Orthogonal Polarization Optical Source for SMF Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In communications network base stations, the use of single mode fibre (SMF) for optical links up to 10 Km leads to random fluctuations in the state of polarization of optical signals due to temperature and external forces, causing intensity variations and poor performance of single-polarization devices like optical modulators, while the use of polarization maintaining fibre (PMF) is costly and attenuated.
Innovation Solution
An optical source comprising two lasers with orthogonal polarization states and frequencies, combined using a polarization beam coupler, generates a composite optical signal that maintains optical power within a preselected range across long SMF lengths, using a preselected frequency difference inversely proportional to polarization mode dispersion, ensuring stability against SOP variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If single mode fibre (SMF) is used for optical links up to 10 Km, then cost is reduced and attenuation is lowered, but state of polarization fluctuates randomly causing intensity variations and poor performance of single-polarization devices
Solution Approach 1:
The optical signal is segmented into two separate laser sources with orthogonal polarization states. Each laser generates an unmodulated optical signal with a distinct polarization state (one horizontal, one vertical), and these segmented signals are combined through a polarization beam coupler to form a composite signal that maintains stable optical power despite SOP fluctuations in the SMF.
Solution Approach 2:
The patent creates a composite optical signal by combining two distinct optical signals with orthogonal polarization states. This composite signal behaves differently from individual polarized signals in SMF, as the combined signal maintains stable optical power at the receiver even when the SOP fluctuates, effectively creating a new type of optical transmission medium with improved polarization stability.
2Reliability
If polarization maintaining fibre (PMF) is used to maintain state of polarization, then polarization stability is improved, but cost increases around 30 times and attenuation increases
Solution Approach 1:
Instead of using expensive PMF to physically maintain polarization, the patent creates a virtual copy of the polarization-maintaining effect through signal processing. By transmitting two orthogonal polarized signals simultaneously and combining them at the receiver, the system replicates the polarization stability benefits of PMF using standard SMF, effectively copying the desired behavior without the high cost.
3Device complexity
If laser source and optical device are integrated, then connection complexity is reduced, but distance between source and device is limited to short ranges
Solution Approach 1:
The patent creates a universal optical signal that can be transmitted over long distances through SMF while maintaining compatibility with single-polarization devices. The composite signal formed by combining two orthogonal polarized lasers serves multiple functions: it maintains stable optical power over long distances, is compatible with standard SMF infrastructure, and works with single-polarization optical devices, effectively making the signal adaptable to various transmission scenarios.
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 allows for stable optical signal transmission with minimal power variations, maintaining performance across tens of km of SMF, reducing the need for costly PMF and minimizing signal degradation due to thermal variations.
Implementation Method 1
a first laser arranged to generate a first unmodulated optical signal having a first state of polarisation and a first optical frequency
Implementation Method 2
a second laser arranged to generate a second unmodulated optical signal having a second state of polarisation and having a second optical frequency
Implementation Method 3
a polarisation beam coupler arranged to combine the first unmodulated optical signal and the second unmodulated optical signal into a composite optical signal comprising both the first unmodulated optical signal and the second unmodulated optical signal
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An optical source (10) comprising: a first laser (12) arranged to generate a first optical signal (14) having a first state of polarisation and a first optical frequency; a second laser (16) arranged to generate a second optical signal (18, 48, 78) having a second state of polarisation, substantially orthogonal to the first state of polarisation, and having a second optical frequency, different to the first optical frequency by a preselected frequency difference, Δν; a polarisation beam coupler (20) arranged to combine the first optical signal and the second optical signal into a composite optical signal comprising both the first optical signal and the second optical signal having said substantially orthogonal states of polarisation; and an output (22) arranged to output the composite optical signal (24).