Few-Mode Fiber Mode Coupler for PON Range Extension
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Solution Overview
Problem
Passive optical network (PON) systems face limitations in the upstream power budget and transmission distance due to multi-mode interference, which restricts the number of users and coverage area, especially with existing mode couplers that introduce insertion loss and limit multi-mode transmissions to short distances.
Innovation Solution
Implementing a mode coupler with a few mode fiber between the OLT and the mode coupler, using time division multiplexing (TDM) or time division multiple access (TDMA) to schedule upstream transmissions, allowing the few mode fiber to extend up to 20-40 km, and employing a processor to manage signal power levels and interference, thereby reducing insertion loss and increasing the transmission range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional mode couplers are used in PON systems, then the system can support multi-mode transmissions, but the insertion loss increases and transmission distance is limited to short ranges
Solution Approach 1:
The patent changes the fiber mode parameters by using few-mode fiber (supporting only a few specific modes) instead of conventional multi-mode fiber, and carefully controls which modes are excited and propagated. This parameter change reduces mode coupling and interference, thereby reducing insertion loss while maintaining multi-mode transmission capability for extended distances.
Solution Approach 2:
The patent segments the transmission system into distinct functional sections: single-mode fiber for long-haul transmission, few-mode fiber for mode coupling at the OLT, and separate mode groups for different ONUs. This segmentation allows each section to be optimized for its specific function, reducing overall insertion loss while enabling multi-mode operation where needed.
2Quantity of substance
If conventional multi-mode fiber is used for upstream transmissions, then multiple users can be served, but intermodal cross-talk increases and limits transmission distance to about 20 kilometers
Solution Approach 1:
The patent applies local quality by creating different transmission environments for different spatial locations: single-mode fiber for long-distance trunk lines where cross-talk must be eliminated, and few-mode fiber at the OLT where controlled mode coupling occurs. Each location has the fiber type and mode configuration optimized for its specific requirements, reducing intermodal cross-talk while maintaining multi-user capability.
Solution Approach 2:
The patent introduces a mode coupler as an intermediary device at the OLT that performs controlled mode coupling between single-mode and few-mode fibers. This intermediary enables the system to support multiple users through mode-division multiplexing while confining the complexity and potential cross-talk to a localized, controllable component rather than throughout the entire transmission path.
3Reliability
If time division multiplexing is used to schedule upstream transmissions, then interference between users is reduced, but system complexity increases
Solution Approach 1:
The patent implements periodic time-division multiplexing where each ONU is assigned specific time slots for upstream transmissions. This periodic scheduling ensures that signals from different users are transmitted at different times, eliminating inter-user interference and improving signal quality. The regular, predictable pattern simplifies the scheduling logic compared to ad-hoc approaches.
Solution Approach 2:
The system employs self-service mechanisms where ONUs autonomously follow the assigned time slots and transmission parameters provided by the OLT. Each ONU independently manages its own transmissions according to the schedule, reducing the need for complex centralized control and arbitration logic, thereby managing system complexity while maintaining reliable interference-free operation.
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 extends the reach of multi-mode PON systems, reduces the number of optical fiber lines, and achieves significant cost savings while maintaining acceptable throughput, by eliminating intermodal cross-talk and optimizing power budget through strategic scheduling of upstream transmissions.
Implementation Method 1
a few mode fiber coupled between the OLT and the mode coupler
Implementation Method 2
mode coupler with a few mode fiber between the OLT and the mode coupler
Implementation Method 3
separate upstream data signals from the ONUs into a plurality of data streams corresponding to each transmitting ONU
Data Source
AI summary
An optical line terminal (OLT) comprising a receiver configured to couple to a mode coupler via a multi-mode optical fiber that supports more than one optical communication mode, and couple to a plurality of optical network units (ONUs) via the mode coupler, a processor coupled to the receiver and configured to schedule upstream multi-mode transmissions from the ONUs via the multi-mode fiber and the mode coupler by employing time division multiplexing (TDM), and a transmitter coupled to the processor and configured to transmit schedule data to the ONUs.