OSNR Detection Circuit Using Pilot-Tone Modulation
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Solution Overview
Problem
Traditional interpolation methods fail to accurately measure the optical signal to noise ratio (OSNR) in high-speed optical transmission systems with transmission rates of 40 Gb/s and 100 Gb/s due to the spectral width being approximate to or greater than the channel spacing, making it difficult to measure noise power among channels.
Innovation Solution
An optical signal to noise ratio detection circuit that includes an optical switch, tunable optical filter, photoelectric conversion module, and pilot-tone modulation signal conditioning module, which accesses multiple optical signals, adjusts modulation frequencies, converts signals into voltage signals, amplifies and digitizes AC and DC signals, and calculates OSNR using an FFT algorithm, enabling accurate detection of OSNR in high-speed systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional interpolation method is used to measure OSNR, then measurement process is simple, but measurement precision deteriorates when spectral width is approximate to or greater than channel spacing
Solution Approach 1:
The patent segments the optical signal measurement process into distinct functional modules: optical switching module for signal selection, optical filtering module for spectral isolation, photoelectric conversion module for signal transformation, and signal processing module for OSNR calculation. This segmentation allows each module to perform its specific function with high precision while maintaining overall system manageability despite increased complexity.
Solution Approach 2:
The patent introduces an optical filter as an intermediary component between the optical signal source and the photoelectric converter. This intermediary enables precise spectral filtering to isolate the signal of interest from adjacent channels, thereby achieving accurate OSNR measurement in high-speed systems where spectral width approaches or exceeds channel spacing.
2Productivity
If transmission rate is increased to 40 Gb/s and 100 Gb/s, then transmission capacity is improved, but OSNR detection capability deteriorates due to spectral width issues
Solution Approach 1:
The patent employs a tunable optical filter with dynamically adjustable center frequency and bandwidth parameters. This dynamic capability allows the filter to adapt to different transmission rates (2.5 Gb/s, 10 Gb/s, 40 Gb/s, 100 Gb/s) and corresponding spectral characteristics, maintaining accurate OSNR detection across varying transmission conditions where spectral width changes with transmission rate.
Solution Approach 2:
The patent changes key parameters including optical filter bandwidth, photoelectric conversion bandwidth, and signal processing filter settings to match the spectral characteristics at different transmission rates. By adjusting these parameters dynamically, the system maintains precise OSNR measurement capability even as transmission rate and spectral width increase to 40 Gb/s and 100 Gb/s.
3Measurement precision
If optical filter bandwidth is reduced to improve noise power measurement accuracy, then measurement precision is improved, but signal power loss increases
Solution Approach 1:
The patent performs preliminary optical filtering to isolate the signal spectrum before photoelectric conversion. By pre-filtering the optical signal with an optical filter having controlled bandwidth, the system prepares a clean spectral signal that can be accurately converted and measured, minimizing the need for aggressive post-conversion filtering that would cause signal power loss.
Solution Approach 2:
The patent replaces aggressive electronic filtering (which causes signal power loss) with optimized optical filtering performed before photoelectric conversion. This substitution moves the filtering operation to the optical domain where it can be performed with minimal impact on signal power, as the filtering occurs before the conversion process rather than attenuating the already-converted electrical signal.
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
The solution accurately detects the optical signal to noise ratio of each accessed optical signal, effectively addressing the limitations of traditional interpolation methods and enabling OSNR detection in high-speed optical transmission systems of 40 Gb/s and 100 Gb/s.
Implementation Method 1
a tunable optical filter, configured to adjust a modulation frequency of the to-be-detected optical signal gated by the optical switch as a center frequency of the to-be-detected optical signal
Implementation Method 2
a photoelectric conversion module, configured to convert the to-be-detected optical signal with the adjusted modulation frequency into a voltage signal
Data Source
AI summary
Disclosed are embodiments of an apparatus and method relating to an optical signal to noise ratio detection circuit, adopting an optical switch, a tunable optical filter, a photoelectric conversion module, a pilot-tone modulation signal conditioning module and a control module. After the photoelectric conversion module converts a to-be-detected optical signal to a voltage signal, the pilot-tone modulation signal conditioning module respectively amplifies an AC signal and a DC signal in the voltage signal, correspondingly converts the AC signal and the DC signal to two-way digital signals, determines a modulation depth of the pilot-tone modulation signal and a modulation depth of an ASE noise according to the two-way digital signals, and calculates an optical signal to noise ratio of the optical signal.