Asymmetric square waves in mutually coupled semiconductor lasers with orthogonal optical injection

Area of Science:

• Physics
• Optics
• Laser Technology

Background:

• Mutual optical injection coupling between lasers can lead to complex dynamics.
• Polarization modes in semiconductor lasers are crucial for various applications.

Purpose of the Study:

• To investigate the polarization dynamics of two mutually coupled edge-emitting lasers.
• To explore the tunability of observed oscillations and the underlying mechanisms.

Main Methods:

• Experimental setup involving two edge-emitting lasers with orthogonal optical injection.
• Analysis of polarization mode behavior (TE and TM) under varying pump current and coupling strength.
• Numerical simulations to validate experimental findings and understand noise effects.

Main Results:

• Observed square-wave oscillations in polarization modes of both lasers.
• Antiphase relationship between TE and TM modes within each laser.
• TE mode of one laser leads the TM mode of the other by the one-way time of flight.
• Tunable duty cycle of square waves with pump current and coupling strength; period near roundtrip time.
• Numerical simulations confirm experimental results and highlight noise's stabilizing role.

Conclusions:

• Orthogonal optical injection can induce stable square-wave polarization dynamics in coupled lasers.
• The observed dynamics are tunable and influenced by injection parameters and inter-laser time of flight.
• Noise plays a significant role in stabilizing these unique oscillations, offering potential for novel optical signal generation.