Direct Detection Receiver SSBI Estimation and Subtraction
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Solution Overview
Problem
Optical transport systems employing direct detection suffer from signal-signal beat interference (SSBI), which limits their ability to scale to higher data rates due to chromatic dispersion, especially in short- and medium-reach optical transport links.
Innovation Solution
The system uses single-sideband modulation and innovative signal-processing techniques, including converting the electrical signal into a modified baseband signal, squaring and scaling it to estimate SSBI, and then subtracting this estimate from the original signal to recover the data, thereby reducing SSBI impairments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct detection is used in optical transport systems, then device complexity is reduced and cost is lowered, but signal-signal beat interference (SSBI) increases due to chromatic dispersion
Solution Approach 1:
The patent converts the harmful SSBI signal into a useful estimation by squaring the received electrical signal. The squared signal contains frequency components that correspond to the SSBI, which are then filtered and subtracted from the original signal. This transforms the harmful interference into a measurable quantity that can be removed, enabling direct detection to achieve performance closer to coherent detection without the complexity.
Solution Approach 2:
The patent extracts the SSBI component from the received signal through a series of processing steps. The electrical signal is squared to generate frequency components at twice the optical frequency, then a bandpass filter extracts the SSBI-related components. This extracted SSBI estimate is subsequently subtracted from the original signal, effectively removing the harmful interference while preserving the useful signal information.
2Ease of manufacture
If direct detection is used to simplify the receiver, then manufacturing cost decreases, but measurement precision of the received signal deteriorates due to SSBI
Solution Approach 1:
The patent converts the harmful SSBI signal into a useful estimation by squaring the received electrical signal. The squared signal contains frequency components that correspond to the SSBI, which are then filtered and subtracted from the original signal. This transforms the harmful interference into a measurable quantity that can be removed, enabling direct detection to achieve performance closer to coherent detection without the complexity.
Solution Approach 2:
The patent implements a feedback mechanism where the processed signal (after SSBI estimation and subtraction) is used to improve the accuracy of the final detection. The system continuously estimates and removes SSBI from the received signal, creating a corrected signal that feeds into the data recovery process, thereby improving measurement precision while maintaining direct detection simplicity.
3Productivity
If data rate is increased in direct detection systems, then productivity improves, but SSBI effects worsen due to chromatic dispersion
Solution Approach 1:
The patent converts the harmful SSBI signal into a useful estimation by squaring the received electrical signal. The squared signal contains frequency components that correspond to the SSBI, which are then filtered and subtracted from the original signal. This transforms the harmful interference into a measurable quantity that can be removed, enabling direct detection to achieve performance closer to coherent detection without the complexity.
Solution Approach 2:
The patent changes the processing parameters of the received signal by applying squaring operation and frequency filtering. This transforms the signal into a domain where SSBI components can be separated and removed. By modifying the signal parameters through these mathematical operations, the system can effectively reduce SSBI effects even at higher data rates where chromatic dispersion is more severe.
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 approach significantly reduces SSBI, allowing for efficient data recovery and overcoming chromatic dispersion limitations, providing a cost-effective alternative to coherent detection methods for higher data rate transmission.
Implementation Method 1
an optical detector configured to convert an optical input signal into a first electrical signal proportional to an optical power of the optical input signal
Data Source
AI summary
Disclosed herein is an optical transport system configured to transport an amplitude-modulated optical signal generated at the transmitter using single-sideband modulation of an optical carrier and detected at the receiver using direct optical detection. The receiver is configured to estimate the level of signal-signal beat interference (SSBI) in the electrical signal generated upon direct detection of the received optical signal by first converting this electrical signal into a modified baseband signal configured for single-sideband modulation and then squaring and appropriately scaling this modified baseband signal. The receiver is further configured to subtract the estimated level of SSBI from the electrical signal generated by the direct optical detector and to process the resulting corrected electrical signal to recover the data encoded in the amplitude-modulated optical signal. Example analog and digital circuits for estimating the level of SSBI at the receiver are disclosed.