Design and Analysis of a Slot Photonic Crystal Waveguide for Highly Sensitive Evanescent Field Absorption Sensing in Fluids

The design and modeling of a highly sensitive sensor based on a slot photonic crystal waveguide (slot-PCWG) is presented. The structure consists of cylindrical air rods drilled in a dielectric slab on a triangular lattice, which are filled with SiO2. The waveguide is formed by removing elements from the regular photonic crystal grid in a row, and embedding a slot in the center position. This concept allows for a vast enhancement of the evanescent field ratio, leading to a strong overlap between the field of the waveguide mode and the analyte. In the present work, we show that the sensitivity at the constant slab thickness of the slot-PCWG modes is greatly enhanced, up to a factor of 7.6 compared with the corresponding PCWG modes or Si-slab WGs. The finite-difference time-domain (FDTD) technique and plane wave expansion (PWE) methods were used to study the dispersion and profile of the PCWG mode. The simulation results show the potential of this design, which will be fabricated and tested in the following steps of the project

Chirped Grating IR-Filter on a Waveguide for Sensing Applications

We present results for a specific filter design for silicon waveguides, which features a transmission wavelength and bandwidth well suited for carbon dioxide sensing. Simulations were performed using Comsol Multiphysics and the design was optimized for a central wavelength of 4.26 µm. Furthermore, we included real-world effects like the discrete resolution of the design grid as well as process-specific fabrication tolerances. The devised structures were based on a photonic waveguide concept, which was developed recently for evanescent-field-based sensing applications. Slab waveguides with gratings on top as well as strip waveguides with sidewall gratings were considered. The concept and design are discussed in detail in order to highlight the underlying ideas

Optimization of Si-Based Waveguides for Evanescent-Field Sensors

We present a detailed study of Si-based optical waveguides, which can be used as evanescent field sensors for the quantitative analysis of various gases and liquids. Direct quantitative comparison of simulation with experimental results of directional coupling structures allows fine-tuning the material parameters and provides important input for future sensor design

Numerical Investigations of Infrared Slot Waveguides for Gas Sensing

Sensing of gases is a promising area for applications of photonic sensor devices that operate in the mid-infrared spectral range. We present a numerical investigation of slot waveguides for evanescent field sensing of CO2. The sensor platform is a poly-silicon slot waveguide on silicon dioxide, where both layers are deposited on a standard silicon substrate. The evanescent field ratio, which is a crucial parameter for the sensing performance of the waveguides, was determined and values as high as 42% were obtained

Characterization of a Vertical-Cavity Enhanced Detector for Narrowband Detection in the Mid-Infrared

In this work we present the experimental characterization of a vertical-cavity enhanced resonant detector (VERD) optimized for detection in the mid-infrared. We demonstrate that the VERD shows a 7.1 times higher absorption and responsivity at 4.26 µm compared to a bare metal absorber. As such this design can be easily optimized and integrated to specifically enhance the absorption around the design wavelength

Evanescent-Wave Gas Sensing Using an Integrated Thermal Light Source

The last years showed an increased request for miniaturised, CMOS-compatible gas detectors. In contrast to sensors utilizing metal-oxide chemical interfaces, optical strategies are potentially faster and more robust. Recently we demonstrated CO2 detection by evanescent-wave absorption in the mid-infrared using a combination of an external laser source and silicon waveguides based on CMOS technology. We now go one step further and demonstrate the feasibility of detection of CO2 down to a concentration of 3% with a low-cost integrated thermal source. These results are promising for further technological developments towards on-chip mid-infrared photonic gas sensors, and new designs are currently devised to increase the yet relatively low sensitivity

Photonic Gas Sensor Using a Silicon Strip Waveguide

Sensing of gases is a promising area for applications of photonic systems operating in the mid-infrared spectral range. We present an infrared evanescent-field absorption gas sensor based on a silicon strip waveguide, which was specifically designed for CO2 sensing. We discuss finite element simulations that were used to design the strip waveguide and furthermore present experimental data of quantitative CO2 measurements with the devised structures. The first demonstrator device detects concentrations down to 5000 ppm CO2 which is the workplace exposure limit in most jurisdictions