Generation of optical pulses in VCSELs below the static threshold using asymmetric current modulation

Area of Science:

• Optics and Photonics
• Semiconductor Lasers
• Nonlinear Dynamics

Background:

• Vertical-cavity surface-emitting lasers (VCSELs) are key components in optical communication.
• Direct modulation of VCSELs below threshold typically results in unstable or low-quality optical pulses.
• Understanding the dynamics of VCSELs under specific modulation schemes is crucial for advanced applications.

Purpose of the Study:

• To present a novel method for generating sub-nanosecond optical pulses from directly modulated VCSELs.
• To investigate the generation of irregular optical pulses in orthogonal polarizations.
• To optimize modulation parameters for enhanced pulse characteristics.

Main Methods:

• Utilizing the spin-flip model to simulate VCSEL dynamics.
• Implementing asymmetric triangular modulation with a slow rising ramp and fast decreasing ramp.
• Analyzing pulse properties such as amplitude and dispersion.

Main Results:

• Demonstrated generation of sub-nanosecond optical pulses below the continuous-wave (cw) threshold.
• Achieved irregular optical pulse generation in two orthogonal linear polarizations.
• Identified optimal modulation asymmetry for maximum pulse amplitude and minimum amplitude dispersion (approx. 20% effective threshold reduction).

Conclusions:

• Asymmetric triangular modulation is an effective method for generating high-quality optical pulses from sub-threshold VCSELs.
• The spin-flip model accurately predicts the behavior of VCSELs under these modulation conditions.
• This technique offers a promising approach for improving optical pulse generation in VCSELs.