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Optical Wireless Communication (OWC) systems rapidly increase their importance in very long-distance deep space communication scenarios. However, the high performance requirements of deep space OWC systems demand preliminary experiments which are unmanageable in real conditions. Regarding this issue, an innovative approach for testing deep space optical communication links in controlled laboratory environment is developed. The proposed testbed is based on fibre optics technology and combines various modules which represent a real deep space OWC link. Similar to already demonstrated deep space missions, the implemented optical receiver is Superconducting Nanowire Single- Photon Detector (SNSPD) characterized with single photon sensitivity and high detection efficiency. Consequently, in this paper an authentic deep space Poisson channel is emulated and examined. The given theoretical description of the Poisson process is supported by real SNSPD measurements in terms of high efficient single photon detection. The provided measured graphs clearly show the operation of SNSPD. In addition, a variable optical attenuator (VOA) is applied as a main device emulating the tropospheric part of a deep space optical Poisson channel characterized predominantly by Mie scattering (fog and clouds) and turbulence effects. This OWC channel emulator also contains self-developed software and attenuator control unit based on external Digital Analog Converter (DAC). Moreover, the response time parameter of channel emulator is examined in detail. Two different times in terms of reaching the lowest and the highest allowed attenuation are measured and shown. Finally, the developed channel emulator is tested and evaluated under real attenuation data. The experimental results show that the proposed method can evaluate various deep space optical scenarios.
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