Laser Power Controller Burst-Mode Feedback
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Solution Overview
Problem
In fibre optical communications systems, controlling the output power of laser diodes is challenging due to changes in laser characteristics with temperature and aging, especially in burst-mode transmission where bandwidth limitations of monitor diodes and circuitry restrict accurate estimation of minimum and maximum optical output levels, leading to instability and potential damage.
Innovation Solution
A system comprising selection circuitry, drive circuitry, an optical sensor module, and a controller that alternates between data input and logical high/low values during and after data bursts to accurately measure and control the laser diode's optical output, using a photodiode and trans-impedance amplifier to provide proportional electrical outputs for controlling the drive circuitry and maintaining desired power levels.
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 mechanism where the optical sensor module continuously monitors the actual optical output levels during data bursts, and the controller adjusts the drive current levels based on the difference between measured and target values. This closed-loop feedback system automatically compensates for laser characteristic changes due to temperature and aging, maintaining measurement precision without requiring complex manual recalibration.
Solution Approach 2:
The system dynamically changes the drive current parameters (high and low levels) based on measured optical output characteristics. By adjusting these current parameters in response to temperature and aging effects, the system maintains accurate optical output level estimation despite environmental variations, resolving the contradiction between simple control and precise measurement.
2Measurement precision
If monitor diode bandwidth is increased to improve instantaneous level detection, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The system performs measurements during extension time periods at the end of data bursts, which are predetermined intervals when no data transmission occurs. This preliminary action allows the optical sensor to capture stable high and low optical levels without requiring high bandwidth, as the measurements are taken when the optical signal is stationary rather than changing rapidly.
Solution Approach 2:
The optical sensor module performs measurements periodically during extension time periods between data bursts. This periodic measurement approach allows the use of lower bandwidth circuitry, as the system samples the optical levels at regular intervals rather than continuously tracking rapid changes, thereby reducing device complexity while maintaining measurement precision.
3Reliability
If measurements are taken during data bursts to improve reliability, then measurement precision improves, but the transmitted data payload is disturbed and signal to noise performance is compromised
Solution Approach 1:
The patent segments the transmission cycle into data transmission periods and extension time periods. Measurements are performed exclusively during the extension time periods, separating the measurement function from the data transmission function. This segmentation ensures that measurements do not interfere with data payload integrity while still providing reliable optical level information for control purposes.
Solution Approach 2:
The measurement function is extracted from the data transmission period and placed in the extension time period. By removing the measurement activity from the critical data transmission interval, the system maintains data transmission integrity and signal-to-noise performance while still achieving reliable optical level control through measurements taken during the extracted extension periods.
4Use of energy by moving object
If laser diode is kept off between bursts to save energy, then use of energy improves, but temperature stability deteriorates causing characteristic changes
Solution Approach 1:
The patent replaces physical/thermal stabilization mechanisms with an electrical control mechanism. Instead of maintaining constant temperature through thermal management (which would consume energy), the system uses optical measurements during extension periods to detect characteristic changes and compensates through electrical adjustment of drive current levels. This substitution allows energy-saving off states while maintaining operational stability through electronic compensation.
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 precise control of average and peak power, as well as modulation index, of the laser diode's optical output, ensuring reliable data transmission and avoiding damage by continuously monitoring and adjusting for changes in laser characteristics without disturbing the data payload or compromising signal-to-noise performance.
Implementation Method 1
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
Data Source
AI summary
A laser power controller employs: 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; drive circuitry configured to apply, to a laser diode, a 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, and configured to provide an electrical output proportional to the laser diode's optical output corresponding to the logical high value or the logical low value; and a controller configured to receive desired values regarding 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; the controller being configured to use the received information to provide control values for the drive circuitry.