DML Nonlinearity Pre-correction via Signal Segmentation
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Solution Overview
Problem
Directly modulated lasers (DMLs) experience bandwidth and nonlinearity limitations at higher data rates, leading to signal distortion and noise, making it difficult for receiving nodes to correctly decode the transmitted signal.
Innovation Solution
A method and system that pre-corrects the distortion of DMLs by decomposing input signals into sub-signals and filtering them using pre-equalization functions with specific transfer functions, which are configured to address different amplitude ranges, thereby generating a corrected signal to drive the laser.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If directly modulated lasers are used for high-speed optical transmission, then cost and power consumption are reduced, but bandwidth and nonlinearity limitations cause signal distortion
Solution Approach 1:
The patent applies preliminary action by pre-equalizing the input signal before it is modulated by the DML. The system decomposes the input signal into multiple sub-signals, applies different transfer functions to each sub-signal based on its amplitude range, and then combines them to produce a corrected signal that compensates for anticipated nonlinearities. This pre-correction ensures that when the signal passes through the DML's nonlinear transfer function, the output is minimized distortion, thereby maintaining signal transmission accuracy while using cost-effective DMLs.
2Speed
If directly modulated lasers operate at higher data rates, then transmission speed increases, but nonlinearity and bandwidth limitations worsen
Solution Approach 1:
The patent applies segmentation by dividing the input signal into multiple sub-signals based on their amplitude ranges. Each sub-signal is then processed with a dedicated transfer function that is optimized for its specific amplitude range. This segmentation allows the system to handle different portions of the signal spectrum with appropriate correction functions, enabling high data rate transmission while maintaining accuracy by addressing the nonlinearities specific to each amplitude segment.
Solution Approach 2:
The patent applies parameter changes by using multiple transfer functions with different characteristics tailored to different amplitude ranges. Instead of using a single fixed transfer function, the system adjusts the transfer function parameters dynamically based on the amplitude range of each sub-signal. This allows the system to compensate for the DML's nonlinearities effectively at high data rates, maintaining signal integrity and decoding accuracy.
3Reliability
If pre-equalization functions with multiple transfer functions are used, then signal distortion is reduced, but device complexity increases
Solution Approach 1:
The patent applies local quality by assigning different transfer functions to different amplitude ranges of the signal. Instead of using a uniform correction approach, the system tailors the correction characteristics locally for each amplitude segment. This allows the most appropriate transfer function to be applied to each portion of the signal, maximizing distortion compensation effectiveness while keeping the overall system manageable by organizing the complexity in a structured, amplitude-range-based manner.
Data Source
AI summary
In some implementations, the output of a directly modulated laser (DML) includes nonlinearities with respect to the input signal driving the DML. When the DML is transmitting an amplitude modulated signal, the nonlinearities can induce noise into the signal, which makes it difficult for a receiving node to correctly decode the received signal. The system and methods described herein pre-correct the error caused by the nonlinearities of the DML by filtering (or pre-correcting) the data signal that drives the DML.