Optical Fiber Phase Noise Correction Using Polarization Separation
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Solution Overview
Problem
Radio frequency over fiber networks face challenges in correcting phase noise and drift due to temperature and pressure sensitivity of optical fibers, which existing solutions address with cost-intensive frequency modulation schemes requiring additional sources and paths.
Innovation Solution
A system comprising an optical signal module, optical transport module, sampling module, analysis circuit, and measurement instrument that uses a beam splitter, polarization rotator, and partially reflecting reflector to generate an electric correction signal for phase noise correction, eliminating the need for additional frequency sources or signal paths by utilizing the same fiber for feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency modulation schemes are used to correct phase noise, then phase noise correction is achieved, but device complexity and cost increase due to additional frequency sources and signal paths
Solution Approach 1:
The patent combines the correction signal generation and feedback functions into the existing optical fiber infrastructure. The same fiber that carries the measurement signal also carries the correction signal back to the source, eliminating the need for separate correction signal paths and additional frequency sources.
Solution Approach 2:
The optical fiber is made multi-functional by using it both for transmitting the measurement signal from the measurement instrument to the remote location and for transmitting the correction signal generated at the remote location back to the measurement instrument. This universal usage eliminates additional components.
2Reliability
If frequency modulation schemes are used to correct phase noise, then phase noise correction is achieved, but cost increases due to additional components
Solution Approach 1:
The patent merges the correction signal path with the existing measurement signal path by using the same optical fiber for both directions, thereby eliminating the need for additional expensive components such as separate lasers, modulators, and transmission fibers that would be required in conventional frequency modulation-based correction systems.
Solution Approach 2:
The system generates the correction signal at the remote location where the phase noise actually occurs, using local resources (the received optical signal itself as a reference), and feeds it back through the existing infrastructure. This self-service approach eliminates dependence on additional centralized correction equipment.
3Device complexity
If the same fiber is used for both measurement and correction signals, then device complexity is reduced, but signal interference may occur
Solution Approach 1:
The patent introduces asymmetry in the signal paths by using different polarization states for the measurement signal and the correction signal. The polarization rotator ensures that the correction signal travels through the fiber in a different polarization state than the measurement signal, allowing the beam splitter to separate them effectively and prevent interference.
Solution Approach 2:
The beam splitter acts as an intermediary device that separates the measurement signal and the correction signal based on their different polarization states. This mediator allows both signals to coexist in the same optical fiber without interfering with each other, enabling the system to maintain low complexity while avoiding signal interference.
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 system effectively corrects phase noise and drift in radio frequency over fiber networks with reduced complexity and cost, maintaining signal polarization and scalability, while minimizing losses and allowing for high-frequency measurements across large distances.
Implementation Method 1
The at least one optical signal transport module comprises a beam splitter capable of separating at least backward travelling waves based on polarization
Implementation Method 2
The at least one optical signal transport module further comprises a polarization rotator capable of changing the polarization of the modulated optical signal
Implementation Method 3
The at least one optical signal transport module further comprises a partially reflecting reflector capable of creating a backward travelling wave
Data Source
AI summary
A system for correcting phase noise and/or drift includes an optical signal module, at least one optical transport module, at least one sampling module, an analysis circuit, and a measurement instrument. The optical signal module is capable of outputting a modulated optical signal. The at least one optical signal transport module includes a beam splitter capable of separating at least backward travelling waves based on polarization. The at least one optical signal transport module further includes a partially reflecting reflector capable of creating a backward travelling wave, the partially reflecting reflector being located after the polarization rotator. The at least one sampling module is configured to receive and sample the backward travelling wave created by the partially reflecting reflector and forwarded to the at least one sampling module by the beam splitter, thereby obtaining an electric correction signal. The analysis circuit is configured to correct measurement data obtained by the measurement instrument based on the electric correction signal.