Interference Cancellation in Digital Coherent Optical Transmission
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Solution Overview
Problem
Digital coherent optical transmission systems face signal quality degradation due to reflected light, which existing technologies have not adequately addressed, particularly in short and middle distance transmission systems where high-speed and low-cost solutions are required.
Innovation Solution
An interference cancellation device and method that includes an interference signal generation unit with a buffer circuit to delay and process digital signals to mimic the optical characteristics of reflected light, allowing for the subtraction of interference signals from reception signals, thereby reducing the impact of reflected light on transmission quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If same-wavelength bidirectional transmission is used to simplify wavelength management and reduce cost, then device complexity is reduced, but signal quality deteriorates due to reflected light interference
Solution Approach 1:
The patent converts the harmful reflected light into a useful signal by capturing it with a photodetector and processing it through digital signal processing. The reflected light, which normally degrades signal quality, is transformed into an interference signal that can be analyzed and canceled out, turning the harmful effect into a beneficial measurement and correction mechanism
Solution Approach 2:
The patent applies preliminary anti-action by generating a predicted interference signal based on the transmitted signal characteristics and optical path properties, then subtracting this predicted interference from the received signal before further processing. This pre-cancellation approach prevents the reflected light interference from degrading the signal quality in subsequent processing stages
2Reliability
If digital signal processing is used for waveform equalization to compensate waveform distortion at ultrafast transmission speeds, then signal quality is improved, but device complexity and cost increase due to expensive optical components
Solution Approach 1:
The patent replaces mechanical/optical wavelength dispersion compensation components (such as DCF or TDC) with digital signal processing operations. Instead of using physical optical components to compensate for waveform distortion, the system uses digital filtering and equalization algorithms applied to the electrical signal after photodetection, achieving the same compensation effect without expensive optical hardware
Solution Approach 2:
The patent creates a digital model or copy of the optical channel characteristics through training and adaptation processes. By generating a predicted interference signal that mirrors the actual reflected light interference based on the transmitted signal and channel response, the system can cancel the interference without needing complex optical compensation components
3Reliability
If buffer circuit delays first digital signal to generate second digital signal for interference cancellation, then signal quality is improved by removing reflected light interference, but loss of time occurs due to signal delay
Solution Approach 1:
The patent applies partial delay only to the portion of the signal needed for interference cancellation (the transmitted signal copy), not to the entire received signal processing chain. The buffer circuit delays only the first digital signal to generate the interference prediction, while the main received signal processing proceeds with minimal delay, achieving interference cancellation without excessive overall processing latency
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
The solution effectively suppresses signal quality degradation caused by reflected light, enabling high-speed and reliable optical transmission even in optical fiber paths with incomplete connections, by compensating for wavelength dispersion and polarization effects.
Implementation Method 1
an optical demodulator that mixes a local light 210 outputted from the light source 140 with the signal light 161 and outputs a reception signal 220 that is an electric signal
Implementation Method 2
the wavelength of the transmission signal light is equal to the wavelength of the reception signal light (same-wavelength bidirectional transmission)... wavelength dispersion compensation
Data Source
AI summary
An interference cancellation device includes: an interference signal generation unit including a buffer circuit that accumulates a first digital signal, delays the first digital signal, and outputs the first digital signal as a second digital signal and a digital signal processing circuit that processes the second digital signal in such a way as to have the same optical characteristic change as a reflected light whose optical characteristic changes according to the characteristic of an optical fiber transmission path, wherein the reflected light is a light reflected at a reflection point of the path when a transmission signal light modulated by the first digital signal is transmitted through the path, and outputs the second digital signal as an interference signal; and a subtraction unit that subtracts the interference signal from a third digital signal obtained by converting a reception signal light into an electric signal and outputting the result.