis, the basic theory of radiation method to measure thetemperature, the methods to separate light with different wavelengths, the basictheory of spectrometer, and the basic theory of fiber coupling are reviewed firstly.Then the microlens-fiber coupling method is proposed to enhance the light couplingefficiency. The software of Zemax is used to simulate the spectrum of thespectrometer and the design of microlens. The multi-mode fiber is simulated bynon-sequence mode in Zemax, and the fiber coupling efficiency is calculated byusing the ray-tracing method. The simulation result indicates that by introducingmicrolens, the fiber coupling efficiency can be improved by more than30%. Themain content of the thesis is arranged as follows:The first chapter introduced the basic theory of radiation method to measuretemperature, presented the methods to separate light with multiwavelengths,compared the advantages and disadvantages of the radiation methods, at last of thechapter, we introduce the research content and significance of the subject.The second chapter introduced the light separating system and put greatemphasis on the basic content about spectrometer, including the theory and structureof grating spectrometer, presented the several different structures of spectrometer,different gratings.The third chapter introduced the novel pyrometry system and the spectrumfocusing system. we also introduced the kinds of fiber, the choosing of the fibers andthe choosing of microlens-fiber coupling system.The fourth chapter introduced the main work of this thesis, including the design of microlens using Zemax, the simulation of spectrum of the light, the simulation ofmulti-mode fiber, and the calculation of the microlens-fiber coupling. In addition, thesimulation results were fully discussed.The fifth chapter summarized the results of this thesis, the remaining problemsto be addressed, and the future work needs to do.