Free Space Optical Terminal Dither Alignment Feedback
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Solution Overview
Problem
Free space optical (FSO) communications systems face alignment errors due to mechanical movement and atmospheric turbulence, requiring accurate and rapid adjustment of beam pointing to maintain communication links, especially in unpredictable conditions.
Innovation Solution
A bidirectional FSO system uses a beam-steering unit to dither the transmit beam's angle, with the receive terminal measuring received power and encoding it into a return beam for feedback to adjust the transmit beam direction, employing periodic basis functions to optimize pointing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical mounting structures are used to support FSO terminals, then the terminals can be installed and operated, but mechanical movement and flexing of the mounting structure cause alignment errors between terminals
Solution Approach 1:
The patent implements a feedback mechanism where the receiving terminal measures the received power of the incoming beam and encodes this information back to the transmitting terminal. The transmitting terminal uses this feedback to adjust its beam direction, continuously compensating for alignment errors caused by mechanical movement and flexing of the mounting structure.
Solution Approach 2:
The patent replaces mechanical alignment adjustment mechanisms with an optical feedback and control system. Instead of mechanically adjusting the terminal position to maintain alignment, the system uses dithering and feedback-based beam steering to optically compensate for mechanical instabilities.
2Adaptability or versatility
If FSO terminals are mounted on moving vehicles or towers subject to environmental forces, then operational flexibility is achieved, but rapid changes in conditions require frequent and accurate pointing adjustments
Solution Approach 1:
The patent employs dithering, which is a periodic oscillation of the beam direction about the estimated transmit direction. This periodic action allows the system to probe the alignment conditions and extract feedback information about the optimal beam pointing angle, enabling continuous adaptation to changing environmental conditions.
Solution Approach 2:
The patent implements a dynamic beam steering system that can rapidly adjust the beam direction in response to changing conditions. The beam-steering unit responds to feedback from the receiving terminal by continuously modifying the transmit beam angle, allowing the system to adapt to rapid environmental changes such as vehicle movement or tower sway.
3Measurement precision
If the transmit beam direction is adjusted to compensate for alignment errors, then pointing accuracy improves, but the system requires continuous feedback and control mechanisms
Solution Approach 1:
The patent makes the optical beam serve multiple functions: it carries data information and simultaneously provides alignment feedback through its received power characteristics. The same optical path and detectors used for data reception are also used to measure alignment conditions, eliminating the need for separate alignment sensing systems.
Solution Approach 2:
The system uses its own transmitted beam as the reference for measuring alignment. By analyzing the received power of its own beam at the remote terminal, the system self-diagnoses alignment errors and self-corrects by adjusting its beam direction, without requiring external alignment equipment or complex control mechanisms.
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 approach effectively reduces alignment errors by using dithering to improve pointing accuracy, maintaining communication links under varying conditions by continuously adjusting the beam direction based on real-time power measurements.
Implementation Method 1
the BSU may dither the Tx beam angle about its currently-estimated Tx direction
Implementation Method 2
The Rx terminal of each link measures the received power of the incoming dithered FSO beam
Implementation Method 3
Free space optical (FSO) communications is a communications technology that uses light propagating in free space to wirelessly transmit data
Data Source
AI summary
Embodiments relate to a bidirectional free space optical (FSO) communications system. Specifically, data-encoded FSO beams are transmitted and received between two terminals. A transmit (Tx) direction of a beam transmitted from the first terminal is dithered by a beam steering unit (BSU). As the dithered beam is received by the second terminal, the power levels of the beam are measured. The power levels are then encoded in a data-encoded FSO beam transmitted to the first terminal. This allows the first terminal to decode the received FSO beam and determine the power levels. The power levels allow the first terminal to determine Tx direction misalignments and adjust the Tx direction for the Tx beam sent to the second terminal. This process may be repeated to reduce Tx misalignments and may be performed by both terminals such that each terminal sends power level information to the opposite terminal.