LD Driver Asymmetrical Current for Optical Waveform Symmetry
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Solution Overview
Problem
Shunt driver configurations for laser diodes (LDs) suffer from asymmetrical optical waveform output due to the carrier relaxation mechanism, leading to degraded performance, especially at high transmission speeds, and existing solutions like pre-emphasizing or de-emphasizing driving signals do not adequately compensate for this asymmetry.
Innovation Solution
An LD driver with a delay unit, primary driver, and sub-driver is used to generate driving currents by subtracting the sum of primary and sub-currents from an external bias current, enhancing both the rising and falling edges of the driving current to compensate for the asymmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pre-emphasizing or de-emphasizing driving signal is used, then the optical waveform output is adjusted, but the asymmetry of the optical waveform cannot be compensated
Solution Approach 1:
The patent applies preliminary action by generating a peaking signal in advance that is added to the original driving signal before the LD modulation. This pre-emphasis technique compensates for the intrinsic asymmetry of the LD output waveform by modifying the input signal characteristics beforehand, rather than attempting to correct the asymmetry after it occurs. The peaking signal is designed to counteract the expected waveform distortion, achieving symmetric optical output through advance signal conditioning.
2Use of energy by moving object
If shunt driver configuration with FET is used, then power consumption is reduced, but the response in driving current degrades due to input capacitance
Solution Approach 1:
The patent applies asymmetry by introducing a peaking signal that is asymmetric in nature to counteract the asymmetric degradation caused by the FET input capacitance. The peaking signal is designed with specific amplitude and timing characteristics that are not symmetric, allowing it to compensate for the capacitive effects that differently affect the rising and falling edges of the driving current. This asymmetric correction restores the driving current response speed while maintaining the low power consumption advantage of the shunt configuration.
3Use of energy by moving object
If shunt driver configuration is used, then signal to modulate active device is reduced, but the optical waveform output is degraded compared to series driver
Solution Approach 1:
The patent applies preliminary action by pre-modulating the driving signal with a peaking component before it reaches the LD. This advance signal conditioning compensates for the waveform degradation that would otherwise occur in the shunt configuration. By modifying the input signal characteristics beforehand, the system achieves improved optical waveform quality comparable to series driver configurations while maintaining the power consumption benefits of the shunt architecture.
Data Source
AI summary
An LD driver to generate an asymmetrical driving current with a relatively faster falling edge and an optical transmitter having the LD driver are disclosed. The LD driver includes a primary driver and the sub-driver connected in parallel to the primary driver. The primary driver converts the input signal or the delayed signal delayed from the input signal into the primary current. The sub-driver generates a symmetrical current tracing the input or the delayed signal, and an asymmetrical current formed by the OR operation between the input and delayed signals. The driving current is formed by adding the primary current, the symmetrical current and the asymmetrical current.