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Abstract Arrayed waveguide grating is a versatile and scalable integrated light dispersion device, which has been widely adopted in various applications, including, optical communications and optical sensing. Recently, thin-film lithium niobate emerges as a promising photonic integration platform, due to its ability of shrinking largely the size of typical lithium niobate based optical devices. This would also enable multifunctional photonic integrated chips on a single lithium niobate substrate. However, due to the intrinsic anisotropy of the material, to build an arrayed waveguide grating on X-cut thin-film lithium niobate has never been successful. Here, a universal strategy to design anisotropy-free dispersive components on a uniaxial in-plane anisotropic photonic integration platform is introduced for the first time. This leads to the first implementation of arrayed waveguide gratings on X-cut thin-film lithium niobate with various configurations and high-performances. The best insertion loss of 2.4 dB and crosstalk of −24.1 dB is obtained for the fabricated arrayed waveguide grating devices. Applications of such arrayed waveguide gratings as a wavelength router and in a wavelength-division multiplexed optical transmission system are also demonstrated.

Group velocity and impedance matches are prerequisites for high-speed Mach–Zehnder electro-optic (EO) modulators. However, not all platforms can realize matching conditions, restricting high-speed modulation in many practical conditions. Here, we propose and demonstrate a quasi-matching scheme to satisfy the group velocity and characteristic impedance matches by cascading fast-wave and slow-wave traveling wave electrodes. The effective group velocity can be flexibly adjusted by changing the ratio of fast-wave and slow-wave traveling wave electrodes. Moreover, the quasi-matching scheme is experimentally verified by demonstrating a 6 mm long EO modulator on a thin-film lithium-niobate-on-insulator platform with a silica cladding. The radio frequency signal insertion loss at the boundary of the slow-wave and fast-wave electrodes is less than 0.12 dB. The measured small signal EO response of the quasi-matched EO modulator drops less than 2 dB at 67 GHz, while the measured small-signal EO responses of conventional slow and fast traveling wave EO modulators drop 4 dB at 67 GHz. The measured 100 Gb/s on–off key signal eye-diagrams of the quasi-matched EO modulator also exhibit an overwhelming advantage over conventional schemes. Therefore, our results will open many opportunities for high-speed EO modulators in various platforms.

A matrix-vector multiplication (MVM) optical signal processor based on mode division multiplexing (MDM) was proposed and demonstrated in the current work, which is composed of a mode multiplexer, a multimode beam splitter, a mode demultiplexer, a modulator array and combiners. In addition, the characteristics of MDM obviate the need for multiple wavelengths and therefore multiple laser light sources are unneeded, which greatly reduces the complexity and cost. A 4 × 4 MDM-MVM was realized on a standard silicon-on-insulator (SOI) platform. Combined with the off-chip light source and photodetectors (PDs), 4-level modulation has been demonstrated, and each level of the output signal could represent 2 bits of information.

Recently, high-performance thin-film lithium niobate optical modulators have emerged that, together with advanced multiplexing technologies, are highly expected to satisfy the ever-growing demand for high-capacity optical interconnects utilizing multiple channels. Accordingly, in this study, a compact lithium-niobate-on-insulator (LNOI) photonic chip was adopted to establish four-channel wavelength-division-multiplexing (WDM) transmitters, comprising four optical modulators based on ultracompact 2 × 2 Fabry-Perot cavities and a four-channel WDM filter based on multimode waveguide gratings. The fabricated chip with four wavelength channels has a total footprint as compact as 0.3 × 2.8 mm2, and exhibits an excess loss of ~0.8 dB as well as low inter-channel crosstalk of < –22 dB. Using this LNOI photonic chip, high-capacity data transmissions of 320 Gbps (4 × 80 Gbps) on-off-keying signals and 400 Gbps (4 × 100 Gbps) four-level pulse amplitude signals were successfully realized with the ultra-low power consumption of 11.9 fJ/bit.

Chip-scale programmable optical signal processors are often used to flexibly manipulate the optical signals for satisfying the demands in various applications, such as lidar, radar, and artificial intelligence. Silicon photonics has unique advantages of ultra-high integration density as well as CMOS compatibility, and thus makes it possible to develop large-scale programmable optical signal processors. The challenge is the high silicon waveguides propagation losses and the high calibration complexity for all tuning elements due to the random phase errors. In this paper, we propose and demonstrate a programmable silicon photonic processor for the first time by introducing low-loss multimode photonic waveguide spirals and low-random-phase-error Mach-Zehnder switches. The present chip-scale programmable silicon photonic processor comprises a 1×4 variable power splitter based on cascaded Mach-Zehnder couplers (MZCs), four Ge/Si photodetectors, four channels of thermally-tunable optical delaylines. Each channel consists of a continuously-tuning phase shifter based on a waveguide spiral with a micro-heater and a digitally-tuning delayline realized with cascaded waveguide-spiral delaylines and MZSs for 5.68 ps time-delay step. Particularly, these waveguide spirals used here are designed to be as wide as 2 µm, enabling an ultralow propagation loss of 0.28 dB/cm. Meanwhile, these MZCs and MZSs are designed with 2-µm-wide arm waveguides, and thus the random phase errors in the MZC/MZS arms are negligible, in which case the calibration for these MZSs/MZCs becomes easy and furthermore the power consumption for compensating the phase errors can be reduced greatly. Finally, this programmable silicon photonic processor is demonstrated successfully to verify a number of distinctively different functionalities, including tunable time-delay, microwave photonic beamforming, arbitrary optical signal filtering, and arbitrary waveform generation.

A polarization-insensitive thermo-optic switch is proposed and demonstrated on the silicon-on-insulator platform with a 220 nm silicon core layer. The present device is based on the Mach–Zehnder interferometer structure, consisting of polarization-insensitive power splitters and polarization-insensitive phase shifters (PIPSs). The polarization-insensitive power splitter has been realized by employing an adiabatic directional coupler, which utilizes the fast adiabatic mode evolution by introducing cubic Bézier curves on outer contours, providing broadband 3-dB power splitting for TE and TM polarization modes with only 70 µm coupling length. For the novel PIPSs, the ridge waveguide with large aspect ratio, based on the mode hybridness property, could obtain the same power consumption (Pπ) for an optical switch working at TE and TM polarizations. Experimental results indicate that the measured insertion losses are less than 2 dB and the extinction ratios are larger than 15 dB over a 40 nm wavelength band (covering the C-band).

A compact spectrometer on silicon is proposed and demonstrated with an ultrahigh resolution. It consists of a thermally-tunable ultra-high-Q resonator aiming at ultrahigh resolution and an array of wideband resonators for achieving a broadened working window. The present on-chip spectrometer has a footprint as compact as 0.35 mm2, and is realized with standard multi-project-wafer foundry processes. The measurement results show that the on-chip spectrometer has an ultra-high resolution ∆λ of 5 pm and a wide working window of 10 nm. The dynamic range defined as the ratio of the working window and the wavelength resolution is as large as 1940, which is the largest for on-chip dispersive spectrometers to the best of our knowledge. The present high-performance on-chip spectrometer has great potential for high-resolution spectrum measurement in the applications of gas sensing, food monitoring, health analysis, etc.

Qudit-based quantum devices can outperform qubit-based ones, but a programmable qudit-based quantum computing device is still missing. Here, the authors fill this gap using a programmable silicon photonic chip employing ququart-based encoding, showing the scaling advantages compared to the qubit counterpart.

A novel Si/In2O3 hybrid plasmonic waveguide modulator was experimentally realized by using an asymmetric directional coupler (ADC), which consists of a silicon photonic waveguide and a Si/In2O3 hybrid plasmonic waveguide. All the silicon cores are covered with a silica layer, above which there is a metal–oxide–semiconductor (MOS) capacitor consisting of the In2O3/HfO2/Au layers. The Au layer sitting on the top of the MOS capacitor works as the top-electrode, while the In2O3 thin film covers the sidewall and contacts with the Au bottom-electrode. When the bias voltage is not applied, light launched from the silicon photonic waveguide is weakly coupled into the Si/In2O3 hybrid plasmonic waveguide, and thus, one has a high transmission at the through port of the ADC. On the other hand, when the bias voltage is applied, the carrier density in the In2O3 layer is changed, which introduces some modification to the refractive index of the In2O3 thin film. As a result, light is strongly cross-coupled from the silicon photonic waveguide to a Si/In2O3 hybrid plasmonic waveguide, and one has low transmission at the through port. In this Letter, an ultra-compact Si/In2O3 hybrid plasmonic waveguide modulator is realized with a 3.5-μm-long ADC. In the experiments, the fabricated waveguide modulator works well and exhibits a high modulation bandwidth of >40 GHz for the first time.

Ultra-compact silicon photonic filters with box-like responses and high extinction ratios are proposed and demonstrated by introducing tenth-order adiabatic elliptical-microrings (AEMs) with bent directional couplers. For the AEMs, the waveguides in the non-coupling regions are wide and have a minimal bending radius, while the waveguides in the coupling regions are narrowed and have a maximal bending radius. The present silicon photonic filters based on tenth-order AEMs show a free spectral range as large as 37 nm for the first time. Even fabricated with commercial complementary metal–oxide–semiconductor-compatible 248 nm deep-ultraviolet lithography processes, the present devices show high performances with excess losses as low as ∼1 dB and extinction ratios as high as >60 dB. More importantly, the present silicon photonic filters work very well all-passively without any thermal control for calibration.

Thin-film lithium niobate (TFLN) based traveling-wave modulators maintain simultaneously excellent performances, including large modulation bandwidth, high extinction ratio, low optical loss, and high modulation efficiency. Nevertheless, there still exists a balance between the driving voltage and modulation bandwidth. Here, we demonstrate an ultra-large bandwidth electro-optic modulator without compromising the driving voltage based on the TFLN platform on a silicon substrate, using a periodic capacitively loaded traveling-wave electrode. In order to compensate the slow-wave effect, an undercut etching technique for the silicon substrate is introduced to decrease the microwave refractive index. Our demonstrated devices represent both low optical and low microwave losses, which leads to a negligible optical insertion loss of 0.2 dB and a large electro-optic bandwidth with a roll-off of 1.4 dB at 67 GHz for a 10 mm-long device. A low half-wave voltage of 2.2 V is also achieved. Data rates up to 112 Gb s−1 with PAM-4 modulation are demonstrated. The compatibility of the proposed modulator to silicon photonics facilitates its integration with matured silicon photonic components using, e.g., hybrid integration technologies.

Applying natural mineral water to skin care is a popular tendency and many cosmetics products based on thermal spring water have been developed. The special location and environmental conditions provide Dead Sea water (DSW) with unique ion composition and concentrations, which bring comprehensive positive effects on skin health. This article reviews two potential action modes of DSW, and the biological function of DSW and its related complex in dermatology and skin care. Previous studies have proved the functions of skin moisturization, anti-inflammation, skin barrier repair, and anti-pollution. Especially, the anti-aging effect of DSW and related complexes can act in three different ways: keratinocyte rejuvenation, photo-protection, and cellular energy elevation. Additionally, the issues that need further investigation are also discussed. We hope that this review will help to improve the understanding of DSW and its related complex, and further contribute to product development in the skincare industry.

We report the designs of on-chip grating couplers for the silicon hybrid plasmonic waveguides, which is the first proposal, to the best of our knowledge, for the direct coupling between a standard single-mode fiber and a hybrid plasmonic waveguide. By leveraging the apodized gratings and a two-stage-taper mode converter, we obtain a theoretical coupling efficiency of 79% (−1.03 dB) at the 1550 nm wavelength and a 3-dB bandwidth of 73 nm between the fiber and a 100 nm-wide silicon hybrid plasmonic waveguide with a bottom metal layer. We further propose grating couplers for three other sorts of silicon hybrid plasmonic waveguides with a metal cap and theoretically achieve good performances with coupling efficiencies larger than 47% and bandwidths larger than 51 nm. The proposed direct coupling scheme can avoid extra insertion losses and additional alignment processes that conventional indirect coupling schemes produce. It is believed to be a new step forward to the CMOS-compatible and large-scale integration based on the plasmonic waveguides.

The members of the Nesterenkonia genus have been isolated from various habitats, like saline soil, salt lake, sponge-associated and the human gut, some of which are even located in polar areas. To identify their stress resistance mechanisms and draw a genomic profile across this genus, we isolated four Nesterenkonia strains from the lakes in the Tibetan Plateau, referred to as the third pole, and compared them with all other 30 high-quality Nesterenkonia genomes that are deposited in NCBI. The Heaps’ law model estimated that the pan-genome of this genus is open and the number of core, shell, cloud, and singleton genes were 993 (6.61%), 2782 (18.52%), 4117 (27.40%), and 7132 (47.47%), respectively. Phylogenomic and ANI/AAI analysis indicated that all genomes can be divided into three main clades, named NES-1, NES-2, and NES-3. The strains isolated from lakes in the Tibetan Plateau were clustered with four strains from different sources in the Antarctic and formed a subclade within NES-2, described as NES-AT. Genome features of this subclade, including GC (guanine + cytosine) content, tRNA number, carbon/nitrogen atoms per residue side chain (C/N-ARSC), and amino acid composition, in NES-AT individuals were significantly different from other strains, indicating genomic adaptation to cold, nutrient-limited, osmotic, and ultraviolet conditions in polar areas. Functional analysis revealed the enrichment of specific genes involved in bacteriorhodopsin synthesis, biofilm formation, and more diverse nutrient substance metabolism genes in the NES-AT clade, suggesting potential adaptation strategies for energy metabolism in polar environments. This study provides a comprehensive profile of the genomic features of the Nesterenkonia genus and reveals the possible mechanism for the survival of Nesterenkonia isolates in polar areas.