Application Of Multi-wavelength Swept Source In NIR Spectrometer

With the rapid development of NIR spectroscopy, NIR spectrometer has attractedconsiderable attention among researchers worldwide. This paper studied resolution ofnear-infrared spectrometer, and proposed NIR spectrometer based onmulti-wavelength swept source to enhance resolution of NIR spectrometer. Intensityof the same wavelength before and after frequency shift was recorded by the samepixel, and all the records would be arranged in accordance with the order of thewavelength. Resolution of spectrometer increased to0.08pm, which was much higherthan the current commercial spectrometer resolution10pm. And it turned out that thestudy has great scientific significance and application value.In order to verify the correctness of the method, a NIR fiber optic spectrometerwas developed, with a resolution of0.03nm, applicable to1520nm-1570nmwavelength. The research comprises of three major parts:1) Based on spectrometer design theory, principle and structure of the NIRspectrometer system with multi-wavelength swept source, the parameters of FP LD,collimating lens, grating, convergent lens and InGaAs linear array detector wereobtained, and the system was completed with these elements.2) The theory of semiconductor laser was analyzed, and the power characteristics,temperature characteristics of FP laser are thoroughly considered. Solution wasderived that frequency shift of the FP laser was precisely controlled by laser currentsource and temperature controller, with correlation between wavelength shift andinjection current0.003nm/mA.The interval of multi-wavelength output is0.33nm, andeach frequency shift of0.03nm was adopted in this experiment.3) FBG reflection spectrum and the spectrum of filter was measured by the system. Thedemodulation accuracy of FBG reflection spectrum reached0.03nm, and the temperature detectionaccuracy of2.4°C is realized, eleven times higher than the resolution of NIR spectrometer with thesame structure.Via256pixels detector,2816sampling pionts were measured instead of256,thus increasing sampling points for data collections and measured resolution.It was testified that multi-wavelength swept source can effectively increase theresolution of NIR spectrometer, and it was a useful approach for the development ofNIR spectrometer.