Laser Power Control Circuit Using Incoherent Light for Safety
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Solution Overview
Problem
Current laser control systems require additional photodetectors and optical systems to ensure single fault-proof operation, increasing costs and complexity, as they are not inherently insensitive to temperature variations or other environmental factors.
Innovation Solution
A method and circuit that utilize a single photodetector integrated within the laser module, pumping the laser below the stimulated emission threshold to emit incoherent light, which is insensitive to temperature variations, and using dual microcontrollers to monitor and adjust the laser power, ensuring safe operation without additional photodetectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dual-channel control circuit with an additional photodiode is used to ensure single fault-proof operation, then the safety level is improved, but the device complexity and cost increase
Solution Approach 1:
The patent merges the safety monitoring function into the existing single photodiode by utilizing the LED region emissions. The microcontroller performs dual-channel equivalent safety checks by measuring the incoherent light from the LED region and comparing it against expected values, thereby achieving dual-channel safety control without requiring a second photodiode or separate optical path
Solution Approach 2:
The existing photodiode is made multi-functional by using it to detect both the coherent laser light (for power control) and the incoherent LED region light (for safety monitoring). This universal use of the single photodiode eliminates the need for additional photodetectors while maintaining safety requirements
2Reliability
If an additional photodiode and optical system are added to ensure safety, then the safety level is improved, but the manufacturing cost increases
Solution Approach 1:
The patent combines multiple safety monitoring functions into the existing photodiode and microcontroller system. By using the same photodiode to detect both laser power and safety conditions through the LED region emissions, the invention eliminates the need for additional photodetectors and optical components, thereby reducing manufacturing costs while maintaining safety levels
Solution Approach 2:
The laser diode itself provides the safety monitoring signal through its LED region emissions. The incoherent light emitted in the LED region serves as a built-in reference that the photodiode uses to verify proper operation, eliminating the need for external safety monitoring components and reducing overall system cost
3Power
If the laser is pumped above threshold to emit coherent light, then the laser power is improved, but the temperature sensitivity increases
Solution Approach 1:
The patent segments the laser emission characteristics into two distinct regions: the coherent laser emission above threshold (for power output) and the incoherent LED region emission (for temperature-insensitive safety monitoring). By separately utilizing these two emission regions, the system maintains both high laser power and temperature stability for safety checks
Solution Approach 2:
The patent changes the operational parameter from solely relying on coherent laser emission (which is temperature-sensitive) to also utilizing the incoherent LED region emission (which is temperature-insensitive). This parameter change allows the safety monitoring function to be performed using emissions that are substantially insensitive to temperature variations
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 provides reliable, cost-effective, and temperature-insensitive laser power control, preventing dangerous situations by using existing photodetectors and reducing the need for external photodetectors, thus achieving higher safety standards without modifying the laser or photodetector arrangement.
Implementation Method 1
a semiconductor junction (LD), which is adapted to emit laser light when it is crossed by an electric current (I LD )
Implementation Method 2
a photodiode (PD), which is adapted to detect the light emitted by the junction LD and to produce accordingly an electric current (I PD )
Implementation Method 3
The first part of the curve (A) has the appearance of a straight line or of a substantially straight segment and corresponds to a state of the laser diode in which the emitted light is substantially incoherent
Data Source
Figure 1~3
Figure 4
Figure 5
AI summary
A method for safely controlling the emission power of a laser coupled to a photodetector, in which the power emitted by the laser is substantially insensitive to variations in temperature or other environmental variables for at least one value of the pumping intensity, comprising the steps of: pumping the laser, at preset instants, according to the at least one value of the pumping intensity, and measuring a corresponding response of the photodetector to the light emitted by the laser during these instants, in order to check the correct operating condition of the photodetector.