Laser Diode Driver Multiple Current Sources Waveform Control
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Solution Overview
Problem
Conventional laser diode drivers using current-controlled devices struggle to precisely control the waveform of the modulation current, leading to degradation of the optical output waveform due to relaxation oscillation and resonance oscillation, especially in long-reach optical communication systems.
Innovation Solution
The proposed laser diode driver employs multiple switched current sources with bipolar transistors, allowing independent adjustment of current amplitude, phase, and pulse width, and incorporates an auto-power-control loop with a photodiode to maintain constant optical output, effectively suppressing resonance oscillation and improving the optical output waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If current-controlled devices such as bipolar transistors are used in the driver circuit, then the device complexity is reduced and ease of manufacture is improved, but the manufacturing precision and control precision of the modulation current waveform deteriorate due to large trans-conductance making precise analogue control difficult
Solution Approach 1:
The modulation current is divided into multiple independent current sources (first modulation current source and second modulation current source), each controlled by separate control signals. This segmentation allows precise control of different waveform parameters (amplitude, phase, pulse width) independently, overcoming the limitation of single current-controlled devices while maintaining ease of manufacture using bipolar transistors.
Solution Approach 2:
The driver circuit dynamically adjusts multiple current sources with independently controllable parameters. By varying the amplitude, phase, and pulse width of each current source dynamically according to control signals, the system achieves precise waveform control that adapts to different operating conditions, resolving the contradiction between using simple bipolar transistors and achieving precise analogue control.
2Device complexity
If a single modulation current source is used, then the device complexity is reduced, but the ability to control amplitude, phase, and pulse width independently deteriorates, limiting the capability to suppress resonance oscillation and improve output waveform
Solution Approach 1:
The single modulation current source is segmented into multiple independent current sources, each capable of being controlled separately. This allows independent adjustment of amplitude, phase, and pulse width parameters without significantly increasing overall system complexity, as each segment uses similar circuit topology controlled by dedicated signals.
Solution Approach 2:
Each current source is designed with multi-functionality to control multiple waveform parameters (amplitude, phase, pulse width) through independent control signals. This universal design allows the same circuit structure to perform multiple control functions, increasing adaptability without proportionally increasing device complexity.
3Device complexity
If the modulation current waveform is not precisely controlled, then the device complexity is reduced, but the optical output waveform degradation due to relaxation oscillation and resonance oscillation increases, especially in long-reach optical communication
Solution Approach 1:
The driver circuit incorporates feedback mechanisms where control signals are generated and adjusted based on desired output waveform characteristics. By using feedback control to adjust the amplitude, phase, and pulse width of multiple current sources, the system precisely controls the modulation current waveform to suppress relaxation oscillation and resonance oscillation, improving optical output quality without excessive complexity.
Solution Approach 2:
The circuit applies preliminary anti-action by pre-shaping the modulation current waveform through multiple controlled current sources before it reaches the laser diode. By anticipatorily adjusting the waveform parameters (amplitude, phase, pulse width) to counteract expected relaxation oscillation and resonance oscillation effects, the system prevents waveform degradation before it occurs, improving reliability without complex post-correction mechanisms.
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 solution enables precise control of the modulation current waveform, reducing transmission penalties and maintaining optical output stability across varying conditions, thereby enhancing the performance of long-reach optical communication systems.
Implementation Method 1
The photo diode monitors a portion of an optical output from the LD
Implementation Method 2
The LD-driver drivers the LD by receiving a driving signal and applying a modulation current modulated by the received driving signal
Data Source
AI summary
The present invention is to provide an LD-driver that enables to adjust the waveform of the driving current to the LD even the driver is constituted with a current controlled device such as bipolar transistor. The LD-driver of the invention provides a plurality of modulation current sources each having a function to set the amplitude, the phase and the pulse width of the current output independently. The LD is provided with the modulation current superposed with each current derived from respective current sources.