Observation of stable cylindrical modes in electrically pumped circular grating-coupled surface-emitting lasers

Area of Science:

• Optics and Photonics
• Semiconductor Lasers

Background:

• Circular grating-coupled surface-emitting lasers (CGCSELs) are crucial for various photonic applications.
• Understanding and controlling their modal behavior is essential for optimizing performance.
• Previous studies have explored different resonator designs to achieve stable operation.

Purpose of the Study:

• To experimentally investigate the modal behavior of CGCSELs with resonant second-order gratings.
• To evaluate the impact of a central indentation on laser stability and mode operation.
• To enhance beam quality through improved spatial coherence.

Main Methods:

• Fabrication of electrically pumped circular grating-coupled surface-emitting lasers.
• Inclusion of a passive, unpumped 0.7-microm-deep indentation at the resonator's center.
• Experimental characterization of modal behavior under varying current levels.

Main Results:

• Achieved stable cylindrical mode operation with azimuthal orders m = 1 and m = 52.
• Observed significantly enhanced modal stability with the central indentation, suppressing mode hopping.
• Demonstrated lasing of two orthogonal m = 1 modes and one higher-order mode up to 2.2 times threshold.
• Confirmed improved spatial coherence and beam quality due to stable cylindrical modes.

Conclusions:

• A central indentation is an effective method for stabilizing modal behavior in CGCSELs.
• This technique promotes robust cylindrical mode operation and superior beam quality.
• The findings offer a pathway for developing more reliable and high-performance surface-emitting lasers.