Microcavity-enhanced Kerr nonlinearity in a vertical-external-cavity surface-emitting laser

Area of Science:

• Optics and Photonics
• Semiconductor Lasers
• Nonlinear Optics

Background:

• Self-mode-locking is a key technique for generating ultrashort pulses in vertical-external-cavity surface-emitting lasers (VECSELs).
• Kerr nonlinearity is typically assumed to be the driving mechanism for mode-locking in these systems.
• Understanding and controlling Kerr nonlinearity is essential for optimizing VECSEL performance.

Purpose of the Study:

• To investigate and quantify the Kerr nonlinearity in a VECSEL gain chip.
• To explore the role of microcavity enhancement on Kerr nonlinearity.
• To demonstrate wavelength-tuning of Kerr nonlinearity for tailored mode-locking behavior.

Main Methods:

• Utilized the Z-scan technique for wavelength-dependent measurements of nonlinear absorption and refractive index change.
• Employed a VECSEL gain chip in the (InGa)As/Ga(AsP) material system.
• Varied the angle of incidence of a probe beam to tune the Kerr nonlinearity.

Main Results:

• Confirmed strong Kerr nonlinearity, including negative nonlinear refraction up to 5x10^-12 cm²/W.
• Revealed significant enhancement of Kerr nonlinearity due to the microcavity.
• Demonstrated wavelength-tuning of Kerr nonlinearity, correlating with microcavity resonance.

Conclusions:

• The study provides evidence of strong Kerr nonlinearity and its microcavity enhancement in VECSELs.
• Wavelength-tunable Kerr nonlinearity offers a novel approach for controlling self-mode-locking.
• These findings pave the way for designing cost-effective, robust, and compact femtosecond pulsed semiconductor lasers.