Lithium niobate-on-insulator (LNOI) has recently emerged as a promising material platform for high-density and advanced photonics integrated circuits (PICs). And single-mode waveguides (SMW) are the most basic building blocks for structuring various PICs. In this paper, single-mode conditions (SMCs) for shallowly etched LNOI rib waveguides in x-cut LNOI wafer are investigated with the finite element method (FEM) in consideration of the lateral leakage and the magic width for the first time, to our best knowledge. Our results indicate that due to the lateral leakage and the magic width these shallowly etched x-cut LNOI rib waveguides have unique and complex SMCs. Our method and results provide a guidance in designing low-loss LNOI SMW and high-performance PICs.

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We propose a long-period grating assisted directional coupler in lithium niobate (LN) for the realization of electro-optic tunable mode filtering functionality. Our typical device, fabricated with the annealed proton-exchange process and designed for filtering out the fundamental mode in a two-mode LN waveguide, achieves a maximum mode extinction ratio of 29 dB at 1551.7 nm wavelength and a 20 dB bandwidth of ~2.5 nm with an electrical wavelength tuning sensitivity of 0.182 nm/V.

Alkylation of benzene with ethanol for synthesis of ethylbenzene was performed over parent zeolites and zeolites modified with La2O3, such as HMCM-22, HBeta and nano HZSM-5 in a fixed-bed reactor at CO2 flow. The properties of zeolites and catalysts were characterized by XRD, BET and NH3-TPD. The results indicated that zeolite catalysts modified with La2O3 showed high conversion of benzene and high selectivity of ethylbenzene, i.e., 25 % conversion of benzene and 92.72% selectivity of ehtylbenzene over 3%La2O3-HZSM-5(Si/Al=200) respectively. The high selectivity of ethylbenzene is attributed to the proper acid property of modified HZSM-5, and it can be concluded that acid properties is the main factor to affect on this Alkylation. In addition, the deactivation obviously restricted over 5%La2O3-HMCM-22 and 3%La2O3-HZSM-5(Si/Al=200) on time on-stream of reaction, due to enhancement of anti-coking capability and hydrothermal stability after modification.

It is essential to bias a thin-film lithium-niobate Mach-Zehnder electro-optic (EO) modulator at the desired operation condition to ensure optimal performance of the modulator. While thermo-optic (TO) control can solve the problem of bias drift, it consumes significant electric power. In this paper, we propose a technique to largely reduce bias power consumption by combining passive bias and TO bias. In our design, waveguide sections with different widths are introduced in the two arms of the MZ modulator to produce a desired phase difference of π/2 rad (the desired operation condition), and local heating with electrode heaters placed on the waveguides is employed to provide compensation for any phase drift caused by fabrication errors and other effects. As the TO control only serves to compensate for small errors, the electric power required is low and the response is fast. To demonstrate our technique experimentally, we fabricate several modulators of the same design on the same chip. Our experimental modulators can operate up to ∼40 GHz with a half-wave voltage of ∼2.0 V over a wide optical bandwidth, and the performances are insensitive to ambient temperature variations. The TO bias powers required range from 1 mW to 15 mW, and the thermal rise and fall times are 47 µs and 14 µs, respectively. Our technique can facilitate the development of practical high-speed EO modulators on the lithium-niobate-on-insulator platform.