Harmonic superposition for tailored optical frequency comb generation by a Mach-Zehnder modulator.

Area of Science:

• Photonics and Optical Engineering
• Nonlinear Optics
• Integrated Optics

Background:

• Optical frequency combs (OFCs) are crucial for precise optical measurements and communications.
• Generating flat-spectrum OFCs is challenging but essential for many applications.
• Mach-Zehnder modulators are widely used for OFC generation.

Purpose of the Study:

• To demonstrate a novel method for generating tailored optical frequency combs.
• To achieve a quasi-rectangular OFC spectrum with high flatness.
• To investigate the influence of RF signal harmonics on OFC generation.

Main Methods:

• Utilizing a Lithium Niobate (LiNbO3) Mach-Zehnder modulator.
• Driving the modulator with a combination of first- and second-order harmonics of an RF signal.
• Experimentally introducing a slight second-order harmonic (0.1 times the half-wavelength voltage).

Main Results:

• A quasi-rectangular optical frequency comb with 11 lines was experimentally generated.
• The generated OFC exhibited a flatness of less than 1 dB among the 11 lines.
• Experimental results showed good agreement with theoretical calculations.

Conclusions:

• The presented method effectively generates tailored, flat optical frequency combs.
• The introduction of a second-order RF harmonic is key to achieving quasi-rectangular OFC shapes.
• This technique offers a viable route for controlling OFC spectral properties, including efficiency and bandwidth.