High-resolution, broadband on-chip spectrometer with tunable multi-mode waveguide Bragg gratings.

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Spectroscopy

Background:

• On-chip spectrometers offer compact, lightweight, and low-complexity solutions for diverse applications.
• Achieving both high spectral resolution and broadband detection simultaneously is a key challenge in integrated spectrometer design.

Purpose of the Study:

• To propose and demonstrate an innovative on-chip filter spectrometer based on a silicon-on-insulator (SOI) waveguide platform.
• To achieve simultaneous high spectral resolution and broadband detection using thermo-optically tunable multimode waveguide Bragg gratings (MM-WBGs).

Main Methods:

• Fabrication of an on-chip spectrometer using SOI waveguides and four thermo-optically tunable MM-WBGs with varying periods.
• Analysis of the conversion mechanism of incident fundamental mode spectra to multi-order even mode reflection spectra.
• Characterization via thermo-optic modulation with integrated heating electrodes and spectral reconstruction experiments.

Main Results:

• Demonstrated a stable spectral resolution better than 150 pm within a 35 nm operational bandwidth.
• Achieved narrow-linewidth reflection spectra by reducing fundamental-mode field distribution at grating edges.
• Explored spiral-MM-WBGs for improved spatial efficiency and narrow linewidth MM-WBGs (∼40 pm) for enhanced resolution.

Conclusions:

• The proposed on-chip filter spectrometer offers an innovative approach for integrated spectral analysis.
• The device achieves high resolution, broadband operation, and low complexity, suitable for various scientific and diagnostic fields.
• Further development with spiral and narrow linewidth MM-WBGs shows potential for enhanced performance and miniaturization.