Mode coupling in FM-EDFAs caused by fiber bending: theory and experiments

Area of Science:

• Optical Engineering
• Fiber Optics
• Telecommunications

Background:

• Erbium-doped fiber amplifiers (EDFAs) are crucial for optical communications.
• Fiber bending inevitably causes refractive index perturbations, leading to mode coupling.
• This mode coupling can cause discrepancies between theoretical predictions and experimental results in EDFA performance.

Purpose of the Study:

• To develop a theoretical model for frequency-modulated EDFA (FM-EDFA) that accounts for mode coupling induced by fiber bending.
• To experimentally validate the theoretical model through a proof-of-concept experiment.

Main Methods:

• A theoretical model was developed to simulate FM-EDFAs considering mode coupling from fiber bending.
• A 3.2-m-long erbium-doped fiber (EDF) stretcher was used for experimental validation.
• Modal gain fluctuations were measured for LP01 and LP11 modes under fiber bending conditions.

Main Results:

• Fiber bending caused modal gain fluctuations of approximately 1.5 dB for LP01 and LP11 modes.
• The LP11 mode experienced a larger fluctuation of about 2.5 dB due to bending.
• The developed theoretical model accurately predicts the impact of fiber bending on FM-EDFA performance.

Conclusions:

• Mode coupling due to fiber bending significantly affects modal gain in EDFAs.
• The proposed theoretical model provides a more accurate tool for designing FM-EDFAs, especially when fiber bending is present.
• This research enhances the understanding and design of robust EDFA systems.