Low Loss Silica High-Mesa Waveguide for Infrared Sensing

Significant Propagation Loss Reduction on Silicon High-Mesa Waveguides Using Thermal Oxidation Technique

“…As a result, the main reasons of α in our case are the scattering loss αscattering origining from the rough sidewall and the absorption loss αabsorption from damaged Si caused by the ICP etching. Oxidation of Si has been shown to be effective at reducing the sidewall scattering and recovering the damaged Si [4]. After oxidation, a thin Si layer near the sidewall is oxidized into SiO2, so that the effective refractive index (neff) of waveguide is reduced and the damaged Si is recovered.…”

“…3. On the chip, it integrates a tunable laser (TL), a semiconductor optical amplifier (SOA), an optical coupler (CP) with a splitting ratio 9:1, a 1 m long waveguide gas sensing (WGS) cell and a photo-detector (PD) [4]. In this work, This work take CH4 for the targeted gas as an example and use the 3 μm wide waveguide with the measured α=0.2 dB/cm and the calculated Γair =2.6%.…”

“…In this work, This work take CH4 for the targeted gas as an example and use the 3 μm wide waveguide with the measured α=0.2 dB/cm and the calculated Γair =2.6%. In the CRDS system, the ringdown times are 200, which means the effective sensing path is 200 m [4]. Consequently, the sensitivity of the integrated CRDS circuit is determined by the α and Γair of the WGS and the CH4 absorption cross section.…”

“…In order to detect ppm-order breath content in addition to the real time sensing, breath sensing system based on cavity ring-down spectroscopy (CRDS) technique has been researched as a candidate [2]. Compared to the conventional bulk CRDS system [3], utilizing waveguide as the gas sensing cell may realize several meters sensing path which is needed for measuring ppm-order components in human breath within a compact area [4]. This brings the possibility of integrating CRDS system into a cell phone or other mobile equipment for powerful in-situ and real-time health-monitoring.…”

“…A 1 m-long waveguide with the propagation loss ≤ 0.2 dB/cm is required to be applied as the sensing cell. Recently, a novel high-mesa waveguide structure has been proposed by our group for the compact and high-sensitive CRDS system [4,6,7]. Compared to the slot waveguide [8] and the conventional channel waveguide, it not only provides the evanescent field sufficient touching the breath gas, but also avoids the surface to be contaminated by particles in air.…”