Coherent Optical Receiver Using Polarization Multiplexing
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Solution Overview
Problem
The existing optical receivers in coherent optical communication systems require complex analog addition and subtraction operations, which can be simplified by converting optical signals to digital signals earlier in the process, reducing the number of components needed.
Innovation Solution
An optical receiver configuration that combines local and signal lights of orthogonal polarizations, converts these signals into electric signals using photodiodes, and performs necessary operations to generate Stokes parameters for demodulation, allowing for simpler analog processing and subsequent digital computation, using fewer photodiodes and analog-to-digital converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two 90° optical hybrid circuits, four balanced receivers, and four ADCs are used for coherent optical reception, then demodulation capability is achieved, but device complexity is high
Solution Approach 1:
The patent combines multiple optical hybrid circuits into a single integrated optical hybrid circuit that performs both I and Q channel demodulation functions. This merging reduces the total number of separate components while maintaining the necessary demodulation capabilities through shared optical and electronic resources.
Solution Approach 2:
The optical hybrid circuit is designed to perform multiple functions simultaneously - it can demodulate both I and Q channels using the same optical components, and the balanced receivers can serve multiple detection purposes. This multi-functionality reduces the overall component count while preserving demodulation performance.
2Device complexity
If three PDs and two ADCs are used with 3×3 couplers, then device complexity is reduced, but complicated weighted addition/subtraction must be performed in analog domain
Solution Approach 1:
The patent replaces complex analog weighted addition and subtraction operations with simpler digital signal processing operations. By converting the optical signals to electrical signals first using the reduced PD configuration, and then performing the necessary addition/subtraction operations in the digital domain through the ADCs and subsequent processing, the system eliminates the need for complicated analog weighting circuits while maintaining computational accuracy.
3Ease of operation
If three electric signals are converted to digital signals using three ADCs, then analog processing is simplified, but device complexity increases due to additional ADC
Solution Approach 1:
The patent merges the functionality of multiple ADCs into a single ADC by utilizing the optical hybrid circuit's ability to combine multiple optical signals before detection. This allows the system to perform demodulation of multiple channels through a single analog-to-digital conversion, reducing the total number of ADCs required while maintaining the capability to process multiple signal components.
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 coherent optical reception with a simpler setup compared to previous systems, reducing the complexity of analog operations and potentially lowering processing loads while maintaining effective demodulation capabilities.
Implementation Method 1
first conversion means for converting the first combined light to a first electric signal
Implementation Method 2
second conversion means for converting a component of the first combined light that has passed through the first polarization means to a second electric signal
Implementation Method 3
third conversion means for converting a component of the first combined light that has passed through the first delay means and the second polarization means to a third electric signal
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An optical receiver includes: means for outputting first combined light by combining local light of first polarization and signal light of second polarization that is orthogonal to the first polarization; means for converting the first combined light to a first electric signal; first polarization means for allowing a component of polarization plane having an angle of 45 degrees relative to each of polarization planes of the first polarization and the second polarization to pass through; means for converting a component of the first combined light that has passed through the first polarization means to a second electric signal; first delay means for delaying light of the first polarization or the second polarization by 1/4 wavelength; second polarization means for allowing a component of polarization plane having an angle of 45 degrees relative to each of polarization planes of the first polarization and the second polarization to pass through; means for converting a component of the first combined light that has passed through the first delay means and the second polarization means to a third electric signal; means for outputting a fourth electric signal and a fifth electric signal by branching the first electric signal; means for subtracting the fourth electric signal from the second electric signal; and means for subtracting the fifth electric signal from the third electric signal.