Multi-mode Optical Transmitter Mode Mixture
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Solution Overview
Problem
Multi-mode optical fibers experience significant optical degradation, including attenuation, cross-talk, and nonlinear distortion, due to mode-dependency during data transmission, which can render data-modulated optical carriers too degraded for demodulation at the receiver, especially when transmitted through a single propagating mode rather than a set of orthonormal modes with differing intensity and phase profiles.
Innovation Solution
An optical transmitter is configured to spread the optical power of each data-modulated carrier substantially uniformly over a set of orthonormal optical propagating modes with nontrivially differing intensity and/or phase profiles, using an optical end-face coupler that directs data-modulated optical carriers into a pattern of light beams to illuminate the end-face of a multi-mode optical fiber, thereby exciting multiple modes with varying energies and reducing mode-dependent losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If data-modulated optical carriers are transmitted through a single propagating mode, then the device complexity is reduced, but optical degradation including attenuation, cross-talk, and nonlinear distortion increases significantly
Solution Approach 1:
The patent divides the optical transmission into multiple orthogonal propagating modes (LP01, LP11, LP21, etc.), where each mode carries a portion of the optical power. This segmentation of the transmission path reduces the degradation experienced by any single mode, thereby improving overall reliability without requiring complex adaptive systems.
Solution Approach 2:
The patent changes the transmission parameter from single-mode to multi-mode operation by carefully controlling the launch conditions and fiber parameters. By adjusting the numerical aperture, core diameter, and launch angle, the system excites multiple modes with different propagation characteristics, reducing mode-dependent losses and improving reliability.
2Use of energy by moving object
If optical power is concentrated in a single propagating mode, then the power transmission efficiency is high, but mode-dependent losses cause significant optical degradation
Solution Approach 1:
The patent assigns different power distribution characteristics to different modes based on their propagation properties. By optimizing the power split among modes according to their individual loss characteristics, the system achieves both efficient power transmission and reduced mode-dependent losses.
Solution Approach 2:
The patent combines multiple propagating modes to carry optical power, where the total power is distributed across LP01, LP11, LP21, and other modes. This merging of multiple transmission paths diversifies the loss mechanisms, reducing the impact of any single mode's degradation while maintaining overall power transmission efficiency.
3Reliability
If multiple orthonormal optical propagating modes are excited, then optical degradation is averaged beneficially, but the device complexity increases
Solution Approach 1:
The patent employs dynamic control of the optical launch conditions to optimize mode excitation. By adjusting parameters such as launch angle, position, and numerical aperture in real-time based on transmission conditions, the system maintains reliable transmission without requiring complex static configurations.
Solution Approach 2:
The multi-mode fiber system naturally provides mode mixing and mode-dependent loss compensation through its inherent physical properties. The different modes experience different propagation characteristics that automatically balance the overall transmission, reducing the need for external active compensation systems.
4Loss of energy
If data is transmitted through multiple propagating modes, then mode-dependent losses are reduced, but cross-talk and nonlinear distortion increase
Solution Approach 1:
The patent applies preliminary mode conditioning at the transmitter end, where the optical launch conditions are carefully controlled to excite modes in a specific sequence and with specific power ratios. This preliminary action prevents excessive mode coupling and reduces cross-talk before transmission begins.
Solution Approach 2:
The patent uses a limited set of lower-order modes (primarily LP01, LP11, LP21) rather than exciting all possible modes. This partial action approach reduces the complexity of mode management and minimizes nonlinear interactions while still achieving sufficient diversity to reduce mode-dependent losses.
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 reduces the dependency on individual optical propagating modes, leading to beneficial averaging of optical degradation, lower insertion losses, and facilitates equalization and MIMO processing at the optical receiver, enabling more reliable data transmission and recovery of digital data streams.
Implementation Method 1
optical propagation mode-multiplexing has been studied as a method for providing optical communication. In optical propagation mode-multiplexing, a set of orthonormal optical propagating modes of a multi-mode optical fiber carries data between an optical transmitter and an optical receiver
Implementation Method 2
Some of the multi-mode fiber spans of the sequence may be hybrid optical fiber spans constructed to provide differential group delay compensation
Data Source
Figure 1
Figure 2
Figure 3A~3
AI summary
An apparatus includes an optical transmitter having a plurality of optical data modulators and an end-face coupler. Each of the optical data modulators is configured to output a corresponding data-modulated optical carrier. The optical end-face coupler is configured to direct the data-modulated optical carriers into a pattern of light beams to illuminate an end-face of a multi-mode optical fiber with a pattern of light spots. The optical end-face coupler is configured to cause each of the data- modulated optical carriers to excite a set of orthonormal optical propagating modes of the multi-mode optical fiber. Some of the orthonormal optical propagating modes of the set have nontrivially differing intensity and/or phase profiles.