Laser Driving Circuit Speckle Noise Reduction via High-Frequency Modulation
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Solution Overview
Problem
Laser display apparatuses and other devices using coherent laser light suffer from speckle noise due to variations in optical path length, leading to random interference fringes and reduced image quality.
Innovation Solution
A laser driving circuit and method that generate multiple laser driving currents for laser light sources of different wavelengths, superpose a high-frequency signal with a frequency higher than the video signal band on the driving current, and correct the waveform of the high-frequency signal to reduce coherence and mitigate speckle noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If laser light sources are used to provide coherent light, then image brightness and clarity are improved, but speckle noise appears due to interference fringes caused by optical path length variations
Solution Approach 1:
The patent applies periodic action by superimposing a high-frequency signal on the laser driving current. This periodic modulation causes the laser wavelength to vary periodically, thereby expanding the wavelength spectrum and reducing coherence. The high-frequency signal creates periodic wavelength shifts that prevent stable interference patterns, effectively reducing speckle noise while maintaining image brightness.
Solution Approach 2:
The patent employs parameter changes by modifying the wavelength spectrum of the laser light through high-frequency current modulation. By changing the driving current parameters (superimposing high-frequency components), the laser emits light with a broader wavelength range, which reduces coherence and consequently reduces speckle noise while preserving illumination intensity.
2Object-affected harmful factors
If a high frequency signal is superposed on the laser driving current, then the wavelength spectrum is expanded and coherence is reduced, but the emission light waveform may deteriorate
Solution Approach 1:
The patent applies feedback by using a waveform correction section that detects the emission light waveform and adjusts the high-frequency signal accordingly. The correction section provides feedback control to compensate for waveform distortions caused by the superimposed high-frequency signal, ensuring that the waveform remains within acceptable ranges while still achieving coherence reduction and speckle noise suppression.
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 approach effectively reduces speckle noise by expanding the wavelength spectrum of the laser light, improving image quality while maintaining a stable emission light waveform.
Implementation Method 1
light rays of different phases enter the eye in response to a variation in optical path length and interfere with each other to produce speckle noise by which innumerable interference fringes wherein the intensity is distributed at random appear
Implementation Method 2
In the case of coherent light which is uniform in wavelength and phase like laser light
Data Source
AI summary
Disclosed herein is a laser driving circuit, including: a plurality of laser driving video current generation circuits configured to generate a plurality of kinds of laser driving current for driving a plurality of laser light sources configured to emit laser light having wavelengths different from each other based on an inputted video signal; a high frequency superposition section configured to superpose a high frequency signal having a frequency higher than a frequency band of the video signal on the laser driving current generated by the laser driving video current generation circuits; and a waveform correction section configured to correct a waveform of the high frequency signal.