Whispering-gallery mode resonators for highly unidirectional laser action

Area of Science:

• Photonics and Optical Engineering
• Laser Physics
• Materials Science

Background:

• Optical microcavities utilizing total internal reflection support high-quality factor (Q factor) whispering-gallery modes (WGMs).
• Conventional microcavity lasers exhibit non-directional emission and inefficient power coupling due to radial symmetry.
• Addressing these limitations is crucial for practical applications like microcavity lasers.

Purpose of the Study:

• To design elliptical resonators enabling in-plane, highly unidirectional laser emission from WGMs.
• To investigate the impact of a wavelength-size notch on WGM properties and emission directionality.
• To demonstrate a robust and scalable design for low-threshold, unidirectional microcavity diode lasers.

Main Methods:

• Design of elliptical optical resonators incorporating a wavelength-size notch.
• Utilizing mid-infrared injection quantum cascade lasers (λ ∼ 10 μm) as a model system.
• Characterization of beam divergence and optical power output at room temperature.

Main Results:

• Achieved in-plane laser emission with a beam divergence as narrow as 6 degrees.
• Demonstrated a peak optical power of approximately 5 mW.
• Confirmed that beam divergence is insensitive to pumping current and notch geometry, indicating design robustness.

Conclusions:

• The notched elliptical resonator design effectively enables highly unidirectional laser emission from WGMs.
• The Q factor of WGMs remains high despite the presence of the notch, ensuring efficient light confinement.
• This scalable design paves the way for developing highly unidirectional, low-threshold microcavity diode lasers across various spectral ranges.