Optical Receiver Structure with Retroreflector Calibration
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Solution Overview
Problem
Optical data signals transmitted through the atmosphere experience severe losses due to phase interference and angular errors when coupled into single-mode fibers, particularly in satellite and aircraft communication systems, where the reception aperture is small compared to the phase disturbance, leading to inefficient fiber coupling and data throughput.
Innovation Solution
A structure for receiving optical data signals that includes input optics, an optical receiving fiber, a detector, a reception calibration source, and a retroreflector to adjust the distance between the receiving collimation optics and the fiber end facet for optimal focusing, along with a four-quadrant sensor and tiltable mirror for angular error compensation, ensuring effective coupling into the fiber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the reception aperture is made very small to reduce phase disturbance, then the phase disturbance becomes low-order (angular errors only), but the coupling efficiency into the fiber remains insufficient due to angular errors
Solution Approach 1:
A retroreflector is introduced as an intermediary element in the optical path. The retroreflector reflects the outgoing calibration light back through the same optical components (collimation optics and focusing optics), creating a return path that allows measurement of angular errors without requiring an external tracking sensor. This mediator enables the system to measure and correct angular deviations that cause coupling losses.
Solution Approach 2:
The system implements feedback by using a four-quadrant sensor to detect angular errors in the returned light from the retroreflector. The detected angular errors are fed back to the tiltable mirror, which adjusts the incoming light path to compensate for the angular deviations, thereby maximizing coupling efficiency into the fiber.
2Measurement precision
If an external tracking sensor is added to measure angular errors, then angular error measurement becomes possible, but the device complexity and alignment requirements increase significantly
Solution Approach 1:
The measurement function is merged with the existing optical components. The collimation optics and focusing optics that are already part of the system are used to create the return path for the retroreflector. The four-quadrant sensor, which is simpler than an external tracking sensor, detects angular errors in the returned light, combining measurement and correction functions within the existing optical train.
Solution Approach 2:
The retroreflector serves as a mediator that enables the use of a simpler four-quadrant sensor instead of a complex external tracking sensor. By reflecting the light back through the optical components, the retroreflector allows angular error measurement using the existing optical path, eliminating the need for separate external sensing and alignment systems.
3Ease of manufacture
If the distance between the receiving collimation optics and fiber end facet is not optimally adjusted, then the system is easier to assemble, but the coupling efficiency and power detection decrease
Solution Approach 1:
The system performs self-adjustment using the retroreflector and four-quadrant sensor. By measuring the angular errors in the returned light and feeding this information to the tiltable mirror, the system automatically optimizes the coupling efficiency without requiring manual adjustment of the distance between the collimation optics and fiber end facet. The system self-corrects for misalignments.
Solution Approach 2:
The retroreflector is positioned in the optical path before final assembly is completed. This allows the optical components to be pre-aligned using the return path measurement, establishing the correct distance and angular relationships between the collimation optics, focusing optics, and fiber end facet before the system is fully assembled and deployed.
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 solution allows for reliable and efficient coupling of optical data signals into the receiving fiber, maximizing power detection and compensating for angular errors, thereby enhancing data throughput and reducing signal losses in satellite and aircraft communication systems.
Implementation Method 1
a retroreflector that can be folded into the beam path, which is folded into the beam path to adjust the structure, so that the light from the reception calibration source is reflected back and focused on the end facet of the reception fiber by means of the reception collimation optics
Implementation Method 2
Light from the reception calibration source leaves the reception fiber at its end facet and is collimated by the reception collimation optics
Implementation Method 3
A detector is connected to the optical receiving fiber for detecting the optical data signal and converting it into an electrical signal
Data Source
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AI summary
The invention relates to a structure for receiving an optical data signal having input optics for receiving the optical data signal. An optical receiving fibre with an end facet is further provided, wherein the optical data signal can be injected into the optical receiving fibre by means of an optical collimation system. A detector for detecting the optical data content is connected to the optical receiving fibre. A receive calibration source is further provided, wherein the receive calibration source is connected to the optical receiving fibre, particularly in a fibre-based manner, by means of a circulator. A folding retroreflector is provided in the light path, which retroreflector can be folded for adjusting the structure into the light path so that the light from the receive calibration source is reflected back and is focussed by means of the optical collimation system onto the end facet of the receiving fibre. Furthermore, the distance in the z-direction between the optical collimation system and the end facet of the receiving fibre is variable, the distance being adjusted as a function of the power of the light from the receive calibration source detected by the detector.