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Porous α-Fe2O3 hollow rods/reduced graphene oxide (α-Fe2O3 HR/RGO) composites with unique morphological characteristics and a high surface area are prepared through a template strategy, which was systematically studied and found to have outstanding supercapacitive properties. When served as active material in a three-electrode setup, the optimized α-Fe2O3 HR/RGO-30, comprised 76.5 wt% α-Fe2O3 and 23.2 wt% RGO, was able to offer the largest specific capacitance of 426.3 F g−1, an excellent rate capability as well as satisfactory cycle life with capacitance retention of 87.7% and Coulombic efficiency of 98.9% after continuously charging/discharging at 10 A g−1 for beyond 10,000 cycles. Such electrochemical behaviors of the α-Fe2O3 HR/RGO-30 electrode can rival or even surpass those of many Fe2O3-based electrodes documented in the previous literature. Later, a symmetric supercapacitor cell of α-Fe2O3 HR/RGO-30//α-Fe2O3 HR/RGO-30 was fabricated. The assembled device offers the maximum energy density of 18.7 Wh kg−1, and also exhibits commendable rate capability, and features stable cycling durability (with capacitance retention of 83.2% together with a Coulombic efficiency of 99.3% after 10,000-cycle charge/discharge at 5 A g−1). These notable electrochemical performances enable the α-Fe2O3 HR/RGO-30 composite to be a high-potential material for advanced energy storage systems.

Silicon nitride (Si3N4) has a higher nonlinear threshold compared to silicon, which reduces the effect of two-photon absorption. However, the low thermo-optic coefficient and the reduced refractive index contrast of thin Si3N4 waveguides lead to a low thermal tuning speed and low thermal efficiency. This paper demonstrates a widely tunable III-V/Si3N4 hybrid-integrated external cavity laser with a relatively faster switching time. The Si3N4 external feedback circuit is based on 800-nm-thick Si3N4 waveguides with an optical confinement factor of 87%. It allows the reduction of the oxide under-cladding layer thickness to 4 μm and the oxide upper-cladding layer to 1.7 μm without additional loss. The switching time between two non-adjacent lasing wavelengths is 60.7 μs. The maximum output power is 34 mW under 500 mA injection current. The side mode suppression ratio is more than 70 dB over the tuning range of 58.5 nm. The laser intrinsic linewidth is 2.5 kHz.

In this paper, we demonstrate a method to generate a low-chirp ultra-wideband pulse (UWB) signal based on a silicon single-drive push-pull segmented Mach-Zehnder modulator (SMZM). The concept is analyzed theoretically and demonstrated experimentally. We get positive monocycle pulses with different relative time delays between the two driving signals. The center frequency and fractional bandwidth of the generated positive monocycle pulse is 5.97 GHz and 161% with a relative time delay of 56 ps. By changing the operating point of the SMZM, we can get negative monocycle pulses. We modulate the UWB signals with on-off keying and pulse position formats by properly coding the driving signal. As far as we know, this is the first time to realize low-chirp UWB signals using only one silicon modulator. The successful generation of UWB signals poses a significant step in realizing a compact low-cost and low-chirp UWB generator on the silicon photonics platform.

We demonstrate a high-efficiency silicon Mach-Zehnder modulator with U-shaped PN junctions. The depletion region of the U-shaped PN junction has a large overlap with the waveguide optical mode, leading to a low drive voltage. The calculated modulation efficiency is 0.33 V·cm at 0 V bias and 0.55 V·cm at -2 V bias. On-off keying (OOK) modulation and four-level pulse amplitude modulation (PAM-4) are achieved at 32 Gb/s and 64 Gb/s data rates under 2 V drive voltage, respectively. The bit error rate for the PAM-4 modulation is below the hard-decision forward error correction threshold of 3.8 × 10-3.

We report a reconfigurable optical filter chip based on the Si3N4 waveguide platform. Microwave filtering is realized using a device with optical-to-electrical mapping. The filter chip is based on a lattice structure with the dual-ring-coupled Mach-Zehnder interferometers (DR-MZIs) as the basic elements. Both the lattice and ring couplers are tunable, making the chip reconfigurable to various filter functions. A theoretical model is developed to analyze its optical filtering performance. Measurement reveals that the filter passband can reach hundreds of megahertz in the lower limit and several gigahertz in the upper limit. Various orders of infinite impulse response filters are implemented with a tailorable passband. The flexibility in tuning filter center frequency and passband makes it suitable in high-resolution adaptable microwave signal front-end processing.

Based on the strong interaction between histidine and copper ions and the signal enhancement effect of gold-labeling carbon nanotubes, an electrochemical sensor is established and used to measure copper ions in river water. In this study the results show that the concentrations of copper ion have well linear relationship with the peak current in the range of 10−11–10−7 mol/L, and the limit of detection is 10−12 mol/L. When using this method to detect copper ions in the Xiangjiang River, the test results are consistent with the atomic absorption method. This study shows that the sensor is convenient to be used in daily monitoring of copper ions in river water.