Doped Optical Fiber Absorption Measurement via Side Emission

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Solution Overview

Problem

Conventional methods for measuring the absorption coefficient of doped optical fibers are destructive, prone to errors due to cladding modes, and require precise alignment and efficient coupling, making them inefficient and unsuitable for certain fiber types like ZBLAN and large-mode-area fibers.

Innovation Solution

A non-destructive method using side-light analysis with a system comprising a laser source, single-mode optical fiber, and multimode fibers to collect spontaneous emissions, allowing for the calculation of absorption coefficients without the need for precise alignment or efficient coupling, and unaffected by cladding modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the conventional cutback method is used to measure absorption coefficient, then the measurement can be performed, but the doped optical fiber is destroyed and precise alignment is required

Engineering Contradiction:

Improveabsorption coefficient measurementVSAvoidalignment requirement

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

Instead of measuring pump power transmitted through the fiber end-on (conventional method), the invention measures spontaneous emission light from the side of the fiber. This inversion of the measurement approach eliminates the need for precise alignment and coupling, as the multimode fibers collect light from the fiber side surface without requiring end-face alignment.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention introduces multimode fibers as intermediaries to collect spontaneous emission light from the doped optical fiber side. These multimode fibers act as light guides that collect and transport the emitted light to detectors, eliminating the need for direct alignment between the measurement system and the doped fiber end face.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If the conventional cutback method is used, then absorption coefficient can be measured, but the method is destructive and time-consuming

Engineering Contradiction:

Improveabsorption coefficient measurementVSAvoidmeasurement efficiency

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The invention performs measurements on the complete doped optical fiber without cutting it into segments. By using side-light collection of spontaneous emission, the entire fiber can be measured in one go, eliminating the need for preliminary cutting and multiple alignment steps required in the conventional cutback method.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The doped optical fiber itself serves as the light source through spontaneous emission when pumped. This self-emitting property eliminates the need for external light sources and complex coupling arrangements, allowing direct side-collection of emission light for absorption measurement.

Inventive Principle:

Principle #25Self-service

3Object-affected harmful factors

If index matching gel is applied to reduce cladding modes, then some cladding modes are reduced, but cladding modes close to the doped core remain unaffected

Engineering Contradiction:

Improvecladding modesVSAvoidabsorption coefficient measurement

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The invention extracts only the spontaneous emission light from the doped core region by using multimode fibers positioned to collect light specifically from the side of the doped section. This selective collection eliminates contamination from cladding modes that propagate through the undoped cladding regions, as only light originating from the doped core is collected.

Inventive Principle:

Principle #2Taking out (Extraction)

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

Enables accurate and cost-effective measurement of absorption coefficients without damaging the fibers, reducing errors associated with cladding modes and alignment issues, and is applicable to a wide range of fiber types, including mechanically fragile ones.

Implementation Method 1

a laser source configured to transmit laser light at a selectable wavelength... coupled to an end of a single-mode optical fiber that is spliced to the doped optical fiber

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Implementation Method 2

two or more multimode fibers at a side of the doped optical fiber, spaced apart along the side of the doped optical fiber, configured to collect spontaneous emissions from the side of the doped optical fiber

Methodology Applied

Scientific EffectSpontaneous emission: Luminescence

Data Source

PatentUS10739229B2Systems and methods for measuring absorption coefficients of doped optical fibers

Publication Date: 2020.08.11 STC UNM

AI summary

A system for measuring an absorption coefficient of a doped optical fiber may include: a laser source configured to transmit laser light at a selectable wavelength; a single-mode optical fiber including an end configured to splice to the doped optical fiber; two or more multimode fibers at a side of the doped optical fiber, spaced apart along the side of the doped optical fiber, configured to collect spontaneous emissions from the side of the doped optical fiber; and/or a photodiode or power meter connected to the two or more multimode fibers. A method for measuring an absorption coefficient of a doped optical fiber may include: collecting, from a side of the doped optical fiber, an emission spectrum using two or more multimode fibers; and/or calculating the absorption coefficient form using the emission spectrum and McCumber theory.