Laser Diode Optical Power Control Without Monitoring Photodiode
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Solution Overview
Problem
Fiber-optic transceivers face challenges in controlling optical power and extinction ratio over an entire temperature range without using a monitoring photodiode, lookup table, or closed-loop control circuit, leading to increased complexity and cost, and difficulty in applying them to fiber-optic communication systems effectively.
Innovation Solution
A method that utilizes manufacturer-provided characteristic data of laser diodes, such as threshold currents and slope efficiencies at specific temperatures, to determine the relationship between optical power and on-current over the entire temperature range, allowing for manual adjustment of bias and modulation currents to maintain optimal optical power and extinction ratio, and stores these parameters in a controller IC for automatic temperature compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a monitoring photodiode and closed-loop control circuit are used to control optical power and extinction ratio, then the optical power and extinction ratio can be maintained at optimal levels, but the device complexity and cost increase
Solution Approach 1:
The patent extracts the monitoring photodiode and closed-loop control circuit from the system, achieving optical power and extinction ratio control through manufacturer-provided characteristic data and manual current adjustment, thereby reducing device complexity while maintaining performance
Solution Approach 2:
The system uses pre-provided characteristic data from the manufacturer to automatically determine control parameters, eliminating the need for additional monitoring hardware and complex control circuits, allowing the laser diode to be controlled based on its inherent characteristics
2Reliability
If a lookup table is used to store operation parameters at different temperatures, then temperature compensation can be achieved, but the device complexity and storage requirements increase
Solution Approach 1:
The patent removes the lookup table approach and instead uses mathematical models (equations) to calculate temperature compensation parameters, reducing storage requirements and simplifying the control data structure while maintaining accurate temperature compensation
Solution Approach 2:
The system uses equations to model the relationship between temperature and laser diode parameters, allowing dynamic calculation of control parameters based on temperature changes rather than storing pre-computed values in a lookup table
3Device complexity
If manufacturer-provided characteristic data is used to determine optical power and on-current relationship, then additional hardware can be eliminated, but the manufacturing precision requirements increase
Solution Approach 1:
The patent leverages the manufacturer's pre-provided characteristic data to determine the relationship between optical power and on-current, eliminating the need for additional measurement hardware while relying on the precision of the manufacturer's data and manual current adjustment
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
Enables commercially available fiber-optic transceivers to automatically control optical power and extinction ratio over an entire temperature range without additional hardware, reducing costs and simplifying the application to fiber-optic communication systems while maintaining optimal performance.
Implementation Method 1
the thermal sensor senses the temperature of the laser diode
Implementation Method 2
the laser driver drives the laser diode to generate a laser beam
Data Source
AI summary
The present invention is to provide a method applicable to a fiber-optic transceiver including a transmitter optical subassembly (TOSA) provided therein with a laser diode, but without a monitoring photodiode, a laser driver controlled by a controller IC for driving the laser diode to generate a laser beam, and a thermal sensor for sensing temperature of the laser diode. The method includes executing an approximation process to characteristic data, i.e. threshold currents of the laser diode at a plurality of specific temperatures and corresponding slope efficiencies (SE), provided by manufacturer for obtaining relationship therebetween over entire temperature range, manually adjusting operation parameters (such as bias current and modulation current) of the laser diode for generating expected optical power and extinction ratio at a normal temperature and for subsequently determining the operation parameters over the entire temperature range, and writing the relationship and operation parameters thus obtained into the controller IC.