Optical Fiber Cladding Shape for Pumping Light Absorption

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Solution Overview

Problem

Existing amplifying optical fibers suffer from inefficient absorption of pumping light due to skew mode propagation, which reduces optical amplification efficiency.

Innovation Solution

The amplifying optical fiber is designed with a cladding shape where the ratio of the inscribed circle diameter to the circumscribed circle diameter is between 0.92 and 0.97, and the cladding has substantially rounded vertices, reducing thickness deviation and suppressing skew mode propagation, thereby enhancing pumping light absorption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-generated harmful factors

If the cladding has a polygonal outer shape to suppress skew mode, then skew mode is suppressed, but thickness deviation in the outer cladding increases causing pumping light loss

Engineering Contradiction:

Improveskew modeVSAvoidpumping light loss

Core Design Contradiction:

Object-generated harmful factorsVSLoss of energy

Solution Approach 1:

The invention uses a polygonal outer shape for the cladding (asymmetric shape) to suppress skew mode propagation, while carefully controlling the asymmetry through the r/R ratio to avoid excessive thickness deviation that would cause pumping light loss.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The invention optimizes the geometric parameters of the polygonal cladding by specifying the r/R ratio between 0.92 and 0.97, which balances the suppression of skew mode with the minimization of thickness deviation-induced pumping light loss.

Inventive Principle:

Principle #35Parameter changes

2Object-generated harmful factors

If the cladding has a polygonal outer shape with small r/R ratio to suppress skew mode, then skew mode is suppressed, but the cladding's ability to confine pumping light diminishes

Engineering Contradiction:

Improveskew modeVSAvoidpumping light confinement ability

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

Inventive Principle:

Principle #35Parameter changes

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 configuration leads to improved absorption of pumping light by the active element in the core, reducing light loss and skew mode propagation, resulting in more efficient optical amplification.

Implementation Method 1

it is known that a portion of pumping light propagates through the claddings without being absorbed by the active elements, which causes a skew mode that does not contribute to optical amplification

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

a portion of pumping light propagates through the claddings without being absorbed by the active elements

Methodology Applied

Scientific EffectOptical absorption: Absorption (EM radiation)

Data Source

PatentEP2503654B1Amplifying optical fiber and optical fiber amplifier using same

Publication Date: 2021.02.17 FUJIKURA LTD

Figure 1~2(B)
Figure 3~4

AI summary

To be provided is an amplifying optical fiber allowing for efficient absorption of pumping light by an active element therein, and an optical fiber amplifier using the amplifying optical fiber. An amplifying optical fiber (20) includes a core (21) doped with an active element, a cladding (22) covering the core (21), and an outer cladding (23) covering the cladding (22). The cladding (22) meets a relationship of 0.92 ≤ r/R ≤ 0.97 where the cladding (22) has a polygonal outer shape in cross section, and the outer shape has an inscribed circle of a diameter r and a circumscribed circle of a diameter R.