End Face Of Optical Fiber Research Articles

A highly sensitive SERS optical fiber probe with PSS modified gold nano-bipyramids for trace detection of water contamination

The combination of surface-enhanced Raman scattering (SERS) and optical fiber has led to the development of SERS optical fiber probe, which demonstrates potential for real-time, in-situ, and flexible detection of water contamination. In this paper, a highly sensitive SERS optical fiber probe of gold nano-bipyramids (Au NBPs) was successfully developed for the first time. The Au NBPs were controllably synthesized by a heat-treated seed growth method. Surface modification of the Au NBPs was carried out by adding poly (sodium 4-styrenesulfonate) (PSS) instead of hexadecyl trimethyl ammonium bromide (CTAB), which changed the Zeta potential of the Au NBPs solution from positive to negative. The SERS properties of the Au NBPs can be significantly enhanced by optimizing the parameters of PSS content. The optical fiber end face was pretreated with silane coupling agent to introduce amino groups and exhibit positive charge. As a result, highly sensitive SERS optical fiber probes were prepared through electrostatic adsorption of the Au NBPs. The performance of the SERS optical fiber probe was evaluated. The crystalline violet (CV) limit concentration of 10−10 mol/L was detected by the optimized SERS optical fiber probe with satisfactory reproducibility and stability. Additionally, a limit concentration of 10−5 mol/L for thiram could also be detected by the SERS optical fiber probe. Finally, the SERS enhancement mechanism was further discussed. The finite element method was utilized to analyze the electromagnetic field distribution of Au NBPs, optical fibers, and SERS optical fiber probes, theoretically explaining the performance advantages of Au NBPs SERS optical fiber probes. Based on our results, the Au NBPs SERS optical fiber probe holds significant value for trace detection of water contamination and biomolecules.

Optical fiber acoustic sensor with gold diaphragm based Fabry-Perot interferometer

This work proposes an optical fiber acoustic sensor using a Fabry-Perot interferometer (FPI), which consists of an optical fiber end face and a gold diaphragm with an effective diameter of 75 µm and a thickness of 20 nm. The sensor has contrast of up to 34 dB and achieves audible acoustic signal sensing over a broad frequency response range from 70 Hz to 20 kHz with a linear response to sound pressure. The minimum detectable sound pressure is 815.5 μPa/Hz1/2 at 70 Hz. The sensor made of a pure gold diaphragm has stable performance and can work consistently over a long period, promising to be applied as an optical microphone for real-time communication in some extreme environments.

Effect of optical fiber end face scratches on laser-induced damage threshold.

The scratches on the fiber end face can enhance the local electrical field, which lowers the damage threshold. The damage mechanism of a high-energy laser is investigated. The effect of scratches on the electric field is simulated by the finite difference time domain (FDTD) solution. The results show that the depth of the scratch has a greater ability to influence the electric field than the width, and multiple scratches have a stronger modulation than a single scratch. In calculation, the damage threshold of the scratch-free end face is 0.456J/c m 2 when the incident light electric field intensity is 50M V/c m, compared to 0.345J/c m 2 in the presence of the scratch on the end face.

High sensitivity and stability probe-type refractive index sensor based on an optical fiber metasurface

A specific probe-type sensor based on an optical fiber metasurface was proposed and simulated for refractive index (RI) sensing. In this work, a metasurface has been integrated with an optical fiber platform, which has huge potential applications in imaging, sensing, and communications. The designed RI sensor consists of stacking layers of Au and ZnO in a 2D structure deposited on the end face of commercial multimode optical fiber. The parameters and performance of the sensor structure are designed and simulated. The results show that the designed sensor structure can generate mode resonance and realize RI sensing. Numerical simulations reveal that when the pair of Au/ZnO layers is 4, the width of the nanopillars is 300 nm, the thickness of the Au layer is 45 nm, the thickness of ZnO layer is 40 nm, and the RI sensitivity of the designed sensor reaches 1415 nm/RIU. In addition, the high RI of Au/ZnO, along with its compatibility with the fiber core (SiO2), makes it a perfect candidate to realize a multifunctional device. It also is a the biocompatible material that can be functionalized easily and used to realize biosensing.

Ampere force fiber optic magnetic field sensor using a Fabry-Perot interferometer.

The paper presents a novel fiber-optic vector magnetic field sensor using a Fabry-Perot interferometer, which consists of an optical fiber end face and a graphene/Au membrane suspended on the ceramic ferrule end face. A pair of gold electrodes are fabricated on the ceramic ferrule by femtosecond laser to transmit electrical current to the membrane. Ampere force is generated when an electrical current flows through the membrane in a perpendicular magnetic field. The change in Ampere force causes a shift in the resonance wavelength in the spectrum. In the magnetic field intensity range of 0 ∼ 180 mT and 0 ∼ -180 mT, the as-fabricated sensor exhibits magnetic field sensitivity of 5.71 pm/mT and 8.07 pm/mT. The proposed sensor has great potential application in weak magnetic field measurements due to its compact structure, cost-effectiveness, ease to manufacture, and good sensing performance.

Flexible and Speedy Preparation of Large-Scale Polystyrene Monolayer through Hemispherical-Depression-Assisted Self-Assembling and Vertical Lifting

Liquid interfacial self-assembled two-dimensional nanomonolayers are promising as colloidal crystal templates or lithographic masks for the mass production of periodic nanoarrays. However, the interfacial self-assembled monolayers usually suffer various defects such as grain boundaries, line defects, vacancy defects, and multilayers due to imperfect process technology. Here, we demonstrated a series of optimized strategies including the hemispherical-depression-assisted self-assembly, dot coating approach, and vertical lifting transfer protocol to eliminate surface defects especially multilayers jointly. After stabilizing the hemispherical depression height to 1.5 mm with a 40° tilted silicon slide, the self-assembly time was significantly shortened to 10 min for a 1 × 2 cm2 area of PS monolayer. The series of strategies were successfully implemented not only on glass and silicon flat substrates but also on the side and end face of optical fiber, even on flexible substrates, while maintaining great morphologies. Besides, in association with nanospherical lens photolithography and nanosphere lithography technologies, various two-dimensional nanoarrays such as nanotriangles and nanoholes could be successfully obtained for subsequent optical properties research, which present broad application prospects in biochemical sensing, medicine, environmental protection, and other fields.

High speed and broadband fiber-integrated WS2/Bi2O2Se avalanche photodetector

Photodetectors based on two-dimensional(2D) materials have attracted tremendous attention in recent years because of their potential for development in compact and integrated devices. Owing to the high carrier mobility and air stability, the newly discovered 2D bismuth oxyselenide (Bi2O2Se) exhibits outstanding optoelectronic properties. However, the high dark current inevitably restricts the performance of the Bi2O2Se-based photodetectors. Here, we propose and demonstrate a fiber-integrated photodetector with a low dark current of ∼10 −10 A by assembling a WS2/Bi2O2Se Van der Waals heterostructure onto the end-face of a standard optical fiber. Benefiting from the narrow bandgap of the 2D materials, the fiber-integrated photodetector exhibits a broadband detection range from 650 to 1630 nm along with a responsivity of 1.13 AW−1. The fast rise time is measured as ∼410μs, while the fall time is ∼600μs. Taking advantage of the built-in potential in the WS2/Bi2O2Se heterostructure, the photodetector can work on self-powered mode. Applied a certainly high reverse voltage, the WS2/Bi2O2Se fiber-integrated photodetector can operate at avalanche breakdown region with an external quantum efficiency of 141% and an avalanche gain of 44 under the input power of 56.7μW. Finally, the fiber-integrated photodetector is applied to measure the wrist bending owing to its high photoresponsivity. These findings indicate that our proposed device has intriguing capabilities in terms of photodetection and on-line power monitoring, which enable our proposed device to have superb application potential in a fiber-integrated multi-function system.

Multilayer all-polymer metasurface stacked on optical fiber via sequential micro-punching process

Abstract Metasurface technology is revolutionizing the field of optics and pursuing expanded functions via technical developments, such as the integration of multiple metasurfaces with optical fibers. Despite several attempts to realize metasurface-on-fiber platforms, negligible fiber-facet areas pose a serious obstacle to efficient and precise fabrication. Herein, we demonstrate a novel sequential micro-punching process that enables rapid and precise stacking of multiple polymer metasurfaces on the end face of a single-mode optical fiber. Mesh-type nanohole metasurfaces are fabricated on a 1.8-μm-thick polymethyl methacrylate (PMMA) layer via e-beam lithography, and the PMMA layer is separated from the substrate and prepared in the form of a membrane using the external frame. Furthermore, the PMMA metasurfaces are sequentially punched through the fiber and stacked on top. Employing a micro-punching process, we demonstrate highly efficient all-polymer metalenses and orbital angular momentum (OAM) metasurfaces coupled with single-mode fibers operating in the telecommunication band. A 1550 nm laser beam passing through three metalens layers stacked on the fiber is focused at a distance of 135 μm with 83% efficiency. In addition, the 1550 nm beam passing through three OAM metasurfaces on the fiber is converted into a perfect vortex beam with a topological charge of 3. We believe that our proposed micro-punching process will cause a breakthrough in the fabrication of metasurface-integrated optical fibers that will be utilized in a wide range of applications.

Luminescent Polymer Composites for Optical Fiber Sensors.

Optical fiber sensors incorporating luminescent materials are useful for detecting physical parameters and biochemical species. Fluorescent materials integrated on the tips of optical fibers, for example, provide a means to perform fluorescence thermometry while monitoring the intensity or the spectral variations of the fluorescence signal. Similarly, certain molecules can be tracked by monitoring their characteristic emission in the UV wavelength range. A key element for these sensing approaches is the luminescent composite, which may be obtained upon allocating luminescent nanomaterials in glass or polymer hosts. In this work, we explore the fluorescence features of two composites incorporating lanthanide-doped fluorescent powders using polydimethylsiloxane (PDMS) as a host. The composites are obtained by a simple mixing procedure and can be subsequently deposited onto the end faces of optical fibers via dip coating or molding. Whereas one of the composites has shown to be useful for the fabrication of fiber optic temperature sensors, the other shows promising result for detection of UV radiation. The performance of both composites is first evaluated for the fabrication of membranes by examining features such as fluorescent stability. We further explore the influence of parameters such as particle concentration and density on the fluorescence features of the polymer blends. Finally, we demonstrate the incorporation of these PDMS fluorescent composites onto optical fibers and evaluate their sensing capabilities.

Constructing the Au nanoparticle multimer on optical fiber end face to enhance the signal of localized surface plasmon resonance biosensors: A case study for deoxynivalenol detection

Localized surface plasmon resonance (LSPR) based optical fiber end-face biosensors have the advantages of convenience, fast, accuracy, and high sensitivity. Because the sensor area (optical fiber end face)) is small, how to improve its signal strength is a challenge faced by researchers. In this study, an Au nanoparticle (AuNP) multimer structure was designed to enhance the LSPR signal by the hot spots effect produced by the AuNP multimers. The fiber end face was coupled with the first batch of AuNPs, on which the second batch of AuNPs was coupled using 3-aminopropyl triethoxysilane as a spacer, then deoxynivalenol (DON) aptamer was coupled on to complete the biosensor. Also, the preparation parameters were optimized. The results showed that this biosensor with the AuNP multimers had a higher signal strength, its LSPR absorbance was 2.1 fold of that of the biosensor with AuNPs. It had a high performance for DON detection, furthermore, the LSPR peak shift value and LOD of this developed biosensor was 3.4 fold and 1/8 of that of LSPR the biosensor with AuNPs. Therefore, it is a good strategy to enhance the signal of the optical fiber LSPR biosensors by constructing the AuNP multimers on the fiber end face.

Multiplexed optical fiber tip refractive index sensor interrogated by microwave photonics

A multiplexed and spatially-resolved optical fiber tip sensor is proposed and demonstrated for multi-point refractive index (RI) sensing based on a microwave-photonic interrogation technique. The RI sensor is simply based on an array of cleaved end facets of optical fibers with different lengths fabricated from off-the-shelf optical fiber couplers. An auxiliary optical fiber endface that serves as the reference reflector is also introduced into the system. As a result, each of the sensing reflectors from the sensor array, together with the reference reflector, forms a Michelson interferometer (MI). Interrogated by a microwave-photonic system operating at an incoherent regime, the interferogram for each of the MIs in the microwave domain can be unambiguously reconstructed. The spatial location and ambient RI of the sensing reflector can be determined based on the free spectral range and magnitude at the resonance of the microwave interferogram. An analytical model is first developed to understand the physics of the sensor, followed by a proof-of-concept demonstration. Two sensing reflectors and a reference reflector are multiplexed in the prototype system, showing high RI sensitivity and low temperature crosstalk. The unique features of the sensor, such as ease of fabrication, low cost, high sensitivity, low temperature dependence, multiplexing and spatially-resolved capabilities, make the sensor a strong candidate for biochemical and environmental sensing applications.

Ultraminiature optical fiber-tip directly-printed plasmonic biosensors for label-free biodetection

Miniaturization of biosensors has become an imperative demand because of its great potential in in vivo biomarker detection and disease diagnostics as well as the point-of-care testing for coping with public health crisis, such as the coronavirus disease 2019 pandemic. Here, we present an ultraminiature optical fiber-tip biosensor based on the plasmonic gold nanoparticles (AuNPs) directly printed upon the end face of a standard multimode optical fiber at visible light range. An in-situ precision photoreduction technology is developed to additively print the micropatterns of size-controlled AuNPs. The AuNPs reveal distinct localized surface plasmon resonance, whose peak wavelength provides an ideal spectral signal for label-free biodetection. The fabricated optical fiber-tip plasmonic biosensor can not only detect antibody, but also test SARS-CoV-2 mimetic DNA sequence at the concentration level of 0.8 pM. Such an ultraminiature fiber-tip plasmonic biosensor offers a cost-effective biodetection technology for a myriad of applications ranging from point-of-care testing to in vivo diagnosis of stubborn diseases.

A Portable Optical Fiber Tip Facet LSPR Aptasensor for Detection of Fumonisin B1

Fumonisin B1 (FB1) is a mycotoxin that mainly contaminates food crops. To avoid the harmful effect of FB1 on the human body, it is necessary to establish a convenient, sensitive, and accurate FB1 detection method. In this study, an optical fiber tip facet biosensor based on the localized surface plasmon resonance (LSPR) that adapts to a general detection platform was developed. An optical fiber end face was assembled with –NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , Au nanoparticles (AuNPs), and aptamer, and the fabricating parameters were optimized. The results showed that the optical fiber LSPR biosensor had a good linear relationship ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{\text {2}}$ </tex-math></inline-formula> = 0.9817) between the logarithmic FB1 concentration and the LSPR peak shifts within the linear range of concentrations of 0.8–200.0 ng/mL and a low limit of detection (LOD) of 0.17 ng/mL, as well as selectivity, recovery rates (96.08%–112.23%), and repeatability relative standard deviation (RSD) of 3.37%. It was validated by corn. Therefore, it was feasible that a tip facet optical fiber LSPR biosensor could be used to detect FB1, with advantages of convenience, renewability, and low cost. It is easy to popularize and apply.

Design and Fabrication of a Differential MOEMS Accelerometer Based on Fabry–Pérot Micro-Cavities

In this paper, a differential MOEMS accelerometer based on the Fabry-Perot (FP) micro-cavities is presented. The optical system of the device consists of two FP cavities and the mechanical system is composed of a proof mass that is suspended by four springs. The applied acceleration tends to move the PM from its resting position. This mechanical displacement can be measured by the FP interferometer formed between the proof mass cross-section and the optical fiber end face. The proposed sensor is fabricated on a silicon on insulator (SOI) wafer using the bulk micromachining method. The results of the sensor characterization show that the accelerometer has a linear response in the range of 1g. Also, the optical sensitivity and resolution of the sensor in the static characterization are 6.52 nm/g and 153ug. The sensor sensitivity in the power measurement is 49.6 mV/g and its resonant is at 1372 Hz. Using the differential measurement method increases the sensitivity of the accelerometer. Based on experimental data, the sensor sensitivity is two times as high as that of a similar MOEMS accelerometer with one FP cavity.

Femtosecond laser 3D printed micro objective lens for ultrathin fiber endoscope

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.

A Security Detection Scheme Based on TTD for NG-PON2 Fiber Links

For improving the physical layer security of next generation passive optical network (NG-PON2), we propose a security detection scheme by detecting the terminal thermal distribution (TTD) at the optical fiber end face on the optical network unit (ONU), when the fiber link is tapped. The principle of the scheme is given that the thermal energy always exists in fiber links and the TTD at the optical fiber end face can be detected. When the link tapping occurs, the leaking light energy induced by bending converts into the thermal energy, which changes the TTD at the optical fiber end face on ONU of NG-PON2. The TTD models of core and cladding layers at the optical fiber end face owing to bending are built with the double cylindrical coordinate systems, based on the bending loss formula of optical fiber and thermodynamic coupling theory. Then, the simulations for the TTD models are carried out under the different conditions of input power, bending radius and distant of detected point from the center of optical fiber end face, respectively. The simulation results indicate three conditions above are the main factors affecting the TTD changes. Finally, we set up an experimental system in the lab, using a light-emitting diode at 1550nm, and a thermal microscope (Telops-FAST-IR). The experimental results show the TTD of core layer at the optical fiber (G.652D) end face changes 72.5% at the input power of 1dBm with the bending radius from 10mm to 5mm, and are consistent with the simulation ones.

Asymmetric Reflection Spectrum of Fabry-Perot Interferometer and the Application in Pressure Sensing

The performance of a fiber optic Fabry-Perot (F-P) sensor largely depends on the spectral characteristics of F-P interference, nevertheless there is little research on the spectral characteristic, such as the asymmetry shapes which are often observed in practical experiments. Here, a simple analytical formula for simulating the reflected spectrum of a F-P resonator have been provided, based on which the asymmetry spectral shape can be diversified through adjusting the refined parameters in the analytical formula. In addition, the composite film of Pt/Ge with different thickness on fiber tip has been theoretically demonstrated to change the parameters, and the F-P interferometer composed by composite film of Pt/Ge on fiber tip and gold film has been simulated to exhibit variated asymmetric reflection spectra. Meanwhile, the reflection spectrum from fiber F-P interferometer based on the composite film deposited on the end face of optical fiber has been experimentally proven to change according to the thickness variation of Ge film. Finally, a fiber based miniature extrinsic Fabry-Perot interferometer (EFPI) showing a saw tooth wave shape spectrum has been fabricated to sense static pressure through a dual-wavelength based intensity demodulation scheme, which possesses the potential to overcome the offset between sensitive and dynamic range for a traditional sensor.

Design and Optimization of All-Dielectric Fluorescence Enhancing Metasurfaces: Towards Advanced Metasurface-Assisted Optrodes.

The need for miniaturized biological sensors which can be easily integrated into medical needles and catheters for in vivo liquid biopsies with ever-increasing performances has stimulated the interest of researchers in lab-on-fiber (LOF) technology. LOF devices arise from the integration of functional materials at the nanoscale on the tip of optical fibers, thus endowing a simple optical fiber with advanced functionalities and enabling the realization of high-performance LOF biological sensors. Consequently, in 2017, we demonstrated the first optical fiber meta-tip (OFMT), consisting of the integration of plasmonic metasurfaces (MSs) on the optical fiber end-face which represented a major breakthrough along the LOF technology roadmap. Successively, we demonstrated that label-free biological sensors based on the plasmonic OFMT are able to largely overwhelm the performance of a standard plasmonic LOF sensor, in view of the extraordinary light manipulation capabilities of plasmonic array exploiting phase gradients. To further improve the overall sensitivity, a labelled sensing strategy is here suggested. To this end, we envision the possibility to realize a novel class of labelled LOF optrodes based on OFMT, where an all-dielectric MS, designed to enhance the fluorescence emission by a labelled target molecule, is integrated on the end-face of a multimode fiber (MMF). We present a numerical environment to compute the fluorescence enhancement factor collected by the MMF, when on its tip a Silicon MS is laid, consisting of an array of cylindrical nanoantennas, or of dimers or trimers of cylindrical nanoantennas. According to the numerical results, a suitable design of the dielectric MS allows for a fluorescence enhancement up to three orders of magnitudes. Moreover, a feasibility study is carried out to verify the possibility to fabricate the designed MSs on the termination of multimode optical fibers using electron beam lithography followed by reactive ion etching. Finally, we analyze a real application scenario in the field of biosensing and evaluate the degradation in the fluorescence enhancement performances, taking into account the experimental conditions. The present work, thus, provides the main guidelines for the design and development of advanced LOF devices based on the fluorescence enhancement for labelled biosensing applications.

All-Fiber Near-Field Optical Tweezer: Reducing Thermal Disturbance

Trapping nanoscale particles in a stable and non-destructive way is of great importance to life sciences. Near-field optical tweezers are a common way to trap nanoparticles. Here we propose and demonstrate an all-fiber near-field optical tweezer for trapping nanoparticles using a laser beam that has been totally reflected three times on a fiber tip with a double frustum structure. The light totally internally reflects on the optical fiber end-face and generates an evanescent field that traps the nanoparticles in water. Simulated results show that the evanescent field with high gradient distribution generating on the optical fiber end face leads to an insignificant temperature rise (0.0765 K). The experimental results demonstrate that all-fiber near-field optical tweezer allows us to trap fluorescent particles as small as 100 nanometers in diameter. The max temperature rise is 0.091 K. Compared with the plasmonic optical tweezers, the all-fiber optical tweezer reduces the thermal effect. The proposed all-fiber near-field optical tweezer plays an essential role in nanoscale optical trapping.

Plasmonic enhanced fluorescence via 3D printing spiral conical tapered gold tip bound to optical fiber

We build a 3D printing spiral conical tapered gold tip directly on the end face of an optical fiber as an efficient fluorescence enhancement device via the two-photon polymerization direct laser writing technology and magnetron sputtering technique. At an optimized geometry achieved via three-dimensional finite-difference time-domain numerical simulations, the gold tip allows the incident light coming from the optical fiber to efficiently excite the surface-plasmon polariton at the outer surface and trigger bright fluorescence of Rodamine dye molecules. The experimental results show that when the incident green laser light at 532 nm has an intensity of 0.5 µW, the fluorescence enhancement factor by the spiral tapered gold tip bound to fiber is about 38 times greater than the reference sample of the flat-cleaved gold film coated fiber. This 3D nanostructured gold-tip bound optical fiber may provide a promising way to improve detection sensitivity in fluorescence-based sensing platforms.