Stokes light induced modulation instability in high power continuous wave fiber amplifiers.

Area of Science:

• Fiber optics
• Nonlinear optics
• Laser physics

Background:

• High power fiber amplifiers are crucial for various applications.
• Modulation instability (MI) can degrade amplifier performance.
• Understanding MI mechanisms in fiber amplifiers is essential.

Purpose of the Study:

• To investigate Stokes light-induced modulation instability (MI) in high power continuous wave (CW) fiber amplifiers.
• To elucidate the roles of inter-modal four-wave mixing (IMFWM) and stimulated Raman scattering (SRS) in MI.
• To analyze the generation and characteristics of the resulting sidebands.

Main Methods:

• Observation of MI in high power CW fiber amplifiers.
• Analysis of signal light modulation via cross-phase modulation (XPM).
• Characterization of sideband generation and amplification through SRS.

Main Results:

• Stokes light from IMFWM and SRS can induce MI via XPM.
• A sideband is generated near the second-order Raman frequency shift.
• This sideband is amplified by SRS, appearing as temporal pulses.
• Sideband frequency shift is influenced by IMFWM and SRS.
• The sideband exhibits a blue-shift with increasing power, indicating MI dominance.

Conclusions:

• Modulation instability in high power fiber amplifiers is significantly influenced by Stokes light.
• IMFWM and SRS are key contributors to MI and subsequent sideband generation.
• SRS acts as an amplification mechanism for the MI-induced sidebands, affecting pulse characteristics.