Optical Transceiver Transfer Function Estimation and Compensation
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Solution Overview
Problem
Existing optical transceivers face challenges in achieving sufficient transmission characteristics at high speeds due to individual variations in optical circuit and analog electric circuit transfer functions, making it difficult to set effective compensation values based on vendor specifications or representative measurements.
Innovation Solution
An optical transmission characteristic estimation and compensation system that includes a transmission unit with a known signal insertion unit, transmitter and receiver compensation units, and transfer function estimation units, which use adaptive filters and Fourier transforms to estimate and compensate the transfer functions of each lane, thereby addressing the variations and improving transmission characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compensation values are set based on vendor specifications or representative measurements, then the optical transceiver can achieve sufficient transmission characteristics at lower speeds, but individual variations in optical circuit and analog electric circuit transfer functions cause insufficient transmission characteristics at high speeds like 400 Gb/s
Solution Approach 1:
The system performs preliminary measurement of the actual transfer function of each lane in the optical transceiver before high-speed transmission. By measuring the transfer function H(f) of each lane (XI, XQ, YI, YQ) using known test signals and FFT analysis, the system establishes baseline characteristics that are used to calculate compensation values in advance, ensuring that individual variations are accounted for before actual operation begins.
Solution Approach 2:
The system changes the compensation parameters (transfer function values) based on actual measurements rather than using fixed vendor specifications. By measuring the actual transfer function H(f) of each lane and calculating compensation values CF(f) = 1/H(f), the system adapts the parameters to match the specific characteristics of each individual transceiver, thereby resolving the issue of individual variations affecting high-speed transmission performance.
2Productivity
If the Baud rate is increased and multi-valuing modulation systems are used to increase transmission capacity, then the transmission capacity increases, but the transmission characteristics deteriorate due to insufficient frequency characteristics and differences among lanes
Solution Approach 1:
Before increasing the Baud rate to 64 Gbaud or higher for high-capacity transmission, the system performs preliminary measurement and compensation of the transfer function for each lane. This preliminary action ensures that the frequency characteristics are sufficient and lane differences are suppressed before high-speed operation begins, preventing transmission characteristic deterioration even at increased Baud rates.
Solution Approach 2:
The system applies lane-specific compensation to each individual lane (XI, XQ, YI, YQ) rather than using a uniform compensation approach. By measuring and compensating the transfer function H(f) separately for each lane and applying lane-specific compensation values, the system addresses local differences among lanes that would otherwise cause transmission characteristic deterioration at high Baud rates.
3Adaptability or versatility
If the optical transceiver is designed to support wide range frequency characteristics, then it can accommodate different Baud rates, but the difference among lanes becomes more significant requiring more complex compensation
Solution Approach 1:
The system uses a universal measurement and compensation approach that works across all lanes and Baud rates. By measuring the transfer function H(f) of each lane using the same methodology and applying the same compensation calculation (CF(f) = 1/H(f)), the system handles wide frequency ranges and multiple Baud rates with a unified process, reducing the perceived complexity despite the broad adaptation requirements.
Solution Approach 2:
The system automatically adjusts compensation parameters based on measured transfer function characteristics rather than using fixed complex compensation schemes. By measuring the actual H(f) of each lane and calculating appropriate compensation values, the system adapts parameters to match the specific frequency characteristics and lane differences, simplifying the compensation process while maintaining effectiveness across wide frequency ranges.
Data Source
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AI summary
A transfer function or an inverse transfer function of an optical transmitter (7) of a transmission unit (1) is estimated from first data acquired by a reception unit (3) when a first known signal is transmitted from the transmission unit (1) to the reception unit (3) of the optical transceiver, and a temporary transfer function or a temporary inverse transfer function of an optical receiver (9) of the reception unit (3). A transfer function or an inverse transfer function of the optical receiver (9) is estimated from second data acquired by the reception unit (3) when a second known signal is transmitted from the transmission unit (1) to the reception unit (3), and the estimated transfer function or the estimated inverse transfer function of the optical transmitter (7).