Forwarding Optical Phase Sensing for PON Vibration Localization
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Solution Overview
Problem
Current PON architectures face challenges in implementing fiber sensing due to high round trip loss and multi-path interference, making it difficult to individually sense multiple fiber paths, and existing distributed fiber sensing solutions are costly and unsuitable for large-scale deployment.
Innovation Solution
A centralized optical phase measurement system using TDM switching on optical reflectors at ONUs, integrated with upstream data channels, allows vibration-induced phase changes to be measured at the OLT, distinguishing sources from individual drop fiber paths and the feeder fiber, without requiring sophisticated amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If distributed fiber sensing (DFS) using back scattering mechanisms is employed, then fiber sensing capability is achieved, but optical signal to noise ratio (OSNR) deteriorates after round-trip splitting loss
Solution Approach 1:
Instead of using back scattering mechanisms where light travels to the fiber endpoint and returns, the patent employs forward scattering mechanisms where light travels in the same direction as the data signal. This inversion of the sensing approach eliminates the round-trip path and associated losses, maintaining high OSNR even after splitting loss in PON architectures.
2Reliability
If reflective optical gain elements and TDM switched sensing control are used, then splitting loss and multi-path interference issues are solved, but system cost increases due to expensive DFS interrogator and additional R-SOA at each ONU
Solution Approach 1:
The patent integrates the sensing function into the existing upstream data channel infrastructure. The same optical carrier generated at the OLT is used for both data communication and vibration sensing. The coherent receiver with digital signal processing handles both data demodulation and phase retrieval, eliminating the need for separate expensive DFS interrogators and reflective gain elements at each ONU.
Solution Approach 2:
The patent merges the sensing function with the existing PON data communication channel. The optical carrier used for upstream data transmission is also utilized for vibration sensing by retrieving phase information through the coherent receiver's digital signal processing, thereby combining two functions into a single infrastructure.
3Ease of operation
If an interrogator is located at the OLT in standard PON architecture, then centralized control is achieved, but all sensing signals from drop fibers are combined together making individual path sensing difficult or impossible
Solution Approach 1:
The patent applies time-domain multiplexing to segment the sensing measurements in the time domain. Each ONU is assigned a specific time slot during which its phase-modulated signal is measured at the OLT. This temporal segmentation allows the centralized OLT to distinguish and measure individual drop fiber paths sequentially, preventing signal combination and enabling path-specific sensing.
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
Achieves high OSNR after round-trip splitting loss, enabling cost-effective identification of vibration sources in PON networks with segment-based localization, compatible with existing PON communication channels.
Implementation Method 1
measure vibration induced phase changes using forwarding optical signals
Implementation Method 2
optical phase interferometry and TDM switching control on reflected optical signals
Implementation Method 3
TDM switching on optical reflectors from different optical networking unit(s) (ONU)
Implementation Method 4
current standard PON architectures include a passive splitter—typically 32× or 64× split—in between an optical line terminal (OLT) and an end-user optical network unit (ONU)
Data Source
AI summary
Aspects of the present disclosure describe systems and methods that advantageously enable vibration-induced optical phase measurement at a centralized optical line terminal (OLT) in a PON architecture. In sharp contrast to existing distributed fiber sensing systems and methods, the optical phase measurements of the present disclosure do not rely on back scattering mechanisms and maintain a sufficient optical signal to noise ratio (OSNR) even after round-trip splitting loss in the PON.