Interest in carbon dioxide (CO2) sensors is growing rapidly due to the increasing awareness of the link between air quality and health. Indoor, high CO2 levels signal poor ventilation, and outdoor the burning of fossil fuels and its associated pollution. CO2 gas sensors based on integrated optical waveguides are a promising solution due to their excellent gas sensing selectivity, compact size, and potential for mass manufacturing large volumes at low cost. However, previous demonstrations have not shown adequate performance for atmospheric-level sensing on a scalable platform. Here, we report the clearly resolved detection of 500 ppm CO2 gas at 1 s integration time and an extrapolated 1σ detection limit of 73 ppm at 61 s integration time using an integrated suspended silicon waveguide at a wavelength of 4.2 µm. Our waveguide design enables suspended strip waveguides with bottom anchors while maintaining a constant waveguide core cross-sectional geometry. This unique design results in a low propagation loss of 2.20 dB/cm. The waveguides were implemented in a 150 mm silicon on insulator (SOI) platform using standard optical lithography, providing a clear path to low-cost mass manufacturing. The low CO2 detection limit of our proposed waveguide, combined with its compatibility for high-volume production, creates substantial opportunities for waveguide sensing technology in CO2 sensing applications such as fossil fuel combustion monitoring and indoor air quality monitoring for ventilation and air conditioning systems.

Graphene mid-IR photodetectors are a promisingchoice for on-chip spectroscopy due to their broadbandphoto-response. However, the low efficiency of couplinglight to single-layer graphene hinders the detectorresponsivity. Here, we demonstrate a plasmon-enhancedgraphene-based photothermoelectric detector operating at4.2 μm wavelength in the mid-infrared. Integratingmetallic resonators with the graphene detector tripled itsresponsivity compared to a pure graphene device,attributed to enhanced graphene-light interaction. Ourminiaturized detector is bias-free and has a fast frequencyresponse of 25.6 kHz. Our detector was implemented in a150 mm silicon-on-insulator (SOI) platform, showing itspotential for on-chip integration and high-volumeproduction. 

Integration of functional materials and structures on the tips of optical fibers has enabled various applications in micro-optics, such as sensing, imaging, and optical trapping. Direct laser writing is a 3D printing technology that holds promise for fabricating advanced micro-optical structures on fiber tips. To date, material selection has been limited to organic polymer-based photoresists because existing methods for 3D direct laser writing of inorganic materials involve high-temperature processing that is not compatible with optical fibers. However, organic polymers do not feature stability and transparency comparable to those of inorganic glasses. Herein, we demonstrate 3D direct laser writing of inorganic glass with a subwavelength resolution on optical fiber tips. We show two distinct printing modes that enable the printing of solid silica glass structures (“Uniform Mode”) and self-organized subwavelength gratings (“Nanograting Mode”), respectively. We illustrate the utility of our approach by printing two functional devices: (1) a refractive index sensor that can measure the indices of binary mixtures of acetone and methanol at near-infrared wavelengths and (2) a compact polarization beam splitter for polarization control and beam steering in an all-in-fiber system. By combining the superior material properties of glass with the plug-and-play nature of optical fibers, this approach enables promising applications in fields such as fiber sensing, optical microelectromechanical systems (MEMS), and quantum photonics.

The affordable and easily accessible sensing of greenhouse gases is a vital Smart City application, serving both climate targets, and digitization goals at a European level. Commonly used spectroscopic solutions, although reliable, remain bulky and costly. Integrated photonics can fill the need for ubiquitous air testing, offering robust, miniaturized systems, with low cost. We present a study of a MID-IR spectroscopy sensing system developed on a silicon photonics platform, utilizing a Bragg grating mirror cavity. For each targeted gas, an optical cavity is designed, allowing the use of multimode radiation in its dedicated spectral window, therefore increasing the interaction length in the silicon waveguide.

We demonstrate a packaging approach to integrate electrical and optical connections in silicon photonic MEMS, utilizing a custom-designed silicon interposer for routing over 118 electrical connections and a 72 channel fiber array to couple to on-chip fiber grating couplers with minimal transmission loss at 1543 nm wavelength.

This is an introduction to the special issue "Micro and nano structured mid-IR to Terahertz materials and devices" which aims to cover recent developments in terms of photonics devices operating from the mid-infrared to terahertz wavelength ranges, with possible applications in spectroscopy, sensing, or communications.

We demonstrate methane gas sensing using suspended silicon waveguides and experimentally validate the sensitivity optimization of waveguide-based gas sensors by varying waveguide lengths. This method enables application-optimized integrated optical gas sensors.

We demonstrate methane gas sensing using suspended silicon waveguides and experimentally validate the sensitivity optimization of waveguide-based gas sensors by varying waveguide lengths. This method enables application-optimized integrated optical gas sensors.

Silica glass is a high-performance material that has become essential in modern life. Functionalization of silica glass is critically important for its optical applications such as in lenses and filters, which is however challenging to realize and manipulate in 3D-printed silica glass. Here, we report 3D printing of solid composites of silica glass and hydrogen silsesquioxane (HSQ) with sub-micrometer resolution. This is achieved by encapsulating HSQ inside silica glass by selectively transforming HSQ to silica glass by multi-photon absorption using a femtosecond laser. Furthermore, we demonstrated selective generation of photoluminescent silicon nanocrystals in the HSQ regions inside the composites by annealing. This is based on our experimental observation that the silica glass transformed from HSQ by multi-photon absorption, unlike HSQ, does not generate silicon nanocrystals upon annealing.

Electrostatic MEMS provide low power consumption to programmable photonics. However, the scaling of programmable photonics also requires solutions for circuit monitoring. We demonstrate a MEMS tunable phase monitor with integrated read-out on a foundry platform.