Scalable multifunctional MOFs-textiles via diazonium chemistry.

Cellulose fiber-based textiles are ubiquitous in daily life for their processability, biodegradability, and outstanding flexibility. Integrating cellulose textiles with functional coating materials can unlock their potential functionalities to engage diverse applications. Metal-organic frameworks (MOFs) are ideal candidate materials for such integration, thanks to their unique merits, such as large specific surface area, tunable pore size, and species diversity. However, achieving scalable fabrication of MOFs-textiles with high mechanical durability remains challenging. Here, we report a facile and scalable strategy for direct MOF growth on cotton fibers grafted via the diazonium chemistry. The as-prepared ZIF-67-Cotton textile (ZIF-67-CT) exhibits excellent ultraviolet (UV) resistance and organic contamination degradation via the peroxymonosulfate activation. The ZIF-67-CT is also used to encapsulate essential oils such as carvacrol to enable antibacterial activity against E. coli and S. aureus. Additionally, by directly tethering a hydrophobic molecular layer onto the MOF-coated surface, superhydrophobic ZIF-67-CT is achieved with excellent self-cleaning, antifouling, and oil-water separation performances. More importantly, the reported strategy is generic and applicable to other MOFs and cellulose fiber-based materials, and various large-scale multi-functional MOFs-textiles can be successfully manufactured, resulting in vast applications in wastewater purification, fragrance industry, and outdoor gears.

Self-Healable Multifunctional Fibers via Thermal Drawing.

The development of soft electronics and soft fiber devices has significantly advanced flexible and wearable technology. However, they still face the risk of damage when exposed to sharp objects in real-life applications. Taking inspiration from nature, self-healable materials that can restore their physical properties after external damage offer a solution to this problem. Nevertheless, large-scale production of self-healable fibers is currently constrained. To address this limitation, this study leverages the thermal drawing technique to create elastic and stretchable self-healable thermoplastic polyurethane (STPU) fibers, enabling cost-effective mass production of such functional fibers. Furthermore, despite substantial research into the mechanisms of self-healable materials, quantifying their healing speed and time poses a persistent challenge. Thus, transmission spectra are employed as a monitoring tool to observe the real-time self-healing process, facilitating an in-depth investigation into the healing kinetics and efficiency. The versatility of the fabricated self-healable fiber extends to its ability to be doped with a wide range of functional materials, including dye molecules and magnetic microparticles, which enables modular assembly to develop distributed strain sensors and soft actuators. These achievements highlight the potential applications of self-healable fibers that seamlessly integrate with daily lives and open up new possibilities in various industries.

Interlocking-Governed Ultra-Strong and Highly Conductive MXene Fibers Through Fluidics-Assisted Thermal Drawing.

High-performance MXene fibers are always of significant interest for flexible textile-based devices. However, achieving high mechanical property and electrical conductivity remains challenging due to the uncontrolled loose microstructures of MXene (Ti3 C2 Tx and Ti3 CNTx ) nanosheets. Herein, high-performance MXene fibers directly obtained through fluidics-assisted thermal drawing are demonstrated. Tablet interlocks are formed at the interface layer between the outer cyclic olefin copolymer and inner MXene nanosheets due to the thermal drawing induced stresses, resulting in thousands of meters long macroscopic compact MXene fibers with ultra-high tensile strength, toughness, and outstanding electrical conductivity. Further, large-scale woven textiles constructed by these fibers offer exceptional electromagnetic interference shielding performance with excellent durability and stability. Such an effective and sustainable approach can be applied to produce functional fibers for applications in both daily life and aerospace.

Crystalline Hydrate Dehydration Sensing Based on Integrated Terahertz Whispering Gallery Mode Resonators.

Water molecules play a very important role in the hydration and dehydration process of hydrates, which may lead to distinct physical and chemical properties, affecting their availability in practical applications. However, miniaturized, integrated sensors capable of the rapid, sensitive sensing of water molecules in the hydrate are still lacking, limiting their proliferation. Here, we realize the high-sensitivity sensing of water molecules in copper sulfate pentahydrate (CuSO4·5H2O), based on an on-chip terahertz whispering gallery mode resonator (THz-WGMR) fabricated on silicon material via CMOS-compatible technologies. An integrated THz-WGMR with a high-Q factor of 3305 and a resonance frequency of 410.497 GHz was proposed and fabricated. Then, the sensor was employed to distinguish the CuSO4·xH2O (x = 5, 3, 1). The static characterization from the CuSO4·5H2O to the copper sulfate trihydrate (CuSO4·3H2O) experienced blueshifts of 0.55 GHz/µmol, whereas the dehydration process of CuSO4·3H2O to copper sulfate monohydrate (CuSO4·H2O) exhibited blueshifts of 0.21 GHz/µmol. Finally, the dynamic dehydration processes of CuSO4·5H2O to CuSO4·3H2O at different temperatures were monitored. We believe that our proposed THz-WGMR sensors with highly sensitive substance identification capabilities can provide a versatile and integrated platform for studying the transformation between substances, contributing to hydrated/crystal water-assisted biochemical applications.

Tunable kilohertz microwave photonic bandpass filter based on backscattering in a microresonator.

A tunable microwave photonic bandpass filter (MPBPF) with a kilohertz bandwidth based on the backscattering mode of a silica microsphere resonator is proposed and experimentally demonstrated. In this work, an ultrahigh-quality-factor microsphere resonator is used to generate a radio frequency bandpass response with a bandwidth of 600 kHz. Meanwhile, scattering-induced coupling between the clockwise mode and the counterclockwise mode is introduced to reduce the number of resonance modes, and a single backscattering mode which has a high extinction ratio is obtained. Therefore, an MPBPF with a tuning range of 40 GHz and a rejection ratio of 16.9 dB is realized. This MPBPF possesses advantages such as ultranarrow bandwidth, large tuning range, and compactness, and shows great potential for microwave photonic applications.

On-chip terahertz isolator with ultrahigh isolation ratios.

Terahertz isolators, one of the typical nonreciprocal devices that can break Lorentz reciprocity, are indispensable building blocks in terahertz systems for their critical functionality of manipulating the terahertz flow. Here, we report an integrated terahertz isolator based on the magneto-optical effect of a nonreciprocal resonator. By optimizing the magneto-optical property and the loss of the resonator, we experimentally observe unidirectional propagation with an ultrahigh isolation ratio reaching up to 52 dB and an insertion loss around 7.5 dB at ~0.47 THz. With a thermal tuning method and periodic resonances, the isolator can operate at different central frequencies in the range of 0.405-0.495 THz. This on-chip terahertz isolator will not only inspire more solutions for integrated terahertz nonreciprocal devices, but also have the feasibility for practical applications such as terahertz sensing and reducing unnecessary reflections in terahertz systems.

Real-time observation of the thermo-optical and heat dissipation processes in microsphere resonators.

This work reports the real-time observation of the thermo-optical dynamics in silica microsphere resonators based on the dispersive time stretch technique. In general, the thermo-optical dynamics of silica microsphere resonators, including the thermal refraction and thermal expansion, can be characterized by the resonance wavelength shift, whose duration is at the millisecond timescale. However, this fast wavelength shift process cannot be directly captured by conventional spectroscopy, and only its transmission feature can be characterized by a fast-scanning laser and an intensity detector. With the advance of the time-stretch spectroscopy, whose temporal resolution is up to tens of nanoseconds, the thermo-optical dynamics can be observed in a more straight-forward way, by utilizing the pump-probe technology and mapping the resonance wavelength to the time domain. Here, the thermo-optical dynamics are explored as a function of the power and the scanning rate of the pump laser. Theoretical simulations reproduce the experimental results, revealing that the thermo-optical dynamics of silica microsphere resonators is dominated by the fast thermo-optical effect and the slow heat dissipation process to the surroundings, which leads to gradual regression of the resonance wavelength. This work provides an alternative solution for studying the thermo-optical dynamics in whispering gallery mode microresonators, which would be crucial for future applications of microresonator photonic systems.

Voltage-actuated thermally tunable on-chip terahertz filters based on a whispering gallery mode resonator.

A tunable integrated terahertz (THz) filter is one of the basic elements for realizing integrated reconfigurable THz communication systems. The state-of-the-art tunable THz filters are discrete or vertically pumped for integrated devices. Here, we propose and demonstrate voltage-actuated thermally tunable on-chip THz bandpass and bandstop filters based on a whispering gallery mode resonator. The quality factors of the bandpass and bandstop filters attain 1867 and 1909, respectively, at approximately 0.4795 THz. Widely continuous tunability is realized by adjusting the voltage applied to a micro-heater. As far as we know, this is the first Letter on on-chip tunability in the THz domain. It provides a simple and reliable tuning method for on-chip THz devices. Furthermore, the implementation of tunable bandpass and bandstop filters plays an important role in THz signal processing.

Mode coupling in a terahertz multi-mode whispering-gallery-mode resonator.

We investigate mode-coupling effects of terahertz whispering-gallery modes (WGMs) in a multi-mode resonator using an extended transfer matrix method. Coupling effects between two WGMs are successfully observed on a well-designed high-Q terahertz Teflon ring resonator that supports low-order WGMs. The extended transmission matrix method is adopted to model, analyze, and reproduce terahertz single-band resonance and asymmetric dual-band resonances caused by mode coupling. Moreover, the terahertz splitting effect based on coupling of two modes in a multi-mode resonator is theoretically illustrated. This detailed analysis not only contributes to understanding physical phenomena, such as mode splitting, but also helps in identifying parameters when designing terahertz devices, such as dual-band filters.

Tunable sub-kHz single-mode fiber laser based on a hybrid microbottle resonator.

We experimentally demonstrated an all-optical tunable sub-kHz single-mode fiber laser based on an ultrahigh-quality (Q)-factor hybrid microbottle resonator. The wavelength tunability is a very important function for fiber lasers, and the all-optical tuning method has rarely been proposed. Here, we use the iron-oxide-nanoparticle-coated silica microbottle resonator with a Q factor of 1.8×108 as the feedback element of the fiber ring laser and suppress the higher-order modes of the microresonator to achieve single-mode lasing with a linewidth of ∼500 Hz and a signal-to-noise ratio of 49 dB. Iron oxide nanoparticles are coated on the tapered area of the microbottle resonator and the control light is fed through the axial direction of the microbottle. The lasing wavelength of the fiber laser can be all-optically and linearly tuned with a range of 2.7 nm due to the strong photothermal effect of iron oxide nanoparticles. With such an excellent tunability and a narrow linewidth, this single-mode fiber laser has great potential in applications, such as optical spectroscopy, sensing, and signal processing.

Whispering gallery modes in a single silica microparticle attached to an optical microfiber and their application for highly sensitive displacement sensing.

A compact and relatively stable structure is experimentally demonstrated to excite whispering gallery modes (WGMs) in a single chemically fabricated silica microparticles with a diameter of around 10.6 µm attached to an optical microfiber. The resonance dip with an extinction ratio of 14 dB and Q factor of around 300 has been achieved. Based on the WGMs in this structure, an in-line fiber-optic displacement sensor is presented with a high sensitivity of 33 dB/mm and a measurement range of over 400 µm. The measurement resolution of this displacement sensor can reach to ~10 µm. The good reversibility and repeatability are also verified. This work offers a scheme to observe the WGMs in a single silica microparticles and demonstrates their application for in-line highly-sensitive displacement sensing.

All-optical control of ultrahigh-Q silica microcavities with iron oxide nanoparticles.

We propose and experimentally demonstrate, to the best of our knowledge, the first all-optical control scheme of ultrahigh-quality (Q)-factor silica microcavities, which can maintain their Q factors over 108 during the tuning process. For silica microcavities, the resonance tunability is very important and is also challenging for many applications. However, almost all previous works on resonance tuning deteriorate the Q factors of silica microcavities at different levels, and evidently these schemes are not suitable for applications in which ultrahigh Q factors are required. In this work, based on the proposed silica microbottle cavity and iron oxide nanoparticles, we realize all-optical control of the silica microcavity and maintain its Q factor of around 1.2×108 during the tuning process. A tuning range of 85.9 GHz (0.68 nm) and a tuning sensitivity of 13.6 GHz/mW are obtained, and it is possible to realize full tunability by bridging the azimuthal free spectral range using six adjacent q-series modes. Moreover, all-optical control of the reflection spectrum is also carried out. This work will broaden the applications of ultrahigh-Q silica microcavities in nonlinear optics, microwave photonics, cavity optomechanics, and cavity quantum electrodynamics.

Tunable megahertz bandwidth microwave photonic notch filter based on a silica microsphere cavity.

We propose and experimentally demonstrate a tunable microwave photonic notch filter with a megahertz order bandwidth based on a silica microsphere cavity coupled by an optical microfiber. The silica microsphere with a quality factor of hundreds of millions offers a full width at half-maximum bandwidth down to the order of megahertz in the transmission spectrum. Due to the coupling flexibility between the microcavity and the optical microfiber, the bandwidth and suppression ratio can be tuned and optimized to get a rejection ratio beyond 30 dB. The tunability of over 15 GHz is also achieved. To the best of our knowledge, this single-stopband microwave photonic filter has the narrowest bandwidth filter that has ever been experimentally demonstrated. This microwave photonic notch filter shows distinct advantages of high selectivity, compactness, flexibility, and low insertion loss.

Tunable polarization beam splitter based on optofluidic ring resonator.

An efficient polarization beam splitter (PBS) based on an optofluidic ring resonator (OFRR) is proposed and experimentally demonstrated. The PBS relies on the large effective refractive index difference between transverse-electric (TE) and transverse-magnetic (TM) polarization states, since the silica-microcapillary-based OFRR possesses a slab-like geometry configuration in the cross section through which the circulating light travels. To the best of our knowledge, this is the first OFRR-based PBS. In our work, the maximum polarization splitting ratio of up to 30 dB is achieved. Besides, water and ethanol are pumped into the core of the silica microcapillary respectively, and the maximum wavelength tuning range of 7.02 nm is realized when ethanol flows through the core, verifing the tuning principle of the PBS effectively. With such a good performance and simple scheme, this OFRR-based PBS is promising for applications such as tunable optical filters, demultiplexers, and routers.