Reflective Optical Network Crosstalk Mitigation
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Solution Overview
Problem
Reflective optical networks face limitations due to power budget constraints and channel cross-talk induced by Rayleigh Back-scattering and reflective sites, which affect the upstream optical path and signal quality.
Innovation Solution
The implementation of a reflective optical network with a transmitter controller that processes data signals to remove low-frequency spectral components and an optical receiver with a high-pass filter, allowing for improved tolerance to reflections and back-scattered signals, and the use of reflective optical modulators that can provide gain while controlling crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reflective modulators are used to provide optical gain at ONUs, then the uplink crosstalk-to-signal ratio is improved, but the gain cannot be increased arbitrarily as it strongly amplifies crosstalk above a threshold
Solution Approach 1:
The patent changes the operating parameters of the reflective modulator by introducing phase modulation of the CW seed signal at frequencies outside the data bandwidth. This parameter change allows the system to achieve acceptable crosstalk-to-signal ratios without requiring high gain, thereby avoiding the amplification of crosstalk while maintaining signal quality.
2Reliability
If phase modulation of the CW seed signal is used, then crosstalk is mitigated, but the modulation must be operated at frequencies outside the data bandwidth making it impractical and expensive
Solution Approach 1:
The patent introduces a new dimension to the modulation strategy by using phase modulation of the seed signal at frequencies outside the data bandwidth. This dimensional approach allows crosstalk mitigation without interfering with the data transmission bandwidth, achieving both practicality and effectiveness in real systems.
3Reliability
If high pass filtering is applied at the receiver, then carrier to signal value degradation is reduced, but the filter must have a cut-off frequency higher than the linewidth of the seed optical signal
Solution Approach 1:
The patent adjusts the filter cut-off frequency parameter to be higher than the linewidth of the seed optical signal. This parameter change allows the high pass filter to effectively reject low-frequency components and reduce carrier to signal value degradation while maintaining compatibility with the seed signal 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 solution enhances the network's resilience to reflections and back-scattering, enabling operation with very low upstream carrier-to-signal values and reducing inter-symbol interference, thus improving signal quality and power measurements.
Implementation Method 1
Said transmitter controller is arranged to control said modulator to apply said data signal to said seed optical signal, to form an optical data signal
Implementation Method 2
Said optical receiver is arranged to receive said optical data signal
Implementation Method 3
Said transmitter controller is further arranged to process said received data signal to substantially prevent said optical data signal comprising spectral components at frequencies lower than a cut-off frequency
Implementation Method 4
The main limiting factor in the uplink channel is coherent crosstalk generated by Rayleigh Back-scattering (RB)
Data Source
AI summary
A reflective optical network (10) comprises an optical network unit (14) and an optical receiver (22). The optical network unit (14) comprises a reflective optical modulator (16) arranged to receive a seed optical signal, and a transmitter controller (18) arranged to receive a data signal (20) and to control the modulator (16) to apply the data signal (20) to the seed optical signal, to form an optical data signal. The transmitter controller (18) is arranged to process the data signal (20) to substantially prevent the optical data signal comprising spectral components at frequencies lower than a cut-off frequency, being the frequency at which a power spectral density of said optical data signal is lower than a peak power spectral density of said optical signal by a cut-off power value. The optical receiver (22) comprises an electrical domain high pass filter (26) having a cut-off frequency higher than a linewidth of the seed optical signal.