Non-linear VCSEL Equalization for Signal Distortion
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Solution Overview
Problem
Vertical-cavity surface-emitting lasers (VCSELs) face challenges in accurately converting electrical input signals to optical output signals due to non-linear modulation transfer functions, resulting in distortions at the rising and falling edges of electrical pulses, which existing technologies have not effectively addressed.
Innovation Solution
A method and system for non-linear VCSEL equalization are introduced, involving the determination of rising and falling edge tap parameters and equalization delay based on isolated-pulse-VCSEL responses and data rates, with adjustments made to the data signal using these parameters and a bias current to reduce distortions in the optical output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If VCSELs are used to convert electrical input signals to optical output signals, then optical capabilities can be provided to semiconductor-based integrated circuits, but non-linear modulation transfer functions cause distortions at the rising and falling edges of electrical pulses
Solution Approach 1:
The patent applies preliminary action by performing equalization processing on the electrical input signal before it is converted to optical signals by the VCSEL. The equalization circuit pre-distorts the electrical signal in a controlled manner using tap parameters and delay elements, so that after VCSEL conversion, the output optical signal accurately reproduces the original data signal. This anticipates and compensates for the non-linear modulation transfer function effects before they occur.
Solution Approach 2:
The patent implements feedback by measuring the actual VCSEL modulation transfer function characteristics and using this information to calculate and adjust the equalization tap parameters. The system characterizes the VCSEL device and uses this feedback information to optimize the equalization coefficients, creating a closed-loop system that adapts to the specific VCSEL device being used.
2Productivity
If standard semiconductor processes are used to fabricate VCSELs, then tens of thousands of VCSELs can be processed on a single wafer, but existing technologies have not effectively addressed the non-linear distortion issues
Solution Approach 1:
The patent applies self-service by implementing the equalization function within the VCSEL system itself through an integrated equalization circuit. Rather than requiring external correction systems, the VCSEL module includes its own equalization capabilities that automatically compensate for its non-linear characteristics, making the system self-correcting and maintaining high signal quality without additional external complexity.
3Ease of manufacture
If VCSELs emit light perpendicular to the surface, then easy fabrication and testing are achieved, but non-linear modulation causes edge distortions in the optical output
Solution Approach 1:
The patent introduces an intermediary equalization circuit between the electrical input signal source and the VCSEL optical converter. This intermediary component processes the electrical signal to pre-compensate for the VCSEL's non-linear modulation transfer function, acting as a mediator that ensures accurate signal transmission while allowing the VCSEL to maintain its simple perpendicular emission geometry and easy fabrication characteristics.
Data Source
AI summary
Technologies are generally described for implementing non-linear VCSEL equalization. In some examples, a rising edge tap parameter, a falling edge tap parameter, an equalization delay and a bias current may be used to equalize a data signal to be output from a VCSEL. A VCSEL model may be used to derive a VCSEL response to one or more isolated data pulses. The derived response may then be used to determine the rising and falling edge tap parameters and an equalization delay, based on a bias current value for the VCSEL and a data rate associated with the data signal. The data signal may then be adjusted based on the equalization delay and the rising and falling edge tap parameter and sent to the VCSEL for output. At the same time, the VCSEL may be biased with a bias current having the bias current value.