Comparison of multimode LD pump beam shaping in step-index and graded-index fibers and its influence on Raman lasing

Alexey G. Kuznetsov, Alexey A. Wolf, Ilya N. Nemov, Sergey I. Kablukov, Sergey A. Babin

Результат исследования: Публикации в книгах, отчётах, сборниках, трудах конференцийстатья в сборнике материалов конференциинаучнаярецензирование

Аннотация

It is known that graded-index fibers (GIF) provide efficient Raman conversion of multimode radiation into a Stokes beam with improved beam quality known as Raman beam cleanup effect, whereas in step-index fibers (SIF) this effect is weak. Here we study propagation of low-coherent (~5 nm wide) highly-multimode (M2~30) pump radiation of high power 940-nm laser diodes (LDs) in GIF and SIF of ~100 µm core diameter. We measured pump beam shapes at the output of fibers with different length. It has been shown that the output beam shape is almost independent of the input pump beam shape approaching to rectangular or parabolic profile after propagation in only ten meters of SIF or GIF, respectively. The output beam shape mimics the refractive-index profile in the multimode fiber core due to random mode coupling. This means that Raman gain is nearly the same for all transverse modes in SIF and has maximum gain for the fundamental mode in GIF that is the main reason of strong Raman beam cleanup effect in GIF. We tested Raman lasing in 1-km GIF/SIF with 940-nm LD pumping of up to ~200 W power with a cavity formed by fiber Bragg gratings (FBGs). The output FBG fs-inscribed in GIF/SIF improves the output beam quality due to spatial filtering property, but in GIF the effect is much stronger.

Язык оригиналаанглийский
Название основной публикацииMicro-Structured and Specialty Optical Fibres VII
РедакторыKyriacos Kalli, Pavel Peterka, Christian-Alexander Bunge
ИздательSPIE
Число страниц7
ISBN (электронное издание)9781510651562
DOI
СостояниеОпубликовано - 2022
СобытиеMicro-Structured and Specialty Optical Fibres VII 2022 - Virtual, Online
Продолжительность: 9 мая 202220 мая 2022

Серия публикаций

НазваниеProceedings of SPIE - The International Society for Optical Engineering
Том12140
ISSN (печатное издание)0277-786X
ISSN (электронное издание)1996-756X

Конференция

КонференцияMicro-Structured and Specialty Optical Fibres VII 2022
ГородVirtual, Online
Период09.05.202220.05.2022

Предметные области OECD FOS+WOS

  • 2.02 ЭЛЕКТРОТЕХНИКА, ЭЛЕКТРОННАЯ ТЕХНИКА, ИНФОРМАЦИОННЫЕ ТЕХНОЛОГИИ
  • 1.03 ФИЗИЧЕСКИЕ НАУКИ И АСТРОНОМИЯ

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