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The quaternary alkaline-earth metal thiophosphate SrAgPS4 has been synthesized. It possesses desirable properties as a preferred IR NLO material: a large band gap (2.97 eV), phase-matched intense second harmonic generation (SHG) (1.10AgGaS2), and moderate birefringence.

A novel noncentrosymmetric chalcogenide (Na3Rb)Hg2Ge2S8 with mixed alkali metals was successfully synthesized and showed a strong second harmonic generation response of 1.4 × AgGaS2 at 2090 nm for infrared nonlinear optics.

Metal-organic framework (MOF) material is one of the most promising porous nanomaterials for volatile organic compound (VOC) adsorption and sensing. The large surface area and the high porosity of MOF contribute to the high sensitivity of MOF-based VOC sensors. In this study, we engineer the coating of the zeolitic imidazolate framework material ZIF-8 grown on the surface of a long-period fiber grating (LPFG) for acetone vapor sensing. Being a periodic structure formed in a single-mode optical fiber, an LPFG is designed to couple light from the core to the cladding of the fiber at a specific resonance wavelength. Adsorption of acetone vapor molecules in the framework of the ZIF-8 coating can change the refractive index of the coating and cause a shift in the resonance wavelength of the LPFG. The sensitivity of the resonance shift of the LPFG to the acetone vapor concentration depends strongly on the thickness of the ZIF-8 coating. To create a dense ZIF-8 coating, at least five growth cycles of ZIF-8 (30 min growth for one cycle) are required, and nine growth cycles can create a 500 nm thick coating. The LPFG coated with nine growth cycles of ZIF-8 provides a high sensitivity of 21.9 nm ppm

Two novel metal chalcogenides Cs2InPS4X2 (X = Cl, Br) were successfully synthesized and exhibit large optical band gaps induced by the [InS4X2]7− mixed-anion groups.

A vapochromic dye was synthesized and coated on a long-period fiber grating sensor for specific benzene vapor sensing with an ultra-large dynamic range.

The continuous exploration of multinary chalcogenide semiconductors has provided a variety of new functional materials. In this paper, four new quaternary chalcogenides AHgPS4 (A+ = Na+, K+, Rb+, Cs+) have been prepared by solid-state syntheses. These findings complement the lack of research on this quaternary system. Influenced by the size effect of cations and the coordination mode of Hg, the four compounds crystallize in four different space groups [NaHgPS4, P4n2; KHgPS4, Pnn2; RbHgPS4, P21/n; CsHgPS4, P212121] and show an interesting evolution from a 3D framework structure to a 1D chain structure. Moreover, all of these compounds feature noncentrosymmetric (NCS) structures except for RbHgPS4. The materials exhibit wide band gaps of 2.7 eV < Eg < 3.0 eV. The NCS- related second-harmonic-generation (SHG) property of NaHgPS4 and KHgPS4 was also studied. They display strong powder SHG responses (3.14 × AgGaS2 for NaHgPS4; 4.15 × AgGaS2 for KHgPS4), which indicate their intriguing potential as IR nonlinear-optical materials. Moreover, first-principles theoretical calculations were performed to understand the structure-property relationships of these materials.

In this work, a compact sub-wavelength-pitch silicon waveguide array with low crosstalk is proposed and analyzed. The crosstalk is suppressed by periodic silicon nano-blocks symmetrically arranged along the silicon strip waveguides. The silicon nano-blocks are properly designed to work in the resonant region as a high-reflection boundary so that the evanescent fields of the silicon waveguide, which directly contribute to the coupling between waveguides, can be truncated. Meanwhile, the nano-blocks periodically perturb the evanescent fields to form a weak-radiating grating, leading to a millimeter-long effective radiation length required for highly directive optical phased arrays. Simulation results show that the crosstalk between the waveguides in the proposed design is at least 10 dB lower than traditional waveguide array with identical sizes within the 1500–1590 nm bandwidth. Furthermore, the proposed design achieves an effective radiation length up to 1.47 mm, resulting in a theoretical narrow beam width of 0.052°. Combining both the low crosstalk and the long effective radiating length, our design offers a promising platform for high-performance two-dimensional scanning optical phased array with a large field of view and a narrow beam width.

Metal-organic framework (MOF) nanomaterials are emerging porous coordinative polymers with large surface area and high porosity. Their application scenarios highly depend on adsorption/desorption dynamics of guest molecules in the framework. For representative ZIF-8 with framework flexibility, the study of molecule transportation in the pore channels of ZIF-8 will address the ambiguity of unclear application scenarios. In this study, the integration of lab-on-fiber technology and nanotechnology are demonstrated for real-time monitoring of adsorption/desorption dynamics of heterocyclic volatile compounds (VOCs) with kinetic diameters larger than the window aperture of ZIF-8. The in-line fiber interferometer with cascaded long-period gratings is used to monitor the real-time refractive index change of VOC adsorption/desorption. The structure-effect relationship between guest VOCs and framework flexibility is analyzed. It shows that the adsorption dynamics is highly related to the molecular geometry and kinetic diameter. The framework flexibility results in the trapping of guest VOCs toluene, pyridine, and tetrahydrofuran in the frameworks. The methanol adsorption/desorption is an effective strategy for the fast desorption of trapped residual VOCs in the framework. Finally, we conceptually demonstrated the real-time monitoring of trace toluene enrichment using ZIF-8 for indoor air purification. This study paves the way for the in-depth understanding of framework flexibility for MOF’s application.

A new noncentrosymmetric (NCS) quaternary sulfide, SrAgAsS

Forest-to-pasture conversion is known to cause global losses in plant and animal diversity, yet impacts of livestock management after such conversion on vital microbial communities in adjoining natural ecosystems remain poorly understood. We examined how pastoral land management practices impact soil microorganisms in adjacent native forest fragments, by comparing bacterial communities sampled along 21 transects bisecting pasture-forest boundaries. Our results revealed greater bacterial taxon richness in grazed pasture soils and the reduced dispersal of pasture-associated taxa into adjacent forest soils when land uses were separated by a boundary fence. Relative abundance distributions of forest-associated taxa (i.e., Proteobacteria and Nitrospirae) and a pasture-associated taxon (i.e., Firmicutes) also suggest a greater impact of pastoral land uses on forest fragment soil bacterial communities when no fence is present. Bacterial community richness and composition were most related to changes in soil physicochemical variables commonly associated with agricultural fertilization, including concentrations of Olsen P, total P, total Cd, delta 15 N and the ratio of C:P and N:P. Overall, our findings demonstrate clear, and potentially detrimental effects of agricultural disturbance on bacterial communities in forest soils adjacent to pastoral land. We provide evidence that simple land management decisions, such as livestock exclusion, can mitigate the effects of agriculture on adjacent soil microbial communities.

The development of novel chemical nitro-explosive sensors with high sensitivity, low cost and a compact size is essential for homeland security, environmental protection and addressing military challenges. Polymeric optical waveguides based on refractive index sensing are widely used in biochemical detection due to their advantages of large-scale integration, low cost, high sensitivity and anti-electromagnetic interference. In this study, we designed and fabricated a polymer waveguide Mach–Zehnder interferometer (MZI) sensor to detect 2,4-dinitrotoluene (DNT) in water. One phase shifter of the MZI waveguide was functionalized by coating a thin cladding layer of polycarbonate with dipolar chromophores and used as the sensing arm; the other arm was coated with passive epoxy resin cladding and used as the reference arm. The phase difference between the two arms of the MZI was modulated using the refractive index (RI) change in the polycarbonate cladding when dipolar chromophores interacted with electro-deficient DNT. The theoretical sensitivity of the designed MZI can reach up to 24,696 nm/RIU. When used for explosive detection, our fabricated sensor had a maximum wavelength shift of 4.465 nm and good linear relation, with an R2 of 0.96 between the wavelength shift and a concentration ranging from 3.5 × 10−5 to 6.3 × 10−4 mol/L. The sensitivity of our device was 6821.6 nm/(mol/L). The design of an unbalanced MZI sensor, together with the sensing material, provides a new approach to using low-cost, compact and highly sensitive devices for in-field explosive detection.

In silicon photonic waveguides, the on-chip integration of high-performance nanomaterials is considerably important to enable the waveguide sensing function. Herein, the in situ self-assembly of the low refractive index (RI) metal-organic framework nanomaterial ZIF-8 with a large surface area and high porosity on the surface of a designated SiO2 waveguide for evanescent wave sensing is demonstrated. The surface morphology and transmission loss of the nano-functionalized waveguide are investigated. The specific design and fabrication of asymmetric Mach-Zehnder interferometers (AMZIs) are performed based on the optical properties of ZIF-8. Such efforts in waveguide engineering result in an output interfering spectrum of nano-functionalized AMZI with an ultra-high extinction ratio (28.6 dB), low insertion loss (∼13 dB) and suitable free spectral range (∼30 nm). More significantly, the outstanding sensing features of ZIF-8 are successfully realized on the SiO2 waveguide chip. The results of ethanol detection show that the AMZI sensor has a large detection range (0 to 1000 ppm), high sensitivity (19 pm ppm-1 from 0 to 50 ppm or 41 pm ppm-1 from 600 to 1000 ppm) and low detection limit (1.6 ppm or 740 ppb). This combination of nanotechnology and optical waveguide technology is promising to push forward lab-on-waveguide technology for volatile organic compound (VOC) detection.

Inorganic metal chalcohalides are significant semiconductive materials for photovoltaics, photodetetion and infrared optics. Thus it is considerably rewarding to develop a new synthetic strategy to provide more degrees of freedom for atomic coordination to tune the optical and electronic properties of metal chalcohalides. In this work, the mixed-anion strategy is performed to synthesize two new metal chalcohalides Cs

Metal chalcogenides play a critical role in the infrared (IR) nonlinear optical (NLO) field. However, Eu-based chalcogenide-type IR NLO materials are still scarce up to now. In this paper, two new quaternary Eu-based chalcogenides, EuHgGeSe4 and EuHgSnS4, containing the "NLO active groups" [HgQ4]6- (Q = S, Se) and [GeSe4]4-/[SnS4]4- were synthesized through traditional high-temperature solid-state reactions. They possess noncentrosymmetric structures, crystallizing in the Ama2 space group, and exhibit strong phase-matchable second-harmonic-generation (SHG) responses (3.1× and 1.77× that of AgGaS2 for EuHgGeSe4 and EuHgSnS4, respectively). Meanwhile, the optical band gaps of EuHgGeSe4 (1.97 eV) and EuHgSnS4 (2.14 eV) were determined from UV-vis-NIR diffuse reflectance spectra. Differential scanning calorimetry (DSC) analyses reveal the congruent-melting behavior of EuHgGeSe4. Furthermore, structural analysis and theoretical calculations verify the critical driving effects of [HgQ4]6- tetrahedra on the strong SHG activity. The overall results demonstrate that EuHgGeSe4 and EuHgSnS4 are potential IR NLO materials.

This study reports the facile synthesis, characterization and quantitative structure-property relationship analysis of molecular and material properties of tricyanofuran-based (TCF) dipolar heptamethines with different electron donors of indoline ( F1 ), benzo[ e ]- indoline ( F2 ), benz[ cd ]indoline ( F3 ), and Michler’s base derivatives ( M1 and M2 ). The linear and nonlinear optical (NLO) properties of these chromophores have been thoroughly investigated, and the relationship between molecular and bulk response has been analyzed and compared with dipolar tetraene AJLZ53 as one of the best chromophores for electro-optic (EO) devices. In particular, we provide responsible data collection and analysis of optical and EO properties for poled thin films using a widely-recognized and accredited methodology of prism coupling system with the help of rigid oriented gas model. We found that these push-pull heptamethines with synthetic efficacy exhibit high near-infrared absorption, excellent chemical stability and large hyperpolarizabilities ( β ) varied from 1,023×10−30 esu for F1 , 3,047×10−30 esu for M1 , and 3,547×10−30 esu for F3 at 1,304 nm in poled films, respectively. The β values of these molecules are among the highest ones for TCF-based dipolar chromophores, and also agree well with reported analytical results in the solutions. In poled polymers with a modest chromophoric loading density of 1.3× 1020 cm−3, M1 and M2 give a high poled-induced noncentrosymmetric order and relatively large r 33 values around 40 pm V−1 at 1,304 nm, indicative of large μβ values and suitable structural modification for high poling efficiency. Furthermore, a binary EO polymer based on the co-loading of M1 and AJLZ53 achieve a large r 33 value of 143.3 pm V−1 at 1,304 nm. Our studies suggest that concise synthesis and molecular design of push-pull polymethines can be well guided by the tabulation of their linear and NLO properties in bulk materials, and streamline future development of high performance organic EO materials for photonic applications.

Aim: Investigation of characteristics of different duodenal microbial colonization states in patients with liver cirrhosis (LC). Materials & methods: Deep-sequencing analyses of the 16S rRNA gene V1-V3 regions were performed. Results: Both bacterial compositions and richness were different between the three-clustered LC microbiotas, in other words, Cluster_1_LC, Cluster_2_LC and Cluster_3_LC. Cluster_1_LC were more likely at severe dysbiosis status due to its lowest modified cirrhosis dysbiosis ratio. OTU12_ Prevotella and OTU10_ Comamonas were most associated with Cluster_1_LC and Cluster_3_LC, respectively, while OTU38_ Alloprevotella was vital in Cluster_2_LC. Pyruvate-ferredoxin/flavodoxin oxidoreductase, dihydroorotate dehydrogenase and branched-chain amino acid transport system substrate-binding protein were most associated with Cluster_1_LC, Cluster_2_LC and Cluster_3_LC, respectively. Conclusion: The three duodenal microbial colonization states had distinct representative characteristics, which might reflect the health status of cirrhotic patients.

Electro-optic materials at the shortwave infrared window (850 nm) is significant for optical modulation in free-space communication and short-distance local area networks. However, most of the current high-performance organic nonlinear optical chromophores (absorption bandgap ∼1.5 eV) are designed for operating at 1310 nm (O band) or 1550 nm (C band) and do not exhibit optical transparency at 850 nm (bandgap ∼1.45 eV). The design and synthesis of chromophores exhibiting optical transparency at 850 nm are more challenging because regular bandgap engineering to improve microcroscopic nonlinearity (μβ value) might not be available due to the bandgap restriction (optical transparency) at 850 nm. In this respect, this manuscript utilizes the strategy of suitable site-isolation in molecular engineering to optimize the comprehensive performance of chromophores for electro-optics at 850 nm. Vilsmeier formylation has been facilitated on symmetric or asymmetric donor–π–donor intermediate dyes to form donor–π–acceptor (D–π–A) chromophores C1 and C2 with tunable conjugated steric hindrance (a site-isolator). Without significant red-shifts in the absorption spectra, conjugated steric hindrance groups contribute to large enhancement in the μβ values of the chromophores and ensure optical transparency at 850 nm. The μβ values of C1 (6706 × 10−48 esu) and C2 (7279 × 10−48 esu) with conjugated site-isolation groups are much higher than that of previously reported chromophores at 850 nm. The structure–property relationship reveals that a suitable site-isolator is extremely significant for realizing highly efficient translation of microscopic hyperpolarizability into macroscopic electro-optic coefficients. As a result, an electro-optic coefficient of 94 pm V−1 at 830 nm was achieved. To the best of our knowledge, this is the highest value for organic electro-optic materials at 850 nm.

Organic nonlinear optical (NLO) materials are very important for high-speed information processing in addressing the challenges of reduced energy consumption and enhanced speed and bandwidth. In particular, organic second-order NLO materials are very promising for meeting the combined requirements of ultra-low energy and ultra-high bandwidth in electro-optic (EO) modulation, while organic third-order NLO materials have good potential for applications in ultra-speed all-optical signal processing (AOSP). This review highlights the recent significant progress made in organic second- and third-order NLO materials. For second-order NLO materials, the recent advances in the efficient and cost-effective synthesis of dipolar polyene chromophores and thin-film engineering for efficient electric field poling are summarized. The applications and prospects of these high-performance EO materials are also discussed. For third-order NLO materials, we discuss the molecular design strategies of cyanine dyes for AOSP applications, particularly focusing on anionic tricyanofuran (TCF)-based cyanines. We aim to provide a better understanding of the structure–property relationships for cyanine-based AOSP materials. Finally, a summary and outlook for advancing high-performance organic NLO materials are provided.

Optical polymers can easily be functionalized as versatile waveguide materials for chemical sensing. The ultimate endeavour of material innovation is to utilize a new material to functionalize a waveguide device, and meanwhile greatly simplify device processing to optimize the device performance. Herein, we show that a functional polycarbonate containing side-chain dipolar chromophores is sensitive to ultraviolet (UV) light and electron-deficient nitrobenzene (NB) explosive vapor. UV light induced photo-bleaching of the active cladding material polycarbonate is employed to selectively regulate the refractive index (RI) for the optimization of the waveguide evanescent field, which simply and greatly improves the sensitivity for RI sensing. In explosive vapor detection, polycarbonate acts as a sensitive cladding for NB vapor sensing, in which the dipole–dipole interactions between electron-deficient NB and side-chain dipolar chromophores result in the RI change of the polycarbonate cladding. Our efforts in materials and device engineering enable a significant change in the phase difference between the two arms of the fabricated asymmetric Mach–Zehnder interferometer (AMZI) waveguide in response to a very small change in concentration of NB and hence improve the sensitivity of the sensor. The fabricated photo-bleached (80 min) AMZI sensor exposed to NB vapor showed a wavelength shift of 6.8 nm, showing about 95% sensitivity improvement in comparison with the photo-bleached (40 min) AMZI. Our strategies leverage the photo-bleaching to improve the sensitivity for electron-deficient analyte detection of dipolar polycarbonate, which is simple, effective and does not require additional microfabrication for cost-effective and sensitive on-chip explosive detection.

Textile-based wearable devices have attracted increasing attention because of their softness, breathability, and biocompatibility, which makes them durable and wearable for long-term application. To date, the fabrication of multifunctional wearable electronic textiles (E-textiles) that integrate sensing and heating properties via an energy-saving method remains a great challenge. Herein, we have proposed a multifunctional integration strategy using integrated nanowire-coated fabrics that can deliver pressure sensing capabilities simultaneously with thermal insulation, Joule heating, and particulate matter (PM) filter features. The collective effect of the fiber/yarn/fabric multi-scale contacts produces a highly sensitive multifunctional E-textile, with a sensitivity of approximately 3.24 × 105 kPa−1 at 0–10 kPa and 2.16 × 104 kPa−1 at 10–100 kPa, respectively. Each layer contained a conductive network of metallic nanowires (NWs) that could reflect the infrared radiation (IR) emitted by the human body and synergistically enhance the thermal insulation property of the multifunctional E-textile, thus enabling a 5 °C decrease in the setpoint as compared to the normal cotton textile. In addition to passively insulating heat loss, the E-textile can also function as a wearable heater, inducing fast thermal response and uniform electroheating. Furthermore, it can act as a high-efficiency air filter for high-temperature PM2.5 particle removal. The outstanding integrated property is expected to be applicable in the fields of smart clothes, human monitoring and healthcare, air filtration, and lightweight body armor in extreme climate conditions.

The continuous exploration of multinary chalcogenide semiconductors has provided a variety of new functional materials. In this paper, four new quaternary chalcogenides AHgPS

A simple planar light-wave circuit-based switchable

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.

In silicon photonic waveguides, the on-chip integration of high-performance nanomaterials is considerably important to enable the waveguide sensing function. Herein, the in situ self-assembly of the low refractive index (RI) metal-organic framework nanomaterial ZIF-8 with a large surface area and high porosity on the surface of a designated SiO

We analyze and explore the potential of using a polymer horizontal slot waveguide as light-analyte interactive region to implement a low-cost and highly sensitive liquid refractive index sensor. Numerical analysis shows that the optimized polymer horizontal slot waveguide is able to realize high waveguide sensitivity. With the optimized horizontal slot waveguide, polymer liquid refractive index sensors based on Mach-Zehnder interferometer (MZI) and microring resonator (MRR) are then investigated numerically, and the results show that the MZI-based sensor can achieve high sensitivity of 17024nm/RIU and low limit of detection (LOD) of 1.76×10−6 RIU while the MRR-based sensor can achieve the sensitivity of 177nm/RIU and the LOD of 1.69×10−4 RIU with a very small footprint. Compared with the sensors employing conventional silicon or silicon nitride vertical slot waveguide, the sensors employing polymer horizontal slot waveguide exhibit comparable performances but simpler and lower fabrication costs.

Monolithic electro-optic (EO) molecular glasses are promising materials for optical waveguide device owing to their high chromophore loading density, high refractive indices and large EO coefficients (r33 values) for the optimization of in-device figure of merit (n3r33). However, the stability of EO molecular glasses including the poling induced r33 stability, chemical stability under both high temperature and high voltage in poling is still an obstruction for their real application. Herein, we used the chemical structural optimization, by means of introducing a large conjugated electron-bridge indacenodithiophene (IDT), to synthesize a monolithic EO molecular glass IDTC. Comprehensive properties of excellent glass-forming ability, high thermal stability (Td = 315 °C), and high glass transition temperature (Tg = 137 °C) was achieved in monolithic IDTC thin films. More significantly, refractive index of monolithic film was exceptionally high (n = 1.8294 @ 1310 nm and n = 1.7645 @1550 nm). The poled IDTC film exhibited the r33 value of 87.6 pm/V with large figure of merit (n3r33: 536 pm/V @1310 nm), and the EO activity can be retained over 85% of the initial value after 300 h annealing at 85 °C. Meanwhile, it was found that there is no decomposition of IDTC in poled films after high temperature and high voltage poling as well as long term annealing. The poled chromophores are recyclable EO materials for the sustainable application in low-cost EO devices.

The removal of four dissolved organic matter (DOM) fractions, non-acid hydrophobics, hydrophobic acids, hydrophilics and transphilics, was achieved by coagulation-UV/H2O2 oxidation in post-pharmaceutical wastewater (PhWW). Coagulation with Polyferric chloride (PFC), Polymeric ferric sulfate (PFS) and Polymeric aluminum ferric chloride (PAFC) was studied separately to evaluate the effects of the initial pH and coagulant dosage. The coagulation-UV/H2O2 oxidation method resulted in much higher reduction rates for dissolved organic carbon (DOC) (by 75%) and UV254 (by 92%) than coagulation or UV/H2O2 oxidation alone. The proportion of non-acid hydrophobics, hydrophobic acids, transphilics and hydrophilics removed by coagulation was 54%, 49%, 27% and 12 %, while the combined treatment removed 92%, 87%, 70% and 39%, respectively. Parallel factor analysis (PARAFAC) of fluorescence measurements revealed that the humic-like fluorescent component C4 showed the highest removal (by 44%) during the coagulation stage. After coagulation-UV/H2O2 treatment, the humic-like fluorescent component C3 had the highest removal (by 72%), whereas xenobiotic organic fluorescent components C1 and C4 remained recalcitrant to decomposition. Significant correlations (R2 > 0.8) between C1 and the hydrophobic acids and non-acid hydrophobics suggested the possibility of using fluorescence spectroscopy as an effective tool to assess variations in DOM fraction treatment efficacy in coagulation-UV/H2O2 systems. After the combined treatment, toxic inhibition of cellular activity by post PhWW decreased from 88% to 47% and biodegradability increased from 0.1 to 0.52.

Owing to the compact size, immunity to electromagnetic interference, high sensitivity and real-time monitoring, optical waveguide sensors based on a refractive index change have become an emerging approach for smart sensing in the internet-of-things system. For this purpose, the synergetic efforts in material engineering (sensing materials) and optical engineering (waveguide design and fabrication) are both indispensable. Here we report a Mach–Zehnder interferometer (MZI) waveguide with photochromic dye-doped polymer sensing films for UV light detection. Firstly, UV light induced photochromism of a synthesized dye DAECHO in solution and in the solid state is investigated to understand the relationship between their structure and optical properties, especially the photochromism-induced refractive index change for waveguide sensors. Then the MZI structure is designed and simulated to optimize the performance of refractive index sensing. Following the standard microfabrication process of double photolithography-development, the device is fabricated with a DAECHO doped polymer as a sensing cladding material for UV light detection. The evanescent sensing of MZI is performed to detect weak UV light from 10 μW cm−2 to 100 μW cm−2 at 365 nm. Our demonstration of MZI for UV light detection indicates the potential of portable and highly sensitive UV light waveguide sensors for real-life applications.

An on-chip asymmetric Mach-Zehnder interferometer (AMZI) with nanoporous ZIF-8 for ethanol vapor detection has been proposed. We demonstrated the sensitivity of AMZI sensor can reach as high as 19 pm/ppm. © 2021 The Author(s)

We propose an electro-optic mode-selective switch based on cascaded three-dimensional lithium-niobate waveguide directional couplers fabricated with a single-step annealed proton-exchange process. To compensate for discrepancies due to uncertainties in the fabrication process, we develop a post-tuning technique to improve the performance of the coupler by means of depositing a layer of titanium oxide (TiO2) onto one of the waveguides of the coupler. By integrating two cascaded dissimilar directional couplers, we experimentally demonstrate switchable (de)multiplexing of the LP01, LP11a, and LP11b modes, where the LP11a mode can be switched at an efficiency over 75% from 1530 nm to 1612 nm with an applied voltage varying between –9 V and +30 V, and the LP11b mode can be switched at an efficiency higher than 90% from 1534 nm to 1577 nm with an applied voltage varying between –21 V to 0 V. The switching times are 230–300 ns. Our proposed waveguide platform could be employed to develop advanced switches for applications in areas where high-speed switching of spatial modes is required, such as reconfigurable mode-division-multiplexing communication.

Metal chalcogenides play a critical role in the infrared (IR) nonlinear optical (NLO) field. However, Eu-based chalcogenide-type IR NLO materials are still scarce up to now. In this paper, two new quaternary Eu-based chalcogenides, EuHgGeSe

Optical phased arrays based on optical waveguides are compelling components enabling efficient and accurate beam steering. However, to avoid crosstalk between the waveguides, the element pitch is typically larger than one wavelength, which gives rise to grating lobes in real space. In this Letter, we report that near-wavelength gratings can be employed to suppress the grating lobes by utilizing the angular low-pass-filter characteristics. The properly designed near-wavelength grating acts as an angle-sensitive transmission structure. Nearly 100% transmissivity can be realized at small incident angles. However, it quickly declines to a low level when the incident angle is over the critical one. Then, a simple line current array is utilized to demonstrate the grating lobe suppression effect with the grating designed for TE-polarized incidence. Finally, we demonstrate that by loading the proposed grating designed for TM-polarized incidence upon a waveguide grating array with a 2.4 µm pitch, a grating lobe suppression of 10 dB can be achieved when scanning up to ± 14 ∘ .

We propose electric poling of electro-optic (EO) polymer films with graphene electrodes. The use of graphene electrodes can waive the use of buffer layers and minimize the poling voltage. To demonstrate the idea, we prepared EO polymer thin-film waveguides for poling with traditional Au/ITO electrodes and graphene electrodes, where the EO polymer is a guest–host system formed by doping 15 wt% of dipolar polyene chromophore AJLZ53 into the random copolymer P(S-co-MMA). Our experiments confirm that the use of graphene electrodes can significantly reduce the poling voltage. For a 3.8-µm-thick EO polymer film, we achieve high EO coefficients of 82 pm/V at 1541 nm and 110 pm/V at 1300 nm with a poling voltage of 420 V. In addition, the use of graphene electrodes allows more flexible waveguide designs and can potentially simplify the fabrication of devices based on EO polymer.

The utilization of refractive index (RI) change due to guest–host interactions between the guest volatile organic compound vapor and porous metal–organic frameworks (vapor–MOF interactions) is promising in photonic vapor sensors. Therefore, the study of light–matter interactions in nanoporous metal–organic frameworks (MOFs) is fundamental and essential for MOF-based photonic devices. In this work, the manipulation of light in MOFs to investigate the vapor–MOF interactions by using optical fiber devices is demonstrated. The vapor–MOF interactions and the light–vapor interactions (light in MOFs to sense the RI changes resulting from the vapor–MOF interactions) are investigated. The cladding mode is excited by a long-period fiber grating (LPFG) for evanescent field sensing in a ZIF-8 sensitive coating. The experimental results combining quantum chemical calculations and optical simulations reveal the relationships between the microscopic energy of vapor desorption, RI changes and evanescent field enhancement in ZIF-8 during the vapor–MOF interactions. With exceptionally large RI changes, the evanescent field of cladding mode in ZIF-8 is greatly enhanced to sense the vapor–MOF interactions. As a proof-of-concept, a LPFG sensor with ZIF-8 coating showed a high sensitivity of 1.33 pm ppm−1 in the linear range from 9.8 ppm to 540 ppm for the sensing of ethanol vapor. The investigation of light–matter interactions in ZIF-8 provides a useful guideline for the design and fabrication of MOF-based optical waveguide/fiber sensors.

We demonstrate an electro-optic mode-selective switch based on the structure of cascaded lithium-niobate asymmetric waveguide directional couplers, where a high-index oxide layer is deposited on a waveguide of the coupler for post-tuning its switching efficiency. © 2020 The Author(s)

We demonstrate the photo-bleaching of dipolar sensitive polymer cladding to optimize the evanescent sensing of asymmetric Mach-Zehnder interferometer. The sensitivity of waveguide sensor for nitrobenzene explosive vapor detection is significantly enhanced by more than 100%.

Two novel second order nonlinear optical (NLO) chromophores based on N,N-diethylaniline as a donor, verbenone based tetraene as a bridge, and tricyanofuran (TCF) or tricyanofuran derivatives with a dendritic moiety as an acceptor have been synthesized in good overall yields and systematically characterized. Besides, a facile applicable synthetic approach for a NLO dendritic acceptor was developed. Compared with C7, after introducing dendritic derivative steric hindrance groups into the acceptor, chromophore C8 had good thermal stabilities with high thermal decomposition temperatures which were 33 °C higher than that of chromophore C7. At the same time, cyclic voltammetry (CV) experiments were performed to determine the different redox properties. The conjugated verbenone tetraene segments in two chromophores could significantly improve the glass-forming ability and molecular polarization of chromophores as revealed by UV-vis-NIR absorption measurements. The bulky dendritic moiety linked by a short C–C bond is closer to the TCF acceptor, which is the most polar part in the chromophore, compared to conventional isolation groups. The results obtained from electro-optic (EO) coefficients indicate that this TCF acceptor with a unique dendritic structure can prevent antiparallel packing between chromophores, improving the poling efficiency and enhancing the EO performance. These properties, together with the good solubility, suggest the potential use of these new chromophores as materials for advanced photonic devices.

In organic electro-optic (EO) materials, strong dipole–dipole interactions hinder the highly efficient poling of nonlinear optical chromophores. Supramolecular self-assembly through π–π stacking of fluoroaromatics was proved to be one of the most effective strategies to simultaneously achieve high chromophore loading density and highly efficient poling. Herein, we demonstrated a new strategy of supramolecular homodimerization to self-assemble EO dendritic films, in which two dendritic units with semifluorinated dipolar 1,2,3-trifluorobenzene (TFB) moieties were attached to the donor end and the π-bridge centre of push–pull tetraene chromophores. In these new dendrimers, the use of monolithic and semifluorinated TFB rings to replace the heterodimers of phenyl and pentafluorophenyl moieties has greatly simplified the synthesis of dendrimers and their intermixing, and can further potentially enable more efficient and rapid intermixing of interacting moieties in the solid states than those in binary and ternary systems. Photophysical property analysis and DFT calculations were carried out to understand the macroscopic supramolecular self-assembly and microscopic polarizability of new TFB-based EO dendrimers. The poled films of these self-assembled dendritic EO films exhibited very large EO coefficients up to 248 pm V−1 at a wavelength of 1310 nm and excellent temporal stability at room temperature with a very minimal change of ∼5% for over 1000 hours. Our study therefore illustrates that homodimer stacking of TFB rings through dipole–dipole coupling provides stabilization energy similar to that of quadrupolar interaction of phenyl and pentafluorophenyl heterodimeric pairs. Due to the highly efficient poling and excellent temporal EO stability, TFB self-assembled EO dendrimers show great potential for application in photonic devices.

A simple planar light-wave circuit-based switchable L P 11 a − L P 11 b mode rotator for reconfigurable mode division multiplexing is proposed, which consists of a polymer waveguide and an electrode heater located on the waveguide. Because of the asymmetric refractive index distribution in the horizontal and vertical directions, induced by the thermo-optic effect, mode rotation between the L P 11 a and L P 11 b modes can be achieved when the heater is ON but there can be no mode rotation when the heater is OFF. Numerical simulations show that our well-designed mode rotator with optical polymer materials, which has a length of 2750 µm, can achieve a mode conversion efficiency (MCE) larger than 84% over the entire C + L band (1530–1610 nm) and a maximum MCE of 96% at 1550 nm. The switching electric power is 161.5 mW. The calculated temperature within the waveguide core is from 186°C (close to the heater) to 86°C (away from the heater).

Coupling light from in-plane guided light into free space or optical fibers is crucial for many photonic integrated circuits and vice versa. However, traditional grating couplers or waveguide grating antennas suffer from low upward coupling efficiency due to the light radiating in both upward and downward directions simultaneously. In this paper, a compact aperture-coupling nanoslot antenna array is proposed for high-efficiency unidirectional radiation, where a two-dimensional high-contrast grating (HCG) is employed as a mirror to reflect the undesired downward radiation. Upon the HCG separated by a low-index spacing layer, a thin silver layer is deposited. Finally, a series of H-shaped slots are patterned on the silver thin film to arrange the aperture fields and radiate the in-plane guided light into free space. The proposed nanoslot antenna array features a front-to-back ratio (F/B) over 10 dB within the wavelength range of 1500 ∼ 1600 nm. At the same time, a high radiation efficiency of over 75% and a maximum radiation efficiency of 87.6% are achieved within the 100 nm bandwidth. The high-efficiency unidirectional antenna array is promising for the integrated photonic applications including wireless optical communications, light detection and ranging, and fiber input/output couplers.

Organic conjugated dyes have received extensive attention due to their broad applications in nonlinear optics and light-emitting and fluorescent sensors. Herein, we report the two-step synthesis of donor–acceptor dyes with triene-conjugated bridges. Via Vilsmeier formylation and Knoevenagel condensation, the dyes 1–4 with respectively varied electron-withdrawing moieties were successfully synthesized with high yields in short duration times. Photophysical properties showed gradually enhanced intramolecular charge-transfer (ICT) strength from dye 1 to dye 4 and diverse absorption and fluorescence properties. This structure–property tuning ensured their different applications in optofluidic lasers and nonlinear optics. Moreover, an optofluidic laser obtained using dye 1 in toluene as the gain material was demonstrated. Narrow linewidth (1.6 nm) of the optofluidic laser (peak wavelength: 610 nm) with a threshold of 94.2 μJ mm−2 was obtained. In electro-optic (EO) activities, four dyes in guest–host EO films showed the step-up EO coefficients from dye 1 (3 pm V−1) to dye 4 (76 pm V−1). This trend was in accordance with the results of ICT energy gap and DFT calculations, and it showed the effective tuning of structure–property relationship for electro-optics. The facile synthesis of NLO dyes, fine-tuning of their intramolecular charge-transfer, as well as the experimental demonstration in nonlinear optics and optofluidic lasers indicated their significant applications in organic photonic devices.