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A fast shape reconstruction optical frequency domain reflectometry (OFDR) system that employs graphics processing unit (GPU) to parallelly calculate the cross correlation wavelength shift of the two outer cores of a standard multicore fiber (MCF) was proposed and demonstrated. The effect of the number of threads in each block on the time consumption was studied. The consumption time was 50.86 ms, when the simulated data size and the number of threads per block were 10 MS and 256, respectively. Compared to the serial computing with CPU, the time consumption was reduced by nearly 21 times for 2-D and 3-D fast shape sensing. At the spatial resolution of 5 mm, the maximum reconstruction errors for 2-D and 3-D shape sensing were 3.23% and 2.47%, respectively, with MCF lengths of 47.1 and 43.6 cm.

Fiber-integrated micro/nanostructures play a crucial role in modern industry, mainly owing to their compact size, high sensitivity, and resistance to electromagnetic interference. However, the three-dimensional manufacturing of fiber-tip functional structures beyond organic polymers remains challenging. It is essential to construct fiber-integrated inorganic silica with designed functional nanostructures for microsystem applications. Here, we develop a strategy for the 3D nanolithography of fiber-integrated silica from hybrid organic–inorganic materials by ultrafast laser-induced multiphoton absorption. Without silica nanoparticles and polymer additives, the acrylate-functionalized precursors can be locally cross-linked through a nonlinear effect. Followed by annealing at low temperature, the as-printed micro/nanostructures are transformed to high-quality silica with sub-100 nm resolution. Silica microcantilever probes and microtoroid resonators are directly integrated onto the optical fiber, showing strong thermal stability and quality factors. This work provides a promising strategy for fabricating desired fiber-tip silica micro/nanostructures, which is helpful for the development of integrated functional device applications.

The emergence of antibiotic and antifungal resistant microorganisms represents nowadays a major public health issue that might push humanity into a post-antibiotic/antifungal era. One of the approaches to avoid such a catastrophe is to advance rapid antibiotic and antifungal susceptibility tests. In this study, we present a compact, optical fiber-based nanomotion sensor to achieve this goal by monitoring the dynamic nanoscale oscillation of a cantilever related to microorganism viability. High detection sensitivity was achieved that was attributed to the flexible two-photon polymerized cantilever with a spring constant of 0.3 N/m. This nanomotion device showed an excellent performance in the susceptibility tests of Escherichia coliand Candida albicanswith a fast response in a time frame of minutes. As a proof-of-concept, with the simplicity of use and the potential of parallelization, our innovative sensor is anticipated to be an interesting candidate for future rapid antibiotic and antifungal susceptibility tests and other biomedical applications.

A microbubble probe-based fiber optical sensor for micro-displacement sensing is proposed. The sensor is composed of an air bubble and a probe that provides high spatial resolution. It was fabricated by CO2 laser machining with the process introduced in detail. Due to the inherent closed cavity, the proposed device can be less influenced by external contaminants. The displacement sensitivity is measured as 83.9 pm/ $\mu \text{m}$ with a linearity of 99.7%. The resolution is determined to be $0.24 ~\mu \text{m}$ . The repeatability, hysteresis, and stability were examined. Tested by a tube furnace and liquid nitrogen, the sensor is proved to be able to withstand a high temperature of 600 °C and a low temperature of ${\sim }-196\,\,^{\circ }\text{C}$ , respectively. With considerable overall performance and resistance to external disturbances, the sensor exhibits a potential for displacement measurement in extreme environments.

Basal cell carcinoma (BCC) is a common type of skin cancer. Conventional approaches to BCC diagnosis often involve invasive histological examinations that can distort or even destroy information derived from the biomolecules in the sample. Therefore, a non-invasive, label-free examination method for the clinical diagnosis of BCC represents a critical advance. This study combined spectral- and time-resolved two-photon microscopy with a spectral phasor to extract rich biochemical information describing macroscopic tumor morphology and microscopic tumor metabolism. The proposed optical imaging technique achieved the rapid and efficient separation of tumor structures in systematic research conducted on normal and BCC human skin tissues. The results demonstrate that a combination of multidimensional data (e.g., fluorescence intensity, spectrum, and lifetime) with a spectral phasor can accurately identify tumor boundaries and achieve rapid separation. This label-free, real-time, multidimensional imaging technique serves as a complement to the conventional tumor diagnostic toolbox and demonstrates significant potential for the early diagnosis of BCC and wider applications in intraoperative auxiliary imaging.

High-resolution measurement of forces in micro/nano scale is essential to various applications. A novel miniature force sensor based on a whispering-gallery-mode (WGM) microbubble probe resonator (MPR) is presented in this work. The resonator consists of a thin-wall microbubble and a probe. The highest quality factor obtained is 1.10 × 107. Predominately, the MPR achieves a promising force sensitivity of 19.7 pm/mN and a dynamic range of 0-36 mN. The MPR was used to measure the Young's modulus of a single mode optical fiber (SMF), and the result is coincided with the reported value. High force resolution and spatial resolution are achieved simultaneously. The sensor shows considerable performance and exhibits a potential in micro-force sensing and related applications such as material examination and Young's modulus measurement.

The most important optical component in an optical fiber endoscope is its objective lens. To achieve a high imaging performance level, the development of an ultra-compact objective lens is thus the key to an ultra-thin optical fiber endoscope. In this work, we use femtosecond laser 3D printing to develop a series of micro objective lenses with different optical designs. The imaging resolution and field-of-view performances of these printed micro objective lenses are investigated via both simulations and experiments. For the first time, multiple micro objective lenses with different fields of view are printed on the end face of a single imaging optical fiber, thus realizing the perfect integration of an optical fiber and objective lenses. This work demonstrates the considerable potential of femtosecond laser 3D printing in the fabrication of micro-optical systems and provides a reliable solution for the development of an ultrathin fiber endoscope.

We report on a cylindrical telescope assisted femtosecond laser direct writing technology for fabricating plane-by-plane Bragg gratings in sapphire fibers. This approach could effectively extend the width of refractive index modulation (RIM) regions. Meanwhile, we propose the spherical aberration to elongate the RIM regions. Such expanded RIM regions lead to the improvement of the spectral characteristics of sapphire fiber Bragg gratings (SFBGs). The effects of the pulse energy and the number of pulses on morphology of RIM regions were studied, after optimizing these parameters, an enlarged RIM region was induced into a sapphire fiber with a diameter of 100 μm. The maximums of the length and the width of RIM region are 25 μm and 15 μm, respectively. Note that this RIM region could be used to cover roughly 50% of fundamental mode field distribution, increasing the reflectivity of the fundamental mode. An SFBG formed by these RIM regions exhibits an enhanced reflectivity of 6.34% and a reduced −3 dB bandwidth (full width at half-maximum [FWHM]) of 3.43 nm. The fabrication time for such an SFBG only requires ∼20 s. Moreover, the high temperature response of this SFBG was studied, and the results showed it can withstand a high temperature of 1612 °C. Such an SFBG can be developed for temperature measurement in many fields, i.e., boilers, reactor cores, and aviation engines.

Second-harmonic generation (SHG) is a noninvasive imaging technique that enables the exploration of physiological structures without the use of an exogenous label. However, traditional SHG imaging is limited by optical diffraction, which restricts the spatial resolution. To break this limitation, we developed a novel approach called multifocal structured illumination microscopy-SHG (MSIM-SHG). By combination of SHG with MSIM, SHG-based super-resolution imaging of material molecules can be achieved, and this SHG super-resolution imaging has a wide range of applications for biological tissues and cells. MSIM-SHG achieved a lateral full width at half-maximum (fwhm) of 147 ± 13 nm and an axial fwhm of 493 ± 47 nm by imaging zinc oxide (ZnO) particles. Furthermore, MSIM-SHG was utilized to quantify collagen fiber alignment in various tissues such as the ovary, muscle, heart, kidney, and cartilage, demonstrating its feasibility for identifying collagen characteristics. MSIM-SHG has potential as a powerful tool for clinical diagnosis and biological research.

Optical fiber humidity sensors have sparked enormous interests in many fields because of their excellent features. However, it remains a great challenge to balance sensitivity, humidity response, temperature crosstalk, and wet hysteresis for real-world application. To overcome this trade-off, an optical fiber humidity sensor is developed here by coating functional graphene oxide (GO)/polyelectrolyte nanocomposite film on the excessively tilted fiber grating (ex-TFG), in which GO/polyelectrolyte nanocomposite film is employed for enhancing the hydrophilicity and accelerating the adsorption/desorption of water molecule, while the ex-TFG is utilized for improving the sensitivity of refractive index and eliminating the crosstalk of temperature. By this design, optical fiber humidity sensors achieve high sensitivity, rapid response and recovery, low hysteresis, and temperature crosstalk as well as excellent repeatability and stability in large relative humidity (RH) range. Our work provides a promising platform for effective RH monitoring systems that can be widely applied in rapid diagnostics, pharmacy, precision medicine, and so forth.

A multicore fiber Bragg grating (MC-FBG) array shape sensor is a powerful tool for a variety of applications. However, the efficient fabrication of high-quality MC-FBG arrays remains a problem. Here, we report for the first time, to the best of our knowledge, a new method of directly writing FBG arrays in a seven-core fiber (SCF) through the protective coating using femtosecond laser auto-positioning point-by-point technology, which is accomplished by image recognition and micro-displacement compensation. An MC-FBG array consisting of 140 individual FBGs with a grating length of 2?mm was successfully inscribed into seven cores of a 440?mm-long SCF. Each core contained 20 wavelength-division-multiplexed (WDM) FBGs with wavelengths ranging from 1522.11?nm to 1579.28?nm. In other words, the MC-FBG array consisted of 20 WDM nodes with an interval of 2?cm along the fiber, and each node contained seven identical FBGs integrated in parallel into the fiber cross-section. Moreover, the fabricated MC-FBG array exhibited a strong orientation dependence in bend sensing, with a maximum sensitivity of 55.49 pm/m^−1. Subsequently, 2D and 3D shape sensing were demonstrated using the fabricated MC-FBG array, with maximum reconstruction errors per unit length of 4.51% and 10.81%, respectively. Hence, the MC-FBG arrays fabricated using the proposed method are useful in many applications, such as posture monitoring, smart robotics, and minimally invasive surgery.

Fiber Bragg grating has been successfully fabricated in the silica microfiber by the use of femtosecond laser point-by-point inscription. Temporal thermal response of the fabricated silica microfiber Bragg grating has been measured by the use of the CO2laser thermal excitation method, and the result shows that the time constant of the microfiber Bragg grating is reduced by an order of magnitude compared with the traditional single-mode fiber Bragg grating and the measured time constant is ~ 21ms.

A new type of human immunoglobulin G (IgG) sensors based on the surface plasmon resonance (SPR) in the low refractive index (RI) plastic optical fiber (POF) and an antibody immobilization method is presented. A 50-nm-thick gold film was formed on the polished D-shaped fiber surface by magnetron sputtering. The RI response of the POF sensor is 30 049.61 nm/RIU, which is 26.5 times higher than that of single mode fiber (SMF) SPR sensors. The proposed SPR biosensor can be developed by simple and rapid modification of the gold film with 11-mercapto undecanoic acid (MUA). Upon immobilization of the goat anti-human IgG antibody, the resonance wavelength shifts by 11.2 nm. The sensor can be used to specifically detect and quantify the human IgG at concentrations down to 245.4 ng/mL with the sensitivity of 1.327 7 nm per µg/mL, which offers an enhancement of 12.5-fold compared to that of the conventional SMF based SPR sensors. The proposed device may find the potential applications in the case of use at the point of care.

Localized tilted fiber Bragg gratings (TFBGs) with low insertion loss are reported. A series of second-order TFBGs with tilt angles of 0°, 7°, 14°, and 21° was inscribed line by line directly in a single-mode fiber. For the 7° TFBG, the Bragg resonance was 2.4 dB at 1550 nm, and the maximum cladding-mode resonance reached 24.6 dB with an insertion loss of 0.8 dB, the same level as that for TFBGs fabricated by the phase-mask method. The range in cladding-mode resonance for the TFBGs obtained was wider than 170 nm with an intensity exceeding 20 dB. Combined with microscope images, the formation of these localized TFBGs and their spectral performance are discussed. The effect of an inscription offset along the $y$-axis direction was further investigated. With increasing offset, the intensity of the cladding-mode resonance dropped rapidly. The refractive index response sensitivity of the 7° TFBG was measured at 507.54 nm/RIU.

Detection of individual molecules is the ultimate goal of any chemical sensor. In the case of gas detection, such resolution has been achieved in advanced nanoscale electronic solid-state sensors, but it has not been possible so far in integrated photonic devices, where the weak light-molecule interaction is typically hidden by noise. Here, we demonstrate a scheme to generate ultrasensitive down-conversion four-wave-mixing (FWM) in a graphene bipolar-junction-transistor heterogeneous D-shaped fiber. In the communication band, the FWM conversion efficiency can change steeply when the graphene Fermi level approaches 0.4 eV. In this condition, we exploit our unique two-step optoelectronic heterodyne detection scheme, and we achieve real-time individual gas molecule detection in vacuum. Such combination of graphene strong nonlinearities, electrical tunability, and all-fiber integration paves the way toward the design of versatile high-performance graphene photonic devices.

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 %–1when 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.

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.

Background: Cell lytic enzyme is a kind of highly evolved protein, which can destroy the cell structure and kill the bacteria. Compared with antibiotics, cell lytic enzyme will not cause serious problem of drug resistance of pathogenic bacteria. Thus, the study of cell wall lytic enzymes aims at finding an efficient way for curing bacteria infectious. Compared with using antibiotics, the problem of drug resistance becomes more serious. Therefore, it is a good choice for curing bacterial infections by using cell lytic enzymes. Cell lytic enzyme includes endolysin and autolysin and the difference between them is the purpose of the break of cell wall. The identification of the type of cell lytic enzymes is meaningful for the study of cell wall enzymes. Objective: In this article, our motivation is to predict the type of cell lytic enzyme. Cell lytic enzyme is helpful for killing bacteria, so it is meaningful for study the type of cell lytic enzyme. However, it is time consuming to detect the type of cell lytic enzyme by experimental methods. Thus, an efficient computational method for the type of cell lytic enzyme prediction is proposed in our work. Methods: We propose a computational method for the prediction of endolysin and autolysin. First, a data set containing 27 endolysins and 41 autolysins is built. Then the protein is represented by tripeptides composition. The features are selected with larger confidence degree. At last, the classifier is trained by the labeled vectors based on support vector machine. The learned classifier is used to predict the type of cell lytic enzyme. Results: Following the proposed method, the experimental results show that the overall accuracy can attain 97.06%, when 44 features are selected. Compared with Ding's method, our method improves the overall accuracy by nearly 4.5% ((97.06-92.9)/92.9%). The performance of our proposed method is stable, when the selected feature number is from 40 to 70. The overall accuracy of tripeptides optimal feature set is 94.12%, and the overall accuracy of Chou's amphiphilic PseAAC method is 76.2%. The experimental results also demonstrate that the overall accuracy is improved by nearly 18% when using the tripeptides optimal feature set. Conclusion: The paper proposed an efficient method for identifying endolysin and autolysin. In this paper, support vector machine is used to predict the type of cell lytic enzyme. The experimental results show that the overall accuracy of the proposed method is 94.12%, which is better than some existing methods. In conclusion, the selected 44 features can improve the overall accuracy for identification of the type of cell lytic enzyme. Support vector machine performs better than other classifiers when using the selected feature set on the benchmark data set.

A gas pressure sensor, based on a phase-shifted fiber Bragg grating (PS-FBG) modulated by a hollow cavity, is proposed and demonstrated in this Letter. The device was fabricated by fusing a hollow-core fiber (HCF) between two single-mode fibers (SMFs) exhibiting FBGs that were inscribed using line-by-line femtosecond (fs) laser etching. A pair of micro-channels were drilled orthogonally into the HCF using an fs laser to allow the argon gas to get in and out freely. Such a sensor exposes a high spectrum finesse, e.g., a $Q$Q-factor of $\sim\! 7302$∼7302, which can be improved by increasing the grating pitch quantity. Furthermore, a high gas pressure sensitivity of 1.22 nm/Mpa is obtained, corresponding the improved sensor with a grating pitch quantity of 300 and a hollow cavity length of 88.3 µm. In addition, the device exhibited a low temperature sensitivity of 8.92 pm/°C.

Benefiting from the great advances of the femtosecond laser two-photon polymerization (TPP) technology, customized microcantilever probes can be accurately 3-dimensional (3D) manufactured at the nanoscale size and thus have exhibited considerable potentials in the fields of microforce, micro-vibration, and microforce sensors. In this work, a controllable microstructured cantilever probe on an optical fiber tip for microforce detection is demonstrated both theoretically and experimentally. The static performances of the probe are firstly investigated based on the finite element method (FEM), which provides the basis for the structural design. The proposed cantilever probe is then 3D printed by means of the TPP technology. The experimental results show that the elastic constant kof the proposed cantilever probe can be actively tuned from 2.46 N/m to 62.35 N/m. The force sensitivity is 2.5 nm/µN, the Q-factor is 368.93, and the detection limit is 57.43 nN. Moreover, the mechanical properties of the cantilever probe can be flexibly adjusted by the geometric configuration of the cantilever. Thus, it has an enormous potential for matching the mechanical properties of biological samples in the direct contact mode.

A femtosecond-laser-induced fiber Bragg grating (FBG) usually has a higher insertion loss at the shorter wavelength than at the reflection wavelength, i.e., so-called short-wavelength loss. High-quality FBGs are inscribed in different types of small-core single-mode fibers (SMFs) by the use of femtosecond laser point-by-point technology in order to investigate the effect of the fiber core diameter on the grating inscription efficiency and on the short-wavelength loss. A lower laser pulse energy is required to achieve the same grating reflectivity in a smaller-core fiber than in a large-core fiber. The short-wavelength loss of the small-core FBG is lower than that of the large-core FBG with the same reflectivity. Furthermore, a series of FBGs with a low short-wavelength loss are inscribed in a small-core SMF along the fiber axis to achieve so-called series-integrated FBGs (SI-FBGs). Finally, the effect of the input light direction on the reflection peak of the SI-FBGs is investigated to reduce the influence of the grating short-wavelength loss in the sensing and communication applications.

An all-fiber mode-locked holmium-doped fiber laser operating in the noise-like pulse regime is reported. Employing a nonlinear amplifying loop mirror as the artificial saturable absorber, the laser generates pulses with energy up to 280 nJ, which is, to the best of our knowledge, the highest pulse energy ever achieved from mode-locked holmium-doped fiber lasers. We also discover a peculiar mode-locking operation mode using the laser. The peculiar mode falls into the category of a noise-like pulse, while it possesses a number of unique features (strong spikes in the optical spectrum, high temporal coherence, and chair-like pulse profile) that are not observed in previous research works regarding noise-like pulse lasers.

We demonstrate the fabrication of multi-layer sapphire fiber Bragg gratings (SFBGs) using a femtosecond laser line-by-line scanning technique. This multi-layer grating structure enlarges the index modulation area and can effectively increase the reflectivity of SFBGs. The spectral characteristics of multi-layer SFBGs with different layer quantities and spacings were studied. A double-layer SFBG with a layer spacing of 5 μm exhibits a reflectivity of 34.1%, which is much higher than that of a single-layer SFBG (i.e., ∼6.3%). Moreover, the higher-order modes of multi-layer SFBG could be suppressed by offset coupling, leading to a reduced SFBG bandwidth (full width at half-maximum [FWHM]) of 1.32 nm. In addition, the high-temperature response of the multi-layer, offset-coupled SFBGs was also studied. The SFBG can withstand a high temperature of 1612°C and exhibits a sensitivity of 45.2 pm/°C at high temperatures. Such multi-layer, offset-coupled SFBGs could be developed for high-temperature sensing in metallurgical, chemical, and aviation industries.

A novel surface plasmon resonance (SPR) configuration based on fiber-interface waveguide was proposed and realized by combining the technology of femtosecond laser writing waveguide with SPR effect for measuring refractive index (RI) of analyte. A U-shaped waveguide is inscribed in the coreless fiber and its bottom is very close to the fiber surface, which can produce strong evanescent field being sensitive to ambient media. When the fiber surface is coated with a layer of gold film, the strong evanescent field can excite the SPR effect on the fiber surface. Most importantly, different from some types of fiber SPR sensors with a fragile physical structure, the fiber-interface waveguide SPR sensor exhibits an excellent mechanical strength. Such a SPR sensor exhibits a high sensitivity of ∼3352  nm/RIU at the RI value of ∼1.395, which may have important practical applications in medicine, environmental monitoring, and food safety.

A polarization-independent orbital angular momentum (OAM) generator, based on a chiral fiber grating (CFG), is proposed and demonstrated for the first time, to the best of our knowledge. Helical phases were successfully excited in this device for the arbitrary polarization states of the input light, and the resulting OAM modes could be produced with a desired polarization state. The employed CFG was fabricated by twisting a fused few-mode fiber during hydrogen-oxygen flame heating. The polarization characteristics, helical phase, and purity of the coupled modes in the CFG were experimentally investigated for varying input light polarization states. The results showed that the coupled higher-order modes had the same polarization as the input fundamental mode. The chirality of the excited OAM was polarization-independent and determined solely by the helicity of the CFG. The purity of the OAM mode was higher than 93% with a slight fluctuation of 2% which occurred during measurement processing.

Luminogens with aggregation‐induced emission characteristics (AIEgens) are considered good options for two‐photon (2P) probes, owing to their flexibility of design, heavy‐metal‐free composition, and resistance to photobleaching. However, the design principles for large 2P absorption cross‐section (δ) generally require high coplanarity, strong donor–acceptor (D‐A) interactions, and long conjugation, which can severely weaken the brightness of AIEgens at the aggregated state and undermine their potential in 2P fluorescence imaging (2PFI). Exploration of a feasible approach to overcome the “Buckets Effect” of AIEgen‐based 2P probes is thus a fascinating yet challenging task. Herein, an AIEgen, namely (Z)‐2‐(4‐aminophenyl)‐3‐(5‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)thiophen‐2‐yl)acrylonitrile (MTAA) is designed to have a big δ according to the calculation result and a low fluorescence quantum yield (QY) of 2.2% in dimethyl sulfoxide (DMSO). Impressively, upon integrating into bovine serum albumin (BSA), the protein‐sized MTAA@BSA dots exhibit a 25‐fold higher fluorescence QY compared to MTAA molecules, contributing to an imaging depth of 818 µm in the brain vasculature. The retention and clearance of MTAA@BSA dots in the liver and kidney are also studied using 2PFI. Overall, this work provides a facile approach to overcome the “Buckets Effect” of AIEgen to generate highly efficient, reliable, and biocompatible 2P probes. The “Buckets Effect” of two‐photon AIEgen probes, low fluorescence quantum yield, is smartly addressed by integrating AIEgens into the bovine serum albumin. Taking advantage of the highly enhanced brightness and highly biocompatible nature, MTAA@BSA dots not only exhibit good performance in two‐photon fluorescence imaging but also have negligible safety concerns.

Optical fibers are typically used in telecommunications services for data transmission, where the use of fiber tags is essential to distinguish between the different transmission fibers or channels and thus ensure the working functionality of the communication system. Traditional physical entity marking methods for fiber labeling are bulky, easily confused, and, most importantly, the label information can be accessed easily by all potential users. This work proposes an encrypted optical fiber tag based on an encoded fiber Bragg grating (FBG) array that is fabricated using a point-by-point femtosecond laser pulse chain inscription method. Gratings with different resonant wavelengths and reflectivities are realized by adjusting the grating period and the refractive index modulations. It is demonstrated that a binary data sequence carried by a fiber tag can be inscribed into the fiber core in the form of an FBG array, and the tag data can be encrypted through appropriate design of the spatial distributions of the FBGs with various reflection wavelengths and reflectivities. The proposed fiber tag technology can be used for applications in port identification, encrypted data storage, and transmission in fiber networks.

Vacuum ultraviolet (VUV) light sensing shows great potential applications in the space science, materials, biophysics, and plasma physics. In this work, an all-optical detection method is proposed for VUV sensing by constructing an optical fiber-end Fabry-Pérot interferometer based on a single aluminum nitride (AlN) microwire. Compared with the traditional electrical devices, this all-optical detection method overcomes the difficulties like the fast response and electromagnetic interference immunity in detecting VUV bands at the present stage, and improves the response speed. The proposed device shows the excellent performance of VUV detection, with the static sensitivity of 1.03 nm/(W·cm−2), response rise time of down to 10 µs, and decay time of 0.64 ms. Beneficial from the excellent radiation resistance of AlN microwires and UV resistance of silica fibers, the proposed device is expected to have the good stability and potential applications in the fields of the solar physics and space exploration.

We propose and demonstrate the fabrication of single-crystal sapphire fiber Bragg gratings (SFBGs) using a femtosecond laser line-by-line scanning technique. This approach provides a robust method for producing SFBGs at various Bragg wavelengths with an acceptable reflectivity. The spectrum characteristics of the SFBGs with various fiber diameters, track lengths, and grating pitch quantities were investigated. An SFBG with a reflectivity of 6.3% was obtained via optimization of fabrication parameters. Additionally, a serial array consisting of five SFBGs at different wavelengths was successfully constructed. The high-temperature response of these SFBGs was tested and the experimental results showed the SFBGs could withstand a high temperature of 1612°C. Moreover, a temperature sensitivity of 36.5 pm/°C was achieved in the high-temperature region. Such SFBGs could be developed for promising high-temperature sensors in aero engines.