Critical coupling in cavity-resonant integrated-grating filters (CRIGFs)

Area of Science:

• Photonics
• Integrated Optics
• Nonlinear Optics

Background:

• Miniature grating-coupled resonators, or cavity-resonant integrated-grating filters (CRIGFs), are key components in integrated photonic circuits.
• Achieving critical coupling is essential for optimizing light-matter interactions and enhancing nonlinear optical phenomena.

Purpose of the Study:

• To experimentally demonstrate critical coupling in CRIGFs.
• To investigate the control of in-and out-coupling rates while maintaining constant internal losses and resonant wavelength.
• To correlate critical coupling with the enhancement of second harmonic generation (SHG).

Main Methods:

• Utilized asymmetric grating coupler designs for nonlinear CRIGFs.
• Employed a variant of coupled-modes theory to analyze resonator characteristics.
• Measured reflection and transmission spectra to estimate physical properties.

Main Results:

• Successfully demonstrated critical coupling in CRIGFs.
• Achieved fine control over resonator in-and out-coupling rates.
• Observed that critical coupling coincides with maximum enhancement of the second harmonic generation signal.

Conclusions:

• Critical coupling can be precisely controlled in CRIGFs.
• This control enables optimized performance for nonlinear integrated photonic devices.
• The findings pave the way for enhanced nonlinear optical signal generation using CRIGFs.