Nonlinear Fiber-Optic Encoder With Metric-Based Symbol Shaping
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Solution Overview
Problem
Existing fiber-optic communication systems face significant challenges due to optical fiber nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM), which limit the maximum achievable transmission distance and signal quality, and there is a lack of a common methodology to minimize these effects effectively.
Innovation Solution
An encoder for fiber-optic communication that translates information bit sequences into modulation symbol sequences with a minimized nonlinear metric, reducing optical nonlinear effects like SPM, XPM, and FWM during propagation by employing a shaping procedure that selects symbol sequences with the smallest value of a defined metric, applicable to QAM and PSK constellations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If input power is increased to improve SNR, then signal-to-noise ratio is improved, but optical fiber nonlinear effects are intensified
Solution Approach 1:
The patent changes the statistical distribution parameters of modulation symbols from uniform to non-uniform (probabilistic shaping), where outer constellation points are used less frequently than inner points. This parameter change in symbol distribution reduces the average and peak power without changing the modulation format itself, thereby improving SNR while suppressing nonlinear effects.
Solution Approach 2:
The patent applies probabilistic shaping at the transmitter before signal transmission to pre-limit the occurrence of high-power symbols. By shaping the symbol distribution in advance according to a probability distribution function, the system prevents excessive power peaks that would cause nonlinear effects during propagation, rather than compensating for them after transmission.
2Productivity
If traditional QAM modulation is used to achieve high data rates, then transmission capacity is increased, but capacity penalty occurs due to nonlinear effects
Solution Approach 1:
The patent modifies the probability distribution parameters of QAM constellation points, transitioning from uniform distribution to non-uniform distribution where inner points have higher probability and outer points have lower probability. This parameter change allows traditional QAM to achieve higher effective capacity by reducing nonlinear-induced errors while maintaining the same modulation order.
3Object-generated harmful factors
If probabilistic shaping is applied to reduce nonlinear effects, then nonlinear distortion is reduced, but constellation shaping complexity increases
Solution Approach 1:
The patent pre-calculates and stores the probability distribution function and mapping relationships between bits and shaped symbols in lookup tables before transmission. This preliminary preparation simplifies the real-time transmitter operation, as the shaping process becomes a table lookup rather than a complex real-time optimization problem, reducing implementation complexity while maintaining nonlinear distortion reduction benefits.
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 proposed encoder reduces optical nonlinear effects, improving signal quality and transmission distance by minimizing distortion and maintaining forward error correction performance, thereby enhancing the efficiency and reliability of fiber-optic communication.
Implementation Method 1
a modulation symbol sequence for modulating an optical carrier signal
Implementation Method 2
transmits an information from one place to another place, through an optical fiber
Implementation Method 3
Optical fiber nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM) and scattering effects, may happen due to use of increased input power
Implementation Method 4
Optical fiber nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM) and scattering effects
Implementation Method 5
Optical fiber nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM) and scattering effects
Implementation Method 6
Optical fiber nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM) and scattering effects
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
Provided is an encoder (100) for fiber-optic communication. The encoder (100) includes an input (102) that is configured to receive an information bit sequence (110, 302), a digital signal processor (DSP) (106) that is configured to translate the information bit sequence (110, 302) into a modulation symbol sequence (112, 310, 400, 700) for modulating an optical carrier signal, and an output (108) that is configured to output the modulation symbol sequence (112, 310, 400, 700). The DSP (106) is configured to translate the information bit sequence (110, 302) into the modulation symbol sequence (112, 310, 400, 700) such that the modulation symbol sequence (112, 310, 400, 700) has, among all symbol sequences in a candidate set of symbol sequences, a smallest value of a metric. The metric is defined as Formula (I) for any symbol sequence Z = (Z[0],..., Z[N - 1]) in the candidate set.