All-optical controlled switching between time-periodic square waves in diode lasers with delayed feedback.

Area of Science:

• Nonlinear dynamics
• Semiconductor lasers
• Optical feedback systems

Background:

• Edge-emitting diode lasers exhibit complex dynamics under optical feedback.
• Square-wave (SW) self-modulation is a key phenomenon in laser dynamics.
• Understanding and controlling SW oscillations is crucial for laser applications.

Purpose of the Study:

• To investigate the square-wave (SW) self-modulation output of edge-emitting diode lasers with polarization-rotated optical feedback.
• To analyze the coexistence of different SW periods and their harmonic relationships.
• To demonstrate a method for controlling SW switching using conventional optical feedback.

Main Methods:

• Experimental characterization of laser output under varied optical feedback conditions.
• Theoretical analysis using laser rate equations.
• Numerical simulations to confirm experimental findings and control schemes.

Main Results:

• Observed coexistence of fundamental 2τ-periodic SWs with shorter-period harmonic oscillations.
• Identified harmonic periods as P(n)≃2τ/(1+2n), where n is an integer.
• Demonstrated effective control of SW switching between different periodicities by adjusting feedback delay.

Conclusions:

• The multistability of SW solutions in diode lasers with optical feedback is confirmed.
• Weak conventional optical feedback provides a controllable method for selecting specific SW harmonics.
• The feedback delay is identified as the critical parameter for stabilizing desired harmonic oscillations.