Ultra-flat wideband single-pump Raman-enhanced parametric amplification

Area of Science:

• Optoelectronics
• Nonlinear Optics
• Fiber Optics

Background:

• Fiber optical parametric amplifiers (FOPAs) are crucial for optical communications, but optimizing their gain spectral bandwidth and gain variation (GV) remains challenging.
• Achieving a flat and wide gain spectrum is essential for amplifying broadband signals without distortion.

Purpose of the Study:

• To experimentally optimize a single pump fiber optical parametric amplifier (FOPA) for maximum gain spectral bandwidth and minimal gain variation (GV).
• To investigate the impact of pump wavelength, fiber length, and spectral merging on FOPA performance.

Main Methods:

• Experimental optimization of a single pump FOPA using dispersion-stable highly nonlinear fiber (HNLF).
• Tuning the pump laser to the zero-dispersion wavelength of the HNLF.
• Varying the HNLF length and analyzing the combined Raman and parametric gain spectra.
• Testing the amplifier with a 60 Gbit/s QPSK signal.

Main Results:

• Optimal FOPA performance was achieved when the pump was tuned to the zero-dispersion wavelength of the HNLF.
• Decreasing the HNLF length further improved parametric gain bandwidth and reduced GV.
• Merging Raman and parametric gain spectra from the same pump significantly enhanced overall gain bandwidth while maintaining low GV.
• An ultra-flat gain of 9.6 ± 0.5 dB over 111 nm (12.8 THz) was demonstrated.
• Amplification of a 60 Gbit/s QPSK signal showed an Optical-to-Noise Ratio (OSNR) penalty of less than 1 dB for Q² below 14 dB.

Conclusions:

• Tuning the pump to the zero-dispersion wavelength and optimizing HNLF length are key to FOPA performance.
• Merging Raman and parametric gain spectra offers a novel method for achieving ultra-wide and flat gain bandwidths.
• The demonstrated FOPA exhibits excellent performance suitable for high-speed optical signal amplification.