Laser Diode Pulse Width Control via Relaxation Oscillation
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Solution Overview
Problem
Generating short pulse-width laser light is challenging due to the difficulty in creating driving currents of tens to hundreds of picoseconds using simple circuits, and high-frequency techniques in the microwave band are not suitable for outdoor devices due to complexity, cost, and power consumption.
Innovation Solution
A method involving a capacitive reactance circuit and a resistance circuit connected in parallel, with a switching element, to control the laser light source and differentiate circuit, allowing for adjustment of capacitance and resistance values to achieve initial relaxation oscillation pulses with a short pulse width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If high frequency technique in microwave band is used to generate pulse-like driving current, then pulse width can be reduced to tens to hundreds of picoseconds, but device complexity and power consumption increase significantly
Solution Approach 1:
The patent changes the operating parameters of the laser diode by applying a current pulse with a sharp rising edge that exploits the relaxation oscillation phenomenon. Instead of using high-frequency microwave techniques, the invention uses a simplified circuit that generates a current pulse with a rise time of several picoseconds, allowing the laser to naturally oscillate and emit short pulses without complex high-frequency equipment.
Solution Approach 2:
The patent replaces the mechanical/electromagnetic high-frequency oscillator system with a simpler electrical circuit that utilizes the inherent relaxation oscillation characteristics of the laser diode itself. The circuit uses a current source with fast switching capability to trigger the laser's natural oscillation mode, substituting complex external high-frequency generation with the laser's own dynamic response.
2Duration of action of moving object
If high frequency technique in microwave band is used to generate pulse-like driving current, then pulse width can be reduced to tens to hundreds of picoseconds, but power consumption increases
Solution Approach 1:
The patent changes the operating parameters of the laser diode by applying a current pulse with a sharp rising edge that exploits the relaxation oscillation phenomenon. Instead of using high-frequency microwave techniques, the invention uses a simplified circuit that generates a current pulse with a rise time of several picoseconds, allowing the laser to naturally oscillate and emit short pulses without complex high-frequency equipment.
3Device complexity
If simple circuit is used to generate driving current, then device complexity is reduced, but pulse width cannot be reduced to tens to hundreds of picoseconds
Solution Approach 1:
The patent replaces the mechanical/electromagnetic high-frequency oscillator system with a simpler electrical circuit that utilizes the inherent relaxation oscillation characteristics of the laser diode itself. The circuit uses a current source with fast switching capability to trigger the laser's natural oscillation mode, substituting complex external high-frequency generation with the laser's own dynamic response.
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 enables the emission of light with a short pulse width using a simple structure, reducing the need for complex high-frequency circuits and minimizing power consumption, while maintaining precision in applications like distance measurement.
Implementation Method 1
The capacitive reactance circuit exhibits low impedance immediately after the electric current is applied and is charged by the electric charge
Implementation Method 2
The resistance circuit discharges the electrical charge charged in the capacitive reactance circuit after a predetermined time passes after the electric current is applied
Implementation Method 3
The laser light source generates relaxation oscillation immediately after electric current is applied thereto for driving light emission
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
Light with a short pulse width is emitted using a simple structure. A light source 101, a differentiation circuit 102, and a switch 103 are connected in series. When the switch 103 is switched on, inrush current flows in a capacitor 102b forming the differentiation circuit 102, and accordingly the light source 101 is supplied with electric current and thereby emits light. When the capacitor 102b is charged, electric current flows in a resistor 102a, and voltage drops at the resistor 102a. Then, the voltage applied to the light source 101 is decreased, whereby the light source 101 stops emitting light. The values of the resistor 102a and the capacitor 102b are adjusted so that the above phenomenon occurs.