Optical Receiver Phase Error Evaluation via Transfer Function Decomposition

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Solution Overview

Problem

Existing methods for evaluating phase error between optical 90-degree hybrids in optical receivers are inaccurate due to channel skew, particularly when using beat frequency evaluation methods, which fail to separate phase errors caused by hybrid misalignment and channel delays.

Innovation Solution

A method involving the decomposition of the optical receiver's transfer function into matrix products, specifically using shear, scaling, and rotation matrices to isolate and calculate phase errors between 90-degree hybrids, allowing for accurate evaluation even with channel skew.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the beat frequency evaluation method is used to measure phase error between optical 90-degree hybrids, then the measurement process is simple, but the measurement precision deteriorates due to channel skew

Engineering Contradiction:

Improvemeasurement process simplicityVSAvoidphase error measurement accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent segments the transfer function measurement into distinct components by applying different known signals (first known signal for I-channel, second known signal for Q-channel) to separately identify the transfer characteristics of each channel. This segmentation allows the phase error and skew to be independently calculated and distinguished, resolving the measurement precision issue while maintaining operational simplicity through systematic signal injection and separate analysis of channel responses.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces known signals as intermediary test inputs that mediate between the optical receiver's internal transfer function and the measurement system. By using these known signals with distinct characteristics (first and second known signals with different properties), the system can isolate and measure specific transfer function components, enabling accurate separation of phase error from skew without requiring direct observation of the mixed output.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If digital signal processing is used to compensate for phase error, then transmission characteristics improve, but device complexity increases

Engineering Contradiction:

Improvetransmission characteristicsVSAvoidsignal processing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies preliminary action by pre-calculating and storing the transfer function characteristics (phase error and skew values) through measurement using known signals before actual data transmission. These pre-determined parameters are then used to configure compensation filters or adjustment algorithms, allowing the system to maintain improved transmission characteristics without requiring complex real-time processing during normal operation, thus reducing operational device complexity.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS11736202B2Optical receiver evaluation method and optical receiver evaluation apparatus

Publication Date: 2023.08.22 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

There are provided an evaluation method and an evaluation device for an optical receiver capable of evaluating only a phase error between optical 90-degree hybrids with high accuracy even when there is a skew between channels in the optical receiver. In the evaluation method and the evaluation device for the optical receiver including optical 90-degree hybrids, a phase error between the optical 90-degree hybrids is calculated by calculation of decomposing a transfer function of the optical receiver into a product of matrixes to evaluate the optical receiver.