Multilayer stacked crystalline silicon switch with nanosecond-order switching time.

To realize compact and denser photonic integrated circuits, three-dimensional integration has been widely accepted and researched. In this article, we demonstrate the operation of a 3D integrated silicon photonic platform fabricated through wafer bonding. Benefiting from the wafer bonding process, the material of all layers is c-Si, which ensures that the mobility is high enough to achieve a nanosecond response via the p-i-n diode shifter. Optical components, including multimode interferences (MMIs), waveguide crossing, and Mach-Zehnder interferometer (MZI)-based switch, are fabricated in different layers and exhibit great performance. The interlayer coupler and crossing achieve a 0.98 dB coupling loss and <-43.58 dB cross talk, while the crossing fabricated in the same layer shows <-36.00 dB cross talk. A nanosecond-order switch response is measured in different layers.

Temperature-insensitive and fabrication-tolerant coarse wavelength division (de)multiplexing on a silica platform using an angled multimode interferometer.

Wavelength division (de)multiplexing (WDM) device is a crucial component for optical transmission networks. In this paper, we demonstrate a 4 channel WDM device with a 20 nm wavelength spacing on silica based planar lightwave circuits (PLC) platform. The device is designed using an angled multimode interferometer (AMMI) structure. Since there are fewer bending waveguides than other WDMs, the device footprint is smaller, at 21 mm × 0.4 mm. Owing to the low thermo-optic coefficient (TOC) of silica, a low temperature sensitivity of 10 pm/°C is achieved. The fabricated device exhibits high performance of an insertion loss (IL) lower than 1.6 dB, a polarization dependent loss (PDL) lower than 0.34 dB, and the crosstalk between adjacent channels lower than -19 dB. The 3 dB bandwidth is 12.3∼13.5 nm. Moreover, the device shows a high tolerance with a sensitivity of central wavelength to the width of multimode interferometer < 43.75 pm/nm.

Oxygen vacancies-dominated reactive species generation from peroxymonosulfate activated by MoO3-x for pollutant degradation.

Interface oxygen vacancies (OVs) are commonly used to improve the catalytic performance of activators in persulfate-based advanced oxidation processes, but the underlying mechanism was not fully explored. This work reports a facile heat treatment method to regulate OVs in MoO3-x to elucidate the mechanism of peroxymonosulfate (PMS) activated by OVs to degrade 2,4,4-Trichlorobiphenyl (PCB28). Electron spin resonance, free radical quenching, X-ray photoelectron spectroscopy, and Raman spectroscopy confirmed that both reducing Mo species and OVs of MoO3-x surface were responsible for PMS activation. Further experiments and Density Function Theory (DFT) calculation suggest that OVs in MoO3-x induced the formation of superoxide radical (O2•-), and then O2•- was transformed into singlet oxygen (1O2) or mediated PMS activation to generate radicals, which contritbued to 70.2% of PCB28 degradation. The steady-state concentrations of free radical calculated with the kinetics model show that OVs were more favorable to mediate PMS to generate hydroxyl radicals (•OH) under oxic conditions, while reducing Mo species would like to induce PMS to produce sulfate radicals (SO4•-). Overall, this study is dedicated to a new insight into the in-depth mechanism of PMS activation by OVs-rich catalysts and provides a novel strategy for reactive species regulation in PMS based oxidation process.

On-Chip E00-E20 Mode Converter Based on Multi-Mode Interferometer.

Mode converters is a key component in mode-division multiplexing (MDM) systems, which plays a key role in signal processing and multi-mode conversion. In this paper, we propose an MMI-based mode converter on 2%-Δ silica PLC platform. The converter transfers E00 mode to E20 mode with high fabrication tolerance and large bandwidth. The experimental results show that the conversion efficiency can exceed -1.741 dB with the wavelength range of 1500 nm to 1600 nm. The measured conversion efficiency of the mode converter can reach -0.614 dB at 1550 nm. Moreover, the degradation of conversion efficiency is less than 0.713 dB under the deviation of multimode waveguide length and phase shifter width at 1550 nm. The proposed broadband mode converter with high fabrication tolerance is promising for on-chip optical network and commercial applications.

Polymer/Silica Hybrid Waveguide Thermo-Optic VOA Covering O-Band.

In this paper, a polymer/silica hybrid waveguide thermo-optic variable optical attenuator (VOA), covering the O-band, is demonstrated. The switch is fabricated by simple and low-cost direct ultraviolet (UV) lithography. The multimode interferences (MMIs) used in the Mach-Zehnder interferometer (MZI)-VOA are well optimized to realize low loss and large bandwidth. The VOA shows an extinction ratio (ER) of 18.64 dB at 1310 nm, with a power consumption of 8.72 mW. The attenuation is larger than 6.99 dB over the O-band. The rise and fall time of the VOA are 184 µs and 180 µs, respectively.

Efficient activation of peroxymonosulfate by copper sulfide for diethyl phthalate degradation: Performance, radical generation and mechanism.

Copper-containing minerals have been extensively used in Fenton-like processes for degradation of pollutants and have exhibited great potential for environmental remediation. This work reports the first use of copper sulfide (CuS), a typical Cu-mineral, for the activation of peroxymonosulfate (PMS) for pollutant degradation; the study also elucidates the underlying mechanism of these processes. Copper sulfide effectively activated PMS to degrade diethyl phthalate (DEP). Electron paramagnetic resonance, free radical quenching, X-ray photoelectron spectroscopy, X-ray diffraction analyses and DFT calculations confirmed that ≡Cu (I)/≡Cu (II) cycling on the surface of CuS provided the main pathway to activate PMS to produce highly oxidative species. Unlike conventional sulfate radical-based PMS activation processes, hydroxyl radical (•OH) were found to be the dominant radical in the tested CuS/PMS system, which performed more efficiently than an alternative •OH-based oxidation system (CuS/H2O2) for DEP degradation. In addition, the presence of anions such Cl- and NO3- has limited inhibition effects on DEP degradation. Overall, this study provides an efficient pathway for PMS-based environmental remediation as well as a new insight into the mechanism of PMS activation by Cu-containing minerals.