Asymmetric gain-saturated spectrum in fiber optical parametric amplifiers

Area of Science:

• Nonlinear Optics
• Fiber Optics
• Optical Amplification

Background:

• Saturated fiber optical parametric amplifiers (FOPAs) are crucial for optical signal processing.
• Understanding gain spectrum behavior under saturation is essential for device performance.
• Traditional models often assume symmetric gain spectra based on phase-matching in unsaturated conditions.

Purpose of the Study:

• To investigate and explain the observed spectral asymmetry in the saturated gain spectrum of single-pump FOPAs.
• To identify the underlying physical mechanisms responsible for breaking the expected gain symmetry.
• To explore the dependence of this asymmetry on amplifier properties, particularly dispersion.

Main Methods:

• Experimental demonstration of spectral asymmetry in a single-pump FOPA setup.
• Numerical simulations to model the amplifier dynamics and validate experimental findings.
• Analysis of the influence of higher-order four-wave mixing and third-order dispersion on signal energy transfer.

Main Results:

• An unexpected spectral asymmetry was experimentally and numerically observed in the saturated gain spectrum.
• Higher-order four-wave mixing products and dispersive waves from third-order dispersion were identified as key contributors.
• The energy transfer to the signal, and thus the gain asymmetry, was found to depend on the signal's detuning from the pump.
• The spectral asymmetry exhibits local maxima at specific amplifier dispersion values.

Conclusions:

• The saturated gain spectrum of single-pump FOPAs is not symmetric, contrary to expectations from unsaturated models.
• Third-order dispersion and its interaction with higher-order nonlinear processes are critical for spectral asymmetry.
• The observed phenomenon offers insights into nonlinear fiber amplifier design and performance optimization, particularly concerning dispersion management.