Optical Arrangement Reducing Power Variances in Free-Space Receivers
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Solution Overview
Problem
Free-space optical systems face challenges in accurately coupling light into single-mode fibers due to environmental factors and the small core diameter of these fibers, leading to high bit error rates (BER) and power fluctuations.
Innovation Solution
An optical arrangement comprising a multi-mode fiber, a single-mode fiber, and a fiber mode scrambler is used to stabilize the mode distribution within the multi-mode fiber, allowing for predictable light coupling into the single-mode fiber without the need for active feedback systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct free-space coupling to single-mode fiber is used, then the system complexity is reduced, but the power fluctuations increase causing high bit error rates
Solution Approach 1:
A multi-mode fiber is introduced as an intermediary component between the free-space optical beam and the single-mode fiber. The multi-mode fiber with its larger core diameter (e.g., 50 μm) serves as a mediator that can more easily capture the incoming beam, and through mode scrambling, enables stable coupling into the single-mode fiber without requiring complex active feedback systems.
Solution Approach 2:
The invention changes the fiber parameter from single-mode to multi-mode for the coupling stage. By using a multi-mode fiber with larger core diameter and appropriate numerical aperture, the system can tolerate beam jitter and pointing errors much better than direct single-mode coupling, thereby reducing power fluctuations and bit error rates.
2Ease of operation
If multi-mode fiber is used for light coupling, then the ease of operation improves, but the transition losses to single-mode fiber increase
Solution Approach 1:
The multi-mode fiber acts as an intermediary that decouples the difficult task of precise beam alignment from the requirement of single-mode input. The mode scrambler within the multi-mode fiber creates a stable mode distribution that enables predictable coupling into the single-mode fiber, reducing transition losses despite the mode field mismatch.
Solution Approach 2:
The multi-mode fiber performs preliminary mode conditioning and scrambling before the light enters the single-mode fiber. This preliminary action of mode mixing and stabilization in the multi-mode fiber prepares the light in a way that minimizes subsequent coupling losses to the single-mode fiber.
3Stability of the object's composition
If active feedback systems like FSM or AO are used, then the power stability improves, but the device complexity and cost increase
Solution Approach 1:
The multi-mode fiber with mode scrambler provides self-service power stabilization without requiring external feedback control. The inherent mode mixing and scrambling properties of the multi-mode fiber automatically compensate for beam pointing errors and jitter, providing passive power stability that eliminates the need for complex active feedback systems.
Solution Approach 2:
The invention extracts and removes the complex active feedback systems (FSM, AO) from the optical coupling path. By using the multi-mode fiber's natural mode scrambling properties, the system achieves power stability without the bulky and expensive feedback hardware, thereby simplifying the overall system.
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 reduces power variances and bit error rates in optical receivers by ensuring stable light coupling, even in dynamic environments, while minimizing transition losses and avoiding deep fades in the received signal.
Implementation Method 1
Multi-mode fibers, on the other hand comprise a larger core diameter and are able to transmit multiple higher order modes of the light
Implementation Method 2
Single-mode fibers have a smaller core diameter than multi-mode fibers, thereby allowing them to transmit only a single mode of light
Implementation Method 3
The fiber mode scrambler is attached to the multi-mode fiber, such that a stabilized equilibrium mode distribution of the light received at the first input end is generated within the multi-mode fiber
Data Source
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Figure 4~6
AI summary
An optical arrangement (100) for coupling light with reduced power variances into an optical receiver (200) is provided. The optical arrangement (100) comprises a multi-mode fiber (110), a single-mode fiber (120), and a fiber mode scrambler (130). The multi-mode fiber comprises a first core (113) having a first core diameter (114), a first input end (111), and a first output end (112); The single-mode fiber (120) comprises a second core (123) having a second core diameter (124), a second input end (121), and a second output end (122). The first input end (111) is configured to receive a light beam (310) from a sender (300) external to the optical arrangement (100). The second output end (122) is configured to be coupled to an optical input (210) of the receiver (200). The first output end of the multi-mode fiber (110) is coupled to the second input end (121) of the single-mode fiber (120). The fiber mode scrambler (130) is attached to the multi-mode fiber (110), such that a stabilized equilibrium mode distribution of the light received at the first input end (111) is generated within the multi-mode fiber (110). Further, a system (500) comprising such an optical arrangement (100) and a vehicle (400) comprising such an optical arrangement (100) is provided.