High Energy Fiber Laser Modulator PRBS Phase Control
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Solution Overview
Problem
High energy fiber lasers face performance degradation due to stimulated Brillouin scattering (SBS), which is challenging to mitigate with existing techniques such as varying refractive index or modulating pump light with RF noise sources, as these methods may not be optimal or desirable.
Innovation Solution
Employing a pseudorandom bit sequence (PRBS) modulation scheme in combination with a polarization filter to modulate the light before it enters a phase modulator, optimizing the PRBS pattern length to avoid in-phase backward propagation and achieve phase mismatch in the active fiber, thereby reducing SBS occurrence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional techniques such as varying refractive index or modulating pump light with RF noise sources are used, then SBS may be reduced, but device complexity and/or performance optimization is compromised
Solution Approach 1:
The patent applies parameter changes by modifying the modulation characteristics of the pump light. Specifically, it uses pseudorandom binary sequence (PRBS) modulation with optimized pattern lengths (e.g., 7-bit or 15-bit patterns) to change the temporal and spectral parameters of the pump light. This approach reduces SBS by creating phase mismatch between forward and backward propagating waves, while maintaining manageable device complexity through electronic sequence generation rather than complex optical modulation schemes.
2Power
If high energy is delivered, then output power increases, but SBS occurrence increases
Solution Approach 1:
The patent applies preliminary action by pre-modulating the pump light with PRBS patterns before the light enters the active fiber for amplification. This preliminary modulation creates a time-varying refractive index profile that prevents the buildup of coherent backward-propagating Stokes waves. By establishing this protective modulation regime in advance, the system can deliver high output power without experiencing SBS-induced power saturation or backward propagation, thus resolving the contradiction between high power delivery and SBS suppression.
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 enhances the output power of high energy fiber lasers while minimizing bandwidth, achieving a two-fold increase in power delivery and narrowing the linewidth by a factor of 1.6 to 2 without reducing output power, and supports beam encoding for coherent beam combining in high power applications.
Implementation Method 1
The phase modulator may be configured to apply a PRBS modulation scheme to the polarization filtered output based on the PRBS pattern
Implementation Method 2
SBS occurs when light in a medium encounters optical density variations that may alter its energy and path
Implementation Method 3
The polarizer may be optically coupled to receive an output of the seed laser and may generate a polarization filtered output
Data Source
AI summary
A laser device includes a seed laser, a polarizer, a pseudorandom bit sequence (PRBS) pattern generator, and a phase modulator. The polarizer may be optically coupled to receive an output of the seed laser and may generate a polarization filtered output. The PRBS pattern generator may be configured to generate a PRBS pattern. The phase modulator may be configured to apply a PRBS modulation scheme to the polarization filtered output based on the PRBS pattern. The PRBS pattern may be generated to have a length above a first threshold for avoiding an occurrence of backward propagation being in phase with forward propagation in an active fiber receiving an output of the phase modulator when the pattern repeats and below a second threshold for phase mismatch in the active fiber.