Optical Equalizer Placement for Multi-Level Signal Compensation
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Solution Overview
Problem
Existing optical communication systems with non-binary symbol constellations, such as DQPSK formats, face bandwidth limitations due to modulator constraints, and prior art suggests placing optical equalizers at the transmitter end, which is not effective for compensating non-linear mapping and noise addition in multi-level signal formats.
Innovation Solution
An optical equalizer can be placed at either the transmission or receiver end of the optical communications link, with adjustable tap delay characteristics to compensate for non-linear mapping and simultaneous operation on multiple WDM channels, allowing for effective equalization of multi-level optical signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an optical equalizer is placed at the transmitter end as suggested by prior art, then the device complexity is reduced, but the equalization effectiveness for multi-level signal formats deteriorates due to inability to compensate non-linear mapping and noise addition
Solution Approach 1:
The patent inverts the conventional placement of the optical equalizer from the transmitter end to the receiver end. This inversion allows the equalizer to process signals after non-linear mapping and noise addition have occurred, thereby achieving effective equalization for multi-level signal formats while maintaining device complexity at acceptable levels
2Device complexity
If the tap delay characteristic is determined by symbol spacing, then the equalizer structure is simplified, but the compensation capability for non-linear mapping and WDM channels is insufficient
Solution Approach 1:
The patent changes the tap delay parameter from being determined by symbol spacing to being adjustable to compensate for non-linear mapping effects and to support simultaneous operation on multiple WDM channels. This parameter adjustment enables the equalizer to adapt to different signal formats and channel configurations while maintaining a relatively simple structure
Data Source
AI summary
A method of optically equalizing a multi-level (amplitude or phase) optical signal through the effect of an optical equalizer wherein the optical equalizer (OEQ) is placed at either a transmission end or a receiver end of the optical communications link and a tap delay characteristic of the OEQ need not be determined by symbol spacing, rather it may advantageously be adjusted to desirably compensate non-linear mapping performed in the modulation process or simultaneous operation on a plurality of wavelength division multiplexed (WDM) channels.