Modulation efficiency of a LiNbO3 waveguide electro-optic intensity modulator operating at high microwave frequency

Area of Science:

• Photonics
• Optical Engineering
• Materials Science

Background:

• Lithium niobate (LiNbO3) waveguide electro-optic modulators are crucial for optical communications.
• High-frequency modulation can lead to performance degradation.
• Their application in Brillouin-distributed fiber-sensing systems presents unique challenges.

Purpose of the Study:

• To investigate the severe degradation of modulation efficiency in LiNbO3 waveguide electro-optic modulators under high-frequency microwave modulation.
• To analyze the impact of this degradation when the modulator is used as a frequency translator in Brillouin-distributed fiber-sensing systems.
• To derive an analytical expression for the observed attenuation.

Main Methods:

• Derivation of an analytical expression for modulation efficiency attenuation.
• Analysis focused on phase-velocity mismatch and impedance mismatch during modulation.
• Experimental validation using a 15 Gb/s LiNbO3 optical intensity modulator.

Main Results:

• High-frequency microwave modulation significantly degrades the modulation efficiency of LiNbO3 waveguide electro-optic modulators.
• Phase-velocity mismatch and impedance mismatch are identified as key factors contributing to attenuation.
• Experimental results confirm the theoretical predictions.

Conclusions:

• The study provides a theoretical framework and experimental evidence for modulation efficiency degradation in LiNbO3 modulators at high frequencies.
• Understanding these mismatches is critical for optimizing electro-optic modulators in demanding applications like fiber-optic sensing.
• The findings are essential for improving the performance of frequency translators in Brillouin-distributed fiber-sensing systems.