Objective  After nearly half a century of development, infrared spectroscopy has been widely used in food, medicine, biological diagnosis, agriculture, textile, oil refining and chemical industries. The optical path of the traditional infrared spectrometer is more complex, and often with moving parts, so the requirement of machining accuracy is very high, and the optical components in the optical path are also expensive. These factors make the infrared spectrometer expensive and the stability, reliability and working environment adaptability of the system weak. Small spectrometers have received extensive attention and developed rapidly due to their significant advantages in size, weight, and power consumption. In particular, computational spectral analysis technology based on speckle detection can obtain high-precision spectral information by recording and analyzing the speckle patterns formed by scattering elements on the measured light. Speckle computational reconstruction spectrometer has the advantages of both small size and high resolution, and because the preparation of scatterers is simpler and costs less than various strictly designed micro-nano structures or materials with different components, it is a spectral analysis technology with great application potential.

  Methods  A set of speckle calculation recombination spectrometer system is designed in this paper. The spectroscopic structure was designed using chalcogenide glass IG2 and polymethyl methacrylate (PMMA) materials. The uniform random distribution method of these two materials was studied. The disordered scattering structure was constructed based on the difference in refractive index changes of the two materials (Fig.3). The spectrometer system was tested by Tracepro software design simulation experiment.

  Results and Discussions  The speckle calculation recombination spectrometer system adopts a special spectroscopic structure. The spectroscopic structure is designed based on the uniform random distribution of chalcogenide glass IG2 and polymethyl methacrylate (PMMA), which can generate speckles with uniform distribution and high contrast, and has good spectroscopic effect (Fig.6). Multiple sets of simulation experiments were designed by Tracepro software to verify the performance of the system. In the 1-10.9 μm wavelength range, the relative error of the simulation results of the test light composed of the calibration light is 1.29% (Fig.7). The relative error of the simulation results of the uncalibrated 5.01 μm wavelength monochromatic light is 3.37% (Fig.8). The simulation results of uncalibrated 3 000 K blackbody radiation are fitted by 6-order polynomial. The maximum absolute error of the calculated value is 2.581 6 W, and the maximum absolute error of the fitting curve is 0.678 7 W (Fig.9). In the high-resolution simulation of 1-2 μm wavelength range, the simulation results of 3 000 K, 4 000 K and 5 000 K blackbody radiation are fitted by 6-order polynomial. The maximum relative errors of the fitting curves are 2.07%, 5.32% and 4.28%, respectively (Fig.10). The results of the simulation test show that the system can maintain small error under the condition of wide range or high resolution.

  Conclusions  A speckle calculation recombination spectrometer system with working wavelengths of 1-10 μm and 1 000-2 000 nm was designed. The system is characterized by small size, no moving components, simple and stable structure, low production cost and easy production. The system function was simulated by using Tracepro software. The resolution reached 0.1 μm in the spectral range of 1-10.9 μm, and the maximum relative error of the test results was 3.77%. The resolution reaches 10 nm in the spectral range of 1 000-2 000 nm, and the maximum relative error of the test results is 5.32%. The simulation results show that the system has large range, high resolution and low error, and can select the corresponding wavelength range according to the actual situation to meet different application requirements.