Fully suspended slot waveguides for high refractive index sensitivity

Abstract

A fully suspended mid-infrared (FSMIR) slot waveguide is proposed and experimentally demonstrated on a silicon-on-insulator (SOI) platform for the first time. The slotted waveguide core is mechanically supported by lateral subwavelength grating claddings. The fabricated waveguides possess low propagation loss, which is measured to be 7.9 dB/cm at the wavelength of 2.25 μm. With the underlying buried oxide (BOX) removed, the FSMIR slot waveguide has a broad spectral range of transparency that is limited only by the absorption of silicon. Numerical simulation shows that its sensitivity, defined as the ratio between the change of the effective index and the ambient refractive index, can reach 1.123, which is 9.7% higher than the maximal sensitivity of conventional SOI slot waveguides on BOX.

A High-Efficiency Multispectral Filter Based on Plasmonic Hybridization between Two Cascaded Ultrathin Nanogratings

“…For the practical realization of the proposed multispectral plasmonic color filter, its fabrication dimension is supposed to be finite. Referring to the fabrication method of fully suspended slot waveguide and free-standing plasmonic metal-dielectric-metal filter in literature reports [16,32,33], our designed multilayer plasmonic structure can be realized based on the electron beam evaporation, focused ion beam etching, and chemical gas/solution etching technology. During the practical fabrication process, the precise control of the structural parameters, such as the nanograting thickness, the slit width, the air and SiO 2 layer thickness, the misaligned distance between the upper and bottom nanogratings, etc., are cumbersome to achieve.…”

Subwavelength Engineering in Silicon Photonic Devices

“…Aimed at enhancing the optical mode overlap with the analyte in integrated optical gas and microfluidic sensors, we introduced the subwavelength-structured FSSW in 2017 [53]. In 2018, we extended this approach to a full platform, including directional couplers, microring resonators, and mode convertors operating in the mid-IR spectral region [54].…”

“…Recently, the optical dispersion of devices were also engineered using SWG resulting in demonstrations of ultra-broadband couplers [36], polarizationindependent couplers [43], polarization beam splitters [44], sharp waveguide bends [40], and ring resonators [45]. For nearand mid-infrared (IR) applications, we developed subwavelength-engineered waveguide grating couplers (GCs) since 2009 [38,[46][47][48][49][50][51] and fully suspended waveguide platforms since 2012 [52][53][54][55][56][57], which will be reviewed in Sections II and III, respectively.…”

Suspended low-loss germanium waveguides for the longwave-infrared

“…By utilising this approach, a minimum loss of 0.82 dB/cm was achieved at 3.8 µm [15] and 3.1 dB/cm at 7.67 µm [17]. The same approach has recently been implemented to create suspended Si slot waveguides [18] at 2.25 µm. However, the intrinsic absorption of silicon at wavelengths longer than 7.7 µm (i.e.…”