Optical Transmitter Phase Difference Adding for CMA Demultiplexing
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Solution Overview
Problem
The existing polarization demultiplexing technology using the constant modulus algorithm (CMA) struggles to demultiplex polarization multiplexed optical signals generated by optical phase modulation systems like BPSK, 16QAM, where symbol points are not on the same circumference, leading to false bit sequence regeneration.
Innovation Solution
An optical transmitter with first and second optical quadrature modulation means for phase modulation, an optical phase difference adding means to introduce a varying phase difference between the signals, and polarization multiplexing to orthogonalize the signals, enabling effective demultiplexing using the CMA in the optical digital coherent communication system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the constant modulus algorithm (CMA) is used for polarization demultiplexing, then the demultiplexing process can be simplified, but it fails to accurately demultiplex signals from optical phase modulation systems like BPSK where symbol points are not on the same circumference
Solution Approach 1:
The patent applies preliminary action by introducing an optical phase difference adding means that pre-adjusts the phase relationship between the two optical signals before they enter the polarization multiplexer. This preliminary phase adjustment ensures that when the CMA algorithm processes the signals, the symbol points are effectively positioned on the same circumference, enabling accurate demultiplexing without requiring complex post-processing algorithms.
2Reliability
If optical phase modulation systems like BPSK are used, then the system can achieve long-haul transmission with good noise tolerance, but the symbol points are not on the same circumference making demultiplexing difficult
Solution Approach 1:
The patent introduces an intermediary mechanism - the optical phase difference adding means - that acts as a mediator between the optical phase modulation process and the polarization multiplexing process. This intermediary component adjusts the phase relationship between signals to transform them into a format suitable for CMA-based demultiplexing, thereby maintaining the noise tolerance benefits of BPSK while simplifying the demultiplexing process.
3Device complexity
If the optical phase difference between signals is not compensated, then the system structure remains simple, but the demultiplexing accuracy deteriorates leading to false bit sequence regeneration
Solution Approach 1:
The patent applies preliminary action by incorporating an optical phase difference adding means that pre-compensates for phase differences between the two optical signals before polarization multiplexing. This ensures that the phase relationship is controlled and known, allowing the receiving end to accurately demultiplex the signals without requiring complex phase compensation algorithms, thus maintaining simple system structure while achieving high demultiplexing precision.
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 configuration allows for accurate regeneration of transmitting signals across various optical phase modulation systems, including BPSK, by ensuring the optical phase difference is compensated, facilitating reliable demultiplexing and bit sequence recovery.
Implementation Method 1
first optical quadrature modulation means for performing a phase modulation on a first continuous light beam and outputting a first transmitting light beam
Implementation Method 2
optical phase difference adding means for adding an optical phase difference varying temporally between the first transmitting light beam and the second transmitting light beam
Implementation Method 3
polarization multiplexing means for polarization-multiplexing the first transmitting light beam and the second transmitting light beam in the state where their polarizations are made to be orthogonal to each other
Implementation Method 4
a 90-degree optical hybrid receiving the polarization multiplexed transmitting light beam and local oscillation light with approximately the same optical frequency
Implementation Method 5
photoelectric conversion means for photoelectrically converting the first received light beam and the second received light beam and outputting a first received signal and a second received signal
Data Source
AI summary
It becomes difficult to regenerate transmitting signals depending on modulation systems for the optical phase modulation in a polarization multiplexed optical communication system employing the optical digital coherent communication system, therefore, an optical transmitter according to an exemplary aspect of the invention includes first optical quadrature modulation means for performing a phase modulation on a first continuous light beam and outputting a first transmitting light beam; second optical quadrature modulation means for performing a phase modulation on a second continuous light beam belonging in the same frequency band as that of the first continuous light beam and outputting a second transmitting light beam; optical phase difference adding means for adding an optical phase difference varying temporally between the first transmitting light beam and the second transmitting light beam; and polarization multiplexing means for polarization-multiplexing the first transmitting light beam and the second transmitting light beam in the state where their polarizations are made to be orthogonal to each other and outputting a polarization multiplexed transmitting light beam.