Study On The Computational Spectrometer Based On Random Pixelated Grating

The miniaturization of traditional spectrometer often degrades the instrument performances,such as spectral resolution and sensitivity.In recent years,based on the correlation between the speckle pattern and the incident wavelength,researchers at home and abroad have proposed a computational spectrometer scheme,which has the advantages of simple structure,low cost and low hardware requirements.It can not only simplify the spectrometer structure,but also improve the spectral resolution.Importantly,it can overcome the problem of mutual restraint between the size and the resolution for miniature spectrometer.Byreplacing the dispersive element in traditional spectrometer with a random scattering medium,the computational spectrometers can achieve a high resolution.However,the existing computational spectrometers generally have the disadvantages of low utilization ratio of light energy and mutual restriction between resolution and bandwidth.To overcome these problems,this paper proposes to use a random pixelated grating as the scattering medium in the computational spectrometer.With the unique scattering and diffraction properties of the random pixelated grating,this system can not only improve the utilization ratio of light energy,but also obtain higher spectral resolution and broad bandwidth at the same time.The research content of this paper is mainly divided into four parts,including theoretical analysis and simulation of the random pixelated grating,design and fabrication of the random pixelated grating,design and implementation of the Littman external cavity diode laser,as well as the least squares inversion algorithm design and spectral inversion experiment.In the theoretical analysis and simulation section,the Fraunhofer diffraction speckle distribution of the random pixelated grating on the focal plane is derived,and the influences of various parameters on the spectral resolution are investigated through numerical simulation.According to the simulation results,the random pixelated grating samples are designed and subsequently fabricated.In order to verify the feasibility of the computational spectrometer scheme proposed in this paper,an external cavity diode laser with Littman structure was established,which was adopted as the calibration light source.It can achieve a wavelength tuning range of about 10 nm,a tuning resolution of about 0.14 nm,and a line-width smaller than 0.1 nm.Furthermore,an experimental system of the computational spectrometer was built,and the home-made tunable light source was used to calibrate the system's transfer matrix.Finally,to restore the incident spectrum,a least square algorithm was developed for spectral inversion,which successfully reconstructed the spectra of a single-mode output of the external-cavity diode laser and a multi-mode output of the free-running diode laser.The simulation and experimental results prove that this system can realize spectral measurement with a simple and compact structure.Therefore,it has great development prospects.