Fiber-optic frequency comb generation using low-seed power FWM and Brillouin-assisted power equalization

Area of Science:

• Photonics and Optics
• Fiber Lasers and Amplifiers
• Nonlinear Optics

Background:

• Optical frequency combs (OFCs) are crucial for precise frequency measurements and spectroscopy.
• Generating broadband and tunable OFCs in fiber formats remains a challenge.
• Stimulated Brillouin scattering (SBS) and four-wave mixing (FWM) are key nonlinear phenomena for OFC generation.

Purpose of the Study:

• To experimentally demonstrate an all-fiber broadband tunable optical frequency comb (OFC) operating in the C-band.
• To achieve a high comb line count and broad bandwidth through nonlinear fiber propagation.
• To enable wavelength tunability of the OFC using a tunable pump source.

Main Methods:

• Generation of a seed SBS-OFC using a pump and Stokes power recycling cavity.
• Power equalization of the seed SBS-OFC using a Brillouin-assisted power equalization (BAPE) technique.
• Broadening the power-equalized seed SBS-OFC via FWM in a 200 m dispersion-flattened highly nonlinear fiber (HNLF).

Main Results:

• The seed SBS-OFC comprised approximately 15 comb lines with 10.8 GHz spacing and 16 dBm average power.
• The BAPE technique minimized pump contribution, yielding a power-equalized seed SBS-OFC.
• Propagation in HNLF resulted in an OFC with approximately 140 comb lines within a 12 nm bandwidth.
• Wavelength tunability over a 35 nm span was demonstrated by varying the Brillouin pump laser.
• A secondary OFC was observed during the BAPE process.

Conclusions:

• An all-fiber broadband tunable OFC in the C-band was successfully demonstrated.
• The combination of SBS, BAPE, and FWM in HNLF is effective for generating a high-density OFC.
• The achieved tunability and comb characteristics are promising for various spectroscopic and metrology applications.