Laser Diode Power Control Using Below-Threshold Photodiode Slope
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Solution Overview
Problem
Existing methods for controlling the optical output power of laser diodes in optical particle sensors, particularly in miniaturized applications like smartphones, face challenges due to temperature and aging effects, necessitating improved and simplified power control methods that are not practical with external optical feedback.
Innovation Solution
A method involving obtaining optical and electrical trimming parameters under controlled conditions, determining the slope of the photodiode current versus laser diode current below lasing threshold, and using these parameters to control optical output power during operation, eliminating the need for voltage measurements during field operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external optical feedback path is used to measure optical output power, then measurement precision is improved, but device complexity increases and it becomes impractical for miniaturized applications
Solution Approach 1:
The patent integrates the photodiode directly into the laser diode structure, merging the light emission and light detection functions into a single integrated device. This eliminates the need for external optical feedback paths while maintaining the ability to measure optical output power through the integrated photodiode's electrical signals.
Solution Approach 2:
The patent uses electrical measurements (voltage and current) as intermediaries to indirectly determine optical output power. Instead of directly measuring light with external optical equipment, the method uses electrical parameters that correlate with optical power, simplifying the measurement system for miniaturized applications.
2Measurement precision
If optical output power is increased for high measurement sensitivity, then measurement sensitivity is improved, but eye safety is compromised
Solution Approach 1:
The patent implements a feedback control mechanism where the integrated photodiode continuously monitors the optical output power and provides electrical signals back to the control system. This feedback enables dynamic adjustment of the laser diode current to maintain optimal measurement sensitivity while ensuring the optical power remains within eye-safe limits.
Solution Approach 2:
The system dynamically adjusts the laser diode operating parameters based on real-time conditions. By continuously monitoring electrical parameters and adapting the drive current, the system can optimize measurement sensitivity for different conditions while automatically maintaining eye safety compliance.
3Measurement precision
If laser diode current is adjusted to control optical output power during operation, then optical output power control is improved, but temperature and aging effects cause drift requiring frequent recalibration
Solution Approach 1:
The patent uses the integrated photodiode to provide continuous feedback on the actual optical output power through electrical measurements. This feedback loop compensates for drift caused by temperature and aging effects, maintaining stable optical power control without requiring frequent manual recalibration.
Solution Approach 2:
The system performs self-calibration using the integrated photodiode's measurements. By continuously monitoring electrical parameters and comparing them against reference values, the system automatically compensates for environmental changes and aging, eliminating the need for external recalibration procedures.
4Measurement precision
If multiple voltage and current measurements are performed during operation, then optical output power monitoring accuracy is improved, but calibration time and effort increase
Solution Approach 1:
The patent performs comprehensive calibration measurements during the manufacturing process under controlled conditions, storing the results as reference data. This preliminary action eliminates the need for repeated calibration measurements during field operation, reducing calibration time while maintaining monitoring accuracy through comparison with pre-stored reference values.
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 approach provides accurate and simplified power control over a range of optical output powers, reducing calibration time and effort, and accounting for temperature and aging effects, while maintaining high precision and flexibility.
Implementation Method 1
the photodiode converts light received from the laser diode into an electrical photodiode current
Data Source
AI summary
A method of controlling an optical output power of a laser diode associated with a photodiode includes obtaining first optical trimming parameters indicative of a first optical output power of the laser diode at a first laser diode current and a second optical output power of the laser diode at a second laser diode current above lasing threshold. Next, second electrical trimming parameters indicative of a photodiode characteristic curve of photodiode current versus laser diode current are obtained. A first photodiode current and a second photodiode current at a laser diode currents below lasing threshold. A slope of a photodiode current versus laser diode current is determined. The optical output power of the laser diode above lasing threshold is controlled based on the first optical trimming parameters, the second electrical trimming parameters and the slope of the photodiode current versus laser diode current below lasing threshold.