Ultra-low threshold lasing through phase front engineering via a metallic circular aperture.

Area of Science:

• Optoelectronics
• Laser Physics
• Nanophotonics

Background:

• Semiconductor lasers require small active regions and high-quality cavities for low threshold power.
• Diffraction loss at laser facets is a key challenge for ultra-low threshold ridge lasers with reflective coatings.

Purpose of the Study:

• To demonstrate a method for suppressing diffraction loss and enhancing modal reflectivity and transmissivity in laser coatings.
• To achieve room-temperature continuous-wave operation in a quantum cascade laser with significantly reduced power consumption.

Main Methods:

• Introducing a subwavelength aperture into the metallic highly reflective coating of a laser.
• Theoretical modeling and experimental validation of the aperture's effect on phase front correction, modal reflectivity, and transmissivity.
• Implementation of the method on a small-cavity quantum cascade laser.

Main Results:

• The subwavelength aperture enhanced modal reflectivity and transmissivity simultaneously.
• Mirror loss decreased by over 40%, and transmissivity increased by a factor of 10^4.
• Achieved room-temperature continuous-wave lasing at 4.5 μm with 143 mW electrical power consumption.

Conclusions:

• Subwavelength apertures in reflective coatings can significantly reduce mirror loss and enhance laser performance.
• This technique enables ultra-low threshold semiconductor lasers, paving the way for portable optoelectronic devices.
• The method is broadly applicable to various optoelectronic systems.