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Carbon nanotube yarns are embedded in three-dimensional (3D) braided composites with five-axis yarns, which are used as strain sensors to monitor the damage of 3D braided composites. In the cyclic mechanical loading experiment, the strain-sensing characteristics of 3D braided composites were studied by in situ measuring the resistance change of the embedded carbon nanotube yarn. The 3D five-directional braided composite prefabricated part based on carbon nanotube yarns was developed, and the progressive damage accumulation experiments were carried out on carbon nanotube yarns and specimens embedded in carbon nanotube yarns. The research results show that there is a good correlation between the change of relative resistance of the carbon nanotube yarn and the strain of the composite specimen during cyclic loading and unloading. When the tensile degree of the specimen increases beyond a certain range, the carbon nanotube yarn sensor embedded in the specimen shows resistance hysteresis and produces residual resistance. Therefore, the fiber can better monitor the progressive damage accumulation of 3D five-direction braided composites.

A new fiber Bragg grating (FBG) sensor that can measure temperature, vibration, and strain is proposed in this article. The structure of this sensor is designed and optimized via theoretical analysis and the finite-element method (FEM). With an innovatively designed L-shaped cantilever (LSC), this designed sensor can better balance the vibration measurement sensitivity and the resonant frequency. The strain measurement structure is designed as a hollow square so that the reaction force of the sensor for the measured object is only $2.76\times 10^{-3}$ N/ $\mu \varepsilon $ , which ensures that the strain distribution of the measured object is not affected. The designed sensor can significantly amplify the measured strain with a measurement sensitivity (5.44 pm/ $\mu \varepsilon$ ) that is four times greater than that of the bare FBGs. This article uses single-mode FBGs inscribed by a femtosecond laser (FS-FBG) to make the sensors, and the sensing performance is analyzed. The results show that this FS-FBG-based sensor can withstand temperatures up to 1100 °C.

Broadband light amplitude tuning characteristics are demonstrated in a 2-D tin diselenide (SnSe2) nanosheets coated microfiber (MF) structure (SnSe2CMF). Due to the strong absorption characteristics of SnSe2 in broadband wavelengths, the transmitted optical power (TOP) of SnSe2CMF can be tuned by external pump lights with different wavelengths (405, 532, and 660 nm) over a broadband spectrum (1520–1620 nm). Five wavelengths are extracted in order to investigate the tuning performance. The TOP of SnSe2CMF increases with the pump light power and a maximum tuning efficiency of ∼0.3074 dB/mW is achieved. In terms of tuning speed, the minimum response time is ∼3.7/3.9 ms. The experimental results have qualitatively good agreement with the simulations predicted by FEM models. The demonstrated structure has the advantages of broad tuning bandwidth and high tuning efficiency. Therefore, it might be a promising candidate for building high performance broadband fiber-optic sensors and modulators.

A vector magnetometer, composed of a side-polished single-mode-multimode-single-mode fiber structure coated with ferrofluids, is proposed and investigated. The side-polishing of the multimode fiber can expose the evanescent field to the surrounding ferrofluids, whose refractive index in the vicinity of the polished surface can be tuned by both the intensity and direction of the applied magnetic field, thus in turn realizing the magnetic vector sensing. The sensing principles are illustrated in details, and the sensing performances, especially the dependence on the residual thickness (RT) of the side-polished multimode fiber, are well investigated experimentally. It is found that the decrease of the RT can significantly improve the sensitivity to both the magnetic field intensity and the direction, and the highest intensity and direction sensitivities of −0.053 nm/Oe and −5.68 nm/degree have been achieved respectively, when the RT reduces to 50.5 μm. The proposed vector magnetometer, featuring the advantages of simple structure, low cost, and ease of fabrication, can find the potential applications in the fields such as industry, military, and environment.

A novel fiber optofluidic laser biosensor based on nanoparticle-functionalized thin-walled hollow optical fiber is developed for sensitive detection of enzyme horseradish peroxidase (HRP). High sensitivity is achieved thanks to the high surface-to-volume ratio of the nanomaterials. Two kinds of attractive nanomaterials, i.e., Au nanorods and SiO2 nanoparticles, are selected as demonstrative models to be coated onto the inner surface of thin-walled hollow fiber through electrostatic adsorption and biochemical cross-linking, respectively, while the streptavidin-biotin conjugation mechanism acts as a bridge for the specific recognition of enzyme. The nanoparticle-functionalized fiber optofluidic lasers have lower lasing threshold, compared to the control group without nanomaterial. We experimentally demonstrate that the nanomaterials enhanced fiber optofluidic laser biosensors can detect HRP in the range of 75–15 000 pM with a good linearity in semi-logarithmic scale, and with a sensitivity enhancement of 57.4% by using the SiO2 nanoparticles. We believe that this nanoparticle-enhanced fiber optofluidic laser biosensor could provide an efficient strategy for biomolecule detection such as enzyme-linked immunosorbent assay (ELISA).

We present first-principle methods on the conversion of trivalent bismuth center in Bi-doped silica optical fiber. With the increase of Bi-O distance in different member rings, the reaction energy of transition state configurations gradually become larger. The reaction energy of Bi-6MR is greater than that of Bi-4MR, than that of Bi-5MR, respectively. Based on the basis of the time-dependent density functional theory (TDDFT), transition energy levels of bivalent bismuth defect center models are investigated. Our calculations reveal that the ∼1310 nm luminescence of the second optical communication window is likely caused by bivalent bismuth defect center configuration.

We carry out the experimental study on Brillouin erbium fiber laser in two different structure configurations. In the first configuration, Brillouin pump laser directly stimulates the Brillouin scattering light, whilst in the second it gets pre-amplification before stimulating the Brillouin scattering light in silica optical fiber. Employing distributed-feedback fiber laser as the Brillouin pump laser, we get the Brillouin erbium fiber lasers having subhundred Hertz linewidth. The first configuration has a higher pump threshold and a higher maximum output power, which is over 20 mW for a 250 mW 980 nm pump. The second configuration with pre-amplification for Brillouin pump laser has a lower pump threshold and a smaller maximum output power.

The temperature dependency of erbium doped distributed feedback fiber laser output performance is experimentally and theoretically investigated with two major pump schemes. The output power declined linearly as temperature increased from 30 °C to 120 °C for 980 nm and 1480 nm pumped test laser while the later exhibited stronger heat susceptibility. Further experiment and analysis identified the temperature induced absorption and emission cross section variation at pump and signal wavelength together with population inversion rate difference are the originations of the thermal sensitivity discrepancy between the two pump setups. Associated theoretical simulation concludes the erbium doped distributed feedback fiber laser thermal output sensitivity is dependent on its gain dynamics and grating structure simultaneously.

Optofluidic biolaser is an emerging technology for chemical and biomedical sensing. However, the sensitivity of optofluidic laser is still limited by the laser threshold condition. In this paper we report a DC-biased optofluidic biolaser for uric acid (UA) detection. Inside a Fabry-Perot laser cavity, a coupled enzyme reaction was employed to transform the detection of UA into the detection of analyte-converted hydrogen peroxide (H2O2). The fluorescent product of the enzyme-catalyzed reaction, resorufin, was employed as gain medium for optofluidic lasing. An optimized concentration of H2O2 was pre-added as a DC bias to counterbalance the requirement of high analyte concentration for lasing. UA detection with a limit of detection of 3.63 μM was achieved with a low sample volume as small as 10 μl. This work provides a sensitive technology using optofluidic biolaser for the detection of substance in human body fluids that can be converted into H2O2.

Optofluidic laser is an emerging method for biochemical sensing. The topic on, which kind of structure is the best to integrate the laser resonator and microfluidic channel, is worth to be explored. Here, we report a hollow optical fiber optofluidic laser based on a dye-doped polymer film. This fiber microstructure is a promising candidate that serves both as a laser microresonator and a compact microfluidic channel. The refractive index of the polymer film is higher than silica so that the whispering gallery mode can be supported. The coating process is explored in detail. The laser spectra and threshold properties of the HOF microlaser are investigated. The dye-doped polymer film can be controlled to be as thin as 1.6 μm and a threshold of below 1 μJ/mm2 can be reached. Thanks to the strong light-liquid interaction enabled by the polymer coating on the inner interface of HOF, sensitive refractive index detection is demonstrated by monitoring the laser wavelength shift, which has the potential for wavelength division multiplexing. This laser sensor is promising for label-free biochemical detection.

Type I fiber Bragg grating (FBG) regeneration is studied in terms of refractive index modulation (RIM) and characterized using optical low-coherent reflectometry (OLCR) for the first time. Highly resolved spatial OLCR results are used to demonstrate a uniform RIM regeneration ratio along an apodized type I the FBG during the regeneration process. RIM regeneration ratios are hence proved to be similar for FBGs with different RIM amplitudes. A clearer understanding of FBG regeneration results allows the establishment of a novel RIM regeneration ratio method to quantify and accurately evaluate FBG regeneration.

The tungsten diselenide (WSe2) has attracted considerable interest owing to their versatile applications, such as p-n junctions, transistors, fiber lasers, spintronics, and conversion of solar energy into electricity. We demonstrate all-optical tuning of light in WSe2-coated microfiber (MF) using WSe2’s broad absorption bandwidth and thermo-optic effect. The transmitted optical power (TOP) can be tuned using external incidence pump lasers (405, 532, and 660 nm). The sensitivity under 405-nm pump light excitation is 0.30 dB/mW. A rise/fall time of ~ 15.3/16.9 ms is achieved under 532-nm pump light excitation. Theoretical simulations are performed to investigate the tuning mechanism of TOP. The advantages of this device are easy fabrication, all-optical control, high sensitivity, and fast response. The proposed all-optical tunable device has potential applications in all-optical circuitry, all-optical modulator, and multi-dimensionally tunable optical devices, etc.

Distributed acoustic sensing (DAS) technology plays an increasingly important role in the field of underwater acoustic detection because of its own advantages. To measure acoustic pressure sensitivity of seven kinds of optical cables in the same condition synchronously, the experimental setup based on DAS is proposed. Seven kinds of optical cables are connected in series to the DAS system, and the acoustic pressure sensitivity at different locations (different optical cables) is detected simultaneously via the DAS system. The highest acoustic pressure sensitivity of the sensitized optical cable is 69.9 mrad/Pa. The experimental results provide experimental data support for the selection of optical cables.

We report a fiber optofluidic laser based on a commercial air-clad optical fiber (ACF). The ACF with air holes surrounding the silica core supports pseudo whispering gallery mode, which can provide optical feedback for lasing. 1 mm Rhodamine 6G in quinoline (n = 1.63) is withdrawn into the ACF using the capillary action. Due to the high refractive index difference between gain medium and silica, about 83% of light intensity is confined within the liquid gain medium, leading to a low threshold of about 1.1 μJ/mm2. The lasing mechanism is investigated by both numerical simulation and experimental demonstration. The laser emission was observed with various refractive index in the range between 1.52 and 1.63. The proposed fiber optofluidic laser is promising for biochemical sensing.

We report first-principles calculations of cluster silica with and without interstitial Bi0 atom. The size and radial distance of “Si-O-Si” rings are considered to study the equilibrium position of interstitial Bi0 atom in Bi-doped silica optical fiber. Our results reveal that the interstitial Bi0 atom is most likely to stay around ~ 2 A from the center of 6-membered rings. By comparing the transition energy levels with Bi0 atomic spectral data, we find that the transition 2D3/2(1) → 4S3/2 of interstitial Bi0 atom leads to the NIR emission estimated as ~ 1265 nm in Bi-doped silica optical fiber. Our methods will be effective to confirm bismuth-active centers for different valence states of Bi atom.

Razdobreev et al. claim that the energy level diagrams discussed in our paper are absolutely inconsistent with the experimental data. We carefully studied the comment and concluded that the claims on our paper are largely invalid. We maintain that the proposed diagrams in our paper can explain the luminescence in the spectral range of 1.4–1.7 µm and the spectral region 1.15 µm. Our calculated results are reliable for non-defective silica fiber models.

Microstructures can improve both sensitivity and assay time in heterogeneous assays (such as ELISA) for biochemical analysis; however, it remains a challenge to perform the essential wash process in those microstructure-based heterogeneous assays. Here, we propose a sequential bioconjugation protocol to solve this problem and demonstrate a new type of fiber optofluidic laser for biosensing. Except for acting as an optical microresonator and a microstructured substrate, the miniaturized hollow optical fiber (HOF) is used as a microfluidic channel for storing and transferring reagents thanks to its capability in length extension. Through the capillary action, different reagents were sequentially withdrawn into the fiber for specific binding and washing purposes. By using the sequentially bioconjugated FOFL, avidin molecules are detected based on competitive binding with a limit of detection of 9.5 pM, ranging from 10 pM to 100 nM. It is demonstrated that a short incubation time of 10 min is good enough to allow the biomolecules to conjugate on the inner surface of the HOF. Owing to its miniaturized size, only 589 nL of liquid is required for incubation, which reduces the sample consumption and cost for each test. This work provides a tool to exploit the potential of microstructured optical fibers in high-performance biosensing.

In this article a Vernier effect based sensor is analyzed and demonstrated experimentally in a tri-microfiber coupler (Tri-MFC) and polarization-maintaining fiber (PMF) loop interferometer (Tri-MFC-PMF) to provide ultrasensitive refractive index and temperature sensing. The main novelty of this work is an analysis of parameters of the proposed Tri-MFC-PMF with the objective of determining the conditions leading to a “strong” Vernier effect. It has been identified by simulation that the Vernier effect is a primary factor in the design of Tri-MFC-PMF loop sensing structure for sensitivity enhancement. It is furthermore demonstrated experimentally that enhancing the visibility of the Vernier spectrum in the Tri-MFC-PMF allows to achieve an ultrahigh refractive index and temperature sensitivity with improved measurement accuracy. Specifically it is shown that small values of the total phase difference ( π / 16 + N π )∼( π / 4 + N π ), where N is an integer, accumulated over the PMF loop and Tri-MFC loop result in a “strong” Vernier effect. Experimentally an ultrahigh refractive index sensitivity of -20588 nm/RIU and temperature sensitivity of 0.019 nm/°C are demonstrated by utilizing the stronger Vernier effect with “clear” Vernier spectrum. This analysis of the parameters may be useful to future researchers seeking to increase the measurement accuracy of sensors by enhancing the spectral visibility of the Vernier effect in other types of fiber optic interferometers.

The advent of the ‘lab-on-fiber’ concept has boosted the prosperity of optical fiber-based platforms integrated with nanostructured metasurface technology which are capable of controlling the light at the nanoscale for multifunctional applications. Here, we propose an endless single-mode large-mode-area photonic crystal fiber (LMA-PCF) integrated metalens for broadband and efficient focusing from 800 to 1550 nm. In the present work, the optical properties of the substrate LMA-PCF were investigated, and the metalens, consisting of dielectric TiO2 nanorods with varying radii, was elaborately designed in the fiber core region with a diameter of 48 μm to cover the required phase profile for efficient focusing with a high transmission. The focusing characteristics of the designed metalens were also investigated in detail over a wide wavelength range. It is shown that the in-fiber metalens is capable of converging the incident beams into the bright, symmetric, and legible focal spots with a large focal length of 315–380 μm depending on the operating wavelength. A high and average focusing efficiency of 70% was also obtained with varying wavelengths. It is believed the proposed fiber metalens may show great potential in applications including fiber laser configuration, machining, and fiber communication.

Fiber drawing from a 3D printed perform was recently discussed to go beyond the limitations of conventional optical fiber manufacturing in terms of structure and materials. In this work, the photosensitivity of silica optical fibers to femtosecond laser light, and fabricated by 3D printing a preform, is investigated. The writing kinetics and the thermal performance of Type II modifications are studied by varying the laser pulse energy and investigating the birefringence response of the femtosecond (fs)-laser written structures. Compared with a conventional telecom single mode fiber (SMF28), the fiber made by 3D printing is found to have similar writing kinetics and thermal performance. Additionally, the thermal stability of the imprinted fs-laser induced nanostructures is investigated based on the Rayleigh&ndash, Plesset equation, describing a model of nanopores dissolution underpinning Type II modifications with thermal annealing.

This tutorial will focus on key technical aspects and pathways, as well as recent progresses and remaining challenges, in research and development of specialty, custom-design silica optical fibres based on 3D printing technologies.

Disposable optofluidic laser biosensors based on hollow optical fibers (HOFs) are developed. The statistical characteristics of multiple tests greatly reduce the bioassay uncertainty.

The spectral properties of Bi-doped phosphosilicate fiber has been investigated at liquid nitrogen temperature (LNT). It is observed that the NIR luminescence of phosphor-related bismuth active center (BAC-P) has been enhanced greatly at LNT.

Three kinds of Bi-related materials co-doped silica optical fibers (BRDFs), including Bi/Al, Bi/Pb, and Bi/Er co-doped fibers, were fabricated using atomic layer deposition (ALD) and modified chemical vapor deposition (MCVD). Then, the effect of irradiation on the optical properties of BRDFs was investigated. The experimental results showed that the fluorescence intensity, the fluorescence lifetime of BRDFs at the 1150 nm band, increased significantly with low-dose treatment, whereas it decreased with a further increase in the radiation dose. In addition, the merit Mα values of the BRDFs, a ratio of useful pump absorption to total pump absorption, decreased with an increase of the radiation doses. The Verdet constants of different doped fibers increased up to saturation level with increases in the radiation dose. However, for a Bi-doped fiber, its Verdet constant decreased and the direction of Faraday’s rotation changed under low-dose radiation treatment. In addition, the Verdet constant increase of the Bi-doped silica fiber was much faster than that of other single mode fiber (SMF) and Pb-doped silica fibers treated with high-dose radiation. All of these findings are of great significance for the study of the optical properties of BRDFs.

Accurate diagnosis of keratitis is important for the follow up treatment. The confocal microscope can scan different depth and layer of the cornea, therefore is an important tool for clinical diagnosis of keratitis. We collected, augmented and preprocessed the confocal microscopic images. In this paper, three kinds of infectious keratitis samples including viral keratitis, bacterial keratitis, and fungal keratitis were classified with ResNet (Residual Network). The results show that the recognition rate of three kinds of keratitis can reach 91.82%, and the accuracy rate of single keratitis could reach 99.09%. In addition, cross-validation was performed on each patient in the dataset. The classification accuracy rate reached 75.00%). This work extended the previous work of identifying fungal keratitis only to three categories and reach a good classification rate of keratitis.

Bismuth-doped optical fiber (BDF) and bismuth/erbium co-doped optical fiber (BEDF) have attracted much attention due to their ultra-broadband luminescence in the near-infrared (NIR) region. The photobleaching effect on bismuth active centers (BACs) related to the NIR luminescence has been systematically investigated and summarized, in terms of irradiation intensity, irradiation wavelength, and temperature. All these findings not only give the deep insights into the fundamental structure of BACs but also provide an effective way to control the BACs. They play an important role for the development of BDF- and BEDF-based devices with high performance and stability under laser exposure in future.

We report a reproducible optofluidic laser (OFL) for multichannel biochemical sensing. A hollow optical fiber (HOF) serves as both microring resonator for lasing and microfluidic channel. The lasing mechanism is analyzed in spectral domain. Thanks to the precise control of the fiber geometry and the rotational symmetry, the HOF-OFL emission is uniformly distributed in the angular direction ( σ = 0.6%) and can be employed conveniently for disposable or arrayed use. An array of ten OFLs is demonstrated with good reproducibility ( σ = 3.9%) in laser threshold. The arrayed sensing capability of the OFL is also investigated. The HOF-OFLs are highly reproducible, easy to integrate in chip-scale, and have great potential for biochemical detection.

The effects of thermal annealing on the photoluminescence (PL) properties of bismuth/erbium co-doped multicomponent optical fiber (BEDFs) in a temperature range of from room temperature (RT) up to 1100 °C are clarified by PL, Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) measurements. When pumped by an 830 nm laser diode, the fiber exhibits a broad near-infrared (NIR) emission band consisting of three distinctive peaks at the wavelengths of 1100, 1420 and 1530 nm, originating from different luminescence centers, viz., Al-related, Si-related bismuth active centers (BACs) and Er3+, respectively. The relative emission intensities of the BACs and Er3+ vary in distinctively different manners with thermal treatment temperature are comprehensively studied. Three temperature regions, i.e., RT ∼ 300 °C, 300–800 °C, and 800–1100 °C can be distinguished accordingly. The instability of the BACs, formation of non-luminous bismuth centers and crystallization of the fiber are proposed to account for the thermal effects on the PL behaviors of the different luminescent centers in the fiber. A first-ever piece of information is also given concerning the PL reversibility of the various luminescence centers in the BEDFs.

The magneto-optical properties for two kinds of novel doping silica optical fibers, Pb-doped optical fiber and Eu-doped optical fiber, are investigated. A measurement system is set up to analyze the Verdet constants of fiber samples, including Pb-doped optical fiber, Eu-doped optical fiber, single mode optical fiber (SMF) and Er-doped optical fiber (EDF). The system keeps extinction ratio (ER) and power of input linearly polarized light stable. For Pb-doped optical fiber and Eu-doped optical fiber, their Verdet constants are larger than that of SMF at different wavelengths (660, 808, 980, 1310, and 1550 nm), and their Verdet constants are increased with the decreasing of wavelength. Especially, the Verdet constant of Pb-doped optical fiber is 3.08 rad/T/m at 660 nm, which is 27.80% larger than that of SMF (2.41 rad/T/m) at corresponding wavelength. Verdet constant of Eu-doped optical fiber at 660 nm is −4.56 rad/T/m, which is 34.91% larger than that of EDF (−3.38 rad/T/m), and 89.21% larger than that of SMF at corresponding wavelength. Pb-doped silica optical fiber and Eu-doped silica optical fiber exhibit superior magneto-optical properties compared with SMF. Further, the magnetization of fibers are presented in the temperature range of 4–380 K. The magneto-optical property of Pb-doped optical fiber is more stable to temperature than that of EDF.

Sampled fiber grating for high-resolution time-domain signal processing is investigated. Sampled fiber grating is useful to introduce precise time delays in picosecond (ps) across many wavelength channels. We analyze and simulate for Sinc2 sampled fiber grating, and show that a large number linear sub-ps time delays can be achieved by the grating. We present that Gaussian sampled fiber gratings can be fabricated by inscribing optical fiber by Gaussian laser beam, and can realize short time delays over a number of wavelength channels with a required time delay profile. For a Gaussian sampled fiber grating fabricated, an average time delay step of 4.49 ps with 10% linearity for 8 wavelength channels, and an average delay step of 2.5 ps with 8% linearity if for 4 channels, are realized. A physical model of cascaded equivalent Fabry-Perot cavities together with rectangular truncation of the inscription laser beam for the Gaussian sampled refractive index is suggested, and used to explain the grating spectra. A technique for time delay step tunability of the grating is presented. Some issues are discussed with conclusions given. We demonstrate that the sampled fiber gratings have capability to provide a large number of picosecond time delays with good linearity. This offers a simple technique for ps-high-resolution signal processing in time-domain and THz signal generation.

Microbubbles have broad applications for optofluidic devices, optical manipulation, and sensing. Here we report a series of experimental observations, demonstrating the controllable generation and assembly of microbubbles by using an optical fiber-coupled laser. The microbubbles can be photothermally generated with high efficiency in deionized water, without adding light-absorbing nanomaterials. The temporal evolution and assembled pattern, quantified by diameter, number and density of the microbubbles, can be flexibly controlled by the surface area of liquid, the insertion depth of fiber, and the laser power for heating. Good repeatability is confirmed for the microbubble generation. This kind of microbubble may have the potential for sensing, microstructure formation, etc.

Monovalent bismuth-related centers in pure silica optical fiber are calculated by using first-principle methods. Transition energy levels of three different structural models are investigated on the basis of the time-dependent density functional theory (TDDFT). Compared with the experimental data of near-IR luminescence, our calculated results suggested that luminescence near 1492 nm is likely caused by SiOBi configuration; and luminescence at 1147 nm and 1403 nm may be caused by interstitial Bi2O molecule. Moreover, SiBi configuration, which might be the origin of the luminescence near 1629 nm, is difficult to directly form because of its relatively high formation energy.

We report first-principles calculations of cluster SiO2 (24-atom) with and without divalent bismuth (Bi2+). Heyd–Scuseria–Ernzerhof functional is introduced. The influences of members of “Si-O-Si” rings are considered to study atomic structures, electronic structures, and optical properties of Bi-doped optical fiber. Our results reveal that Bi-doped in 3-membered rings are main contributions to the characteristic absorption bands (around 500 nm), which will lead a red emission in Bi-doped optical fiber. Our methods will be effective to confirm bismuth-active centers for different valence states of Bi atom.

We demonstrate distributed acoustic sensor using broadband weak fiber Bragg grating array for large temperature tolerance in an $\varphi $ -optical time domain reflectometry system with a balanced Michelson interferometer. The system was tested with large difference in local temperature, 18 °C and 50 °C, simultaneously, and achieves a relatively flat frequency response from 20 Hz to 1200 Hz.

We report silica fiber with trivalent bismuth (Bi3+) in first-principles calculations. The influences of members of “Si–O–Si” rings are considered to study atomic structures, frontier molecular orbital and optical properties of Bi-doped optical fiber. Our results reveal that the luminescence of Bi3+-doped optical fiber is the result of a combination of Bi3+ ions and silica matrix. Different ring structures affect the luminescence properties, which explained why Bi3+-doped silica fiber usually cover a broad spectral range from the UV to visible light.

The membered ring microstructures are considered to study the influences of the structure parameters, frontier molecular orbital, and luminescence properties in Ge-doped silica optical fiber material with trivalent cerium. The calculations indicate that Ce3+ ion is more likely to exist outside the membered ring structures than embedded into the membered rings. The results reveal that after the Ce incorporation, a strong absorption peak and an emission peak appear with a combination of Ce3+ ions and GeO2 matrix. Moreover, the energy levels for Ce-doped silica optical fiber are investigated, which explained the influence of different membered rings on the luminescence properties.

The crystalline and nano-sized {[Cu(tipe)(H2O)](2,2′-bpdc)·11H2O·DMF}n (1·11H2O·DMF or Cu-tipe) (tipe ​= ​1,1,2,2-tetrakis (imidazole-1-yl)phenyl)ethylene, 2,2′-bpdc ​= ​2,2′-biphenyldicarboxylate) were synthesized and structural analysis by X-ray diffraction, scanning electron microscopy, optical band gaps, photoluminescence and thermal stability. Cu-tipe and graphene oxide (GO) nanocomposite (Cu-tipe/GO) was synthesized with sonochemical method and characterized. Cu-tipe exhibits a (4,4)-coordinated 2D network showing the point symbol {44·62}{44·62}. The photocatalytic and sonocatalytic decolorization of methylene blue (MB), methyl violet (MV), rhodamine B (RhB) under visible light and ultrasound irradiation showed that the catalytic efficiencies of decolorization organic dyes for Cu-tipe/GO composite are higher than these of most of MOF and MOF composite. Crystalline and nano-sized Cu-tipe also showed high decolization efficiencies. The radicals trapping experiments were carried out to study the active species and the degradation mechanism was proposed.

Optofluidic lasers (OFLs) are an emerging technological platform for biochemical sensing, and their good performance especially high sensitivity has been demonstrated. However, high-throughput detection with an OFL remains a major challenge due to the lack of reproducible optical microcavities. Here, we introduce the concept of a distributed fibre optofluidic laser (DFOFL) and demonstrate its potential for high-throughput sensing applications. Due to the precise fibre geometry control via fibre drawing, a series of identical optical microcavities uniformly distributed along a hollow optical fibre (HOF) can be achieved to obtain a one-dimensional (1D) DFOFL. An enzymatic reaction catalysed by horseradish peroxidase (HRP) can be monitored over time, and the HRP concentration is detected by DFOFL-based arrayed colorimetric detection. Experimentally, five-channel detection in parallel with imaging has been demonstrated. Theoretically, spatial multiplexing of hundreds of channels is achievable with DFOFL-based detection. The DFOFL wavelength is tuned over hundreds of nanometers by optimizing the dye concentration or reconfiguring the liquid gain materials. Extending this concept to a two-dimensional (2D) chip through wavelength multiplexing can further enhance its multi-functionality, including multi-sample detection and spectral analysis. This work opens the door to high-throughput biochemical sensing.

Targeting the huge unused bandwidth (BW) of modern telecommunication networks, Bi/Er co-doped silica optical fibers (BEDFs) have been proposed and developed for ultra-broadband, high-gain optical amplifiers covering the 1150–1700 nm wavelength range. Ultrabroadband luminescence has been demonstrated in both BEDFs and bismuth/erbium/ytterbium co-doped optical fibers (BEYDFs) fabricated with the modified chemical vapor deposition (MCVD) and in situ doping techniques. Several novel and sophisticated techniques have been developed for the fabrication and characterization of the new active fibers. For controlling the performance of the active fibers, post-treatment processes using high temperature, g-radiation, and laser light have been introduced. Although many fundamental scientific and technological issues and challenges still remain, several photonic applications, such as fiber sensing, fiber gratings, fiber amplification, fiber lasers, etc., have already been demonstrated.

We propose and experimentally demonstrate a compact fiber-optic vibration sensor in which a tilted Bragg grating is inscribed in the core of a depressed cladding fiber. The sensor provides resolution up to $2\times 10^{-2} \text {m/s}^{2}$ and a linear acceleration response between 0.2 and 6.0 m/s2, together with a flat frequency response between 1 and 120 Hz. The sensor takes advantage of a cost-effective interrogation scheme by monitoring the total reflection power of the fiber sensor. We use the calibrated output to eliminate the potential light source and fiber loss-induced power fluctuations. The proposed sensing system has been used to measure the vibration of a mechanical damper in electrical transmission lines and the results agree well with those from a commercial sensor.

A new sampled fiber grating scheme is investigated for WDM signal queuing in time domain. The queuing is aimed at achieving very short constant time intervals down to picoseconds (ps) for many wavelength channels by a single fiber device. Theory and modeling predict that a consistence of linear spectral profiles exists between reflectivity or transmission spectrum and time delay spectrum. A sampled fiber grating based on Gaussian beam writing is proposed to offer a large number of wavelength channels and time delays within an approximate linear profile. Results for simulating a Gaussian sampled fiber grating show that the time delay minima of 8 channels within a section of the spectral profile have an average time delay step of 2.83 ps and standard deviation of 7.4% from linearity. Fiber gratings were successfully written by Gaussian laser beam in fabrication. A Gaussian sampled fiber grating was measured for time delay spectrum of 4 wavelength channels. An average time delay step of 9.67 ps is obtained. Some issues and related analysis and discussion are given. Our preliminary experiment suggests that the sampled fiber grating scheme can achieve ps-time steps for WDM signal queuing such as high-resolution time delay lines.

The recombinant thermostable β-glucosidase from Thermotoga thermarum DSM 5069T exhibited high selectivity to catalyze the conversion of ginsenoside Re and Rg1 to the more pharmacologically active minor ginsenoside Rg2 and Rh1, respectively. At a concentration of 1.36 U/mL of the enzyme, a temperature of 85°C, and pH 5.5, 10 g/L ginsenoside Re was transformed into 8.02 g/L Rg2 within 60 min, and 2 g/L ginsenoside Rg1 was transformed into 1.56 g/L Rh1 within 60 min. This paper provides the first report on the production of ginsenoside Rg2 and Rh1 by a highly thermostable β-glucosidase.

We investigated the spectroscopic properties of bismuth/erbium co-doped optical fibre (BEDF) under 830 nm pumping and observed considerable up-conversion in blue along with the typical near infrared (NIR) emission. The influence of pump power and fibre length upon both up-conversion and NIR emission has been studied and analyzed in details. Amplified spontaneous emission (ASE) at 1420 nm has been observed in BEDF by 830 nm pumping. The results demonstrate that the up-conversion has effect upon the emission at 1420 nm. The relationship between the pump absorption and emission has also been discussed to illuminate the possible energy transition processes in BEDF.

The influence of the linear birefringence on magneto-optical property measurement for optical fibers is investigated theoretically and experimentally. The evolution of polarization in fibers is simulated by the Jones matrix. To verify this theoretical model, a magneto-optical system is built to measure the input azimuth, output azimuth and ellipticity. The Faraday rotation of spun fibers with different pitches is measured. The Verdet constant increases, while the linear birefringence decreases as the pitch becomes smaller. For spun fibers with 1 mm pitch, the Verdet constant can be enhanced by about 20.7% at 660 nm, compared with that of the unspun fiber. The results indicate that smaller linear birefringence can provide more accurate Faraday rotation measurement.

Disposable biosensors are of great importance in disease diagnosis due to their inherent merits of no cross-contamination and ease of use. Optofluidic laser (OFL) sensors are a new category of sensitive biosensors; however, it is challenging to cost-effectively mass-produce them to achieve disposability. Here, we report a disposable optofluidic laser immunosensor based on thin-walled hollow optical fibers (HOFs). Using a fiber draw tower, the fabrication parameters, including drawing speed and gas flow rate, are explored, and the HOF geometry is precisely controlled, which allows identical laser microring resonators to be distributed along the fibers. The disposable OFL immunosensor detects the protein concentration in the HOF through a wash-free immunoassay. Enabled by the disposable sensors, the statistical characteristics of 80 tests for each concentration greatly reduces the bioassay uncertainty. A low coefficient of variation (CV) of 3.3% confirms the high reproducibility of the disposable HOF-OFL sensors, and the mean of the normal distribution of the logarithmic OFL intensity serves as the sensing output. A limit of detection of 11 nM within a short assay time of 15 min is achieved. These disposable immunosensors possess the advantages of low cost, high reproducibility, fast assay, and low-volume consumption of sample and reagents. We believe that this work will inspire disposable optofluidics through the mass production of multifunctional microstructured optical fibers.

© 2020 OSA - The Optical Society. All rights reserved. Based on 3D printing technology, multi-core doped silica optical fibre has been fabricated. The demonstration heralds a new fibre manufacturing milestone one that enables the design of fibres not previously feasible.

Shape memory polymers (SMPs) and their composites (SMPCs) can hold a programmed temporary shape and recover to their original shape once exposed to a particular external stimulus. The stimulus light has the advantage of being both an excitation energy source and a control signal carrier for remote actuation of SMP materials. Here we present the capability of D-shaped optical fibres to send near infrared (NIR) light into a light activated shape memory polymer composite (LASMPC) which generates the adequate photothermal effect necessary for the shape recovery process of relatively large samples. A D-shaped optical fibre enables dispersion of light through the polished area around the fibre than the dispersion of light through the tip of the fibre. Embedment of a D-shaped optical fibre in a LASMPC creates a single unit smart actuator, which can be remotely activated by light. Remotely controllable smart actuators can be located at any difficult to reach positions and controlled safely with light energy. It would be a breakthrough technology for biomedical, aerospace and many other engineering applications.

We propose and demonstrate a directional bend sensing based on Mach-Zehnder interferometer in a high birefringence dual-core photonic crystal fiber. Its curvature sensitivity is up to 4.24 nm/m–1 within the curvature range of 2.19-3.99 m–1.

We demonstrate that under appropriate conditions it is possible to build in tolerance to poor design of a structured optical fibre like photonic crystal fibre. During drawing its internal symmetry of the structure is improved.