Spatial Multiplexing Receiver With Independent CW Local Oscillators
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Solution Overview
Problem
The high cost and complexity of polarization-maintaining optical devices in coupled spatial multiplexing optical transmission systems, due to the need for common CW light in all modes, and the increased branching loss with multiple channels, hinder efficient signal reception.
Innovation Solution
A spatial multiplexing optical receiver using independent CW light for each mode as local oscillator light, combined with frequency offset compensation and MIMO signal processing, to reduce the need for expensive polarization-maintaining devices and simplify the optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If common CW light is used in all modes to maintain polarization state, then reception reliability is improved, but device complexity and cost increase due to polarization-maintaining devices
Solution Approach 1:
The patent divides the optical receiver into multiple independent coherent receivers, each handling a specific spatial channel. Each coherent receiver uses independent CW light sources rather than sharing a common light source, allowing parallel processing of multiple modes without requiring polarization-maintaining devices for the entire system.
Solution Approach 2:
The patent applies different approaches to different parts of the system: each coherent receiver is designed to be polarization-insensitive locally, using independent CW light sources and polarization diversity reception. This eliminates the need for system-wide polarization-maintaining devices while maintaining reception reliability for each spatial channel.
2Reliability
If common CW light is used in all modes, then signal synchronization is improved, but loss of energy increases due to branching loss in optical couplers
Solution Approach 1:
The patent segments the light source allocation so that each coherent receiver has its own independent CW light source. This eliminates the need for optical couplers to branch a common light source to multiple receivers, thereby removing the source of branching loss while maintaining signal synchronization through independent frequency offset compensation for each receiver.
3Reliability
If polarization-maintaining devices are used, then reception characteristics are improved, but cost of receiver increases
Solution Approach 1:
The patent replaces expensive polarization-maintaining devices with cheaper polarization-insensitive components. Each coherent receiver uses standard optical components that do not require polarization maintenance, significantly reducing the cost of the receiver while achieving comparable reception characteristics through polarization diversity reception and frequency offset compensation.
4Ease of operation
If uncoupled system with small coupling between spatial channels is used, then ease of operation is improved by using existing optical transceivers, but productivity decreases due to limit on number of spatial channels
Solution Approach 1:
The patent changes the coupling parameter from small (uncoupled) to large (coupled), enabling the use of coupled spatial multiplexing with MIMO signal processing. This allows a greater number of spatial channels to be transmitted simultaneously over the same optical fiber, increasing transmission capacity while using standardized coherent receivers that maintain ease of operation.
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 approach reduces the cost of the receiver by eliminating the need for polarization-maintaining devices and improves reception characteristics by compensating for frequency offsets before MIMO signal processing, thereby enhancing the efficiency of the optical transmission system.
Implementation Method 1
a plurality of coherent receivers configured to coherently receive each of signals of a plurality of modes spatially multiplexed and transmitted
Implementation Method 2
a plurality of frequency offset compensators configured to perform, independently for each mode, frequency offset compensation based on a correlation between a known training signal and a signal of each mode
Data Source
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AI summary
A spatial multiplexing optical receiver includes a plurality of coherent receivers configured to coherently receive each of spatially multiplexed and transmitted signals of a plurality of modes by using continuous wave light independent for each mode as local oscillator light, a plurality of frequency offset compensators configured to perform frequency offset compensation based on a correlation between a known training signal and a signal of each mode independently for each mode, for each of the coherently received signals of the plurality of modes, and a MIMO signal processing unit configured to perform MIMO signal processing on the signals of the plurality of modes subjected to the frequency offset compensation in the frequency offset compensator.