Optical Source Polarization Stability Faraday Rotator Mirror
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Solution Overview
Problem
The challenge in communications network base stations is maintaining the state of polarization (SOP) of optical signals over long single-mode fibers, as temperature and external forces cause fluctuations, leading to performance issues with single-polarization devices, and existing solutions like polarization maintaining fibers are costly and attenuate signal strength.
Innovation Solution
An optical source comprising a reflective optical amplifier and a faraday rotator mirror that generates amplified spontaneous light emission with a narrower bandwidth by rotating polarizations, allowing for efficient transmission over tens of kilometers while maintaining SOP, using an optical power splitter to direct signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polarization maintaining fibre is used to deliver optical signals, then the state of polarization is maintained, but the cost increases significantly and attenuation is higher
Solution Approach 1:
The invention changes the spectral parameter of the optical source from broad bandwidth (ASE) to narrow bandwidth (laser-like), which fundamentally alters how the signal interacts with the fibre's polarization properties. This parameter change enables the use of standard single-mode fibre while maintaining polarization stability, avoiding both the high cost and high attenuation of polarization-maintaining fibre.
2Reliability
If unpolarised ASE light source is used, then SOP fluctuations are avoided, but the bandwidth is too wide for long distance transmission
Solution Approach 1:
The invention transforms the spectral bandwidth parameter from wide (ASE) to narrow (laser-like) while preserving the polarization stability benefit. This is achieved by using a laser source that generates coherent light with a narrow spectral width, enabling long-distance transmission through standard single-mode fibre without chromatic dispersion issues.
3Length of moving object
If laser with multiple longitudinal modes is used, then bandwidth is reduced, but mode competition requires complex control systems
Solution Approach 1:
The invention uses a simple distributed feedback (DFB) laser or external cavity laser that naturally produces single-mode or few-mode operation without requiring complex active control systems. The laser's physical structure (grating or cavity design) inherently suppresses mode competition, eliminating the need for costly and complex monitoring and control apparatus.
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 configuration enables stable transmission of optical signals with reduced power fluctuations and narrower bandwidth, ensuring good performance of single-polarization devices, such as modulators, over long distances with lower costs compared to traditional solutions.
Implementation Method 1
generate an optical signal, the optical signal comprising an amplified spontaneous light emission having a plurality of light modes
Implementation Method 2
a reflective mirror, spaced from the reflective optical amplifier, and arranged to receive the optical signal and to rotate a polarisation of each light mode in the received optical signal
Data Source
AI summary
There is provided an optical source. The optical source comprises a reflective optical amplifier configured to generate an optical signal, the optical signal comprising an amplified spontaneous light emission having a plurality of light modes each having a respective wavelength. The optical source further comprises a reflective mirror, spaced from the reflective optical amplifier, and arranged to receive the optical signal and to rotate a polarization of each light mode in the received optical signal, to form a further optical signal. The optical source further comprises an optical power splitter arranged to receive the further optical signal and to split the further optical signal into a first optical signal which is directed to the reflective optical amplifier for amplification thereby, and a second optical signal. The optical source further comprises an output arranged to output the second optical signal. There is also provided a communications network optical apparatus and a communications network base station.