Multi-aperture digital coherent combining for free-space optical communication receivers

Area of Science:

• Optical communication systems
• Digital signal processing
• Space technology

Background:

• Space-to-ground optical communication systems require reduced size, weight, and power for space terminals.
• Large single-aperture ground terminals are effective but costly for increasing collection area.
• Existing systems face challenges in balancing performance and cost for ground receivers.

Purpose of the Study:

• To present a cost-effective ground terminal receiver architecture for space-to-ground optical communication.
• To demonstrate an efficient method for combining multiple small apertures into a large effective aperture.
• To maintain high receiver sensitivity while reducing the power-aperture product on space platforms.

Main Methods:

• Implementing coherent detection behind each small aperture.
• Digitizing the signals from each aperture.
• Combining digitized signals using a digital signal processing chain.

Main Results:

• Demonstrated lossless coherent combining of four laser communication signals.
• Achieved effective aperture creation using multiple small, less-expensive apertures.
• Maintained excellent receiver sensitivity at low power levels (below 0.1 photons/bit/aperture).

Conclusions:

• The proposed architecture offers a viable solution for cost-effective, high-sensitivity ground terminals in space-to-ground optical communication.
• Digital combining of optical signals from multiple small apertures is feasible and efficient.
• This technology can significantly reduce the power-aperture product requirements for space terminals.