4-Port Filter Node for Single-Fiber Bidirectional Links

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Solution Overview

Problem

In single-fiber bidirectional communication networks, the cascaded arrangement of multiple filters leads to significant insertion loss, limiting the network's reach and capacity due to high isolation loss and cross-talk penalties.

Innovation Solution

Implementing a 4-port filter node that alternates the transmission and reception wavelengths between adjacent nodes, using a single 4-port filter for both add and drop functions in each direction, thereby reducing insertion loss and improving isolation by ensuring wavelengths are only reused after two filter passages.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple filters are cascaded to perform add/drop functions in bidirectional communication, then the add/drop functionality is achieved, but the insertion loss increases significantly

Engineering Contradiction:

Improveadd/drop functionalityVSAvoidinsertion loss

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent combines multiple filter functions (add/drop for both directions) into a single 4-port filter device. This merging eliminates the need for cascading multiple separate filters, thereby reducing the cumulative insertion loss while maintaining full add/drop functionality for bidirectional communication.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The 4-port filter is designed to perform multiple functions simultaneously: it handles add/drop operations for both eastbound and westbound directions within a single device. This multi-functionality replaces what would traditionally require multiple separate filter components, reducing overall system loss.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If multiple filters are cascaded to provide add/drop for both directions, then the communication capability is improved, but the isolation loss increases

Engineering Contradiction:

Improvebidirectional communication capabilityVSAvoidisolation loss

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent integrates isolation functions for both communication directions into a single 4-port filter. By combining the isolation mechanisms that would otherwise be distributed across multiple cascaded filters, the system achieves the required bidirectional isolation without the cumulative isolation loss that results from cascading.

Inventive Principle:

Principle #5Merging (Combining)

3Adaptability or versatility

If multiple filters are cascaded to enable wavelength selection, then the wavelength routing capability is improved, but the cross-talk penalties increase

Engineering Contradiction:

Improvewavelength routing capabilityVSAvoidcross-talk penalties

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The 4-port filter consolidates wavelength selection and routing functions for both directions into a single device. This merging ensures that wavelength-specific isolation and cross-talk suppression are applied uniformly without the cumulative cross-talk penalties that result from signal passage through multiple cascaded filters.

Inventive Principle:

Principle #5Merging (Combining)

4Productivity

If more filter components are used to achieve add/drop functions, then the network capacity is improved, but the component cost increases

Engineering Contradiction:

Improvenetwork capacityVSAvoidcomponent cost

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The 4-port filter is designed as a universal component that performs add/drop functions for both communication directions simultaneously. This single multi-functional component replaces what would traditionally require multiple separate filter devices, thereby reducing component count and cost while maintaining or enhancing network capacity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 significantly reduces insertion loss and improves isolation, allowing for increased network reach and capacity while maintaining low component costs, suitable for fronthaul networks like 4G or 5G mobile networks.

Implementation Method 1

a filter comprising at least four ports... configured to add a first wavelength to the first direction and the second direction, and configured to drop a second wavelength from the first direction and the second direction

Methodology Applied

Scientific EffectOptical filtering: Filter (optical)

Data Source

PatentEP3453127B1A method and network node for communication over a bidirectional communication link

Publication Date: 2020.10.28 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

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AI summary

A network node (400) for use with a single-fiber bidirectional communication link comprises a filter (300). The filter (300) comprises at least four ports. A first port (301) is configured to communicate with the single-fiber in a west direction. A second port (303) is configured to communicate with the single-fiber in an east direction. A third port (305) is configured to add/drop in the west direction. A fourth port (307) is configured to add/drop in the east direction. The network node is configured to add a first wavelength (λΑ) to the west direction and the east direction, and configured to drop a second wavelength (λΒ) from the west direction and the east direction.