Dense wavelength division (de-)multiplexer for space application

Dense wavelength division multiplexing techniques are widely used in terrestrial state-of-the-art telecom applications. The optical link between the terminals requires a data rate in the terabyte range which is typically realized by transmitting multiple wavelengths though one common channel. For satellite communications, completely new requirements and demands arise where the common technologies cannot be used without further ado. In space, it is also completely impractical to set up repeaters at short distances, so the WDM must have a capacity of tens of Watts power capability to cover the very long propagation length. The development and realization of a space-suitable Dense Wavelength Division Multiplexer and Demultiplexer are described. Both units combine (or split, respectively) ten channels into / from one common channel. The design central wavelength is around 1070 nm and the channels are chosen with a separation of 92-GHz corresponding to approximately 0.35 nm. The multiplexer has a target power handling of at least five Watts per channel. The input channels are equipped with PM fibers, whereas the multiplexed output is free space propagating, avoiding nonlinear effects and thermally induced fiber damage. The Demultiplexer is fiber coupled at input and output ports due to the reduced power requirements of sub Milliwatts. In both cases a diffraction grating is used as wavelength selective element. Its nonlinear angular dispersion is compensated with a non-equidistant fiber arrangement. The WDMs are characterized regarding optical parameters. The components are designed for space suitability, using appropriate materials and thermal design.