Study and control of the intermodal energy transfer in high-power fiber laser systems

• Applicant: Cesar Jauregui Misas, Ph.D.
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 416342891

• Final Report Year: 2024

Final Report Abstract

Despite the difficulties posed by the pandemic to fulfil the planned schedule, we have managed to achieve most of the objectives of the project. We have worked in different characterization techniques for dynamic modal interactions in optical fibers and come up with novel approaches. For example, we have proposed and demonstrated the use of a mode multiplexer to obtain a real-time modal decomposition of an optical beam with an all-optical setup. In the same vein, we have employed a position-sensitive 4- quadrant photodiode to characterize the onset of transverse mode instability (TMI). This is so reliable that it has become our standard characterization method of the beam stability in our setups. Finally, we have devised a completely new approach, based on artificial intelligence routines, to measure the modes propagating in an optical fiber. We have also managed to settle a long-lasting discussion in the fiber laser community about the driver for TMI. We could demonstrate that this effect is driven by intensity noise, primarily, of the pump light. Additionally, we could demonstrate for the first time the control of the modal energy transfer in a high-power optical fiber even above the TMI-threshold. This is a remarkable result since we have managed to demonstrate fundamental mode operation, even at powers higher than 60% above the TMI threshold. The rest of the project has been devoted to developing a system able to induce travelling waves in optical fiber systems as a way to gain ultimate control on the modal energy transfer processes happening in them. In general, all the activities have been successful and they have led to 13 publications.

Publications

• Intensity noise as a driver for transverse mode instability in fiber amplifiers. PhotoniX, 1(1).
  Stihler, Christoph; Jauregui, Cesar; Kholaif, Sobhy E. & Limpert, Jens
  
• Transverse mode instability. Advances in Optics and Photonics, 12(2), 429.
  Jauregui, Cesar; Stihler, Christoph & Limpert, Jens
  
• Characterization of transverse mode instability in fiber-laser systems using a position-sensitive detector. Fiber Lasers XVIII: Technology and Systems, 34. SPIE.
  Kholaif, Sobhy E.; Tu, Yiming; Stihler, Christoph; Jauregui, Cesar & Limpert, Jens
  
• Control and stabilization of the modal content of fiber amplifiers using traveling waves. Optics Express, 29(21), 34452.
  Jauregui, Cesar; Stihler, Christoph; Kholaif, Sobhy; Tu, Yiming & Limpert, Jens
  
• Mitigation of transverse mode instability through a dynamic modification of the inversion in high-power fiber amplifiers. Fiber Lasers XVIII: Technology and Systems, 28. SPIE.
  Stihler, Christoph; Jauregui, Cesar; Kholaif, Sobhy E.; Tu, Yiming & Limpert, Jens
  
• Transverse mode instability and thermal effects in thulium-doped fiber amplifiers under high thermal loads. Optics Express, 29(10), 14963.
  Gaida, Christian; Gebhardt, Martin; Heuermann, Tobias; Wang, Ziyao; Jauregui, Cesar & Limpert, Jens
  
• Mitigation of transverse mode instability by heat load modulation in high-power fiber laser amplifiers. Fiber Lasers XIX: Technology and Systems, 57. SPIE.
  Kholaif, Sobhy E.; Jáuregui-Misas, César; Tu, Yiming & Limpert, Jens
  
• Real-time modal decomposition of fiber laser beams using a spatial mode multiplexer. Fiber Lasers XIX: Technology and Systems, 59. SPIE.
  Tu, Yiming; Jáuregui-Misas, César; Kholaif, Sobhy E. & Limpert, Jens
  
• Characterization of transverse mode instability with a 4-quadrant photodiode. Optics Express, 31(6), 10633.
  Kholaif, Sobhy; Jauregui, Cesar; Tu, Yiming & Limpert, Jens
  
• Characterizing the transverse modes of optical fibers by singular value decomposition. Fiber Lasers XX: Technology and Systems, 27. SPIE.
  Tu, Yiming; Pfleghar, Christian; Jauregui, Cesar & Limpert, Jens
  
• Fiber-Modes Characterization Using Singular Value Decomposition. 2023 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 1-1. IEEE.
  Tu, Yiming; Pfleghar, Christian; Jauregui, Cesar & Limpert, Jens
  
• Mitigation of transverse mode instability by heat-load modulation. Optics Express, 31(16), 26496.
  Kholaif, Sobhy; Jauregui, Cesar & Limpert, Jens
  
• Investigation of transverse mode instability threshold on the modal contents of the seed light in fiber amplifiers. Fiber Lasers XXI: Technology and Systems, 3. SPIE.
  Tu, Yiming; Jáuregui-Misas, César & Limpert, Jens