Laser Power Controller Burst-Mode Extinction Ratio
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Solution Overview
Problem
In fibre optical communications systems, existing methods struggle to accurately control the optical output power of laser diodes due to changes in temperature and aging, especially in burst-mode transmissions where bandwidth limitations hinder precise measurement of minimum and maximum optical levels, affecting reliable data reception.
Innovation Solution
A system comprising selection circuitry, drive circuitry, an optical sensor module, and a controller that selects and measures logical high and low values during data bursts, providing control values to maintain desired optical output levels without disturbing the data payload or compromising signal quality, using a photodiode and trans-impedance amplifier for monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional factory setup of high and low drive current levels is used, then device complexity is reduced, but measurement precision of optical output levels deteriorates due to laser characteristic changes with temperature and aging
Solution Approach 1:
The patent implements a feedback control system where the optical output of the laser diode is monitored during data bursts and extension periods, and the measured levels are used to adjust the drive current levels. The controller receives feedback about the actual high and low optical levels and modifies the drive current to maintain the desired modulation index, resolving the contradiction by continuously adapting to laser characteristic changes without requiring complex manual recalibration.
Solution Approach 2:
The system dynamically changes the drive current parameters (high level and low level) based on measured optical output levels. By adjusting these current parameters in response to temperature and aging effects, the system maintains precise measurement and control of optical output levels without increasing overall device complexity.
2Measurement precision
If monitor diode bandwidth is increased to improve measurement speed, then measurement precision of instantaneous optical levels improves, but device complexity and cost increase
Solution Approach 1:
The system performs measurements during extension periods that occur before and after data bursts. By utilizing these pre-defined time intervals for measurement purposes, the system can use lower bandwidth monitor diodes since the measurements are taken during known time windows rather than requiring high-speed continuous monitoring during the entire data transmission.
Solution Approach 2:
The measurement process is implemented periodically during extension periods rather than continuously during data transmission. This periodic measurement approach allows the use of lower bandwidth monitor diodes while still achieving adequate measurement precision for controlling the modulation index.
3Stability of the object's composition
If laser diode is kept on continuously to maintain stable temperature, then temperature stability improves, but energy consumption increases
Solution Approach 1:
The system performs optical level measurements during extension periods that occur before data bursts begin. By completing measurements in advance during these extension periods, the laser can be turned off or reduced to low power between bursts, maintaining temperature stability through controlled operation while reducing overall energy consumption compared to continuous operation.
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 accurate and continuous measurement of optical output levels during data bursts, effectively controlling the average and peak power of laser diodes, ensuring reliable data transmission and maintaining the extinction ratio within system specifications, even under varying temperature conditions.
Implementation Method 1
an optical sensor module configured to provide a sensor module output corresponding to the optical output of the laser diode
Implementation Method 2
The optical sensor module may comprise an optical sensor and a trans-impedance amplifier, the trans-impedance amplifier being configured to provide the sensor module output
Data Source
AI summary
A system for transmitting a sequence of at least two data bursts in a fibre optical communications system includes: selection circuitry configured to select one of a data input value, a logical high value or a logical low value such that the selection circuitry selects the data input value during a data transmission period during a defined burst period and selects one of the logical high value and the logical low value during an extension time period during the defined burst period and immediately following the data transmission period, such that for the sequence of at least two bursts, at least one burst has a logical low value extension period and at least one burst has a logical high value extension period; drive circuitry configured to apply a current to a laser diode, the current corresponding to the value selected by the selection circuitry during the defined burst period or a zero value otherwise, the current being such that the laser diode is configured to provide an optical output; an optical sensor module configured to provide a sensor module output corresponding to the optical output of the laser diode; wherein the sensor module output is configured to provide an electrical output proportional to the laser diode's optical output corresponding to the logical high value and the logical low value in the sequence of at least two bursts, and further configured to provide an output corresponding to an average value of the sensor module output during only the data transmission period during the sequence of bursts; and a controller configured to receive values regarding desired minimum and maximum optical output power levels of the laser diode and to receive the electrical output from the optical sensor module proportional to the optical output power level corresponding to the logical high and the logical low values, and to receive the output corresponding to the average value of the sensor module output during only the data transmission period during the sequence of bursts; wherein the controller is configured to use the received information to provide control values for the drive circuitry.