Compact Fiber Laser Projector Speckle Reduction
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Solution Overview
Problem
Existing laser-based projector systems suffer from severe speckle noise due to the coherent nature of laser illumination, which current solutions like multimode fibers cannot adequately address without increasing system complexity and size.
Innovation Solution
A compact, all-fiber pulsed laser system with high-brightness, tunable RGB technology that produces ultra-short pulses and broadens the linewidth of the signal light, reducing speckle noise through a single-pass frequency doubling scheme and chirped pulse amplification, resulting in a compact and efficient light source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If laser sources are used for illumination, then image brightness and power efficiency are improved, but speckle noise degrades image quality
Solution Approach 1:
The patent employs pulsed laser operation with ultra-short pulse durations (femtosecond to picosecond range) to generate high peak power while reducing coherence effects. The periodic pulsing action allows the laser to achieve high brightness during pulse peaks while the short duration and repetition rate reduce the buildup of speckle patterns, resolving the contradiction between image brightness and speckle noise
Solution Approach 2:
The patent utilizes frequency doubling (second harmonic generation) to convert the laser wavelength, which simultaneously changes the temporal and spectral parameters of the light. This parameter transformation allows the system to maintain high brightness while the broadened linewidth from the nonlinear conversion process reduces speckle contrast, addressing both image quality and brightness requirements
2Object-affected harmful factors
If direct-emission green laser diodes are used to reduce speckle, then coherence is reduced, but linewidth remains too narrow
Solution Approach 1:
The patent employs second harmonic generation, a nonlinear optical phase transition process, to convert the fundamental laser frequency to the desired green wavelength. This phase transition in the optical domain simultaneously broadens the linewidth and reduces coherence length, achieving speckle reduction while maintaining sufficient power and brightness that direct-emission diodes cannot provide
3Stability of the object's composition
If multimode fiber is used for speckle suppression, then mechanical stability is improved, but system complexity and size increase
Solution Approach 1:
The patent extracts and eliminates the need for complex multimode fiber assemblies by using ultra-short pulse generation and frequency doubling in a simplified all-fiber configuration. The high peak power of ultra-short pulses inherently provides sufficient mode mixing and decorrelation, making the complex multimode fiber architecture unnecessary while maintaining mechanical stability through the all-fiber design
4Object-affected harmful factors
If ultra-short pulses are used to broaden linewidth, then speckle is reduced, but power consumption increases
Solution Approach 1:
The patent uses pulsed operation where the laser emits ultra-short high peak power pulses followed by low-power intervals. The average power consumption is reduced because the high power is maintained only during the brief pulse duration, while the repetition rate is optimized to provide sufficient linewidth broadening for speckle reduction without requiring continuous high power operation
5Power
If high peak power is achieved through ultra-short pulses, then frequency conversion efficiency is improved, but system complexity increases
Solution Approach 1:
The patent merges the ultra-short pulse generation and frequency doubling processes into a single integrated nonlinear optical stage. The all-fiber MOPA configuration combines the master oscillator, amplifier, and frequency conversion elements in a unified system where the high peak power from ultra-short pulses directly drives efficient second harmonic generation, achieving high conversion efficiency without adding separate complex subsystems
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 effectively minimizes speckle noise, reduces power consumption, and lowers operating costs while maintaining high image quality and efficiency, achieving a more compact and simpler projector system.
Implementation Method 1
a laser-illuminated projection system (10) which includes a compact Green pulsed laser fiber source
Implementation Method 2
Individually, ultra-short pulses cause the broadening of linewidth of signal light at the fundamental frequency emitted from a seed source and, therefore, speckle reduction
Implementation Method 3
Both these characteristics in combination provide efficient conversion of the fundamental frequency into the desired frequency of Green light
Data Source
Figure 1~4
Figure 5~7
AI summary
A laser illuminated projector system is configured with multiple Red, Green and Blue laser sources. The Green laser source has an all fiber master oscillator power amplifier configuration in which pump light is coupled into the output end of the fiber amplifier in a counter-propagation direction rendering the structure of the Green source and therefore projector system compact. The Green laser source is operative to emit signal light pulses at about 1064 nm wavelength with a pulse repetition reaching of up to about 3000 kHz, pulse duration between about a 100 fm to about 100 psec, an average power between 1.5 W to above 30 W, a peak power above 5 MW, a pulse energy exceeding 100 μJ and a beam quality parameter M2 ranging between 1.2 and 1.5. The thus configured Green laser source substantially reduces speckle otherwise visible on the laser illuminated screen.