Integrating inverse design and partially etched platform: an ultra-compact polarization splitter and rotator as an example.

Silicon photonics devices benefit greatly from a partially etched platform and inverse design. Herein, we propose a bi-layer polarization splitter and rotator with a topology pattern and demonstrate it on a silicon-on-insulator platform. Our device exhibits a significantly reduced physical footprint of only 2µm×6µm, compared to traditional directional couplers and tapered waveguides. The device accomplishes the functions of polarization conversion and separation in such a compact design without redundant tapered or bending waveguides. The tested minimum insertion loss with the fabrication batch reaches 0.57 and 0.67 dB for TE and TM modes, respectively. The TE mode demonstrates a wider bandwidth and lower ILs than the TM modes, averaging around 1 dB from 1530 to 1565 nm. The M modes exhibit approximately 2 dB ILs at the same wavelength range, decreasing to about 1 dB between 1565 and 1580 nm. Improved designs and fabrication conditions strongly suggest the potential for further performance enhancement in the device. This successful initiative validates the exceptional performance resulting from the integration of the partially etched platform and inverse design, providing valuable insights for future photonic integrated device designs.

Compact dual-mode waveguide crossing based on adjoint shape optimization.

We design, fabricate, and characterize a compact dual-mode waveguide crossing on a silicon-on-insulator platform. The dual-mode waveguide crossing with high performance is designed by utilizing the adjoint shape optimization. This adjoint-method-based optimization algorithm is computationally efficient and yields the optimal solution in fewer iterations compared with other iterative schemes. Our proposed dual-mode waveguide crossing exhibits low insertion loss and low crosstalk. Experimental results show that the insertion losses at the wavelength of 1550 nm are 0.83 dB and 0.50 dB for TE0 and TE1 modes, respectively. The crosstalk is less than -20 dB for the two modes over a wavelength range of 80 nm. The footprint of the whole structure is only 5 × 5 µm2.

Compact hybrid five-mode multiplexer based on asymmetric directional couplers with constant bus waveguide width.

We experimentally demonstrate a hybrid mode division multiplexer (MDM) based on asymmetric directional couplers (ADCs) without transition tapers in between. The proposed MDM can couple five fundamental modes from access waveguides into the bus waveguide as the hybrid modes (TE0, TE1, TE2, TM0, and TM1). To eliminate the transition tapers between cascaded ADCs as well as to enable arbitrary add-drop to the bus waveguide, we maintain the bus waveguide width to be the same, while a partially etched subwavelength grating is introduced to reduce the effective refractive index of the bus waveguide. The experimental results demonstrate a working bandwidth of up to 140 nm.

[Effects of Land-use Conversion on Soil Nitrification and NO & N2O Emissions in Tropical China Under Different Moisture Conditions].

Rain and heat conditions are abundant in tropical areas, and rubber and tea are widely planted in this region; the nitrification process produces nitrate content, which is not conducive to the maintenance of nitrogen nutrients, and has negative environmental effects (nitrogen oxide emissions). The characteristics of soil nitrification rate and nitrogen oxide emission under different land use patterns remain unclear. An incubation experiment was conducted under the 5 a (T5) and 15 a (T15) tea plantation soils and the nearby typical rubber plantation (XJ) soils in Baisha county of Hainan province under two moisture contents (50% WFPS-L and 80% WFPS-H) for 71 d at 25℃. The results showed that:① after the rubber plantation was converted to a tea plantation, the net nitrification and soil NO and N2O emissions were significantly reduced under high moisture content. The overall trend was in the order of XJH>T15H>T5H, and the values of soil net nitrification and NO and N2O emissions were as high as 4.2 mg·(kg·d)-1, 1.4 mg·kg-1, and 14.3 mg·kg-1 in the XJH treatment, respectively. Under the low moisture content, soil NO emissions in tea field soil were significantly reduced relative to those in rubber plantation soil, N2O emissions had no significant difference among different treatments, and net nitrification had no significant difference between the XJ and T15 treatments. There was a significant positive correlation between NO emissions and net nitrification rate (P<0.01). ② The net nitrification of XJH was higher than that of XJL, but the net nitrification values under different moisture contents in tea field soil was in contrast to that in rubber plantation soil. The NO emissions of XJ and T15 under different moisture contents were consistent with the trend of net nitrification, and the high nitrification promoted NO emissions, whereas NO emissions of T5 were not significantly affected by moisture content. The high moisture content treatment significantly promoted N2O emissions relative to those under the low moisture content treatment. The results showed that SOM, TN, pH, and moisture content were the key factors affecting soil net nitrification rate, NO, and N2O emissions. The conversion of the rubber plantation to a tea plantation significantly reduced the net nitrification rate and negative impact on the environment under high moisture content.

To Wear or Not to Wear: Analysis of Individuals' Tendency to Wear Masks during the COVID-19 Pandemic in China.

During the COVID-19 pandemic, the percentage of Chinese people wearing masks was very high, as was the acceptance and initiative toward mask wearing. This national action merits our exploration of the psychological reasons as well as the general social and environmental factors behind this behavior. In this article, we integrated the Unified Theory of Acceptance and Use of Technology 2 (UTAUT 2) as well as Health Belief Model and set up a mask acceptance model. We used a questionnaire survey and received 337 valid questionnaires. The results indicate that social influence, perceived susceptibility to COVID-19, perceived hedonic benefit (appearance enhancement), and a perceived barrier (hindrance to communication) exert significant influences on the willingness to wear masks. Meanwhile, social influence plays an intermediary role between interdependent self-construal and intention to wear a mask. We hope to reveal the micro psychological reasons for the national action and reflect on the cultural characteristics of Chinese people in the special context of the COVID-19 pandemic.

Ultra-compact dual-mode mode-size converter for silicon photonic few-mode fiber interfaces.

Fiber couplers usually take a lot of space on photonic integrated circuits due to the large mode-size mismatch between the waveguide and fiber, especially when a fiber with larger core is utilized, such as a few-mode fiber. We demonstrate experimentally that such challenge can be overcome by an ultra-compact mode-size converter with a footprint of only 10 µm. Our device expands TE0 and TE1 waveguide modes simultaneously from a 1-µm wide strip waveguide to an 18-µm wide slab on a 220-nm thick silicon-on-insulator, with calculated losses of 0.75 dB and 0.68 dB, respectively. The fabricated device has a measured insertion loss of 1.02 dB for TE0 mode and 1.59 dB for TE1 mode. By connecting the ultra-compact converter with diffraction grating couplers, higher-order modes in a few-mode fiber can be generated with a compact footprint on-chip.

Ultra-broadband and ultra-compact polarization beam splitter based on a tapered subwavelength-grating waveguide and slot waveguide.

In this work, we propose an ultra-broadband and ultra-compact polarization beam splitter (PBS) on a standard silicon-on-isolator platform. Assisted by a tapered subwavelength-grating waveguide and a slot waveguide, the working bandwidth of the directional-coupler-based PBS covers the entire O-, E-, S-, C-, L- and U-bands and the coupling length is only 4.6 µm. The insertion losses (ILs) of the device are simulated to be less than 0.8 dB and the extinction ratios (ERs) are larger than 10.9 dB at the wavelength range of 1260-1680 nm for both TE and TM polarizations. The experimental results show the average ILs are less than 1 dB for both polarizations at our measured wavelength ranges, which are consistent with the simulation results. It has the largest 1-dB bandwidth among all the reported broadband PBSs to the best of our knowledge.