OSNR Determination via Electrical Noise Injection
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Solution Overview
Problem
Existing methods for determining the optical signal-to-noise ratio (OSNR) in optical transmission systems are either inaccurate, complex, or impossible to perform during operation, especially when channel separations are small, and require high BER measurements that interfere with error correction.
Innovation Solution
A method that determines OSNR after opto-electrical conversion by adding noise currents to the electrical data signal, calculating the mean signal and noise currents using a noise model, and optimizing the decision threshold to calculate the OSNR, which can be implemented in existing receivers or as an autonomous unit, independent of data formats and rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical spectrum analyzer is used to determine OSNR, then measurement capability is provided, but measurement becomes virtually impossible when channel separations are very small (25 or 50 GHz)
Solution Approach 1:
The patent replaces optical measurement methods with electrical measurement methods. Instead of using an optical spectrum analyzer to measure OSNR optically, the invention performs opto-electrical conversion and measures the electrical signal characteristics (mean signal current, mean noise current) in the electrical domain, allowing OSNR determination for small channel separations that are impossible to measure optically
Solution Approach 2:
The patent changes the measurement domain from optical parameters to electrical parameters. By converting the optical signal to electrical signal and measuring current values (mean signal current <I1>, mean noise current <Inoise>), the system can determine OSNR using electrical measurement techniques that are not limited by optical channel separation constraints
2Measurement precision
If polarization nulling method is used, then signal separation is achieved, but measurement accuracy deteriorates due to polarization mode dispersion and depolarization
Solution Approach 1:
The patent replaces the polarization-based optical separation method with an electrical measurement method. Instead of relying on polarization filters and polarization control, the invention measures electrical current characteristics after opto-electrical conversion, eliminating sensitivity to polarization mode dispersion and depolarization effects
Solution Approach 2:
The patent extracts the noise measurement from the optical domain and performs it in the electrical domain. By measuring the mean noise current <Inoise> electrically after opto-electrical conversion, the system avoids the complexity and inaccuracies of optical polarization-based noise separation methods
3Measurement precision
If channel switching method is used, then OSNR measurement is possible, but operation during transmission is prevented
Solution Approach 1:
The patent enables continuous OSNR measurement during transmission by measuring electrical signal characteristics in real-time. Instead of briefly switching off channels for measurement, the system continuously monitors the electrical mean signal current and mean noise current, allowing OSNR determination without interrupting the optical transmission
Solution Approach 2:
The patent replaces the mechanical channel switching method with continuous electrical measurement. By performing opto-electrical conversion and continuously measuring electrical current parameters, the system eliminates the need to switch off channels, enabling OSNR monitoring during continuous transmission operation
4Measurement precision
If BER measurement method is used, then OSNR can be determined, but measurements at very high BERs close to 0.5 are required which interfere with error correction
Solution Approach 1:
The patent changes the measurement approach from BER-based measurement to direct electrical current measurement. Instead of measuring bit error rate and extrapolating to determine OSNR, the invention directly measures the mean signal current <I1> and mean noise current <Inoise> electrically, calculating OSNR from these current values without requiring high BER measurements that would interfere with error correction
Solution Approach 2:
The patent extracts the OSNR determination from the BER measurement process. By directly measuring electrical current parameters (<I1> and <Inoise>) and calculating OSNR from these values using the provided formulas, the system eliminates the need for BER measurements close to 0.5, allowing error correction to function normally during OSNR determination
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
Enables accurate and continuous OSNR determination during operation without complex optical devices, allowing for improved power management and transmission quality assessment, including eye opening analysis, while being versatile and adaptable to different noise models.
Implementation Method 1
after the opto-electrical conversion of an optical data signal in a receiver of an optical transmission system
Data Source
AI summary
According to the invention, various noise currents are added to the electrical data signal after the opto-electric conversion of an optical data signal, and an optimum decision threshold for the electrical data signal equipped with this noise current is determined for each noise current. Values for a median signal current and for a median noise current of the amplified spontaneous emission are subsequently determined from the value pairs of the optimum decision threshold and the added noise current in accordance with a computation rule that is based on a noise model, and the optimum signal-to-noise ratio is calculated from their quotient. The method may also be advantageously implemented by means of simple expansions of common receiver devices.