Fabrication Of 1.064?m Sub-nanometer Bandwidth Interference Filter In Near Infrared And Spectral Stability Research

With the development of lidar,free space communications,and laser ranging technology,the new generation of meteorological,ocean,and environmental observation satellites are commonly use sub-nanometer bandwidth filters to achieve spectrum acquisition and to suppress the background light.Compared with other sub-nanometer bandwidth filtering technologies,thin film interference filters have the advantages of small size,compact structure,good stability,and high optical efficiency.Consequently,they are particularly applicable to outer space exploration activities.In this paper,the near infrared bandwidth filters with bandwidth of 0.2 nm at 1.064?m wavelength are designed and fabricated.The stability of the sub-nanometer filters in space environment is simulated and analyzed.The transmission reaches 70%with stable spectral performance.As a common laser wavelength,the1.064 um wavelength bandwidth filters also have an application prospect in laser communication and remote sensing with Si-based CMOS detector.In this research,common design methods of sub-nanometer bandwidth filters including automatic optimization design method,analog microwave filter method,analog LC circuit filter method,iterative Chebyshev method and other design methods,are analyzed and compared at first.They all have their own advantages and disadvantages.However,these methods can't be simply applied to the design of the sub-nanometer bandwidth filter in this article.Therefore,the Matlab program for the design of the sub-nanometer bandwidth filters is studied in this paper.By applying this method,a series of film systems that meet the requirements are designed.The spectral characteristics are evaluated according to the evaluation function.According to the actual requirements and technical conditions,the optimal membrane scheme with a central wavelength of 1.064?m and a bandwidth of 0.2 nm is obtained.Some commonly used thin film preparation techniques are introduced.And the double ion beam sputtering deposition(DIBS)method is selected as the preparation method of the optical filter.Ta₂O₅ and Si O₂ is selected as the high refractive index material and the low refractive index material,respectively.The designed film system is deposited on fused quartz substrate.The optical constants of Ta₂O₅ and Si O₂ thin films are calculated by envelope method.A homogeneity correction membrane system is used to calculate,design and fabricate the uniformity correction plates of high and low refractive index target material.The uniformity of the films is effectively improved owing to the uniformity correction plates.The method of combining optical direct monitoring and time monitoring has been explored to break the technical limitations of the two monitoring methods.Complete control of the whole membrane system with high precision has been achieved through this method.A sub-nanometer bandwidth filter in near-infrared band with a half-power bandwidth of 0.19 nm and a peak transmittance of 70%has been developed.The measurement system of the sub-nanometer bandwidth filter has been built.By comparing the measurement results and the designed spectrum values,the sources of error in the preparation process and the mechanism of errors caused by direct optical monitoring method are analyzed and discussed.The optical constant error and the thickness error are the two main aspects of the sources of error.The error of optical constant is mainly produced during the deposition process.Since the deposition process of DIBS is relatively stable,the error is small.However,the thickness error can be affected by many factors.Despite the influence of the deposition process,the thickness error is mainly due to the errors introduced by monitoring process.Next,the influence of the error on the spectral performance of the filter is analyzed.A random error of 0.01%thickness will have a great impact on the spectral performance of the filter,and a random error of 0.001%thickness can make the deterioration of the spectral performance within an acceptable range.The error effects of the thickness error of the high,low refractive index materials and different layers Spacer layer,reflection layer and coupling layer are studied and compared,respectively.The spectral reliability and stability of the filter has been explored.The performance of the filters in the humidity environment has been studied.The aggregation density of the monolayer film is calculated by calculating the spectral drift of the films before and after absorbing moisture.The temperature stability of the filters has also been studied.Due to the high average aggregation density of the filters,the temperature drift of the spectrum is mainly related to the temperature coefficient of the refractive index of the material and the linear expansion coefficient of the films and the substrate.The spectrum of the filters is measured at different temperatures and the temperature drift of the spectrum is obtained.The effects of different annealing temperatures on the surface morphology and spectral characteristics of the filter are investigated.It is found that the spectral curve of the filters has redshift phenomenon with the increase of annealing temperature,which can be explained by the change of cross-section morphology.Meanwhile,it is also indicated that annealing temperature within 300°C will not significantly affect the surface morphology.Proton irradiation experiments have been performed.After being subjected to proton irradiation with an energy of 70 ke V,a flux of 2×10¹⁵ p⁺/cm² and a duration of 30 minutes,the spectral curves of the filters do not change significantly.