Tunable Optical Filter for In-Service OSNR Measurement
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Solution Overview
Problem
Current methods for measuring in-band optical signal-to-noise ratio (OSNR) in coherent optical transmission systems, such as OSA-based linear interpolation and polarization extinction methods, face challenges like inaccurate noise power measurement due to spectral overlap, service interruption, and inapplicability to PM-QPSK signals, limiting effective in-service monitoring and maintenance in dense wavelength division multiplexing networks.
Innovation Solution
A system comprising a tunable optical filter, optical coherent receiver, analog-to-digital converters, and digital signal processing module for wavelength demultiplexing, polarization- and phase-diversity detection, and real-time estimation of OSNR, dispersion, and polarization dependent loss, enabling in-service measurement of key performance parameters without service disruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If OSA-based linear interpolation method is used to measure in-band OSNR, then measurement can be performed in dense wavelength division multiplexing networks, but measurement precision deteriorates due to spectral overlap between adjacent channels
Solution Approach 1:
The patent extracts the ASE noise power measurement from the signal band by utilizing the out-of-band region. The method measures noise power at wavelengths offset from the signal center frequency (e.g., ±channel spacing/2) where only ASE noise exists without signal interference, then uses this extracted noise measurement to calculate in-band OSNR, thereby resolving the spectral overlap problem
Solution Approach 2:
The patent introduces an intermediary approach by measuring noise power at intermediate wavelengths between the signal channel and adjacent channels. Instead of directly measuring in-band noise (which is contaminated by signal), the method uses out-of-band measurements as intermediaries to infer the in-band noise level through interpolation or direct calculation
2Measurement precision
If signal ON-OFF method is used to measure noise power, then noise power measurement accuracy improves, but service continuity deteriorates due to signal interruption
Solution Approach 1:
The patent enables continuous OSNR measurement during signal transmission by measuring out-of-band noise power while the signal remains active. The useful action of noise measurement continues without interruption by selecting measurement wavelengths that do not require signal shutdown, thus maintaining both measurement accuracy and service continuity
3Measurement precision
If polarization extinction method is used to separate signal and noise, then measurement precision improves for polarized signals, but adaptability deteriorates for polarization-multiplexed signals
Solution Approach 1:
The patent creates a universal measurement method that works for both polarized and polarization-multiplexed coherent signals. By measuring out-of-band noise power and using digital signal processing to separate signal and noise components in the frequency domain, the method achieves broad adaptability across different coherent signal formats without requiring polarization-specific techniques
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
Facilitates real-time monitoring and maintenance of 40 Gbps to 1 Tbps coherent systems, ensuring accurate OSNR measurement and reducing operational costs by enabling continuous service and precise parameter estimation.
Implementation Method 1
a tunable optical filter for processing an incoming optical signal, performing wavelength or optical carrier demultiplexing and out-of-band ASE noise suppression
Implementation Method 2
an optical coherent receiver connected to the above mentioned tunable optical filter, for performing polarization- and phase-diversity detection of the optical signal from the tunable optical filter and converting it into multiple lane baseband electrical signals
Data Source
AI summary
The present invention discloses a method and an apparatus for measuring quality parameters of optical transmission channels. The apparatus comprises: a tunable optical filter for receiving an optical signal, performing wavelength or optical carrier demultiplexing on the optical signal, and out-of-band ASE noise suppression; an optical coherent receiver connected to the tunable optical filter, for performing polarization- and phase-diversity detection on the filtered optical signal and converting it into multiple lane baseband electrical signals; analog-to-digital converters for sampling and quantizing the multiple lane baseband electrical signals so as to convert the them into multiple lane digital signals; a digital signal processing module for processing the multiple lane digital signals to obtain quality parameters; and an display module for displaying the quality parameters. By the device according to an embodiment of the invention, real-time measurement of various key performance parameters of the 40 Gbps, 100 Gbps and extra-100 Gbps (for example, 200 Gbps, 400 Gbps and 1 Tbps) coherent polarization-multiplexed system is achieved simultaneously, especially the issue of real-time measurement of the in-service in-band OSNR is solved. Therefore, the network operation and maintenance are facilitated and the cost of network operation and maintenance is saved.