Low loss Bragg reflectors on SiO(2)-Si(3)N(4)-SiO(2) rib waveguides

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Waveguide Technology

Background:

• Bragg reflectors are crucial components in integrated optics for wavelength selectivity.
• Understanding waveguide attenuation loss is essential for device performance optimization.
• Silicon nitride (Si3N4) and silicon dioxide (SiO2) are common materials in photonic integrated circuits.

Purpose of the Study:

• To quantify the waveguide attenuation loss introduced by Bragg reflector formation.
• To investigate the sources of additional loss beyond scattering from grating roughness.
• To validate theoretical models for mode coupling in Bragg reflectors.

Main Methods:

• Experimental measurement of waveguide attenuation loss in fabricated Bragg reflectors.
• Analysis of scattering loss attributed to Bragg grating surface roughness.
• Identification and characterization of attenuation resonances using spectral measurements.

Main Results:

• Minimal added scattering loss of 0.2 +/- 0.1 dB/cm was measured for a Bragg reflector with a 15-A stop band.
• Attenuation resonances were observed on the high energy side of the Bragg resonance.
• These resonances are attributed to contradirectional coupling into continuum modes of the Si3N4 core and modes of the SiO2 cladding.

Conclusions:

• Bragg reflector formation in waveguides results in low scattering loss.
• Contradirectional mode coupling is a significant source of additional attenuation.
• Experimental results show good agreement with theoretical predictions for coupling wavelengths.