Polarization-Splitting FSO Terminal for Low-SWaP Beam Sharing
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Solution Overview
Problem
Existing free space optical (FSO) communications terminals face challenges in reducing size, weight, and power (SWaP) requirements while maintaining high data rates and security, particularly in applications like aircraft-to-ground communications.
Innovation Solution
The FSO terminal integrates a quarter-wave plate, Faraday rotator, and polarisation splitter to split received circularly polarised light into two arms, allowing shared optical elements for transmitter and receiver, and uses a beam position tracking detector to optimize light distribution, with a controllable Faraday rotator adjusting the light ratio between arms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate arms are used for transmitter and receiver, then functional independence is improved, but size, weight, and power requirements increase
Solution Approach 1:
The patent combines the transmitter and receiver into a single integrated arm, sharing common optical elements including the aperture, collimation optics, relay optics, and beam steering system. This merging reduces the overall terminal weight while maintaining functional independence through optical isolation techniques using Faraday rotators and polarisation beam splitters that separate transmit and receive optical paths within the same physical structure.
Solution Approach 2:
The integrated arm design makes single optical components serve multiple functions: the aperture serves as both transmit and receive aperture, the collimation optics serve both transmission and reception, and the relay optics are shared between transmit and receive paths. This multi-functionality reduces the total component count and terminal weight while maintaining dedicated functional paths.
2Reliability
If separate arms are used for transmitter and receiver, then signal isolation is improved, but device complexity increases
Solution Approach 1:
The patent introduces Faraday rotators and polarisation beam splitters as intermediary components that mediate between the common optical path and the separate transmit/receive functions. These intermediaries provide optical isolation and signal separation through non-reciprocal Faraday rotation effects, enabling clean separation of transmit and receive paths while sharing common optical elements, thus reducing overall system complexity.
3Weight of moving object
If common optical elements are shared, then SWaP requirements are reduced, but beam tracking precision may worsen
Solution Approach 1:
The patent segments the optical path into distinct transmit and receive channels that share common elements (aperture, collimation, relay optics) but have separate beam steering and detection subsystems. This segmentation allows independent optimization of beam tracking for each function while sharing the heavy optical infrastructure, maintaining tracking precision without sacrificing weight reduction benefits.
Solution Approach 2:
The patent implements dynamic beam steering control using fast-steering mirrors and adjustable optics in both transmit and receive paths, allowing real-time compensation for atmospheric turbulence and platform motion. This dynamic control maintains beam tracking precision despite sharing common optical elements, as each path can be independently adjusted to compensate for disturbances.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces SWaP requirements, enhances flexibility and robustness, and improves data communication rates by optimizing light usage and beam tracking, enabling cost-effective network scalability with identical nodes.
Implementation Method 1
the quarter-wave plate converts the received circularly polarised beam to a received linearly polarised beam
Implementation Method 2
the Faraday rotator rotates the polarisation of the received linearly polarised beam to produce a rotated received linearly polarised beam
Data Source
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AI summary
A free space optical communications terminal (100) is disclosed. The free space optical communications terminal (100) comprises an optical arrangement of a quarter-wave plate (105), a Faraday rotator (110), a polarisation splitter (115), a first arm (120) comprising a receiver (126) and a transmitter (128), and a second arm (130) comprising a component (132) configured to utilise a received beam. The optical arrangement allows a received circularly polarised beam to be apportioned between the first and second arm, and a beam produced by the transmitter to be transmitted as a circularly polarised beam.