NIR to LWIR Dichroic Beamsplitter Designed and Manufactured for Space Optical Remote Sensor

The infrared dichroic beamsplitter plays an important role in infrared multi-band imaging systems, especially for infrared remote sensing. This paper presents the design and preparation of a dichroic beamsplitter that is capable of reflecting near infrared (NIR) and shortwave infrared (SWIR), and transmitting medium wave infrared (MWIR) as well as longwave infrared (LWIR). A single crystal germanium (Ge) sheet is used as the substrate of the dichroic beamsplitter, while Ge, zinc sulfide (ZnS) and ytterbium trifluoride (YbF3) are selected as coating materials. The average reflectance of the dichroic beamsplitter is more than 95% in bands 1.28 to 1.38 mu m, 1.58 to 1.83 mu m, and 1.95 to 2.32 mu m, and the average transmittance is more than 92% in bands 3.7 to 6.2 mu m and 7.5 to 12.5 mu m at an incident angle of 45 degrees. The dichroic beamsplitter has been successfully applied in the optical system of infrared remote sensing. It provides a technical approach for other optical systems to separate the optical spectrum from NIR to LWIR.