All Fiber Passively Q-Switched Laser With Mode Transformer
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Solution Overview
Problem
Conventional Q-switched lasers face challenges in achieving high power output with good beam quality due to the limitations of core diameter size, which often results in beam quality degradation from multiple transverse modes.
Innovation Solution
An all-fiber passively Q-switched laser system is developed, featuring a large core gain fiber and a doped single-mode fiber with a mode transformer that filters out higher-order modes, allowing only the fundamental mode to pass through, thereby enhancing beam quality and achieving high power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a large core gain fiber is used to achieve high power output, then power increases, but beam quality deteriorates due to multiple transverse modes
Solution Approach 1:
The fiber system is segmented into two distinct parts: a large core gain fiber for high power generation and a small core single-mode fiber for beam quality control. The mode transformer acts as an interface that couples these two segments, allowing each to perform its specialized function without compromising the other.
Solution Approach 2:
A mode transformer is introduced as an intermediary component between the large core gain fiber and the small core single-mode fiber. This transformer gradually transitions the mode field diameter, enabling efficient coupling while filtering out higher-order modes to maintain beam quality.
2Manufacturing precision
If a small core single-mode fiber is used as saturable absorber, then beam quality is maintained, but power handling capability is limited
Solution Approach 1:
The solution moves the power handling function to a different dimension (the large core gain fiber) while keeping the beam quality control function in the original dimension (the small core single-mode fiber). This dimensional separation allows each component to operate within its optimal power and size constraints.
3Power
If multiple transverse modes are allowed in the gain fiber, then power output increases, but beam quality degrades
Solution Approach 1:
The mode transformer extracts and filters out the harmful higher-order modes from the multi-mode output of the gain fiber, leaving only the fundamental mode to propagate into the single-mode fiber. This extraction process maintains beam quality while preserving the power generation capability of the multi-mode gain fiber.
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 system generates a short pulse, high-energy beam with improved beam quality by quickly saturating the doped single-mode fiber, allowing efficient energy extraction and maintaining high power while minimizing beam quality degradation.
Implementation Method 1
The doped single mode fiber absorbs the light energy until a saturation threshold level is reached. In response to reaching the saturation threshold level, the method includes bleaching the doped single mode fiber to transmit the light energy with a negligible loss.
Implementation Method 2
The mode transformer transforms the transversal mode from the large core fiber to that of the small single-mode fiber. One form of the mode transformer is tapered fiber, which has a core diameter that transitions from the first core diameter to the second core diameter.
Implementation Method 3
The pump energy excites ions in the large core doped gain fiber such that light energy possibly having a plurality of light modes is generated. Because of the large amount of energy already stored in the gain medium, the intensity of light in the laser resonator builds up very quickly; this also causes the energy stored in the medium to be depleted almost as quickly.
Data Source
AI summary
Embodiments relate to an all fiber passively Q-switched laser. The laser includes a large core doped gain fiber having a first end. The large core doped gain fiber has a first core diameter. The laser includes a doped single mode fiber (saturable absorber) having a second core diameter that is smaller than the first core diameter. The laser includes a mode transformer positioned between a second end of the large core doped gain fiber and a first end of the single mode fiber. The mode transformer has a core diameter that transitions from the first core diameter to the second core diameter and filters out light modes not supported by the doped single mode fiber. The laser includes a laser cavity formed between a first reflector positioned adjacent the large core doped gain fiber and a second reflector positioned adjacent the doped single mode fiber.