Miniature Fiber Spectrometer Based On Tilted Fiber Grating

Miniature fiber optic spectrometers have attracted the attention of many domestic and foreign scholars due to their outstanding advantages such as small size,light weight,strong stability,and strong anti-vibration performance.In the past few decades,miniature spectrometers have been widely used in the fields of food quality assessment,gas composition detection,pressure sensing measurement,medical diagnosis and other fields.A tilted fiber grating is a special type of fiber grating.The plane of the grating has a certain tilted angle,which can strengthen the coupling between the core mode forward transmission and the radiation mode or cladding mode backward transmission.This characteristic makes it in the optical fiber sensing,optical fiber filtering and other fields have good application prospects.The radiation mold of tilted fiber gratings has excellent spectral characteristics.The radiation mode of the grating can diffract optical signals of different wavelengths out of the optical fiber at different radiation angles,thereby realizing the wavelength demodulation of the complex optical signal.Due to the optical fiber transmission characteristics,the spectral demodulation system based on tilted fiber gratings greatly reduces the complexity of the system optical path,thereby reducing the size of the instrument and improving the energy utilization rate.In this thesis,by using the tilted fiber grating,the diffraction characteristics research,the system design and software development of the micro spectrometer are carried out,and a high-sensitivity and high-resolution micro spectrometer is built.The main research contents of this thesis include the following aspects:(1)Preparation and diffraction characteristics of tilted fiber gratings: including the principle,preparation process and performance test of tilted fiber gratings.The thesis uses Gaussian optics to construct the theoretical diffraction model,and establishes the relationship between the diffraction angle and the incident light wavelength,grating tilt angle and period,and the refractive index of the core.The grating preparation system is based on excimer lasers and phase masks,and uses commercial spectrum analyzers,optical power meters,tuned lasers,CCD arrays and other equipment for grating performance testing.Experimental results show that light of different wavelengths will be diffracted at different angles,which is consistent with theory.The experiment of testing the splitting ratio and the polarization extinction ratio shows that when the polarization extinction ratio is greater,the splitting ratio is greater and eventually approaches 0.5.The experimental result of the polarization distribution of the test tilted fiber grating is a perfect figure of eight distribution,indicating that the diffracted light after 45 ° tilted fiber grating is linearly polarized.(2)System design of micro fiber spectrometer based on tilted fiber grating: including optical path modeling,ZEMAX design and simulation,optical path construction and system performance evaluation.The Rayleigh criterion is used to derive the resolution expression of the designed optical path system,and the optical design software ZEMAX is used to design the simulation model.After verifying the feasibility,the system prototype was built.The optical path structure only included tilted fiber grating,lens collimation system and CCD detector.The response relationship between the wavelength of the fiber grating diffracted light and the photodetector is studied.The experimental results show that the wavelength resolution of the tilted fiber grating spectrometer is 0.31 nm and the sensitivity is 17.73 μm /nm.(3)Development of signal processing software for miniature optical fiber spectrometer system: including software interface design and programming.It is written in C # language in Visual Studio 2019 compilation and development platform,including serial port control,acquisition control and calibration.By adding Label control,Combo Box control,Button control,etc.,write the code corresponding to each control to generate an application that can display the spectrum measurement results.