Ultra-narrow linewidth measurement based on Voigt profile fitting.

Area of Science:

• Optics and Photonics
• Laser Physics
• Spectroscopy

Background:

• Ultra-narrow linewidth lasers are crucial for advanced applications.
• Traditional linewidth measurement techniques like self-heterodyne suffer from limitations due to frequency noise.
• 1/f frequency noise broadens spectral lines, hindering accurate linewidth determination.

Purpose of the Study:

• To introduce and validate the Voigt profile fitting method for ultra-narrow linewidth measurement.
• To demonstrate the method's ability to filter out 1/f frequency noise.
• To compare the accuracy of Voigt fitting with direct heterodyne spectrum width measurements.

Main Methods:

• Applying Voigt profile fitting to analyze the spectral data of an ultra-narrow-linewidth Brillouin/erbium fiber laser (BEFL).
• Filtering out the spectral broadening effect caused by 1/f frequency noise.
• Extracting the intrinsic Lorentzian lineshape from the measured spectrum.

Main Results:

• The Voigt fitting method significantly enhances spectral resolution compared to direct self-heterodyne measurements.
• Linewidth estimations using Voigt fitting are more accurate for the BEFL.
• Direct measurements from 3-dB and 20-dB heterodyne spectrum widths overestimate the true linewidth.

Conclusions:

• Voigt profile fitting is an efficient and accurate tool for ultra-narrow linewidth measurement.
• The method effectively isolates the Lorentzian lineshape, providing a more precise linewidth value.
• Unlike heterodyne beat techniques, Voigt fitting is applicable to all laser types, enhancing its versatility.