Dual Laser Control for Bidirectional Point-to-Multipoint Networks

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Solution Overview

Problem

In bidirectional optical communication systems, reflections from connectors and Rayleigh backscatter cause coherent crosstalk, degrading performance by introducing distortions in transmitted optical signals. Existing solutions, such as using etalons for laser frequency control, struggle to achieve the necessary accuracy, especially in point-to-multi-point transmission systems where separate transmit and receive lasers are used.

Innovation Solution

The system employs separate transmit and receive lasers in a point-to-multi-point transmission system, where the uplink and downlink transmissions occur at different frequencies. A feedback signal from the hub node, carried through an auxiliary channel, is used to control the transmit laser of leaf nodes, ensuring accurate frequency tuning and preventing collisions or overlaps in the transmitted subcarriers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single laser is shared between transmitter and receiver, then device complexity is reduced, but frequency control accuracy deteriorates due to inability to independently tune transmitter frequency

Engineering Contradiction:

Improvelaser configurationVSAvoidfrequency control accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent segments the laser system into separate transmit and receive lasers, allowing independent frequency control. The transmit laser can be tuned to a frequency offset from the receive laser frequency, enabling full capacity bidirectional transmission without frequency collision while maintaining separate frequency references for each function.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements a feedback mechanism where the receive laser serves as a stable frequency reference, and the transmit laser frequency is adjusted based on feedback from frequency offset monitoring. This ensures the transmit laser maintains accurate frequency control relative to the receive laser, resolving the frequency accuracy issue while using separate lasers.

Inventive Principle:

Principle #23Feedback

2Reliability

If frequency diversity is implemented to avoid reflection degradation, then performance is improved, but transmission capacity is halved

Engineering Contradiction:

ImproveperformanceVSAvoidtransmission capacity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent changes the frequency parameter by introducing a frequency offset between transmit and receive lasers. This offset allows the transmit signal to operate at a different frequency than the receive local oscillator, enabling full capacity transmission in both directions without the need for frequency diversity halving, while still avoiding reflection-induced degradation.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If separate transmit and receive lasers are used, then transmission capacity is maximized, but frequency control accuracy deteriorates due to lack of frequency reference

Engineering Contradiction:

Improvetransmission capacityVSAvoidfrequency control accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent uses the receive laser as an intermediary frequency reference. The receive laser provides a stable, known frequency that serves as a reference for controlling the transmit laser frequency. This intermediary reference enables accurate frequency control of the transmit laser while maintaining separate laser operation for full capacity transmission.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Stability of the object's composition

If etalons are used for frequency control, then frequency stability is improved, but measurement precision is insufficient with accuracy limited to +/- 1.5 GHz

Engineering Contradiction:

Improvefrequency stabilityVSAvoidfrequency control accuracy

Core Design Contradiction:

Stability of the object's compositionVSMeasurement precision

Solution Approach 1:

The patent replaces the mechanical etalon-based frequency control system with an electronic feedback control system. Instead of relying on the physical etalon's frequency selectivity, the system uses electronic frequency offset monitoring and feedback adjustment of the transmit laser, achieving superior frequency control accuracy of +/- 100-200 MHz compared to etalon limitations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS20250038854A1Dual laser control for point-to-multipoint networks using bi-directional transmission

Publication Date: 2025.01.30 INFINERA CORP

AI summary

[Consistent with the present disclosure an apparatus and related method are provided for controlling the leaf-receiver local oscillator laser and leaf-transmitter laser for cases where separate transmit and receive local oscillator lasers are included in a transceiver. As a result, full capacity in bidirectional transmission can be realized on a single fiber. The leaf local oscillator frequency is controlled using a feedback signal generated based on an output from the leaf-digital signal processor (DSP), and the leaf transmit laser is controlled using a feedback signal based on an output of the remote hub-DSP, which is carried from the hub to the leaf nodes by a general communication channel (GCC) as part of a data signal, or a separate subcarrier also referred to as an auxiliary channel or out-of-band channel. This ensures that the frequencies transmitted subcarriers from the leaf nodes do not collide or overlap with one another in frequency.