GaN microdisk with direct coupled waveguide for unidirectional whispering-gallery mode emission.

Area of Science:

• Optoelectronics
• Nanophotonics
• Materials Science

Background:

• Microdisks are effective whispering-gallery mode (WGM) optical resonators.
• Efficient extraction of light from microdisk resonators is challenging due to isotropic in-plane emission.
• Existing evanescent coupling methods require high-precision nanofabrication.

Purpose of the Study:

• To develop a simplified method for efficient light extraction from microdisk resonators.
• To demonstrate non-evanescent coupling between a microdisk and a waveguide.
• To fabricate a directly coupled waveguide-microdisk system on GaN.

Main Methods:

• Fabrication of a 0.16 µm wide waveguide directly coupled to a 10 µm diameter microdisk.
• Use of a 0.77 µm thick GaN thin film with InGaN/GaN multi-quantum wells.
• Application of nanosphere and nanowire lithography techniques.

Main Results:

• Successful fabrication of a directly coupled waveguide-microdisk structure.
• Demonstration of non-evanescent coupling of WGMs from the microdisk to the waveguide.
• Elimination of the need for ultra-precise gap control inherent in evanescent coupling.

Conclusions:

• Directly coupled waveguides offer a simplified and effective approach for light extraction from microdisk resonators.
• The demonstrated fabrication method is robust and avoids stringent patterning requirements.
• This work advances the development of efficient WGM resonator-based optoelectronic devices.