Low kappa, narrow bandwidth Si(3)N(4) Bragg gratings

Area of Science:

• Photonics and Optical Engineering
• Semiconductor Device Physics

Background:

• Achieving narrow linewidths in semiconductor lasers is crucial for applications like optical communications and spectroscopy.
• Low perturbation gratings are essential for controlling light-matter interactions and enhancing laser performance.

Purpose of the Study:

• To investigate and compare three distinct low perturbation grating designs (post, sampled, and high order) for their effectiveness in reducing linewidths.
• To assess the compatibility of these grating designs with Deep Ultraviolet (DUV) lithography.

Main Methods:

• Fabrication of three grating designs on 90 nm thick silicon nitride (Si3N4) strip waveguides.
• Characterization using reflection and transmission spectra measurements to determine coupling constants and Full Width at Half Maximum (FWHM).

Main Results:

• Demonstrated coupling constant (kappa) values ranging from 0.23 cm⁻¹ to 1.2 cm⁻¹.
• Achieved Full Width at Half Maximum (FWHM) linewidths between 74 pm and 116 pm.
• Analyzed tradeoffs between grating geometries regarding linewidth, apodization, and waveguide layout.

Conclusions:

• The investigated low perturbation grating designs are DUV lithography compatible.
• These designs facilitate the creation of long cavity single mode lasers with potential for kHz level linewidths on a monolithic platform.