Optical Loopback in WDM Systems Using Circulators

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Solution Overview

Problem

Optical loopback in wavelength division multiplexing (WDM) systems is challenging due to the difficulty in looping back optical signals when the transmit and receive spectra are different, as receiving filters typically block all transmit wavelengths, requiring costly and complex solutions like multiple optical transceivers or reversed wavelength assignment in test modules.

Innovation Solution

An optical communication device with a transmitter and receiver that includes a demultiplexer, optical coupler, switch, and controller, which routes and separates multiplexed signals between different optical spectra using arrayed waveguide gratings and optical switches to enable loopback without interference, allowing demultiplexing of signals into respective output ports.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a simple fiber patch cord and attenuator are used to loopback the transmit signal, then the loopback implementation is simple, but the receiving filter blocks all transmit wavelengths making it inapplicable to WDM systems with different transmit and receive spectra

Engineering Contradiction:

Improveloopback implementation simplicityVSAvoidapplicability to WDM systems with different spectra

Core Design Contradiction:

Ease of operationVSAdaptability or versatility

Solution Approach 1:

An optical circulator is introduced as an intermediary component to enable loopback in WDM systems. The circulator directs the transmit signal from port 1 to port 2, where it passes through the fiber patch cord and attenuator, then routes the returned signal from port 2 back to port 1, allowing the transmit spectrum to be looped back to the receive port without direct interference with the receive filter

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If optical transceivers with different wavelengths are used to convert signals, then loopback is achievable, but the system requires a large number of transceivers increasing cost and complexity

Engineering Contradiction:

Improveloopback capability in WDM systemsVSAvoidnumber of optical transceivers required

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent extracts the wavelength conversion function from multiple optical transceivers and replaces it with a single optical circulator that enables direct optical loopback. This eliminates the need for electrical conversion and removes the requirement for multiple transceivers with different wavelengths, significantly reducing device complexity and cost

Inventive Principle:

Principle #2Taking out (Extraction)

3Adaptability or versatility

If a WDM transceiver module with reversed wavelength assignment is installed, then loopback test can be performed, but the solution is expensive and adds uncertainty from the test module

Engineering Contradiction:

Improveloopback test capabilityVSAvoidcost and uncertainty of test module

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent replaces the expensive and uncertain reversed wavelength assignment test module with inexpensive, passive components: an optical circulator, a fiber patch cord, and an attenuator. These components are readily available, have well-defined characteristics, and eliminate the need for specialized test equipment, thereby reducing both cost and uncertainty

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 efficient optical loopback in WDM systems by separating and routing multiplexed signals between different spectra, reducing the need for multiple transceivers and costly test modules, and preventing signal interference, thus enhancing connectivity and reducing costs.

Implementation Method 1

The demultiplexer includes an arrayed waveguide grating that separates the multiplexed signals into demultiplexed signals and outputs the demultiplexed signals to a corresponding array of receivers

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

The optical coupler couples the transmit signal to the loopback port

Methodology Applied

Scientific EffectOptical coupling:

Data Source

PatentUS9178610B1Optical loopback in a wavelength division multiplexing system

Publication Date: 2015.11.03 GOOGLE LLC

AI summary

An optical communication device includes a transmitter having a transmitter port and a receiver having loopback and receiver ports. The transmitter transmits a first multiplexed signal in a first optical spectrum from the transmitter port. The receiver receives the first multiplexed signal in the loopback port and a second multiplexed signal in the receiver port. The second multiplexed signal is in a second optical spectrum different from the first optical spectrum. The receiver includes a demultiplexer in optical communication with the loopback port and the receiver port. The demultiplexer demultiplexes the first and second multiplexed signals received by the loopback and receiver ports.