Towards Optical Information Recording: A Robust Visible-Light-Driven Molecular Photoswitch with the Ring-Closure Reaction Yield Exceeding 96.3 .

Diarylethene molecular photoswitches hold great fascination as optical information materials due to their unique bistability and exceptional reversible photoswitching properties. Conventional diarylethenes, however, rely on UV light for ring-closure reactions, typically with modest yields. For practical application, diarylethenes driven by visible lights are preferred but achieving high ring-closure reaction yield remains a significant challenge. Herein, we synthesized a novel all-visible-light-driven photoswitch, TPAP-DTE, by facilely endcapping the dithienylethene (DTE) core with triphenylamine phenyl (TPAP) groups. Owing to the electron-donating conjugation effect of TPAP, the open-form TPAP-DTE responds strongly to short-wavelength visible lights with considerable photocyclization quantum yields and molar absorption coefficient. Upon 405 nm visible-light irradiation, TPAP-DTE achieves a ring-closure reaction yield exceeding 96.3 % (confirmed by both nuclear magnetic resonance spectroscopy and high-performance liquid chromatography). Its ring-opening reaction yield is 100 % upon irradiation with long-wavelength visible light. TPAP-DTE could be regarded as a bidirectional "quasi"-quantitative conversion molecular switch. Furthermore, TPAP-DTE exhibits robust fatigue resistance over 100 full photoswitching cycles and great anti-aging property under 85 °C and 85 % humidity for at least 1000 h. Consequently, its rewritable QR-code, multilevel data storage, and anti-counterfeiting/encryption applications are successfully demonstrated exclusively using visible lights, positioning TPAP-DTE as a highly promising medium for information recording.

Cluster-enabled patterning of copper nanostructures from aqueous solution using a femtosecond laser.

A one-step method for patterning low-resistivity nanoscale copper wire is proposed herein to solve the challenging issues of using common metals rather than noble metal nanostructures fabricated by direct laser writing in solution. A complexing and a reducing agent were introduced for the single-photon absorption of copper solution in the visible range and to enable two-photon absorption with a femtosecond laser. Copper clusters were generated prior to direct laser writing to decrease induced laser energy during two-photon absorption and accelerate copper nanowire patterning to avoid the boiling of copper solution. A surfactant was used to restrain the overgrowth of copper clusters to obtain written nanowires with high uniformity. By controlling the laser writing parameters, the obtained copper wire had a minimum width of 230 nm and a resistivity of 1.22 × 10-5Ω·m. Our method paves the way for the fabrication of common metal nanodevices by direct laser writing.

Direct Imaging of Integrated Circuits in CPU with 60 nm Super-Resolution Optical Microscope.

Far-field super-resolution optical microscopies have achieved incredible success in life science for visualization of vital nanostructures organized in single cells. However, such resolution power has been much less extended to material science for inspection of human-made ultrafine nanostructures, simply because the current super-resolution optical microscopies modalities are rarely applicable to nonfluorescent samples or unlabeled systems. Here, we report an antiphase demodulation pump-probe (DPP) super-resolution microscope for direct optical inspection of integrated circuits (ICs) with a lateral resolution down to 60 nm. Because of the strong pump-probe (PP) signal from copper, we performed label-free super-resolution imaging of multilayered copper interconnects on a small central processing unit (CPU) chip. The label-free super-resolution DPP optical microscopy opens possibilities for easy, fast, and large-scale electronic inspection in the whole pipeline chain for designing and manufacturing ICs.

Femtosecond laser induced in-situ crystallization of Tb-based luminescent metal organic framework.

Luminescent metal-organic frameworks (LMOFs) are a class of interesting and well-investigated MOF materials, which have shown remarkable prospects in the past and have been widely applied in different fields. However, due to their organic hybrid aspect, micro-/nano-patterning LMOFs in devices via a conventional semiconductor process is very challenging. In this work, we have introduced an elegant technique via nonlinear photon-chemical effect to induce the synthesis and growth of LMOFs. A facile technique for local synthesis and micro-pattering Tb-based luminescent metal organic frameworks (Tb(BTC)·G) from a solution of precursors is achieved. A single step approach micro-patterning for device integration with simultaneous chemical synthesis was proposed. Micro-devices with excellent fluorescence performance based on Tb(BTC)·G have been demonstrated. This work first suggested a high resolution bottom-up micro-patterning technique for MOF device fabrication using femtosecond laser direct writing, showing great potential on MOF based micro/nano-devices integration, especially promising for patterning high resolution luminescent MOF devices.

Ultra-high capacity for three-dimensional optical data storage inside transparent fluorescent tape.

In this Letter, we show an ultralarge capacity for three-dimensional optical data storage inside transparent fluorescent tape using the two-photon absorption photo-bleaching method. We can obtain transparent fluorescent tape by means of the simple dip method. We successfully demonstrate recording and reading of six layers of binary data bits with lateral separation of 2 µm and longitudinal layer separation of 3 µm. Thus, this result leads to a storage density of approximately ${80}\;{{\rm Gbits/cm}^3}$80Gbits/cm3. Therefore, we can realize authentic ultrahigh capacity optical data storage using long transparent fluorescent tape in the future, like magnetic tape, and fundamentally solve the data explosion disaster.

Ultra-high capacity for three-dimensional optical data storage inside transparent fluorescent tape: erratum.

In Opt. Lett.45, 1535 (2020)OPLEDP0146-959210.1364/OL.387278, there was an error regarding the corresponding author assignment. That error is corrected here.

Direct laser writing of nanoscale undoped conductive polymer.

The fabrication of poly 3,4-ethylene dioxythiophene (PEDOT) devices generally requires a separated strategy for EDOT polymerization and PEDOT coating, thus increasing th difficulty of their integration. With the goal of insolubility of PEDOT in a common solution, material modifications including grafting vinyl moiety groups on the side chain of the PEDOT can increase its solubility, but also markedly reduce the conductivity. Here, we report direct laser writing of pure EDOT monomer into PEDOT with a feature size of 140 nm. The PEDOT nanowire possesses the high conductivity of 1.28 × 105 S m-1 and can be patterned on solid and flexible substrates with various structures, thus paving the way towards organic highly conductive device fabrication and integration.

Zn2+ responsive fluorescence enhancement for optical data storage.

In this paper, we put forward a new application in optical data storage (ODS) of tetraphenylethene (TPE)-doped photopolymer, which has an aggregation-induced emission attribute. The photopolymer host reacted with the excitation light at the focal point of a high numerical-aperture lens to enhance the fluorescence intensity mainly because of the function of the ${{\rm Zn}^{2 + }}$Zn2+ ion. We recorded data inside the photopolymer matrix by using this property and had distinct fluorescence intensity contrast between the photochemical regions and other regions. This attribute paves a new way for superresolution ODS and opens the way to exploring the possibility of utilizing TPE-doped photopolymers as chemical sensors in the future.

Bragg resonance in microfiber realized by two-photon polymerization.

A new method for microfiber Bragg gratings (µ-FBGs) fabrication by means of two-photon polymerization in photosensitive resin is reported. Such polymerized µ-FBGs were cured along with the surface of microfibers without any damage or distortion to the substrate. The laser intensity was optimized to improve the spectral properties of the polymerized gratings. The refractive index measurement was performed and the maximum sensitivity obtained is ~207 nm/RIU at the refractive index value of 1.440 with the fiber diameter being 1.7 µm. This work opens a new idea for optical structure integration and further optical functionality integration.

Direct laser writing of three-dimensional narrow bandgap and high refractive-index PbSe structures in a solution.

Three-dimensional (3D) micro/nano structures made of narrow electronic bandgap semiconductor materials have important applications in a wide range of disciplines. Direct laser writing (DLW) provides the unparalleled advantage to fabricate 3D arbitrary geometric structures at the micro and nano meter scale. The fabrication of 3D structures within bulk narrow electronic bandgap semiconductor materials by DLW is challenged for the top-down strategy due to their narrow bandgap and high refractive index. Here, we report on the bottom-up strategy for the fabrication of 3D micro/nano structures made from PbSe with an electronic bandgap as narrow as 0.27 eV and a refractive index as high as 4.82 in a solution.

Simultaneous synthesis and integration of nanoscale silicon by three-photon laser direct writing.

Typical fabrication processes of compact silicon quantum dot (Si QD) devices or components entail several synthesis, processing and stabilization steps, leading to manufacture and cost inefficiency. Here we report a single step strategy through which nanoscale architectures based on Si QDs can be simultaneously synthesized and integrated in designated positions by using a femtosecond laser (532 nm wavelength and 200 fs pulse duration) direct writing technique. The extreme environments of a femtosecond laser focal spot can result in millisecond synthesis and integration of Si architectures stacked by Si QDs with a unique crystal structure (central hexagonal). This approach involves a three-photon absorption process that can obtain nanoscale Si architecture units with a narrow line width of 450 nm. These Si architectures exhibited bright luminescence peaked at 712 nm. Our strategy can fabricate Si micro/nano-architectures to tightly attach to a designated position in one step, which demonstrates great potential for fabricating active layers of integrated circuit components or other compact devices based on Si QDs.

Direct Laser Writing of Functional QD-Polymer Structure with High Resolution.

Promising direct laser writing (DLW) technology has been introduced to process functional quantum dot (QD)-polymer nanocomposites. The results reveal that after surface modification, the QDs are compatible with the SR399 monomer, and the homogeneous incorporation of QDs is accordingly obtained owing to the copolymerization and resultant cross-linking of QDs into SR399 resin under DLW processing with a laser wavelength (λ) of 532 nm. Moreover, compared with other scholars, we have proved that the surface modified QDs incorporated into the nanocomposites that can be successfully processed via DLW can reach a concentration of up to 150 mg/mL. Owing to the threshold behavior and nonlinear nature of the DLW process, it is feasible to modify the attendant exposure kinetics and design lines of any small size by selecting an appropriate laser power (P) and scan speed (v). The superfine feature size of 65 nm (λ/8) of the red QD-polymer suspended line can be tailored by applying the optimized P of 15 mW and v of 700 µm/s, and the finest green QD-polymer suspended line also reaches 65 nm (λ/8) with the optimized P of 14 mW and v of 250 µm/s used. Moreover, DLW processed QD-polymer structures present strong and homogeneous photoluminescence emission, which shows great potential for application in high-resolution displays, anti-counterfeit technology, and optical encryption. Additionally, the two types of long pass QD-polymer absorptive filters prepared by DLW exhibit superior optical performance with a considerably high transmittance of more than 90% for red QD-polymer block filter, and over 70% for green QD-polymer block filter in the transmittance region, which means that different filters with specific performance can be easily customized to meet the demand of various microdevices. Therefore, the DLW process can be applied to produce geometrically complex micro- and nanoscale functional structures, which will contribute to the development of advanced optoelectronic devices.

Three-Dimensional Nanolithography with Visible Continuous Wave Laser through Triplet Up-Conversion.

Direct laser writing (DLW) technology usually fabricates micronanostructures based on the principle of two-photon polymerization. However, two-photon polymerization requires high laser intensity which can be achieved by expensive femtosecond lasers. To address the issue, a direct laser writing method has been proposed in this work; it is based on triplet up-conversion which is characterized by its low cost, high precision, multidimensional property, and rapid processing. The feasibility of this method is jointly verified by applying both dynamic modeling and experiments. Based on the obtained results, the low laser intensity fabrication of multidimensional nanostructures is achieved. The minimum line width (∼50 nm) of micronanostructures is reached when the laser intensity is set at 2.5 × 105 W/cm2 along with a processing speed of 150 µm/s. As a result, the direct laser writing method, based on triplet up-conversion, offers a new route to achieve low-intensity and high-precision micronanostructure fabrication.

Measurement of Interfacial Adhesion Force with a 3D-Printed Fiber-Tip Microforce Sensor.

With the current trend of device miniaturization, the measurement and control of interfacial adhesion forces are increasingly important in fields such as biomechanics and cell biology. However, conventional fiber optic force sensors with high Young's modulus (>70 GPa) are usually unable to measure adhesion forces on the micro- or nano-Newton level on the surface of micro/nanoscale structures. Here, we demonstrate a method for interfacial adhesion force measurement in micro/nanoscale structures using a fiber-tip microforce sensor (FTMS). The FTMS, with microforce sensitivity of 1.05 nm/µN and force resolution of up to 19 nN, is fabricated using femtosecond laser two-photon polymerization nanolithography to program a clamped-beam probe on the end face of a single-mode fiber. As a typical verification test, the micronewton-level contact and noncontact adhesion forces on the surfaces of hydrogels were measured by FTMS. In addition, the noncontact adhesion of human hair was successfully measured with the sensor.

High-photosensitive resin for super-resolution direct-laser-writing based on photoinhibited polymerization.

An ethoxylated bis-phenol-A dimethacrylate based photoresin BPE-100 of relatively high photosensitivity and modulus is used for the creation of sub-50 nm features. This is achieved by using the direct laser writing technique based on the single-photon photoinhibited polymerization. The super-resolution feature is realized by overlapping two laser beams of different wavelengths to enable the wavelength-controlled activation of photoinitiating and photoinhibiting processes in the polymerization. The increased photosensitivity of the photoresin promotes a fast curing speed and enhances the photopolymerization efficiency. Using the photoresin BPE-100, we achieve 40 nm dots for the first time in the super-resolution fabrication technique based on the photoinhibited polymerization, and a minimum linewidth of 130 nm. The influence of the power of the inhibiting laser and the exposure time on the feature size is studied and the results agree well with the prediction obtained from a simulation based on a non-steady-state kinetic model.

Lifetime distribution of spontaneous emission from emitter(s) in three-dimensional woodpile photonic crystals.

Spontaneous emission lifetime distribution in the basic unit cell or on a plane of the excited emitters embedded in woodpile photonics crystals with low refractive index contrast are investigated. It is found that the spontaneous emission lifetime distribution strongly depends on the position and transition frequency of the emitters, and has the same symmetry as that of the unit cell. The lifetimes of emitters near the upper gap edge are longer than that in the center of the pseudo-gap, which is quite a contrast to the conventional concept. Furthermore, it is revealed that the polarization orientation of the emitters has significant influence on the lifetime distribution, and may result in a high anisotropy factor (defined as the difference between the maximum and minimum values of the lifetime) up to 4.2. These results may be supplied in probing the lifetime distribution or orientation-dependent local density of states in future experiments.

Fiber-tip polymer clamped-beam probe for high-sensitivity nanoforce measurements.

Micromanipulation and biological, material science, and medical applications often require to control or measure the forces asserted on small objects. Here, we demonstrate for the first time the microprinting of a novel fiber-tip-polymer clamped-beam probe micro-force sensor for the examination of biological samples. The proposed sensor consists of two bases, a clamped beam, and a force-sensing probe, which were developed using a femtosecond-laser-induced two-photon polymerization (TPP) technique. Based on the finite element method (FEM), the static performance of the structure was simulated to provide the basis for the structural design. A miniature all-fiber micro-force sensor of this type exhibited an ultrahigh force sensitivity of 1.51 nm µN-1, a detection limit of 54.9 nN, and an unambiguous sensor measurement range of ~2.9 mN. The Young's modulus of polydimethylsiloxane, a butterfly feeler, and human hair were successfully measured with the proposed sensor. To the best of our knowledge, this fiber sensor has the smallest force-detection limit in direct contact mode reported to date, comparable to that of an atomic force microscope (AFM). This approach opens new avenues towards the realization of small-footprint AFMs that could be easily adapted for use in outside specialized laboratories. As such, we believe that this device will be beneficial for high-precision biomedical and material science examination, and the proposed fabrication method provides a new route for the next generation of research on complex fiber-integrated polymer devices.

High-Speed All-Optical Modulator Based on a Polymer Nanofiber Bragg Grating Printed by Femtosecond Laser.

On-chip optical modulator for high-speed information processing system has been widely investigated by many researchers, but the connection with the fiber system is difficult. The fiber-based optical modulator is a good solution to this problem. Fiber Bragg Grating has good potential to be used as an optical modulator because of its linear temperature response, narrow bandwidth, and compact structure. In this paper, a new fiber-integrated all-optical modulator has been realized based on a polymer nanofiber Bragg grating printed by a femtosecond laser. This device exhibits a fast temporal response of 176 ns and a good linear modulation of -45.43 pm/mW. Moreover, its stability has also been studied. This work first employs Bragg resonance to realize a fiber-integrated all-optical modulator and paves the way toward realization of multifunctional lab-in-fiber devices.

Fiber-Tip Polymer Microcantilever for Fast and Highly Sensitive Hydrogen Measurement.

Hydrogen as an antioxidant gas has been widely used in the medical and biological fields for preventing cancer or treating inflammation. However, controlling the hydrogen concentration is crucial for practical use due to its explosive property when its volume concentration in air reaches the explosive limit (4%). In this work, a polymer-based microcantilever (µ-cantilever) hydrogen sensor located at the end of a fiber tip is proposed to detect the hydrogen concentration in medical and biological applications. The proposed sensor was developed using femtosecond laser-induced two-photon polymerization (TPP) to print the polymer µ-cantilever and magnetron sputtering to coat a palladium (Pd) film on the upper surface of the µ-cantilever. Such a device exhibits a high sensitivity, roughly -2 nm %-1 when the hydrogen concentration rises from 0% to 4.5% (v/v) and a short response time, around 13.5 s at 4% (v/v), making it suitable for medical and environmental applications. In addition to providing an ultracompact optical solution for fast and highly sensitive hydrogen measurement, the polymer µ-cantilever fiber sensor can be used for diverse medical and biological sensing applications by replacing Pd with other functional materials.

Femtosecond Laser Microprinting of a Polymer Optical Fiber Interferometer for High-Sensitivity Temperature Measurement.

Femtosecond laser induced multi-photon polymerization technique can be applied to fabricate an ultracompact polymer optical fiber interferometer which was embedded in a section of hollow core fiber. The production of the photoresin, used in this work, is described. Such a device has been used for temperature measurement, due to its excellent thermal properties. Transmission spectrum, structural morphology, and temperature response of the polymer optical fiber interferometer are experimentally investigated. A high wavelength sensitivity of 6.5 nm/°C is achieved over a temperature range from 25 °C to 30 °C. The proposed polymer optical fiber interferometer exhibits high temperature sensitivity, excellent mechanical strength, and ultra-high integration. More complex fiber-integrated polymer function micro/nano structures produced by this technique may result in more applications in optical fiber communication and optical fiber sensors.