Structure Design And Characteristic Study Of F-P Thin Film Filter

F-P thin film filter is widely used in optical communication,laser system and optical fiber sensor because of its advantages such as simple structure design,wide tuning center wavelength range,convenient preparation and low cost.Especially in the infrared imaging field of optical readout mode,it has a broad market prospect by using its characteristics of less lithography times,simple principle and no need of refrigeration system,combined with the current mature CCD/CMOS technology.The selection of substrate material,the design and optimization of substrate based film structure,and the selection of preparation scheme based on the existing experimental conditions are all the key factors affecting the performance of F-P thin film filter.Therefore,this paper will start from the theory of thin film transmission,according to the experimental requirements of the filter structure design,on this basis,experimental preparation,theoretical analysis,optimization performance,the performance of F-P thin film filter has a preliminary study.First of all,amorphous silicon and silicon nitride are selected as high and low refractive index materials and amorphous silicon as cavity layer materials from the existing equipment conditions.All dielectric F-P film filters with different structures are deposited on silicon substrate by PECVD?plasma enhanced chemical vapor deposition?equipment.The experimental performance of film filters with different structures is measured and analyzed.The results show that:?1?The number of DBRs?high and low refractive index materials?at both ends of the cavity layer is the same,that is,symmetrical F-P thin film filter.With the increase of DBRs,the FWHM of the filter decreases,and the central wavelength spectral reflectance range(R_max-R_min)is close when DBR number is 1 to 3.When DBR number is 4,the spectral reflectance range decreases,and the average slope((R_max-R_min)/?FWHM/2?)is the largest in 3-period DBR,and its comprehensive performance is the highest in the number of DBRs from 2 to 3.The average slope represents the change amplitude of spectral reflectance under the tuning of unit wavelength.?2?Through theoretical analysis and simulation,it is found that the filter performance is better when the reflectivity of the high reflection film system at both ends of the cavity layer is close,but the presence of substrate reduces the reflectivity of the high reflection film system at the bottom of the cavity layer.On this basis,a new asymmetric filter structure is prepared,which greatly improves the performance of the filter.When the top of the cavity layer is 2-cycle DBR,the bottom of the cavity layer is symmetric junction By adding a period DBR,the performance of the membrane filter is greatly improved.The half peak width is 7Nm,the central wavelength spectral reflectance range is increased to 80.4%,and the average slope is22.97%.When the number of DBRs at the bottom continues to increase,the overall performance of the filter decreases.?3?Inspired by the asymmetric structure filter,reducing the reflectivity of the top high reflection film system can also reduce the reflectivity difference between the two ends of the cavity layer.Therefore,a new thin film filter structure with the antireflection film is designed and prepared.The experimental results show that on the symmetrical structure of DBR in the upper and lower three periods,a layer of antireflection film is deposited and the half peak width is 6nm,the spectral reflectivity range is 83.6%,and the average slope is 27.88 Moreover,the silicon nitride antireflection film on the surface can also be used as the protective layer of the filter.Then,because the film bubbles with the size of tens of microns are observed on the filter surface in the microscope,the basic structure and properties of the surface bubbles are studied,and the influence of bubbles on the filter is analyzed.The problem of bubbles is solved by thermal oxidation of a layer of silicon dioxide buffer layer on the surface of silicon substrate.The simulation analysis shows that the buffer layer can overcome the effect of substrate on the filter structure The influence of optical properties facilitates the subsequent optical optimization design.The symmetrical structure film filter with two periods of DBR was deposited on the thermal oxidation substrate.The half peak width was 5.5nm,the spectral reflectance range was 66.82%,and the average slope was 24.30.The performance of the filter was close to that of the asymmetric structure and the antireflection film structure,and the surface of the filter was even.Finally,the array of thin film filter is studied.The unit structure drawing mask is designed.After gluing,developing,etching and degumming,the array filter structure with uniform unit size and flat surface is obtained.Through measurement and calculation,its tuning performance is 0.035nm/?,and its reflectance changes at unit temperature is 0.16%/??which can directly correspond to the light intensity?,which is 10 times higher than the previous research.This is the main reason If the structure design improves the filter performance,especially the average slope,it will lay a solid foundation for the subsequent application of the array filter.