3D printing at the macroscale has evolved from making plastic prototypes to the production of high-performance functional metal parts for industries such as medical and aerospace. By contrast, MEMS devices today are produced in large quantities using semiconductor manufacturing processes. However, the semiconductor manufacturing paradigm is not cost-effective for producing customized MEMS devices in small to medium volumes (tens to thousands of units per year), and related applications are difficult to address efficiently. 3D printing of functional MEMS devices could play an important role in filling this gap. Here, we discuss recent advances in 3D- printed functional MEMS, addressing the challenges of economical customization at smaller production volumes.

We present a fabrication process for 3D printing of glass sensors directly onto the end of optical fiber tips. Compared to conventional polymeric 3D-printed fiber-tip sensors, our method provides far superior chemical resistance and mechanical durability. We demonstrate the utility of our sensors by reliably measuring the refractive index of aggressive organic solvents - environments where polymer-based sensors are prone to swelling and deformation. This breakthrough opens new avenues for deploying robust glass sensors in demanding industrial settings, such as chemical processing plants and oil refineries, where precise and durable refractive index measurements are essential.

Reconfigurable optical gates control power and phase in programmable photonic circuits. However, state-of-the-art optical gates are power-hungry due to using heaters and large due to using Mach-Zehnder Interferometers. Here, we demonstrate a compact low-power optical gate based on a silicon photonic MEMS dual-drive directional coupler.

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.

In large interferometric circuits on SOI-platforms a high number of phase tuners is required to control the flow of light. Furthermore, reconfigurable circuits rely on the control of the phase in each arm of a balanced Mach-Zehnder interferometer (MZI) to create a 2×2 coupler with full control on the coupling and phase difference between the output ports [1]. Consequently, such circuits require a large amount of phase shifters densely integrated on the chip surface. To enable this, each phase shifter should have a 2π tuning range at a low voltage to ease to co-integration with the driver electronics. Furthermore, as the mesh size increases the insertion loss (IL) should be limited to avoid signal degradation. Since these devices are densely integrated in such circuits, both the footprint and optical length should be as small as possible while avoiding cross-talk between neighbouring devices.

We will present the advancements in AEOLUS, an H2020 project centered on sensing air quality and numerous gases, developing an integrated and miniaturized solution in Silicon photonics (SiPH). Traditional spectroscopic solutions, while reliable, are often bulky and costly, whereas we follow an integrated photonics solution for robust, miniaturized, and cost-effective systems. The integrated sensors NDIR spectroscopy in the mid-infrared (mid-IR), using suspended waveguide as a sensing element, graphene-based photodetectors for broadband and low power detection. The presented solution leveraged a broadband mid-IR source (thermal) that is cost-efficient and integratable and can greatly expand the applications of photonic integrated circuits (PICs). Thermal incandescent sources are advantageous over other mid-IR emitters based on semiconductor materials in terms of compatibility with PICs, manufacturing costs, and bandwidth. The 2D material used is consistent with the detector, i.e. graphene, a semi-metallic two-dimensional material. The demonstrated graphene mid-IR emitters integrated with photonic waveguides are considered for the mid-IR region relevant to absorption peaks of the gases under investigation for the purposes of air quality. A coupling efficiency of up to 68% is estimated with estimated emitter temperatures up to 1000 °C [1], covering the mid-IR region. The overall concept of AEOLUS also includes a Silicon protective capping lid to safeguard the integrated devices on the chip, assembled at the wafer scale. Results from CO2 and CH4 gas detection using AEOLUS suspended waveguides, at 4.2μm and 3.2μm, respectively, will also be shown (leveraging ideal mid-IR absorption spectral peaks for these gases).

Graphene mid-IR photodetectors are a promising choice for on-chip spectroscopy due to their broadband photo-response. However, the low efficiency of coupling light to single-layer graphene hinders the detector responsivity. Here, we demonstrate a plasmon-enhanced graphene-based photothermoelectric detector operating at 4.2 μm wavelength in the mid-infrared. Integrating metallic resonators with the graphene detector tripled its responsivity compared to a pure graphene device, attributed to enhanced graphene-light interaction. Our miniaturized detector is bias-free and has a fast frequency response of 25.6 kHz. Our detector was implemented in a 150 mm silicon-on-insulator (SOI) platform, showing its potential for on-chip integration and high-volume production.

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. 

Nanoelectromechanical (NEM) switches have the advantages of zero leakage current, abrupt switching characteristics, and harsh environmental capabilities. This makes them a promising component for digital computing circuits when high energy efficiency under extreme environmental conditions is important. However, to make NEM-based logic circuits commercially viable, NEM switches must be manufacturable in existing semiconductor foundry platforms to guarantee reliable switch fabrication and very large-scale integration densities, which remains a big challenge. Here, we demonstrate the use of a commercial silicon-on-insulator (SOI) foundry platform (iSiPP50G by IMEC, Belgium) to implement monolithically integrated silicon (Si) NEM switches. Using this SOI foundry platform featuring sub-200 nm lithography technology, we implemented two different types of NEM switches: (1) a volatile 3-terminal (3-T) NEM switch with a low actuation voltage of 5.6 V and (2) a bi-stable 7-terminal (7-T) NEM switch, featuring either volatile or non-volatile switching behavior, depending on the switch contact design. The experimental results presented here show how an established CMOS-compatible SOI foundry process can be utilized to realize highly integrated Si NEM switches, removing a significant barrier towards scalable manufacturing of high performance and high-density NEM-based programmable logic circuits and non-volatile memories.

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.