Active Optical Combiner for RFoG Networks
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Solution Overview
Problem
Optical Beat Interference (OBI) limits upstream and downstream traffic in traditional RFoG networks, and existing mitigation techniques are either ineffective or costly.
Innovation Solution
An active optical combiner system that separates and amplifies upstream signals at each port, eliminating OBI by individually terminating reverse optical signals at detectors, reducing the need for high-power EDFAs and minimizing noise, allowing for longer fiber lengths and higher split counts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional RFoG networks use multiple reverse path transmitters, then upstream traffic capacity increases, but Optical Beat Interference limits both upstream and downstream traffic
Solution Approach 1:
The patent segments the reverse path signal handling by providing separate dedicated receivers at the headend for each ONU, rather than combining signals optically. Each receiver independently processes signals from specific ONUs, eliminating OBI while maintaining upstream capacity.
Solution Approach 2:
The patent introduces wavelength division multiplexing as an intermediary mechanism, using different wavelengths for downstream and upstream paths, and dedicated receivers tuned to specific wavelengths, thereby separating upstream signals in the wavelength domain to eliminate OBI.
2Length of stationary object
If in-line RF amplifiers are placed to compensate for coaxial cable losses, then signal transmission distance increases, but system cost and complexity increase
Solution Approach 1:
The patent replaces the mechanical/electrical RF amplifier system with an optical system. By using optical carriers and optical receivers, the system eliminates the need for RF amplifiers and associated complex impedance matching, filtering, and stabilization circuits.
3Length of stationary object
If optical amplifiers are used to extend fiber reach, then transmission distance increases, but noise increases requiring costly noise-reducing equipment
Solution Approach 1:
The patent uses direct detection with photodiodes that convert optical signals to electrical signals without requiring expensive optical amplifiers. This approach accepts shorter fiber spans but eliminates the need for costly noise-reducing equipment by avoiding optical amplification entirely.
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
The active optical combiner system significantly enhances upstream and downstream capacity, supports higher bandwidths, and reduces costs by eliminating OBI, enabling longer fiber reaches and larger splits without the need for costly noise-reducing equipment.
Implementation Method 1
individually terminating reverse optical signals at detectors
Implementation Method 2
amplifies upstream signals
Data Source
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AI summary
An optical combiner for a communications network transmitting both upstream signals and a downstream optical signal. The communications network includes an array of amplifiers, each receiving a respective instance of the downstream optical signal. The output of each amplifier is split among a plurality of ports in a first splitter/combiner unit. The first splitter/combiner unit transmits the amplified downstream optical signal to respective second splitter/combiner units.