Multimode Combining N-Input Receiver for RFoG OBI Mitigation
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Solution Overview
Problem
Existing RFoG communication systems face impairment due to Optical Beat Interference (OBI), which limits upstream and downstream traffic, and current mitigation methods require additional power, increase costs, or reduce throughput.
Innovation Solution
The implementation of a multimode combiner with a retransmitting laser, which combines multiple single-mode optical signals into a larger core multimode fiber, allowing for low-loss detection and retransmission, thereby minimizing OBI and maintaining high signal-to-noise ratio without significant power increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multiple upstream inputs are combined on a single mode fiber to reduce OBI, then OBI is reduced, but additional power is required to drive photodiodes and retransmitting lasers
Solution Approach 1:
The patent introduces a multimode fiber as an intermediary medium between the combiner and detector. This multimode fiber accepts multiple upstream inputs and combines them without requiring photodiodes at each input point, thereby reducing OBI while minimizing additional power requirements. The multimode fiber acts as a passive intermediary that handles the combining function without active power-consuming components at the input stage.
2Object-affected harmful factors
If wavelength specific or adjustable ONUs are used to reduce OBI, then OBI is reduced, but cost increases and logistical problems arise
Solution Approach 1:
The patent segments the OBI mitigation function from the ONU devices themselves and relocates it to a centralized combiner unit. Instead of making each ONU wavelength-specific or adjustable (which increases device complexity and cost), the solution places a combiner with multimode fiber at the collection point, where multiple standard ONUs can connect without modification. This segmentation transfers the complexity to a single location rather than distributing it across all ONU devices.
3Object-affected harmful factors
If RFoG aware scheduler limits upstream transmissions to one ONU at a time, then OBI is reduced, but upstream channel throughput decreases
Solution Approach 1:
The patent transitions from a time-division approach (one ONU at a time) to a spatial-division approach using multimode fiber. The multimode fiber's larger core allows multiple spatial channels to coexist without significant OBI, enabling simultaneous upstream transmissions from multiple ONUs. This dimensionality change from temporal to spatial multiplexing maintains high throughput while reducing OBI through the physical properties of multimode fiber rather than scheduling constraints.
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 effectively reduces OBI, maintains high signal-to-noise ratio, and supports a large number of optical inputs without degrading receiver performance, while minimizing power dissipation and cost.
Implementation Method 1
combines multiple single-mode optical signals into a larger core multimode fiber
Data Source
AI summary
A multimode combiner or coupler (MMC) may combine the inputs into a larger core multimode fiber. The multimode combiner may be combined with a re-transmitting laser for detecting and re-transmitting signals. Thus, the multi-mode combiner may detect and combine input signals, and then retransmit the detected, combined signal. The detection can be implemented with multiple single mode fibers to small single mode detectors or a multi-mode coupler with a larger multi-mode detectors. In embodiments of the MMC, a bi-directional optical splitter/combiner includes a transmitter for re-transmitting an RF signal received at a receiver, a first wave division multiplexer (WDM) combiner combining the output of the first transmitter in an upstream direction to a downstream signal in a downstream direction, and a second WDM combiner combining split downstream signals in the downstream direction with upstream signals received via at least two optical fiber inputs.