Beyond 20 nm frequency comb generation through a two-section quantum well passively mode-locked semiconductor laser

Area of Science:

• Optoelectronics
• Semiconductor Lasers
• Quantum Optics

Background:

• Optical frequency combs are crucial for precise measurements and spectroscopy.
• Passively mode-locked semiconductor lasers offer compact and efficient comb generation.
• Achieving ultra-wide bandwidths in semiconductor lasers remains a significant challenge.

Purpose of the Study:

• To demonstrate a passively mode-locked semiconductor laser with record-breaking optical bandwidth.
• To investigate the role of material structure in achieving broad and flat gain profiles.
• To characterize the performance of the generated optical comb in terms of bandwidth, pulse duration, and spectral properties.

Main Methods:

• Utilized a two-section InGaAlAs/InP quantum well (QW) passively mode-locked semiconductor laser.
• Optimized a strain-compensated multi-quantum well (MQW) structure to achieve a broad and flat-topped gain profile.
• Measured optical bandwidths at -3 dB and -10 dB levels.
• Characterized femtosecond pulse duration, radiofrequency (RF) beat-note linewidth, and signal-to-noise ratio (SNR).

Main Results:

• Achieved -3 dB optical bandwidth of 20.93 nm and -10 dB bandwidth of 37.26 nm.
• Reported the widest optical bandwidths for any directly electrically pumped passively mode-locked semiconductor laser.
• Measured a pulse duration of 874.5 fs.
• Obtained an RF beat-note -3 dB linewidth of 15.2 MHz and an SNR of 32 dB.

Conclusions:

• The optimized strain-compensated MQW structure is key to enabling ultra-wide optical bandwidths.
• This laser represents a significant advancement in directly electrically pumped passively mode-locked semiconductor laser technology.
• The demonstrated performance opens new avenues for applications requiring broadband optical frequency combs.