Optical Fiber Phase Noise Correction via Polarization Separation
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Solution Overview
Problem
Radio frequency over fiber networks face phase noise and drift issues due to temperature and pressure sensitivity of optical fibers, which existing solutions like frequency modulation address at a high cost by requiring additional frequency sources and signal paths.
Innovation Solution
A system that includes an optical signal module for amplitude-modulating signals, a beam splitter for separating backward traveling waves based on polarization, a polarization rotator, and a partially reflecting reflector to create a feedback loop for phase stabilization, using the same fiber for both signal transmission and feedback without additional frequency sources or signal paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency modulation schemes are used to overcome phase noise, then phase stabilization is achieved, but additional frequency sources and signal paths are required increasing system complexity and cost
Solution Approach 1:
The patent combines the forward signal path and feedback path into a single optical fiber, eliminating the need for separate signal paths. The beam splitter separates backward traveling waves within the same fiber, and the polarization rotator manipulates polarization states to enable phase noise detection and cancellation using the same physical medium for both transmission and feedback.
Solution Approach 2:
The optical fiber serves multiple functions: it carries the forward modulated optical signal from source to receiver, and simultaneously carries the backward traveling wave from receiver to source for phase noise detection. This multi-functionality eliminates the need for dedicated feedback fibers or additional frequency sources, reducing system complexity while maintaining phase stabilization.
2Reliability
If additional feedback loops and components are added for phase stabilization, then phase noise is reduced, but system cost increases
Solution Approach 1:
The system uses the received signal itself as the feedback source. The backward traveling wave is generated by reflections at the receiver end of the same fiber carrying the forward signal. This self-service approach eliminates the need for separate local oscillators or reference signals, reducing component count and system cost while achieving phase noise cancellation through the feedback loop.
3Device complexity
If the same fiber is used for both signal transmission and feedback, then system complexity is reduced, but signal interference may occur
Solution Approach 1:
The system creates asymmetry in polarization states between forward and backward traveling waves using the polarization rotator. The forward signal maintains its original polarization, while the backward wave has its polarization rotated by 90 degrees. The beam splitter exploits this polarization asymmetry to separate the backward wave from the forward signal, preventing interference while allowing both to coexist in the same fiber.
Solution Approach 2:
The beam splitter acts as an intermediary that separates backward traveling waves from forward traveling waves based on polarization. It directs the backward wave to the photodiode for phase noise detection while allowing the forward signal to continue to the receiver, preventing signal interference and enabling simultaneous operation of both paths in the same fiber.
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 stabilizes the phase of optical signals transmitted, canceling out temperature, pressure, and other effects influencing the refractive index, while being cost-efficient and capable of operating in harsh environments without passive stabilization.
Implementation Method 1
an optical signal module (23) that is capable of amplitude-modulating an optical signal while being phase- and/or frequency-shifted
Implementation Method 2
a beam splitter (24) that is capable of separating at least backward travelling waves based on polarization
Implementation Method 3
a polarization rotator (32) capable of changing the polarization of the modulated optical signal
Implementation Method 4
a partially reflecting reflector (36) capable of creating a backward travelling wave
Implementation Method 5
a photodiode (38) capable of receiving the backward travelling wave created by the partially reflecting reflector. The photodiode is capable of generating a detection signal used for detecting phase noise and/or drift
Data Source
AI summary
A system for correcting phase noise and/or drift, the system includes an optical signal module being capable of amplitude modulating the optical signal while being phase- and/or frequency-shifted. Further, the system includes a beam splitter capable of separating at least backward travelling waves based on polarization. Moreover, a fiber connected to the beam splitter and a polarization rotator capable of changing the polarization of the optical signal are provided. The system has a partially reflecting reflector capable of creating a backward travelling wave as well as a photodiode capable of receiving the backward travelling wave. The photodiode is capable of generating a detection signal used for detecting phase noise and/or drift in the backward travelling wave.