Broadband microwave frequency comb based on optoelectronic oscillator assisted by acousto-optic frequency shift

Area of Science:

• Photonics
• Microwave Engineering
• Optical Communications

Background:

• Optoelectronic oscillators (OEOs) are crucial for generating stable microwave signals.
• Traditional OEOs often have limited bandwidth, restricting their applications.
• Broadband microwave frequency combs (MFCs) are essential for high-capacity optical communication systems.

Purpose of the Study:

• To propose and demonstrate an acousto-optic frequency shift (AOFS)-assisted OEO for generating broadband MFCs.
• To enhance the frequency-domain bandwidth of MFCs beyond traditional limitations.
• To achieve switchable modulation frequencies in the generated MFCs.

Main Methods:

• Utilizing an AOFS dual-loop for periodic gain modulation and optical carrier-based microwave interferometry (OCMI).
• Employing phase-shifted fiber Bragg gratings (PS-FBGs) for main frequency oscillation.
• Integrating OCMI to expand the MFC bandwidth and enable switchable modulation.

Main Results:

• Successfully generated MFCs with a bandwidth of 5 GHz.
• Achieved switchable modulation frequencies by adjusting the OCMI's optical path difference (OPD).
• Demonstrated MFCs with various free spectral ranges (FSRs) including 4.92754 MHz, 3.62319 MHz, 2.75362 MHz, and 1.3913 MHz.

Conclusions:

• The AOFS-assisted OEO is a viable method for generating broadband MFCs with multi-GHz bandwidth.
• This technique offers superior bandwidth compared to traditional actively mode-locked OEOs (AML-OEOs).
• The ability to switch modulation frequencies enhances the system's versatility for diverse applications.