Bidirectional Optical Module Stray Light Shielding for OTDR Accuracy

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Solution Overview

Problem

Bidirectional optical modules in OTDRs suffer from increased error in detecting returning light levels and reflecting point positions due to stray light, which complicates the identification of fractures or connections in optical fibers, especially when stray light enters areas with poorer frequency characteristics.

Innovation Solution

Incorporating a stray light shielding member with a pinhole opening between the light branching element and the light receiving element to block stray light while allowing the main light to pass through and be condensed onto the first light receiving area with superior frequency characteristics, thereby reducing measurement errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a light receiving element is used to receive returning light from the optical fiber, then light detection function is achieved, but stray light enters the light receiving element causing increased measurement error

Engineering Contradiction:

Improvedetection accuracy of returning light levelVSAvoidstray light interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

A stray light shielding member is introduced as an intermediary component between the light branching element and the light receiving element. This shielding member has a light transmitting portion that allows the main returning light to pass through while blocking stray light from reaching the light receiving element, thereby resolving the contradiction between achieving light detection function and preventing stray light interference

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The light receiving surface is divided into multiple regions with different functions. The first light receiving area receives the main returning light for measurement, while the second light receiving area is positioned to receive blocked stray light. This segmentation allows the system to distinguish between useful light signals and harmful stray light, improving measurement precision

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If the bidirectional optical module is designed to include light emitting elements, light condensing lenses, and light receiving elements, then optical communication function is achieved, but the module size becomes large

Engineering Contradiction:

Improvebidirectional optical communication functionVSAvoidmodule size

Core Design Contradiction:

Adaptability or versatilityVSVolume of moving object

Solution Approach 1:

Multiple optical components (light emitting elements, light condensing lenses, light branching element, stray light shielding member, and light receiving element) are merged into a single integrated bidirectional optical module structure. This consolidation achieves bidirectional optical communication function while reducing the overall module size compared to separate components

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The optical components are arranged in a nested configuration where the light emitting elements, lenses, and light receiving elements are positioned in close proximity within the module housing. The stray light shielding member is positioned between other components, creating a compact nested structure that reduces module volume while maintaining functionality

Inventive Principle:

Principle #7Nested doll (Nesting)

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 enhances measurement accuracy by minimizing stray light interference, allowing for more precise detection of light levels and reflecting points, and enables a more compact bidirectional optical module design.

Implementation Method 1

a light branching element that guides the light having exited the optical fiber to the light receiving element

Methodology Applied

Scientific EffectLight guidance: Reflection

Implementation Method 2

a stray light shielding member having an opening formed therein, through which light to enter the light receiving element passes, disposed between the light branching element and the light receiving element

Methodology Applied

Scientific EffectLight blocking: Absorption (EM radiation)

Implementation Method 3

a light condensing element that condenses the light having passed through the opening onto the first light receiving area

Methodology Applied

Scientific EffectLight condensation: Focusing

Data Source

PatentUS7889331B2Bidirectional optical module and optical time domain reflectometer equipped with the bidirectional optical module

Publication Date: 2011.02.15 YOKOGAWA ELECTRIC CORP

AI summary

A bidirectional optical module according to the present invention comprises light emitting elements 110, 130 that emit light to enter an optical fiber 71, a light receiving element 190 that receives light having exited the optical fiber 71 and a light branching element 160 that guides the light having exited the optical fiber 71 onto the light receiving element 190. It further includes a stray light shielding member 185 disposed between the light branching element 160 and the light receiving element 190 and having formed therein an opening 186, through which the light to enter the light receiving element 190 passes. The stray light shielding member 185 blocks stray light 100b while light 100a having exited the fiber 71 passes through the opening 186. Therefore, any increase in the extent of error in the detection of the returning light level or the position of a reflecting point is prevented.