Multi-Pump-Pass Fiber Laser for Short Pulse High Power
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Solution Overview
Problem
Current fiber laser systems face challenges in achieving high peak and average power pulses with short pulse durations due to limitations in pump absorption and efficiency when using short active fibers, which result in inefficient laser operation.
Innovation Solution
The use of a multi pump-pass scheme with a high clad numerical aperture to core numerical aperture ratio in short active fibers, such as photonic crystal fibers, combined with specific optical configurations like concave spherical mirrors and coatings, enhances pump absorption and efficiency, allowing for high peak and average power pulses with durations of a few nanoseconds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the active fiber length is reduced to achieve short pulse durations, then the pulse duration is improved, but the pump absorption efficiency deteriorates
Solution Approach 1:
The patent segments the pump absorption process into multiple passes through the short active fiber. By using optical cavities and mirrors, the pump light traverses the fiber multiple times, effectively increasing the interaction length without physically extending the fiber. This allows short pulse durations to be achieved while maintaining high pump absorption efficiency through repeated passes.
Solution Approach 2:
The patent implements continuous pump absorption by circulating pump light through the active fiber multiple times using optical resonators. Instead of a single-pass absorption, the system maintains continuous interaction between pump light and the active medium, ensuring efficient energy transfer even in extremely short fibers used for nanosecond pulse generation.
2Duration of action of moving object
If the active fiber length is reduced to achieve short pulse durations, then the pulse duration is improved, but the laser power output deteriorates
Solution Approach 1:
The patent divides the power generation process into multiple stages by implementing multi-pass pump absorption. Each pass through the short active fiber contributes to cumulative energy extraction, allowing high peak power to be achieved in nanosecond pulses despite the extremely short interaction length. The segmented approach enables power scaling without increasing fiber length.
Solution Approach 2:
The patent employs periodic pumping schemes where pump light is delivered in controlled cycles through the active fiber. By synchronizing the periodic pump pulses with the laser cavity dynamics, the system accumulates energy in the short fiber and releases it as high-power nanosecond pulses, achieving both short duration and high power output.
3Duration of action of moving object
If the active fiber length is reduced to achieve short pulse durations, then the pulse duration is improved, but the beam quality deteriorates
Solution Approach 1:
The patent optimizes the local optical properties within the short active fiber by carefully designing the numerical aperture ratios and mode field distributions. By controlling the local light-matter interaction characteristics and using specialized fiber structures, the system maintains good beam quality despite the extremely short length required for nanosecond pulse generation.
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 significantly increases pump absorption and efficiency, achieving comparable performance to state-of-the-art fiber lasers with high peak and average power outputs while maintaining good beam quality, even with fibers shorter than 30 cm.
Implementation Method 1
the limitation on the shortest pulse duration is the time of flight of the photon in the cavity... low pump absorption in an active fiber, which diminishes exponentially upon reducing the length of the fiber
Implementation Method 2
the active fiber has a high ratio of the clad numerical aperture (NA) to the core NA
Implementation Method 3
the limitation on the shortest pulse duration is the time of flight of the photon in the cavity
Implementation Method 4
a front concave spherical mirror... a highly reflecting rear mirror
Implementation Method 5
the active fiber is one of: a photonic crystal fiber (PCF), an air-clad fiber, or a special double-clad fiber
Data Source
Figure 1A~1C
Figure 1D~1F
Figure 2A~2D
AI summary
The invention is optical configurations for constructing laser oscillators or laser amplifiers that comprise an extremely short fiber (typically tens of cm long or below, e.g. 5cm to 30cm). In order to overcome the absorption limitation due to the very short length of the fiber, the present invention employs a multi pump-pass scheme for pump light confinement. This scheme is based on the small angular overlap between the lasing and pump beams. The multi pump-pass method of the invention leads to efficient fiber laser oscillators and amplifiers having pulse duration of a few ns, with high average and peak power output that is comparable to the state-of-the-art solid state lasers.