Tracking exceptional points above the lasing threshold

Area of Science:

• Non-Hermitian photonics
• Semiconductor laser dynamics
• Exceptional point singularities

Background:

• Exceptional points (EPs) in non-Hermitian optical systems exhibit unique phenomena like unidirectional invisibility.
• Typically, EPs are accessed below the lasing threshold in the linear regime.
• Coupled semiconductor nanolasers are key components in photonic integrated circuits.

Purpose of the Study:

• To experimentally demonstrate the accessibility of EPs above the lasing threshold in coupled semiconductor nanolasers.
• To investigate the role of cavity detuning and carrier-induced frequency shifts in EP formation.
• To explore the nonlinear dynamics and tracking capabilities of EPs in a lasing regime.

Main Methods:

• Experimental realization of coupled semiconductor nanolasers.
• Operation above the lasing threshold.
• Analysis of nonlinear dynamics and EP characteristics under varying pump power and detuning.

Main Results:

• EP singularities were successfully accessed above the lasing threshold, behaving as branch points in a nonlinear dynamical system.
• Cavity detuning was found to be essential for compensating carrier-induced frequency shifts and restoring EPs.
• Pump imbalance at lasing EPs was shown to vary with total pump power, allowing for continuous tracking.

Conclusions:

• Exceptional points in coupled semiconductor nanolasers possess an unstable nature above the laser threshold.
• This research opens avenues for developing self-pulsing nanolaser devices and frequency combs.
• The findings challenge conventional understanding of EP formation in the presence of gain and loss.