Multimode Fiber Waveguide With Adiabatic Mode Concentration

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing multimode optical fibers face challenges in spatially concentrating guided modes at the output face while minimizing optical losses, particularly when transmitting signals to detectors with smaller detection areas, as adiabatic tapering leads to significant optical losses.

Innovation Solution

A multimode waveguide comprising a multimode optical fiber coupled with a frustoconical concentrating structure made of high refractive index material, ensuring adiabatic variation in transverse dimension to maintain mode continuity and minimize losses, with the structure's dimensions and materials chosen to support at least the same number of modes at the output as the input.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If adiabatic tapering is applied to multimode optical fiber, then spatial concentration of guided modes is achieved, but optical losses increase significantly

Engineering Contradiction:

Improveoutput face areaVSAvoidoptical losses

Core Design Contradiction:

Area of stationary objectVSLoss of energy

Solution Approach 1:

The waveguide is divided into two distinct segments: a multimode optical fiber segment for efficient light collection and a concentration structure segment for spatial concentration. This segmentation allows each segment to be optimized for its specific function, avoiding the high losses associated with adiabatic tapering of multimode fibers while still achieving the desired spatial concentration at the output face.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The concentration structure acts as an intermediary element between the multimode optical fiber and the photodetector. It receives light from the fiber, performs spatial concentration through its frustoconical geometry, and delivers concentrated light to the photodetector, thereby enabling mode concentration without the losses of direct fiber tapering.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the output face size is reduced to match photodetector dimensions, then coupling efficiency improves, but spatial concentration losses increase

Engineering Contradiction:

Improvecoupling efficiencyVSAvoidspatial concentration losses

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The concentration structure utilizes changes in refractive index parameters and geometric parameters (frustoconical shape) to achieve spatial concentration. By carefully designing the refractive index profile and the gradual reduction in transverse dimensions, the structure concentrates light modes onto the smaller photodetector face while minimizing radiation losses through controlled parameter transitions.

Inventive Principle:

Principle #35Parameter changes

3Area of stationary object

If a concentration structure with high refractive index is used, then spatial concentration is improved, but manufacturing complexity increases

Engineering Contradiction:

Improveconcentration capabilityVSAvoidmanufacturing complexity

Core Design Contradiction:

Area of stationary objectVSEase of manufacture

Solution Approach 1:

The waveguide employs a composite structure combining the multimode optical fiber material (typically silica) with a concentration structure made of high refractive index material. This composite approach enables the concentration structure to provide enhanced spatial concentration capability through its superior refractive index, while the modular design allows for separate fabrication and assembly, managing manufacturing complexity.

Inventive Principle:

Principle #40Composite materials

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 effectively concentrates guided modes at a smaller output face with minimal optical losses, enabling efficient transmission to photodetectors with reduced detection areas, maintaining high mode support and reducing reflection and radiation losses.

Implementation Method 1

The concentration structure is made of at least one material with a high refractive index n_pc greater than n_fc, having a local transverse dimension d_pc, and surrounded of a medium with a refractive index n_pg less than n_pc

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

The concentration structure presents an adiabatic variation of its local transverse dimension d_pc going from a value d_pc,in at the entrance face to a value d_pc,out at the exit face

Methodology Applied

Scientific EffectAdiabatic variation:

Data Source

PatentEP3968066B1Waveguide comprising a multimode optical fibre and adapted to spatially concentrate the guided modes

Publication Date: 2026.05.06 COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES

Figure 1A~1C
Figure 1D~2
Figure 3A~3C

AI summary

The invention relates to a waveguide 1 comprising a multimode optical fiber 10 assembled to a spatial mode-concentrating structure 20. The concentrating structure 20 exhibits an adiabatic variation of its transverse dimension dpc towards its output face 20b, and a value dpc,in of its transverse dimension dpc being at least equal to a value dfc of the transverse dimension dfc of the core 11 of the multimode optical fiber 10 at the level of the second face 10b thereof.