40 nm wavelength tunable gain-switched optical comb source

Area of Science:

• Photonics and Optical Engineering
• Laser Physics
• Spectroscopy

Background:

• Optical frequency combs are crucial for precise measurements and communications.
• Generating tunable, stable, and broadband combs remains a key research challenge.
• Gain-switched semiconductor lasers offer a compact platform for comb generation.

Purpose of the Study:

• To demonstrate a wavelength-tunable optical frequency comb generated via gain-switching.
• To characterize the comb's spectral properties, linewidth, and noise performance.
• To investigate methods for expanding the number of comb lines.

Main Methods:

• Utilizing an externally seeded Fabry-Pérot laser diode operated in a gain-switching regime.
• Employing an optical phase modulator to increase the number of comb lines.
• Characterizing comb properties using optical spectrum analyzers and linewidth measurement techniques.

Main Results:

• Generation of a tunable optical comb with approximately eight 10 GHz coherent sidebands across the C-band (1530-1570 nm).
• Measured optical linewidth below 100 kHz for individual comb tones.
• Relative Intensity Noise (RIN) of filtered tones comparable to the unfiltered comb, indicating high signal quality.
• Near doubling of comb tones achieved through optical phase modulation.

Conclusions:

• The gain-switched laser diode provides a robust method for generating tunable optical frequency combs.
• The demonstrated comb exhibits excellent spectral characteristics suitable for various applications.
• Optical phase modulation effectively enhances the comb's spectral bandwidth and line density.