TDM Probe Signal for WDM Link Spectral Testing
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Solution Overview
Problem
Current methods for spectral characterization of active wavelength division multiplexed (WDM) optical links face challenges, such as nonlinear impairments and loss of spectral information, especially when trying to measure spectral properties under normal operating conditions without disrupting data traffic or losing important spectral intervals.
Innovation Solution
A system that uses a probe signal generator, time division multiplexing (TDM) with a first and second TDM optical switch to separate the probe signal from the WDM signal within the link, allowing for spectral measurements to be conducted without affecting the link's operation, using acousto-optical switches to manage the probe signal's power and avoid nonlinear effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single scanning channel is used for spectral measurements, then the measurement can be conducted without requiring multiple channels, but nonlinear impairments such as stimulated Brillouin scattering and self phase modulation occur heavily in the probe channel
Solution Approach 1:
The patent applies periodic action by time-division multiplexing the probe signal with the WDM signal, where the probe signal is inserted periodically into the WDM signal stream at specific time slots. This periodic insertion allows the probe signal to share the amplifier output power dynamically, reducing the average power in the probe channel while maintaining measurement capability, thereby avoiding nonlinear impairments like stimulated Brillouin scattering and self phase modulation.
2Measurement precision
If an interleaver is used to block WDM channels from entering the analyzer, then the WDM channels are prevented from disturbing the test measurements, but spectral intervals adjacent to the WDM channels are eliminated from measurements
Solution Approach 1:
The patent extracts only the necessary WDM channels from the full WDM signal using a tunable filter or wavelength selective switch, allowing selective measurement of specific spectral intervals while blocking only the channels that would interfere with measurements. This extraction approach replaces the all-or-nothing interleaver method, preserving spectral information in intervals that were previously eliminated.
3Measurement precision
If traditional testing methods are used, then spectral measurements can be conducted, but data traffic in the transmission link is disrupted
Solution Approach 1:
The patent merges the probe signal with the WDM signal using time-division multiplexing, combining both signals into a single shared optical path that traverses the amplifier and link under test. This merging allows simultaneous transmission of data traffic and probe signals without requiring separate test equipment or disrupting existing data traffic, as both signals coexist in the same physical infrastructure.
4Reliability
If the total output power of the optical amplifier is kept constant at about +20 dBm, then the amplifier operates within safe limits, but the power per channel is limited to about +4 dBm for a 40 channel system
Solution Approach 1:
The patent uses periodic action through time-division multiplexing where the probe signal is inserted into specific time slots of the WDM signal stream. During probe signal transmission, the amplifier output power is dynamically adjusted to provide sufficient power for measurements, while during normal WDM operation, the total power remains constant at +20 dBm. This periodic power adjustment allows higher probe channel power when needed without compromising amplifier reliability.
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 spectral measurements under normal operating conditions, preserving the power difference between the probe and WDM channels, and allowing for real-time correlation of performance and spectral parameters without disrupting data traffic or losing spectral information.
Implementation Method 1
using acousto-optical switches to manage the probe signal's power and avoid nonlinear effects
Data Source
AI summary
A time division multiplexed measurement technique is used for spectral measurements in active wavelength division multiplexed loaded optical links, and offers instantaneous real-time correlation of performance and spectral parameters of the link, which is important for dynamic characterization of link performance during transient effects or polarization mode dispersion fluctuations.