Passive Optical Network Phase-to-Amplitude Conversion
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Solution Overview
Problem
Passive optical networks face limitations in range and chromatic dispersion due to the use of a single optical fiber for both downlink and uplink signals, which restricts transmission rates beyond 10 Gbits/s and introduces distortions, making it challenging to maintain high-speed connections, especially in rural areas where subscribers are farther from optical exchanges.
Innovation Solution
The implementation of a passive optical network that uses phase-modulated downlink optical data signals in NRZ-DPSK format, converted to amplitude-modulated duobinary format at the line termination device, combined with remote amplification and Gaussian filtering, to reduce chromatic dispersion and extend network range while maintaining the passive nature of the network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single optical fiber is used for both downlink and uplink signals to reduce network costs, then network cost-effectiveness is improved, but chromatic dispersion and signal distortion increase, limiting transmission rates beyond 10 Gbits/s
Solution Approach 1:
The patent segments the optical signal processing into distinct functional blocks: a phase-to-amplitude converter that transforms phase-modulated downlink signals into amplitude-modulated signals, and a separate upstream signal generator. This segmentation allows each component to be optimized for its specific function, enabling high-rate transmission while maintaining passive network architecture.
Solution Approach 2:
The patent changes the modulation parameter from phase modulation (NRZ-DPSK) in the downlink to amplitude modulation in the converted signal. This parameter change enables the use of simpler detection methods and reduces the impact of chromatic dispersion, allowing transmission rates to exceed 10 Gbits/s while using the same single optical fiber for both directions.
2Reliability
If transmission power is increased to compensate for optical losses in passive networks, then signal reception quality is improved, but backscattered signals increase, causing reception interference
Solution Approach 1:
The patent introduces an intermediary conversion process where phase-modulated signals are transformed into amplitude-modulated signals before detection. This intermediary step acts as a mediator that allows the system to operate with lower transmission powers, as the amplitude conversion process is more tolerant of signal attenuation and reduces the generation of harmful backscattered signals.
3Length of stationary object
If network range is extended to serve rural areas, then subscriber coverage is improved, but chromatic dispersion accumulates, distorting optical signals
Solution Approach 1:
The patent replaces complex active compensation mechanisms with a passive optical conversion approach. By substituting the need for active signal regeneration and chromatic dispersion compensation devices with a passive phase-to-amplitude conversion process, the system can extend network range to rural areas while maintaining signal integrity through inherently dispersion-tolerant amplitude modulation.
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 compensates for chromatic dispersion and increases the network range, enabling high-speed connections up to 40 Gbits/s, thereby serving rural areas and maintaining the passive network's cost-effectiveness by reducing spectral clutter and backscattering issues.
Implementation Method 1
transmitting a phase-modulated downlink optical data signal in NRZ-DPSK format
Implementation Method 2
first means for converting said first downlink optical signal, phase modulated in NRZ-DPSK format, into an amplitude modulated optical data signal in duobinary modulation format
Implementation Method 3
second means for converting said upward optical signal, phase modulated in NRZ-DPSK format, into an optical data signal modulated in amplitude in duobinary modulation format
Implementation Method 4
a circulator 13, capable of circulating the optical signals going down and up in the single optical fiber 20
Data Source
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AI summary
The invention relates to a passive optical network comprising an optical hub linked by at least one optical fibre to at least one line termination device of said network, able to emit a downgoing optical signal phase modulated in the NRZ-DPSK format and to receive an upgoing optical signal. According to the invention, said line termination device comprises means for converting the downgoing optical signal phase modulated in the NRZ-DPSK format transmitted into an optical data signal amplitude modulated in the duobinary modulation format and means for generating an upgoing optical signal phase modulated in the NRZ-DPSK format on the basis of the downgoing optical signal phase modulated in the NRZ-DPSK format. The optical hub is able to convert the upgoing optical signal phase modulated in the NRZ-DPSK format into an optical data signal amplitude modulated in the duobinary modulation format.