Multifunctional mid-infrared photonic switch using a MEMS-based tunable waveguide coupler

Development of Photonic In-Sensor Computing Based on a Mid-Infrared Silicon Waveguide Platform

Neuromorphic in-sensor computing has provided an energy-efficient solution to smart sensor design and on-chip data processing. In recent years, various free-space-configured optoelectronic chips have been demonstrated for on-chip neuromorphic vision processing. However, on-chip waveguide-based in-sensor computing with different data modalities is still lacking. Here, by integrating a responsivity-tunable graphene photodetector onto the silicon waveguide, an on-chip waveguide-based in-sensor processing unit is realized in the mid-infrared wavelength range. The weighting operation is achieved by dynamically tuning the bias of the photodetector, which could reach 4 bit weighting precision. Three different neural network tasks are performed to demonstrate the capabilities of our device. First, image preprocessing is performed for handwritten digits and fashion product classification as a general task. Next, resistive-type glove sensor signals are reversed and applied to the photodetector as an input for gesture recognition. Finally, spectroscopic data processing for binary gas mixture classification is demonstrated by utilizing the broadband performance of the device from 3.65 to 3.8 μm. By extending the wavelength from near-infrared to mid-infrared, our work shows the capability of a waveguide-integrated tunable graphene photodetector as a viable weighting solution for photonic in-sensor computing. Furthermore, such a solution could be used for large-scale neuromorphic in-sensor computing in photonic integrated circuits at the edge.

Artificial Intelligence-Enhanced Waveguide "Photonic Nose"- Augmented Sensing Platform for VOC Gases in Mid-Infrared

On-chip nanophotonic waveguide sensor is a promising solution for miniaturization and label-free detection of gas mixtures utilizing the absorption fingerprints in the mid-infrared (MIR) region. However, the quantitative detection and analysis of organic gas mixtures is still challenging and less reported due to the overlapping of the absorption spectrum. Here,an Artificial-Intelligence (AI) assisted waveguide "Photonic nose" is presented as an augmented sensing platform for gas mixture analysis in MIR. With the subwavelength grating cladding supported waveguide design and the help of machine learning algorithms, the MIR absorption spectrum of the binary organic gas mixture is distinguished from arbitrary mixing ratio and decomposed to the single-component spectra for concentration prediction. As a result, the classification of 93.57% for 19 mixing ratios is realized. In addition, the gas mixture spectrum decomposition and concentration prediction show an average root-mean-square error of 2.44 vol%. The work proves the potential for broader sensing and analytical capabilities of the MIR waveguide platform for multiple organic gas components toward MIR on-chip spectroscopy.

MEMS Switch Realities: Addressing Challenges and Pioneering Solutions

Micro-Electro-Mechanical System (MEMS) switches have emerged as pivotal components in the realm of miniature electronic devices, promising unprecedented advancements in size, power consumption, and versatility. This literature review paper meticulously examines the key issues and challenges encountered in the development and application of MEMS switches. The comprehensive survey encompasses critical aspects such as material selection, fabrication intricacies, performance metrics including switching time and reliability, and the impact of these switches on diverse technological domains. The review critically analyzes the influence of design parameters, actuation mechanisms, and material properties on the performance of MEMS switches. Additionally, it explores recent advancements, breakthroughs, and innovative solutions proposed by researchers to address these challenges. The synthesis of the existing literature not only elucidates the current state of MEMS switch technology but also paves the way for future research avenues. The findings presented herein serve as a valuable resource for researchers, engineers, and technologists engaged in advancing MEMS switch technology, offering insights into the current landscape and guiding future endeavors in this rapidly evolving field.

Two-axis MEMS positioner for waveguide alignment in silicon nitride photonic integrated circuits

Alignment is critical for efficient integration of photonic integrated circuits (PICs), and microelectromechanical systems (MEMS) actuators have shown potential to tackle this issue. In this work, we report MEMS positioning actuators designed with the ultimate goal of aligning silicon nitride (SiN) waveguides either to different outputs within a SiN chip or to active chips, such as lasers and semiconductor optical amplifiers. For the proof-of-concept, suspended SiN waveguides implemented on a silicon-on-insulator wafer were displaced horizontally in the direction of light propagation to close an initial gap of 6.92 µm and couple the light to fixed output waveguides located on a static section of the chip. With the gap closed, the suspended waveguides showed ∼ 345 nm out-of-plane misalignment with respect to the fixed waveguides. The suspended waveguides can be displaced laterally by more than ±2 µm. When the waveguides are aligned and the gap closed, an average loss of -1.6 ± 0.06 dB was achieved, whereas when the gap is closed with a ± 2 µm lateral displacement, a maximum average loss of ∼ -19.00 ± 0.62 dB was obtained. The performance of this positioner does not only pave the way for active chip alignment, but it could also be considered for optical switching applications.

Application of optical switching technology in a lunar laser ranging system based on a superconducting detector

The TianQin laser ranging station has successfully obtained the effective echo signals of the all five corner-cube reflectors on the lunar surface by using a 1064 nm Nd:YAG laser with 100 Hz repetition frequency and a 2×2 array of superconducting nanowire single-photon detectors (SNSPDs). The application of the SNSPD in the lunar laser ranging system (LLRS) has demonstrated its detection ability, but it loses its superconducting state and cannot work under strong stray light conditions. In this paper, a high-speed optical switch experimental device based on 100 Hz is developed to solve the application problem of the SNSPD in the LLRS, and its main technical parameters are tested. The results show that the maximum running distance of the switch is 200 µm; the switching time is better than 2 ms; and the extinction ratio is better than 57 dB. Moreover, the application of the high-speed optical switch experimental device in the lunar laser ranging system is designed, and the effective detection time between two laser pulses (10 ms) is determined to be 6.1 ms.

Mid-infrared silicon photonic phase shifter based on microelectromechanical system

Mid-infrared (MIR) photonic integrated circuits have generated considerable interest, owing to their potential applications, such as thermal imaging and biochemical sensing. A challenging area in the field is the development of reconfigurable approaches for the enhancement of on-chip functions, where a phase shifter plays an important role. Here, we demonstrate a MIR microelectromechanical system (MEMS) phase shifter by utilizing an asymmetric slot waveguide with subwavelength grating (SWG) claddings. The MEMS-enabled device can be easily integrated into a fully suspended waveguide with SWG cladding, built on a silicon-on-insulator (SOI) platform. Through engineering of the SWG design, the device achieves a maximum phase shift of 6π, with an insertion loss of 4 dB and a half-wave-voltage-length product (V_πL_π) of 2.6 V·cm. Moreover, the time response of the device is measured as 13 µs (rise time) and 5 µs (fall time).

Silicon Photonic Phase Shifters and Their Applications: A Review

With the development of silicon photonics, dense photonic integrated circuits play a significant role in applications such as light detection and ranging systems, photonic computing accelerators, miniaturized spectrometers, and so on. Recently, extensive research work has been carried out on the phase shifter, which acts as the fundamental building block in the photonic integrated circuit. In this review, we overview different types of silicon photonic phase shifters, including micro-electro-mechanical systems (MEMS), thermo-optics, and free-carrier depletion types, highlighting the MEMS-based ones. The major working principles of these phase shifters are introduced and analyzed. Additionally, the related works are summarized and compared. Moreover, some emerging applications utilizing phase shifters are introduced, such as neuromorphic computing systems, photonic accelerators, multi-purpose processing cores, etc. Finally, a discussion on each kind of phase shifter is given based on the figures of merit.

Integrated 1 × 3 MEMS silicon nitride photonics switch

We present a 1 × 3 optical switch based on a translational microelectromechanical system (MEMS) platform with integrated silicon nitride (SiN) photonic waveguides. The fabricated devices demonstrate efficient optical signal transmission between fixed and suspended movable waveguides. We report a minimum average insertion loss of 4.64 dB and a maximum average insertion loss of 5.83 dB in different switching positions over a wavelength range of 1530 nm to 1580 nm. The unique gap closing mechanism reduces the average insertion loss across two air gaps by a maximum of 7.89 dB. The optical switch was fabricated using a custom microfabrication process developed by AEPONYX Inc. This microfabrication process integrates SiN waveguides with silicon-on-insulator based MEMS devices with minimal stress related deformation of the MEMS platform.

Suspended Silicon Waveguide with Sub-Wavelength Grating Cladding for Optical MEMS in Mid-Infrared

Mid-infrared (MIR) photonics are generating considerable interest because of the potential applications in spectroscopic sensing, thermal imaging, and remote sensing. Silicon photonics is believed to be a promising solution to realize MIR photonic integrated circuits (PICs). The past decade has seen a huge growth in MIR PIC building blocks. However, there is still a need for the development of MIR reconfigurable photonics to enable powerful on-chip optical systems and new functionalities. In this paper, we present an MIR (3.7~4.1 μm wavelength range) MEMS reconfiguration approach using the suspended silicon waveguide platform on the silicon-on-insulator. With the sub-wavelength grating claddings, the photonic waveguide can be well integrated with the MEMS actuator, thus offering low-loss, energy-efficient, and effective reconfiguration. We present a simulation study on the waveguide design and depict the MEMS-integration approach. Moreover, we experimentally report the suspended waveguide with propagation loss (−2.9 dB/cm) and bending loss (−0.076 dB each). The suspended waveguide coupler is experimentally investigated. In addition, we validate the proposed optical MEMS approach using a reconfigurable ring resonator design. In conclusion, we experimentally demonstrate the proposed waveguide platform’s capability for MIR MEMS-reconfigurable photonics, which empowers the MIR on-chip optical systems for various applications.

Heterogeneous Wafer Bonding Technology and Thin-Film Transfer Technology-Enabling Platform for the Next Generation Applications beyond 5G

Wafer bonding technology is one of the most effective methods for high-quality thin-film transfer onto different substrates combined with ion implantation processes, laser irradiation, and the removal of the sacrificial layers. In this review, we systematically summarize and introduce applications of the thin films obtained by wafer bonding technology in the fields of electronics, optical devices, on-chip integrated mid-infrared sensors, and wearable sensors. The fabrication of silicon-on-insulator (SOI) wafers based on the Smart CutTM process, heterogeneous integrations of wide-bandgap semiconductors, infrared materials, and electro-optical crystals via wafer bonding technology for thin-film transfer are orderly presented. Furthermore, device design and fabrication progress based on the platforms mentioned above is highlighted in this work. They demonstrate that the transferred films can satisfy high-performance power electronics, molecular sensors, and high-speed modulators for the next generation applications beyond 5G. Moreover, flexible composite structures prepared by the wafer bonding and de-bonding methods towards wearable electronics are reported. Finally, the outlooks and conclusions about the further development of heterogeneous structures that need to be achieved by the wafer bonding technology are discussed.