Metasurface-assisted amorphous germanium-tin waveguide bolometer for mid-infrared photodetection.

An amorphous germanium-tin (a-Ge0.83Sn0.17) waveguide bolometer featuring a one-dimension (1D) metasurface absorber is proposed for mid-infrared photodetection at room-temperature. The device is based on the germanium-on-silicon (GOS) photonic platform. The impacts of the 1D metasurface on the performances of the waveguide bolometer are investigated. The responsivity of the a-Ge0.83Sn0.17 waveguide bolometer could be significantly enhanced by the metasurface. A responsivity of around -3.17%/µW within the 4.1 ∼ 4.3 µm wavelength range is achieved. In addition, a 3-dB roll-off frequency higher than 10 kHz is obtained.

Aluminum scandium nitride on 8-inch Si wafers: material characterization and photonic device demonstration.

The anisotropic optical properties of aluminum scandium nitride (Al1-xScxN) thin films for both ordinary and extraordinary light are investigated. A quantitative analysis of the band structures of the wurtzite Al1-xScxN is carried out. In addition, Al1-xScxN photonic waveguides and bends are fabricated on 8-inch Si substrates. With x = 0.087 and 0.181, the light propagation losses are 5.98 ± 0.11 dB/cm and 8.23 ± 0.39 dB/cm, and the 90° bending losses are 0.05 dB/turn and 0.08 dB/turn at 1550 nm wavelength, respectively.

Waveguide-integrated van der Waals heterostructure photodetector on a lithium niobate on insulator platform.

Lithium niobate (LN) photonics has gained significant interest for their distinct material properties. However, achieving monolithically integrated photodetectors on lithium niobate on an insulator (LNOI) platform for communication wavelengths remains a challenge due to the large bandgap and extremely low electrical conductivity of LN material. A two-dimensional (2D) material photodetector is an ideal solution for LNOI photonics with a strong light-matter interaction and simple integration technique. In this work, a van der Waals heterostructure photodiode composed of a p-type black phosphorus layer and an n-type MoS2 layer is successfully demonstrated for photodetection at communication wavelengths on a LNOI platform. The LNOI waveguide-integrated BP-MoS2 photodetector exhibits a dark current as low as 0.21 nA and an on/off ratio exceeding 200 under zero voltage bias with an incident power of 13.93 µW. A responsivity as high as 1.46 A/W is achieved at -1 V bias with a reasonable dark current around 2.33 µA. With the advantages of high responsivity, low dark current, and simple fabrication process, it is promising for the monolithically integrated photodetector application for LNOI photonic platforms at communication wavelengths.

Non-uniform distributed silicon optical phased array for high directionality and a wide steering range.

A non-uniform distributed silicon optical phased array (OPA) is proposed and numerically demonstrated to realize high directionality and a wide range for beam steering. The OPA is composed of grating antennas with dual-layer corrugations along silicon strip waveguides, which can achieve a high directionality of 0.96 and a small divergence angle of 0.084°. To reduce the crosstalk between adjacent antennas and realize a wide steering range, the genetic algorithm is improved and utilized to arrange the locations of grating antennas. As a proof of concept, a 32-channel non-uniform distributed OPA is designed and thoroughly optimized. The simulation results successfully demonstrate a two-dimensional wide steering range of 70∘×18.7∘ with a side-mode suppression ratio (SMSR) over 10 dB.

All-silicon metalens for broadband achromatic polarization multiplexing in long-wave infrared wavelengths.

Traditional long-wave infrared polarimetry usually relies on complex optical setups, making it challenging to meet the increasing demand for system miniaturization. To address this problem, we design an all-silicon broadband achromatic polarization-multiplexing metalens (BAPM) operating at the wavelength range of 9-12 µm. A machine-learning-based design method is developed to replace the tedious and computationally intensive simulation of a large number of meta-atoms. The results indicate that the coefficients of variation in focal length of the BAPM are 3.95% and 3.71%, and the average focusing efficiencies are 41.3% and 40.5% under broadband light incidence with x- and y-polarizations, respectively.

Tunable slow and fast light in a silicon-on-insulator Fano resonator.

Tunable slow and fast light generation in a silicon-on-insulator (SOI) Fano resonator is proposed and experimentally demonstrated. The slow and fast light generation with symmetric and asymmetric coupling conditions of the Fano resonator is theoretically analyzed. Under a slightly imbalanced coupling condition, the two output ports of the Fano resonator could produce a fast light and a slow light, respectively. By utilizing the thermo-optic (TO) effect to change the phase difference of the two optical beams coupled into the resonator, the transition of fast and slow light can be realized at the fixed resonance wavelength. Experimental results show that a slow-to-fast transition (group delay from 0.852 to -1.057 ns) at one resonance wavelength, and a fast-to-slow transition (group delay from -0.22 to 0.867 ns) at another resonance wavelength are realized simultaneously by controlling the microheater to tune the phase difference.

Transparent nanopaper for ultrashort pulse generation in the near-infrared region.

Transparent nanopaper (T-paper) can be applied in the field of electromagnetic shielding materials, antistatic materials, composite conductive materials, electric pool materials, super capacitors, and thermal management systems. However, this kind of T-paper has not been employed in ultrafast photonics yet. For the first time, to our knowledge, transparent electrical nanopaper is used in fiber lasers, different from the conventional pulsed fiber laser, which operates in the Q-switched regime under low pump power and then in the mode-locked regime under high pump power. Mode-locking is achieved first with a pulse duration of 550 fs under low pump power (166 mW). When further increasing the pump power up to 198 mW, the proposed fiber laser can be converted from a mode-locked to Q-switched state, which is a result of the two-photon absorption effect. The proposed fiber laser based on T-paper can be potentially applied in optical tomography, metrology, spectroscopy, micro-machining technology, and biomedical diagnostics.

Demonstration of polarization-insensitive optical filters on silicon photonics platform.

We experimentally demonstrate a polarization-insensitive optical filter (PIOF) using polarization rotator-splitters (PRSs) and microring resonators (MRRs) on the silicon-on-insulator (SOI) platform with complementary metal-oxide-semiconductor (CMOS) compatible fabrication process. The PRS consists of a tapered-rib waveguide and an asymmetrical directional coupler (ADC), which realize the polarization rotation and splitting, to ensure the connected MRRs-based optical filter operating at one desired polarization when light with different polarizations are launched into the device. The measured results show that the optical transmission spectra of the device are identical for TE and TM polarization input. The box-like filtering spectra are also achieved with a 3-dB bandwidth of ∼0.15 nm and a high extinction ratio (ER) over 30 dB.

CMOS-compatible all-Si metasurface polarizing bandpass filters on 12-inch wafers.

The implementation of polarization controlling components enables additional functionalities of short-wave infrared (SWIR) imagers. The high-performance and mass-producible polarization controller based on Si metasurface is in high demand for the next-generation SWIR imaging system. In this work, we report the first demonstration of all-Si metasurface based polarizing bandpass filters (PBFs) on 12-inch wafers. The PBF achieves a polarization extinction ratio of above 10 dB in power within the passbands. Using the complementary metal-oxide-semiconductor (CMOS) compatible 193nm ArF deep ultra-violet (DUV) immersion lithography and inductively coupled plasma (ICP) etch processing line, a device yield of 82% is achieved.

Surface roughness measurement by depolarization method.

A fiber profilometer based on a polarization manipulation technique is developed to measure both surface roughness and profile simultaneously. The depolarization effect caused by the surface scattering is utilized to characterize the roughness properties. A theoretical model is developed to study the second-order dependence of depolarization to quantify the surface roughness characteristics. Experiments are carried out to demonstrate and verify the relationship between the depolarization and the surface roughness. This technique can simultaneously achieve the properties of the surface profile and roughness based on a fiber profilometer system.

High-resolution fiber profilometer for hard-to-access areas.

A fiber-based profilometer is developed to measure hard-to-access areas. This system utilizes the low-coherence light interferometry technique to detect the internal surface profiles of some samples. A differentiation method is employed to enhance the lateral and vertical resolutions of the measured imaging results. The probe design parameters are optimized for a desired working distance and a small beam size. The performance of the profilometer system, especially its high-resolution property, is demonstrated.

Nanoimprinted TiO2 Metasurfaces with Reduced Meta-Atom Aspect Ratio and Enhanced Performance for Holographic Imaging.

Metasurface holograms, with the capability to manipulate spatial light amplitudes and phases, are considered next-generation solutions for holographic imaging. However, conventional fabrication approaches for meta-atoms are heavily dependent on electron-beam lithography (EBL), a technique known for its expensive and time-consuming nature. In this paper, a polarization-insensitive metasurface hologram is proposed using a cost-effective and rapid nanoimprinting method with titanium dioxide (TiO2) nanoparticle loaded polymer (NLP). Based on a simulation, it has been found that, despite a reduction in the aspect ratio of meta-atoms of nearly 20%, which is beneficial to silicon master etching, NLP filling, and the mold release processes, imaging efficiency can go up to 54% at wavelength of 532 nm. In addition, it demonstrates acceptable imaging quality at wavelengths of 473 and 671 nm. Moreover, the influence of fabrication errors and nanoimprinting material degradation in terms of residual layer thickness, meta-atom loss or fracture, thermal-induced dimensional variation, non-uniform distribution of TiO2 particles, etc., on the performance is investigated. The simulation results indicate that the proposed device exhibits a high tolerance to these defects, proving its applicability and robustness in practice.

Electrostatic Smart Textiles for Braille-To-Speech Translation.

A wearable Braille-to-speech translation system is of great importance for providing auditory feedback in assisting blind people and people with speech impairment. However, previous reported Braille-to-speech translation systems still need to be improved in terms of comfortability or integration. Here, a Braille-to-speech translation system that uses dual-functional electrostatic transducers which are made of fabric-based materials and can be integrated into textiles is reported. Based on electrostatic induction, the electrostatic transducer can either serve as a tactile sensor or a loudspeaker with the same design. The proposed electrostatic transducers have excellent output performances, mechanical robustness, and working stability. By combining the devices with machine learning algorithms, it is possible to translate the Braille alphabet and 40 commonly used words (extensible) into speech with an accuracy of 99.09% and 97.08%, respectively. This work demonstrates a new approach for further developments of advanced assistive technology toward improving the lives of disabled people.

A Flexible Self-Powered Noncontact Sensor with an Ultrawide Sensing Range for Human-Machine Interactions in Harsh Environments.

Noncontact human-machine interactions (HMIs) provide a hygienic and intelligent approach to communicate between humans and machines. However, current noncontact HMIs are generally hampered by the interaction distance, and they lack the adaptability to environmental interference such as high humidity conditions. Here, we explore a self-powered electret-based noncontact sensor (ENS) with moisture-resisting ability and ultrawide sensing range exceeding 2.5 m. A megascopic air-bubble structure is designed to enhance charge-storage stability and charge-recovery ability of the ENS based on the heterocharge-synergy effect in electrets. Besides, multilayer electret films are introduced to strengthen the electric field by utilizing the electrostatic field superposition effect. Thanks to the above improved performances of the ENS, we demonstrate various noncontact HMI applications in harsh environments, including noncontact appliances, a moving trajectory and accidental fall tracking system, and a real-time machine learning-assisted gesture recognition system with accuracy as high as 99.21%. This research expands the way for noncontact sensor design and may further broaden applications in noncontact HMIs.

A Flexible Piezoelectret Actuator/Sensor Patch for Mechanical Human-Machine Interfaces.

Flexible and wearable devices with the capabilities of both detecting and generating mechanical stimulations are critical for applications in human-machine interfaces, such as augmented reality (AR) and virtual reality (VR). Herein, a flexible patch based on a sandwiched piezoelectret structure is demonstrated to have a high equivalent piezoelectric coefficient of d33 at 4050 pC/N to selectively perform either the actuating or sensing function. As an actuator, mechanical vibrations with a peak output force of more than 20 mN have been produced, similar to those from the vibration mode of a modern cell phone, and can be easily sensed by human skin. As a sensor, both the pressure detection limit of 1.84 Pa for sensing resolution and excellent stability of less than 1% variations in 6000 cycles have been achieved. The design principle together with the sensing and driving characteristics can be further developed and extended to other soft matters and flexible devices.

Cloth-Based Power Shirt for Wearable Energy Harvesting and Clothes Ornamentation.

Harvesting ambient mechanical energy from human body motion has attracted great research interest. In this work, a power shirt based on triboelectrification and the electrostatic induction effect between fluorinated ethylene propylene (FEP) and external objects is demonstrated. This power shirt can effectively convert the ambient mechanical energy into electric power, and the working mechanism is systematically discussed. A maximum short-circuit current density of ∼0.37 µA/cm2 and a maximum peak power density of ∼4.65 µW/cm2 were achieved. Simultaneously, 11 blue LEDs were lit by sliding the sleeve and power shirt, indicating the potential application of the power shirt in clothes ornamentation and risk warning. This study develops an efficient path for harvesting human body energy and promoting the development of wearable electronics and smart garments.

Self-Powered Human-Interactive Transparent Nanopaper Systems.

Self-powered human-interactive but invisible electronics have many applications in anti-theft and anti-fake systems for human society. In this work, for the first time, we demonstrate a transparent paper-based, self-powered, and human-interactive flexible system. The system is based on an electrostatic induction mechanism with no extra power system appended. The self-powered, transparent paper device can be used for a transparent paper-based art anti-theft system in museums or for a smart mapping anti-fake system in precious packaging and documents, by virtue of the advantages of adding/removing freely, having no impairment on the appearance of the protected objects, and being easily mass manufactured. This initial study bridges the transparent nanopaper with a self-powered and human-interactive electronic system, paving the way for the development of smart transparent paper electronics.

Paper-Based Active Tactile Sensor Array.

A paper-based active tactile sensor -array (PATSA) with a dynamic sensitivity of 0.35 V N(-1) is demonstrated. The pixel position of the PATSA can be routed by analyzing the real-time recording voltages in the pressing process. The PATSA performance, which remains functional when removing partial areas, reveals that the device has a potential application to customized electronic skins.

Fiber-based generator for wearable electronics and mobile medication.

Smart garments for monitoring physiological and biomechanical signals of the human body are key sensors for personalized healthcare. However, they typically require bulky battery packs or have to be plugged into an electric plug in order to operate. Thus, a smart shirt that can extract energy from human body motions to run body-worn healthcare sensors is particularly desirable. Here, we demonstrated a metal-free fiber-based generator (FBG) via a simple, cost-effective method by using commodity cotton threads, a polytetrafluoroethylene aqueous suspension, and carbon nanotubes as source materials. The FBGs can convert biomechanical motions/vibration energy into electricity utilizing the electrostatic effect with an average output power density of ∼0.1 µW/cm(2) and have been identified as an effective building element for a power shirt to trigger a wireless body temperature sensor system. Furthermore, the FBG was demonstrated as a self-powered active sensor to quantitatively detect human motion.