Mode coupling in large-mode-area double-cladding chirped and tilted fiber Bragg gratings

Area of Science:

• Optics and Photonics
• Fiber Laser Technology
• Materials Science

Background:

• Chirped and tilted fiber Bragg gratings (CTFBGs) are crucial for suppressing stimulated Raman scattering (SRS) in high-power fiber lasers.
• Understanding mode coupling in CTFBGs inscribed in large-mode-area double-cladding fibers is essential for optimizing their performance.

Purpose of the Study:

• To investigate the coupling between core and cladding modes in CTFBGs within large-mode-area double-cladding fibers.
• To analyze the impact of this coupling on the transmission spectra and SRS suppression capabilities.
• To develop a method for mitigating spectral deterioration caused by unwanted mode coupling.

Main Methods:

• Theoretical modeling of mode coupling in CTFBGs.
• Experimental spectral response measurements under varying mode excitations.
• Analysis of the influence of chirp rate on spectral characteristics.

Main Results:

• Core-cladding mode coupling, specifically involving the LP11 mode, was found to degrade the transmission spectra envelope.
• This spectral deterioration negatively impacts the effectiveness of SRS suppression.
• Experimental results confirmed the theoretical predictions regarding mode coupling effects.
• A method involving the selection of an appropriate chirp rate was demonstrated to reduce LP11-excitation-induced spectral deterioration.

Conclusions:

• Core-cladding mode coupling is a significant factor affecting CTFBG performance in suppressing SRS.
• Optimizing the chirp rate of CTFBGs is a viable strategy to enhance Raman suppression in large-mode-area double-cladding fiber lasers.
• This research provides valuable insights for the design and application of CTFBGs in high-power laser systems.