Realizing highly efficient vertical coupling with dielectric deflective metasurfaces.

Using dielectric deflective metasurfaces, we propose a novel, to the best of our knowledge, out-of-plane modulation scheme to realize vertical coupling on a 220 nm silicon-on-insulator platform. The metasurface is used to deflect vertical incident light to an oblique angle with high efficiency in the cladding layer. This deflection introduces a lateral wave vector component, thus preventing bi-directional transmission of traditional vertical coupling due to the second-order Bragg reflection of the grating. Additionally, an apodized design is employed for the subwavelength grating to improve mode matching with a deflection angle incident. The integration of the metasurface and subwavelength grating enables a new vertical coupling scheme with high efficiency. After global optimization, we achieved a simulation coupling efficiency of -2.19 dB. The measured coupling efficiency is -3.36 dB with a center wavelength of 1545.6 nm and a 1-dB bandwidth of 32 nm. The results confirm the feasibility of the proposed new architecture.

Low-loss grating coupler with a subwavelength structure on a thin-film lithium niobate substrate.

We demonstrated a low-loss O-band grating coupler on an x-cut thin-film lithium niobate substrate by implementing subwavelength and apodized structures. The subwavelength gratings were used to mitigate the refractive index discontinuity between the input taper and grating region, which was the first application of such a structure for grating coupler optimization on a thin-film lithium niobate substrate. The coupling efficiency was measured to be -1.99 dB/coupler at a wavelength of 1312.8 nm, which was the lowest loss among the reported lithium niobate grating couplers that do not use metal mirrors. The proposed design does not require metal mirrors or any additional material layers and can be easily fabricated with a single-step lithography and etching processes.

DAC-less PAM4 signal generation using a silicon dual-drive push-pull MZI modulator.

In this study, we demonstrate DAC-less PAM-4 signal generation by driving a silicon MZI modulator based on a series push-pull configuration with two independent binary signals of varying amplitudes. Such configuration boosts transfer speed between PAM4 levels, leading to enhanced performance metrics compared to the differential driving scheme. Experimentally, our scheme demonstrated a lower bit-error rate compared to the differential scheme, proving its cost-efficiency and feasibility for PAM4 generation.

Thin-film lithium niobate-based electro-optic comb cloning for self-homodyne coherent communication.

As the optical communication industry advances, metropolitan area networks (MANs) and radio access networks (RANs) are extensively deployed on a large scale, demanding energy-efficient integrated light sources and simplified digital signal processing (DSP) technologies. The emergence of thin-film lithium niobate (TFLN) has given rise to high-performance, energy-efficient on-chip modulators, making on-chip optical frequency comb (OFC) more appealing. Owing to the phase uniformity and stability of this chip-scale device, it has been possible to eliminate the carrier frequency phase estimation (CPE) in DSP stacks using comb-clone-enabled self-homodyne detection. Here we report the first use, to our knowledge, of a TFLN on-chip electro-optic (EO) frequency comb to realize comb cloning and self-homodyne coherent detection. We transmit three optical pilot tones and eight data channels encoded with 20 Gbaud polarization-multiplexed 16-ary quadrature amplitude modulation (PM-16-QAM) over 10 km and 80 km standard single-mode fibers. The bit error ratios (BERs) of the eight channels reach below 10-3, a result made possible by our on-chip comb. The scalability and mass producibility of on-chip EO combs, combined with the simplified DSP, show potential in our proposed fifth-generation (5G) RAN and MAN transmission scheme.

High-speed silicon-integrated photonic radio frequency switch based on optical switching.

Photonic radio frequency (RF) switches are promising to replace conventional electronic RF switches in modern RF communication systems owing to their high switching speed and immunity to electromagnetic interference. However, existing photonic RF switches are generally based on frequency or polarization filtering. Thus, they require more light sources and filters to increase the number of switching channels, consequently limiting scalability. We propose a silicon-integrated photonic RF switch based on optical switching. RF signals are first modulated into the optical domain and switched through phase control of the phase shifters in the optical switch. Switching is not related to the frequency or polarization of the optical carriers, thus reducing the number of light sources required. Experimental results demonstrate 10-GHz switching of two RF signals with frequencies of 20 GHz and 30 GHz. The proposed photonic RF switch can be further expanded to form a large switch matrix, possibly contributing to the development of large-scale RF communication systems.

Ultrahigh-linearity dual-drive scheme using a single silicon modulator.

Here, a high-linearity dual-drive scheme using a single silicon dual-drive Mach-Zehnder modulator is presented. The bias voltages and RF amplitudes of the two driving arms are adjusted such that the nonlinearity of the transfer function of the Mach-Zehnder interferometer cancels out the nonlinear response of the arms. Using the proposed scheme, the spurious-free dynamic range of the third-order intermodulation distortion is 123.4 dB Hz6/7, which is believed to be a record-breaking value for silicon modulators. In comparison, the result obtained using a conventional single-drive scheme is 102.6 dB·Hz2/3. The proposed scheme could simplify the design of modulators and promote high-performance microwave photonic links.

Low-loss 3-dimensional waveguide crossing with a parabolic taper interlayer coupler based on a SiN-SiN-Si three-layer platform.

We demonstrated a SiN-SiN-Si three-layer silicon waveguide crossing with low-loss crossings and interlayer couplers. The underpass and overpass crossings exhibited ultralow loss (<0.82/1.16 mdB) and cross talk (<-56/-48 dB) in the wavelength range of 1260-1340 nm. To reduce the loss and length of the interlayer coupler, a parabolic interlayer coupling structure was adopted. The measured interlayer coupling loss was less than 0.11 dB from 1260 to 1340 nm, which is, to the best of our knowledge, the lowest loss reported for an interlayer coupler based on a SiN-SiN-Si three-layer platform. The total interlayer coupler length was only 120 µm.

Polarization-insensitive EDG demultiplexer combined with a polarization beam splitter.

Polarization dependence is an inherent challenge for wavelength-division multiplexing transceivers on silicon photonic platforms, causing severe problems with polarization-dependent losses and hindering the implementation of monolithic integrated receivers. In this study, we developed a polarization-insensitive demultiplexer on a silicon nitride (Si3N4) platform, which provides a promising solution to the polarization challenge. Comprising an etched diffraction grating (EDG) and a polarization beam splitter (PBS), the demultiplexer can achieve polarization insensitivity by introducing an additional optical path difference for polarization compensation. The fabricated demultiplexers were experimentally measured to have minimum insertion losses of 1.5 dB, cross talks of better than -25 dB, and polarization-dependent losses of better than 0.7 dB. This is the first, to the best of our knowledge, proposed solution for a polarization-insensitive EDG demultiplexer combined with a PBS on a Si3N4 platform.

High-efficiency thin-film lithium niobate modulator with highly confined optical modes.

We demonstrate a low-loss, high-efficiency lithium niobate electro-optic (EO) modulator with optical isolation trenches to achieve stronger field confinement and reduced light absorption loss. The proposed modulator realized considerable improvements, including a low half-wave voltage-length product of 1.2 V·cm, an excess loss of ∼2.4 dB, and a broad 3-dB EO bandwidth of over 40 GHz. We developed a lithium niobate modulator with, to the best of our knowledge, the highest reported modulation efficiency of any Mach-Zehnder interferometer (MZI) modulator.

Parallel photonic acceleration processor for matrix-matrix multiplication.

We propose and experimentally demonstrate a highly parallel photonic acceleration processor based on a wavelength division multiplexing (WDM) system and a non-coherent Mach-Zehnder interferometer (MZI) array for matrix-matrix multiplication. The dimensional expansion is achieved by WDM devices, which play a crucial role in realizing matrix-matrix multiplication together with the broadband characteristics of an MZI. We implemented a 2 × 2 arbitrary nonnegative valued matrix using a reconfigurable 8 × 8 MZI array structure. Through experimentation, we verified that this structure could achieve 90.5% inference accuracy in a classification task for the Modified National Institute of Standards and Technology (MNIST) handwritten dataset. This provides a new effective solution for large-scale integrated optical computing systems based on convolution acceleration processors.

Massively parallel FMCW lidar with cm range resolution using an electro-optic frequency comb.

Frequency-modulated continuous wave (FMCW) light detection and ranging (lidar) is a promising solution for three-dimensional (3D) imaging and autonomous driving. This technique maps range and velocity measurement to frequency counting via coherent detection. Compared with single-channel FMCW lidar, multi-channel FMCW lidar can greatly improve the measurement rate. A chip-scale soliton micro-comb is currently used in FMCW lidar to enable multi-channel parallel ranging and significantly increase the measurement rate. However, its range resolution is limited due to the soliton comb having only a few-GHz frequency sweep bandwidth. To overcome this limitation, we propose using a cascaded modulator electro-optic (EO) frequency comb for massively parallel FMCW lidar. We demonstrate a 31-channel FMCW lidar with a bulk EO frequency comb and a 19-channel FMCW lidar using an integrated thin-film lithium niobate (TFLN) EO frequency comb. Both systems have a sweep bandwidth of up to 15 GHz for each channel, corresponding to a 1-cm range resolution. We also analyze the limiting factors of the sweep bandwidth in 3D imaging and perform 3D imaging for a specific target. The measurement rate achieved is over 12 megapixels per second, which verifies its feasibility for massively parallel ranging. Our approach has the potential to greatly benefit 3D imaging in fields where high range resolution is required, such as in criminal investigation and precision machining.

Incorporating self-employed maintainers into WEEE formal recycling system: A system dynamic approach.

The establishment and operation of a formal recycling system for waste electrical and electronic equipment is an important measure to reduce environmental hazards and improve the recycling of resources, but how to incorporate self-employed maintainers into the system has formed an important research gap. Based on the perspective of extended producer responsibility, we argue that self-employed maintainers are required to assume the corresponding environmental responsibility for the environmental externality caused by informal maintenance activities. Using qualitative structural analysis techniques of system dynamics approach with quantitative simulation analysis techniques, we construct an incentive model for self-employed maintainers' participation in formal recycling system, based on which we propose four incentive strategies. A simulation analysis is further conducted by using the case of waste mobile phones recycling in Qingdao to verify the effectiveness of our incentive model and strategies.

Ultralow-loss waveguide crossing for photonic integrated circuits by using inverted tapers.

An ultralow-loss silicon planar waveguide crossing operating in the O-band was experimentally demonstrated based on the Gaussian beam synthesis method. Elliptical parabolic inverted tapers were introduced in our design to reduce the crossing loss. According to the measurement results, the proposed device exhibits an insertion loss of 0.008 dB, which is the lowest reported loss for planar silicon waveguide crossings operating in the O-band. The device exhibits a low crosstalk below -40 dB over a 40 nm wavelength range with a compact footprint of 18 × 18 µm2 and can be fabricated in a complementary metal-oxide-semiconductor-compatible process.

Compact vertical grating coupler with an achromatic in-plane metalens on a 220-nm silicon-on-insulator platform.

We proposed a new type of vertical grating couplers (VGCs) with a compact footprint on the 220-nm silicon-on-insulator platform. The overall size of the device containing the L-shaped coupling grating and the taper with achromatic in-plane metalens is only 45 × 15 µm2, and the measured coupling efficiency at 1550 nm is -5.2 dB with a 1 dB bandwidth of 38 nm, around 1.6 dB higher than the VGC without metalens. The incidence angle mismatch has a 1 dB bandwidth of roughly 4°, whereas the displacement mismatch along the x-/y- axis has a bandwidth of around 3/4 µm. Furthermore, we experimentally show that such a design is compatible with VGCs operating in the S, C, and L bands.

High-efficiency grating coupler based on fast directional optimization and robust layout strategy in 130†nm CMOS process.

We experimentally demonstrated a high-efficiency grating coupler by combining an interleaved etch and apodized structure for fiber-to-chip coupling. The grating coupler was optimized using the fast directional optimization method to achieve apodization. The grating coupler utilized a layout strategy involving an extended mask to avoid alignment errors for a multi-etch structure. The coupling efficiency was measured to be -2.2 dB at a wavelength of 1549 nm with a 3 dB bandwidth of 47 nm. The grating coupler, having no gold reflector, subwavelength index matching structure, or additional material layers, was fabricated using a commercial silicon photonics process with a minimum feature size of 140 nm. This grating coupler design provides a robust and effective coupling scheme and the proposed method can be employed to adopt the design in accordance with standard foundry design rules.

Programmable low-threshold optical nonlinear activation functions for photonic neural networks.

We experimentally demonstrate two types of programmable, low-threshold, optically controlled nonlinear activation functions, which are challenging to realize in photonic neural networks (PNNs). These devices rely on on-chip integrated Ge-Si photoelectric detectors and silicon electro-optical switches, and they generate rectified linear unit (ReLU) or sigmoid functions with arbitrary slopes without additional electrical processing. Both devices function at an extremely low threshold of 0.2 mW. The embedding of these nonlinear activation functions into convolutional neural networks facilitates the attainment of high inference accuracies of up to 95% when applied to Modified National Institute of Standards and Technology (MNIST) handwritten digit-classification tasks. The devices are suitable for low-power PNNs with an arbitrary number of propagation layers in photonic-computing chips.

Study on the expression of TRIM7 in peripheral blood mononuclear cells of patients with sepsis and its early diagnostic value.

BACKGROUND: The early diagnosis of sepsis is beneficial to put forward a reasonable clinical treatment plan as soon as possible. This study was to explore the expression of Tripartite Motif 7 (TRIM7) in peripheral blood mononuclear cells (PBMCs) of patients with sepsis and its diagnostic value. METHODS: This is a cross-sectional study. A total of 69 patients with infectious diseases were enrolled in the emergency room. They were divided into the sepsis group (34 cases) and the non-sepsis infection group (35 cases). There were 25 healthy subjects who were selected as the control group. The expression of TRIM7 in PBMCs was observed by immunofluorescence staining. The correlation between the expression of TRIM7 mRNA and acute physiology and chronic health evaluation II (APACHE II) score, sequential organ failure assessment (SOFA) score, white blood cell (WBC), C-reactive protein (CRP), procalcitonin (PCT), tumor necrosis factor (TNF)-α and interleukin (IL)-6 was discussed. The receiver operating characteristic (ROC) curve was utilized for evaluating the value of TRIM7 expression for the early diagnosis of sepsis. RESULTS: The fluorescence intensity representing the expression level of TRIM7 in PBMCs of patients in the sepsis group was the lowest among three groups. The TRIM7 mRNA expression in PBMCs of the sepsis group was greatly decreased in comparison with that of the non-sepsis infection group and control group (P < 0.05). Spearman correlation analysis indicated that TRIM7 mRNA expression was negatively correlated with APACHE II score, SOFA score, WBC, CRP, PCT, TNF-α and IL-6. ROC curve analysis revealed that the area under curve (AUC) of TRIM7 mRNA expression in PBMCs for the diagnosis of sepsis was 0.798, with a 95% confidence interval of 0.691- 0.905, a sensitivity of 73.5%, and a specificity of 77.1%. CONCLUSION: The expression of TRIM7 in PBMCs of patients with sepsis is significantly down-regulated, which has certain clinical value for early diagnosis of sepsis.

Compact broadband silicon 3 dB coupler based on shortcuts to adiabaticity.

We proposed and experimentally demonstrated a compact, broadband, and low-loss-mode-evolution-based 2×23 dB coupler on a silicon-on-insulator platform. The waveguide widths and separations of the coupler were tapered in an optimal manner using the shortcuts to the adiabaticity method. The coupler, with a ∼70 µm total length and 200 nm feature size, exhibited <0.3 dB measured excess loss over a broadband wavelength range from 1500 to 1600 nm. Balanced and unbalanced Mach-Zehnder interferometers fabricated for validation showed extinction ratios larger than 27 and 23 dB, respectively, over a 100 nm bandwidth. The extracted splitting ratio was between 0.48 and 0.52.

Silicon mode (de)multiplexers with parameters optimized using shortcuts to adiabaticity.

We propose and experimentally demonstrate broadband silicon mode (de)multiplexers based on the optimization of system adiabaticity using shortcuts to adiabaticity (STA). The measured insertion losses and crosstalks were less than 1.1 dB and -24 dB, respectively, for the five two-mode mode-division-multiplexing (MDM) links over wavelengths ranging from 1500 nm to 1600 nm. The four-mode MDM link showed measured insertion losses and crosstalks less than 1.3 dB and -23 dB, respectively, within the same wavelength range. The method paves the way for future adaptation of the STA protocols to various components.

Electrically Tunable Bandgaps in Bilayer MoS2.

Artificial semiconductors with manufactured band structures have opened up many new applications in the field of optoelectronics. The emerging two-dimensional (2D) semiconductor materials, transition metal dichalcogenides (TMDs), cover a large range of bandgaps and have shown potential in high performance device applications. Interestingly, the ultrathin body and anisotropic material properties of the layered TMDs allow a wide range modification of their band structures by electric field, which is obviously desirable for many nanoelectronic and nanophotonic applications. Here, we demonstrate a continuous bandgap tuning in bilayer MoS2 using a dual-gated field-effect transistor (FET) and photoluminescence (PL) spectroscopy. Density functional theory (DFT) is employed to calculate the field dependent band structures, attributing the widely tunable bandgap to an interlayer direct bandgap transition. This unique electric field controlled spontaneous bandgap modulation approaching the limit of semiconductor-to-metal transition can open up a new field of not yet existing applications.