John D. Atkinson, Jay Reichman, Chroma Technology Corporation, Bellows Falls, VT
Optical coatings for satellite communication (SatCom) applications using free-space optics (FSO) have demanding requirements for durability and spectral performance. Optical systems for SatCom require high transmission of telecommunication (telecom) bands while providing rejection of unwanted radiation from a wide band extending from UV to IR that correspond to both solar output and thermal energy from the Earth. It is critical that thermal energy from these sources entering the optical system be kept to a minimum in order to reduce the noise in both the data transmit and receive signals, as well as keep the sensitive piezo-driven mirrors within the system from experiencing thermally induced variability. Many systems utilizing polarization-multiplexing also require that optical coatings cause minimal phase retardance upon reflection or transmission. We demonstrate optical coating performance for dichroics and bandpasses used to separate telecom bands while maintaining low phase retardance over particular wavelengths. We will show spectral and phase performance for “solar filters” consisting of sputtered silver- or gold-based induced-transmission type filters with over 90% transmission of the C-band and having high reflection of solar-Earth radiation over the full cone of angles. We will also show durability performance and discuss other applications for these coatings.