Mode Converter for Optical Spatial Multiplexing
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Solution Overview
Problem
Existing optical transmission systems face challenges in efficiently coupling light between single mode fibers and multi mode fibers with low modal crosstalk, particularly in optical spatial multiplexing systems that do not use MIMO processing.
Innovation Solution
An optical coupling device that uses a two-step approach with diffractive optical elements to split and phase-shift light beams, mimicking the spatial arrangement and phases of target modes in multi mode fibers, significantly increasing coupling efficiency while reducing modal crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional coupling methods are used to couple light from single mode fiber to multi mode fiber, then coupling can be achieved, but coupling efficiency is low and modal crosstalk is high
Solution Approach 1:
The patent divides the single mode light beam into multiple split beams using a diffractive optical element. Each split beam corresponds to a specific energy spot in the target mode pattern. This segmentation allows precise control of light distribution across multiple spatial locations, achieving high coupling efficiency while maintaining low modal crosstalk through the one-to-one correspondence between split beams and energy spots
Solution Approach 2:
The patent applies different phase shifts to different split beams according to the local phase requirements of the target mode. Each split beam receives a specific phase adjustment tailored to its position and the target mode's phase distribution at the corresponding energy spot. This local quality approach ensures that each beam contributes optimally to the target mode while minimizing coupling to unwanted modes
2Manufacturing precision
If a simple coupling device is used, then device complexity is low, but coupling precision and mode control are insufficient
Solution Approach 1:
The patent introduces a diffractive optical element as an intermediary component between the single mode fiber and multi mode fiber. This element performs both beam splitting and phase modulation functions, achieving precise mode control without requiring complex multi-component systems. The intermediary element simplifies the overall device structure while maintaining high coupling precision
Solution Approach 2:
The patent utilizes the diffractive optical element's ability to change spatial and phase parameters of light beams. By designing the DOE with specific diffraction patterns, the system transforms a single input beam into multiple beams with controlled spatial distribution and phase relationships, achieving precise mode coupling through parameter transformation rather than mechanical adjustment
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
The solution achieves nearly 100% conversion efficiency with minimal crosstalk, improving performance over existing methods like the 4f-correlator, especially for higher azimuthal order modes.
Implementation Method 1
a first diffractive optical element (DOE) is configured to split the light beam into a plurality of split beams
Implementation Method 2
a second DOE is configured to modify one or more phases of the plurality of split beams to yield a plurality of phase shifted beams
Data Source
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AI summary
The present document relates to a method and system for coupling light into and out from multi mode fibers performing spatial multiplex. An optical coupling device (200) is described, which is configured to couple a light beam (212) from a single mode light source (101) into a target mode of a multi mode waveguide (105). The target mode exhibits a mode pattern comprising a plurality of energy spots in a pre-determined arrangement and with predetermined phases. The optical coupling device (200) comprises a first diffractive optical element (202) configured to split the light beam (212) into a plurality of split beams (213), such that an arrangement of the plurality of split beams (213) corresponds to the pre-determined arrangement of the plurality of energy spots of the mode pattern. Furthermore, the optical coupling device (200) comprises a second diffractive optical element (203) configured to modify one or more phases of the plurality of split beams (213) to yield a plurality of phase shifted beams, wherein phases of the plurality of phase shifted beams correspond to the predetermined phases of the plurality of energy spots of the mode pattern, respectively, and wherein light derived from the plurality of phase shifted beams is coupled into the target mode of the multi mode waveguide.