Dual slow-light enhanced photothermal gas spectroscopy on a silicon chip

TL;DR

This paper introduces a dual slow-light scheme on a silicon chip that significantly enhances photothermal gas sensing sensitivity, achieving record detection limits in a compact, integrated photonic platform.

Contribution

The work demonstrates a novel dual slow-light approach in photonic crystal waveguides that greatly improves gas sensing sensitivity on a CMOS-compatible silicon platform.

Findings

Achieved a photothermal efficiency 3.6x10^-4 rad cm ppm^-1 mW^-1 m^-1, surpassing traditional waveguides.

Demonstrated acetylene detection sensitivity of 1.4x10^-6 NEAL with a 1-mm-long sensor.

Enabled high-sensitivity gas sensing in a compact 0.6 mm^2 device.

Abstract

Integrated photonic sensors have attracted significant attention recently for their potential for high-density integration. However, they face challenges in sensing gases with high sensitivity due to weak light-gas interaction. Slow light, which dramatically intensifies light-matter interaction through spatial compression of optical energy, provides a promising solution. Herein, we demonstrate a dual slow-light scheme for enhancing the sensitivity of photothermal spectroscopy (PTS) with a suspended photonic crystal waveguide (PhCW) on a CMOS-compatible silicon platform. By tailoring the dispersion of the PhCW to generate structural slow light to enhance pump absorption and probe phase modulation, we achieve a photothermal efficiency of 3.6x10-4 rad cm ppm-1 mW-1 m-1, over 1-3 orders of magnitude higher than the strip waveguides and optical fibers. With a 1-mm-long sensing PhCW incorporated in a stabilized on-chip Mach-Zehnder interferometer with a footprint of 0.6 mm2, we demonstrate acetylene detection with a sensitivity of 1.4x10-6 in terms of noise-equivalent absorption and length product (NEAL), the best among the reported photonic waveguide gas sensors to our knowledge. The dual slow-light enhanced PTS paves the way for integrated photonic gas sensors with high sensitivity, miniaturization, and cost-effective mass production.