Optical Transmitter Modulation Format for Linear Performance
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Solution Overview
Problem
Conventional high-dimensional modulation formats for optical coherent transmission systems face challenges in achieving optimal linear and nonlinear performance due to restrictive polarization balance criteria, leading to reduced spectral efficiency and increased fiber nonlinear impairments.
Innovation Solution
The optical transmitter employs a modulation format with symbols having non-identical polarization states in consecutive time slots, relaxing the polarization balance constraint to improve linear performance and allowing for higher spectral efficiencies of 2.5 and 3.5 bits/interval, using a QPSK base constellation and generating overhead bits to optimize symbol selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polarization balance criteria are applied to design high-dimensional modulation formats, then nonlinear performance is improved, but linear performance deteriorates and spectral efficiency is reduced
Solution Approach 1:
The patent changes the polarization state parameter of symbols across consecutive time slots. Instead of maintaining identical polarization states (conventional approach), the invention uses non-identical polarization states in consecutive slots, which transforms the system behavior to achieve both improved linear performance (through increased Euclidean distance) while maintaining nonlinear performance through controlled polarization variation.
Solution Approach 2:
The patent extends the modulation from 4-dimensional (I, Q, X, Y) to 8-dimensional by incorporating time slot indexing as an additional degree of freedom. This dimensional expansion allows the system to achieve higher spectral efficiencies (2.5 and 3.5 bits/interval) while using non-identical polarization states in consecutive time slots, resolving the contradiction between linear and nonlinear performance requirements.
2Device complexity
If conventional modulation formats with identical polarization states are used, then device complexity is reduced, but spectral efficiency is limited and linear performance is suboptimal
Solution Approach 1:
The patent introduces dynamic polarization state selection where the polarization state of symbols changes across consecutive time slots according to a predefined pattern. This dynamic approach allows the system to achieve higher spectral efficiencies (2.5 and 3.5 bits/interval) without requiring complex real-time adaptation, as the polarization sequence is predetermined based on the modulation format design.
3Object-affected harmful factors
If symbols with constant modulus are used, then fiber nonlinear impairments are mitigated, but linear performance and spectral efficiency are compromised
Solution Approach 1:
The patent changes the polarization state parameter of symbols across consecutive time slots. Instead of maintaining identical polarization states (conventional approach), the invention uses non-identical polarization states in consecutive slots, which transforms the system behavior to achieve both improved linear performance (through increased Euclidean distance) while maintaining nonlinear performance through controlled polarization variation.
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 results in better linear and nonlinear channel performance by increasing the Euclidean distance of constellation points, enhancing the optical transmitter's efficiency and reducing fiber nonlinear impairments.
Implementation Method 1
a modulator configured to use in each transmission time slot the first symbol to modulate a first carrier wave and the second symbol to modulate a second carrier wave
Implementation Method 2
transmit the two carrier waves over orthogonal polarizations (referred to as X and Y) of the optical carrier
Data Source
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AI summary
The present invention provides an optical transmitter (100) for transmitting a data signal (101). The optical transmitter (100) comprises an encoder (102) configured to encode the data signal (101) by selecting based on a bit sequence (101, 401) a first symbol and a second symbol from a set (200) of four symbols (201-204) for each one of at least two transmission time slots. The optical transmitter (100) further comprises a modulator (103) configured to use in each transmission time slot the first symbol to modulate a first carrier wave and the second symbol to modulate a second carrier wave, and to transmit the two carrier waves over orthogonal polarizations of an optical carrier (104). Symbols (201-204) in consecutive transmission time slots have non-identical polarization states.