Mode-locked Fiber Laser Pulse Recycling via Faraday Rotation
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Solution Overview
Problem
Conventional figure-8 mode-locked ultra-short pulse fiber lasers waste reverse laser pulses due to the presence of an isolator in the uni-directional loop, limiting the utilization of these pulses.
Innovation Solution
Incorporating a polarization beam splitter and a Faraday rotator in the uni-directional loop of the mode-locked fiber laser device, allowing the reverse laser pulse to be output and utilized effectively, eliminating the need for an isolator and forming a figure-8 optical path with a non-linear loop mirror and optical splitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an isolator is allocated in the uni-directional loop to isolate reverse laser pulse propagation, then the laser pulse directionality is maintained, but the reverse laser pulse is wasted
Solution Approach 1:
The patent converts the previously wasted reverse laser pulse into a useful resource by using the Faraday rotator to rotate its polarization by 45 degrees, enabling it to pass through the polarization beam splitter and be reflected back into the resonator. This transforms the harmful reverse propagation into a beneficial contribution to laser output, effectively utilizing energy that would otherwise be lost.
Solution Approach 2:
The patent changes the polarization state parameter of the reverse laser pulse by introducing a Faraday rotator that rotates the polarization by 45 degrees. This parameter change enables the reverse pulse to interact differently with the polarization beam splitter, allowing it to be reflected back into the resonator rather than being isolated or wasted.
2Loss of energy
If a polarization beam splitter and Faraday rotator are allocated in the uni-directional loop, then reverse laser pulse utilization is improved, but the device complexity increases
Solution Approach 1:
The polarization beam splitter serves multiple functions: it transmits forward laser pulses with the correct polarization, reflects reverse laser pulses after Faraday rotation, and outputs the final laser beam. The Faraday rotator also performs dual roles by rotating polarization for both the reverse pulse recycling and the output coupling. This multi-functionality reduces the need for additional components.
Solution Approach 2:
The patent merges the functions of laser output coupling and reverse pulse recycling into a single optical path configuration. The polarization beam splitter and Faraday rotator are combined to simultaneously handle both the forward and reverse laser pulses, eliminating the need for separate isolators and output couplers, thus reducing overall device complexity.
3Reliability
If an isolator is used to maintain uni-directional propagation, then the laser resonator stability is maintained, but the operational efficiency decreases
Solution Approach 1:
Instead of isolating and wasting the reverse laser pulse as in conventional designs, the patent converts this previously harmful reverse propagation into a beneficial resource. The Faraday rotator rotates the reverse pulse polarization by 45 degrees, enabling it to be reflected by the polarization beam splitter back into the resonator, thereby contributing to laser output and improving operational efficiency while maintaining stability.
Solution Approach 2:
The system uses the reverse laser pulse itself to serve the laser output purpose. By rotating the polarization of the reverse pulse and reflecting it back through the polarization beam splitter, the system enables the reverse pulse to contribute to the forward laser output, making the laser resonator self-sufficient and improving operational efficiency without external intervention.
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
Enables the efficient use of reverse laser pulses, enhancing the operational efficiency of the mode-locked fiber laser by eliminating waste and optimizing the laser output without the requirement of an isolator in the uni-directional loop.
Implementation Method 1
a Faraday rotator, wherein the uni-directional loop is coupled to the non-linear loop mirror through the optical splitter to form a figure-8 optical path. A first output laser pulse output by a first port of the optical splitter is propagated to the polarization beam splitter first, and after the Faraday rotator rotates the first output laser pulse 45 degrees
Data Source
AI summary
A mode-locked fiber laser device is provided in the disclosure. The mode-locked fiber laser device includes a non-linear loop mirror, an optical splitter and a uni-directional loop. The uni-directional loop includes a polarization beam splitter and a Faraday rotator. The uni-directional loop is coupled to the non-linear loop mirror by the optical splitter to form a figure-8 optical path. A first output laser pulse output by the optical splitter is propagated to the polarization beam splitter. After being rotated 45 degrees by a Faraday rotator, the first output laser pulse is propagated back to the non-linear loop mirror to form a laser resonator. A second output laser pulse output by the optical splitter is propagated to the Faraday rotator to rotate the second output laser pulse 45 degrees, and the polarization beam splitter reflects the second output laser pulse to the outside of the mode-locked fiber laser device.