Optical Transmission Module Bias Current Control
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Solution Overview
Problem
Existing optical transmission modules face challenges in achieving a desirable extinction ratio due to non-linear characteristics between optical output power and drive current, especially in high temperature conditions, where secular degradation of laser diodes leads to reduced optical output power and extinction ratio when using conventional APC control.
Innovation Solution
An optical transmission module and control method that include a bias current drive circuit, modulation current drive circuit, light-receiving element, determiner, and controller to measure and correct the bias current based on differences between target and measured optical output power, reducing the bias current when the difference exceeds a threshold to maintain a desirable extinction ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional APC control is used to maintain optical output power, then optical output power is stabilized, but extinction ratio degrades due to non-linear characteristics in high temperature conditions
Solution Approach 1:
The patent implements a feedback control mechanism where the optical output power is measured by a light receiving element, compared with a target value, and the bias current is adjusted based on the difference. This closed-loop feedback system detects when the difference exceeds a threshold and automatically corrects the bias current to maintain both optical output power stability and extinction ratio performance.
Solution Approach 2:
The patent changes the control parameter from fixed bias current to dynamically adjustable bias current based on measured optical output power. By monitoring the actual optical output power and adjusting the bias current accordingly, the system adapts to non-linear characteristics and secular degradation, maintaining desirable extinction ratio while stabilizing optical output power.
2Stability of the object's composition
If bias current is increased to compensate for secular degradation, then optical output power is maintained, but non-linear characteristics worsen and extinction ratio decreases
Solution Approach 1:
The feedback control mechanism measures the actual optical output power, compares it with the target value, and adjusts the bias current only when the difference exceeds a threshold. This prevents excessive bias current adjustment that would exacerbate non-linear characteristics, thereby maintaining both optical output power and extinction ratio.
Solution Approach 2:
The patent applies partial correction by only adjusting the bias current when the difference between measured and target optical output power exceeds a predetermined threshold. This avoids excessive correction that would push the operating point into the non-linear range, thus preventing degradation of extinction ratio while still compensating for secular degradation.
3Stability of the object's composition
If temperature compensation is applied based on measured temperature, then optical output power stability is improved, but the system cannot detect non-linear range operation
Solution Approach 1:
The patent implements feedback control by measuring the actual optical output power with a light receiving element and comparing it with the target value. This direct optical power measurement provides feedback on whether the system is operating in the non-linear range, enabling detection and correction that temperature-based compensation alone cannot achieve.
Solution Approach 2:
The patent replaces temperature-based compensation (indirect method) with direct optical output power measurement and feedback control. By directly measuring the optical output power and using this information for bias current adjustment, the system can detect and respond to non-linear characteristics more accurately than temperature compensation alone.
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
The solution effectively suppresses the influence of non-linear characteristics, ensuring a desirable extinction ratio is achieved even in high temperature conditions, effectively applicable in multi-value modulation methods like PAM4 and DMT.
Implementation Method 1
a light-receiving element configured to measure an optical output power of the light-emitting element
Data Source
AI summary
An optical transmission module includes: a bias current drive circuit to drive a bias current of a light-emitting element, on a basis of an input bias current setting value; a modulation current drive circuit to drive a modulation current of the light-emitting element, on a basis of an input modulation current setting value; a light-receiving element to measure an optical output power of the light-emitting element; a determiner to determine whether a difference between a target value of the optical output power and the optical output power measured by the light-receiving element is equal to or more than a threshold; and a controller configured to perform a correction control to the bias current drive circuit so that the bias current is reduced in accordance with the difference, when it is determined that the difference is equal to or more than the threshold by the determiner.