In the near-infrared band, 1064 μM is a commonly used laser wavelength, and its corresponding lasers and detectors are relatively mature, which is widely used in laser radar, free space optical communication and space optical remote sensing. In these applications, sub nanometer bandwidth spectral filters are needed to suppress the interference of background light. The filter based on the interference principle has the advantages of simple structure, good stability and easy integration, which is particularly suitable for space applications.
The monochromaticity of laser is very good, and its spectral bandwidth is far less than 1 nm, so the spectral bandwidth of the thin film filter used usually reaches the sub nanometer level. The narrower the filter bandwidth, the higher the transmissivity, and the deeper the out of band cutoff, the better the system’s signal-to-noise ratio. At present, the standard bandwidth of the wavelength division multiplexing filter used in 5G optical communication is 0.4 nm, and it works near the wavelength of 1550 nm. It needs to use the most advanced special coating equipment for coating. Restricted by film growth and monitoring technology, it is a challenging task for researchers to develop high-performance sub nanometer bandwidth filters in the near infrared band. At present, there is no report on the research on the space application of sub nanometer bandwidth filters. To meet the needs of space applications, a sub nanometer bandwidth filter was prepared by double ion beam sputtering (DIBS) method. Its central wavelength is (1064 ± 0.05) nm, full width at half peak is 0.19 nm, and the peak transmittance can reach 70.2%.
In order to investigate and reduce the impact of large temperature changes on the filter performance in some applications, our research group conducted annealing treatment at different temperatures (100200300 ℃) on the developed filter, and studied the changes of the film surface morphology and filter spectral characteristics. At present, some scholars have conducted more in-depth research on thermal annealing of optical films,
Some studies show that annealing affects the structure and laser damage threshold of Ta2O5/SiO2 multilayer dielectric mirrors. The results show that the central wavelength shifts to the long wave direction with the increase of annealing temperature;
Some studies have shown that annealing affects the residual stress of HfO2/SiO2 multilayers prepared by electron beam evaporation. The results show that when the annealing temperature is 200 ℃, the stress in the multilayers changes from compressive stress to tensile stress, and the stress increases with the increase of annealing temperature.
However, these studies do not involve the influence of annealing temperature on the spectral characteristics of sub nanometer bandwidth filters. In some space applications, due to the limitation of weight and structure, the temperature control protection is insufficient, and the temperature fluctuation sometimes reaches 100 ℃. Therefore, it is necessary to study the influence of temperature on the spectral characteristics of the filter.
