Research on high surface figure accuracy beam splitters with large incident angle for space communication

With the rapid development of low Earth orbit satellites, satellite communication plays an increasingly prominent role in global coverage and high-speed data transmission, demanding ever-higher precision in data transfer. As a core component of space satellite communication optical systems, the spectral characteristics and surface figure accuracy of beam splitters directly affect the overall transmission performance of the system. Based on optical thin-film interference theory, this study selects suitable substrate and coating materials, and designs a dichroic beam splitter for 1550 nm high reflectance and 1565 nm high transmittance at a large incident angle of 45° using a bandpass structure as the base multilayer design. The film is deposited via ion-assisted electron-beam evaporation. Considering the actual configuration of the coating equipment, a dual-wavelength monitoring method is proposed to improve upon traditional single-wavelength direct light control, achieving monitoring errors of less than 1% for each layer. By applying the principle of double-sided stress balance, appropriate figure correction materials are selected, and a mathematical relationship between substrate height deviation and correction layer thickness is established to precisely calculate the thickness of the figure correction layer. Corrected the surface figure accuracy of the beam splitter. Test results show that it achieves a transmittance of 1.71% at the 1550 nm wavelength, 98.51% at the 1565 nm wavelength, and a surface figure accuracy RMS of 0.0148 λ, which is better than λ/60 at 632.8 nm, meeting the application requirements of space optical communication systems. This work provides an effective solution for designing and fabricating beam splitters with high surface figure accuracy under large incident angles, and holds significant implications for optimizing optical systems in space optical communications.