Fiber Laser System Optical Path Length Design for Stokes Beam Oscillation
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Solution Overview
Problem
Fiber laser systems face instability and malfunction due to high power overlap of forward and backward laser beams, leading to increased probability of Stokes beam oscillation immediately after the excitation light source is turned on, which decreases system reliability.
Innovation Solution
A fiber laser system with multiple fiber lasers, a combiner, and an optical fiber is configured such that the optical path length is set to ensure a time difference between the maximum power of forward and backward Stokes beams is greater than the sum of their half-widths at half-maximum, preventing power increase and reducing Stokes beam oscillation probability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a fiber laser system includes a plurality of fiber lasers and a combiner for combining laser beams, then the output power can reach kW level, but a reflected laser beam may re-enter the system and cause high power overlap between forward and backward beams
Solution Approach 1:
The patent applies preliminary anti-action by setting the optical path length L to satisfy specific inequalities (0.5×c×Δt < L < 1.5×c×Δt) that prevent the harmful overlap of forward and backward Stokes beams before it can occur. By pre-configuring the optical path length to create a time delay greater than the pulse width, the system proactively eliminates the condition for Stokes beam oscillation rather than reacting to it after it occurs.
2Reliability
If the optical path length is set to prevent Stokes beam oscillation, then reliability improves, but the system configuration becomes more complex
Solution Approach 1:
The patent applies parameter changes by transforming the reliability problem from a complex active control system into a simple passive solution through optimizing the optical path length parameter L. By setting L to satisfy the inequalities involving the speed of light c and time delay Δt, the system achieves automatic prevention of Stokes beam oscillation without requiring additional active control components, thereby improving reliability while minimizing complexity.
3Productivity
If multiple fiber lasers are combined to achieve high power, then productivity increases, but the probability of Stokes beam oscillation increases due to power overlap
Solution Approach 1:
The patent applies preliminary anti-action by pre-configuring the optical path length L to create a time delay Δt that exceeds the pulse width, thereby preventing the overlap of forward and backward Stokes beams before oscillation can occur. This proactive measure allows the system to maintain high productivity through multiple combined fiber lasers while proactively eliminating the reliability issue of Stokes beam oscillation that would otherwise increase with higher power levels.
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 configuration reduces the probability of Stokes beam oscillation after the excitation light source is turned on, enhancing the reliability of the fiber laser system by preventing power peaks from overlapping and stabilizing laser output.
Implementation Method 1
an optical fiber which (i) has an input end part and an output end part that are connected to the combiner and the output section, respectively and (ii) guides the combined laser beam from the combiner to the output section
Implementation Method 2
a plurality of fiber lasers which generates respective laser beams
Implementation Method 3
a combiner which combines the laser beams together, so that a combined laser beam is obtained
Data Source
AI summary
The present invention achieves a fiber laser having a high reflection resistance. A length of an optical fiber MMF is set so that a condition is satisfied at each point on an individual optical path of a fiber laser (FL2), the condition being that a difference between time at which a power of a forward Stokes beam (SF) is at a maximum value and time at which a power of a backward Stokes beam (SB) is at a maximum value is greater than a sum of a half width at half maximum of the power of the forward Stokes beam (SF) and a half width at half maximum of the power of the backward Stokes beam (SB).