Coherent Detection for Optical Transmitter TDECQ Assessment
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Solution Overview
Problem
The challenge lies in assessing the quality and interoperability of optical transmitters, particularly in O-band applications, where obtaining the TDECQ measurement is difficult due to the rarity of G.652 optical fibers with worst-case characteristics and low optical signal power, which can be exacerbated by nonlinear effects from amplifiers, and limited optical bandwidth of praseodymium-doped fiber amplifiers.
Innovation Solution
The method involves emulating the noise contribution of the worst-case optical fiber within the test device using a fiber emulator, allowing coherent optical-to-electrical detection and maintaining phase and frequency information to compute the TDECQ value, thereby bypassing the need for actual worst-case fiber configurations and addressing low signal power issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If actual worst-case G.652 optical fiber is used for TDECQ measurement, then measurement accuracy is improved, but device complexity and cost increase due to fiber rarity and configuration difficulty
Solution Approach 1:
The patent creates a virtual copy of the worst-case fiber characteristics through software emulation in the test device. Instead of physically connecting actual worst-case G.652 fiber, the system generates and processes signals that replicate the fiber's noise and dispersion effects digitally, thereby obtaining accurate TDECQ measurements without requiring rare physical fiber configurations.
Solution Approach 2:
The patent replaces the mechanical/physical fiber configuration system with a software-based emulation system. The physical fiber path is substituted by a signal processing chain that mathematically models the fiber's worst-case characteristics, eliminating the need for physical fiber handling and configuration while maintaining measurement accuracy.
2Power
If optical amplifiers are added to boost signal power, then signal power is improved, but harmful nonlinear effects increase
Solution Approach 1:
The patent extracts the signal amplification function from the physical optical domain and relocates it to the electrical signal processing domain. By performing coherent detection and subsequent digital signal processing, the system achieves effective signal enhancement without introducing optical nonlinearities, as the amplification occurs after the optical signal has been converted to electrical signals.
Solution Approach 2:
The patent introduces coherent detection as an intermediary conversion process between optical and electrical domains. This intermediary step allows signal processing to occur in the electrical domain where linear operations can be performed without optical nonlinearities, effectively mediating between the optical signal and the measurement system to avoid harmful nonlinear effects.
3Adaptability or versatility
If praseodymium-doped fiber amplifier is used, then optical bandwidth is limited, but this restricts applicability to certain wavelength ranges
Solution Approach 1:
The patent replaces the optical amplifier with an electrical signal processing system that operates after coherent detection. This substitution eliminates the wavelength-specific limitations of praseodymium-doped fiber amplifiers, as the electrical processing can handle various wavelength ranges without being constrained by the amplifier's optical bandwidth characteristics.
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 simplifies and cost-reduces the assessment of optical transmitter quality and interoperability by accurately emulating worst-case fiber noise contributions, enabling effective TDECQ measurements without requiring specific fiber configurations, thus improving measurement accuracy and compliance with standards.
Implementation Method 1
performing coherent optical-to-electrical detection of the optical signal to produce an in-phase receive signal and a quadrature receive signal
Data Source
AI summary
A method is provided for assessing the quality of an optical transmitter and/or its interoperability with a receiver. The method includes obtaining an optical signal output by an optical transmitter and performing coherent optical-to-electrical detection of the optical signal to produce an in-phase receive signal and a quadrature receive signal. The method further includes a computing device emulating a worst-case configuration of an optical fiber with which the optical transmitter is to be used, based on the in-phase receive signal and the quadrature receive signal to produce a noise contribution associated with the worst-case characteristics of the optical fiber and determining a figure of merit of the optical transmitter based on the noise contribution.