End Face Of Optical Fiber Research Articles

Silicone Rubber Fabry-Perot Pressure Sensor Based on a Spherical Optical Fiber End Face.

To improve the fringe contrast and the sensitivity of Fabry-Perot (FP) pressure sensors, a silicone rubber FP pressure sensor based on a spherical optical fiber end face is proposed. The ratio of silicone rubber ingredients and the diameter and thickness of silicone rubber diaphragm were optimized by a simulation based on experimental tests that analyzed elastic parameters, and the influence of the radius of a spherical optical fiber and the initial cavity length of the sensor on the fringe contrast was investigated and optimized. Pressure sensor samples were fabricated for pressure test and temperature cross-influence test. Gas pressure experimental results within a pressure range of 0~40 kPa show the average sensitivity of the sensor is −154.56 nm/kPa and repeatability error is less than 0.71%. Long-term pressure experimental results show it has good repeatability and stability. Temperature experimental results show its temperature cross-sensitivity is 0.143 kPa/°C. The good performance of the proposed FP pressure sensor will expand its applications in biochemical applications, especially in human body pressure monitoring.

Optical Interferometric Force Sensor Based on a Buckled Beam

This paper reports a novel extrinsic Fabry-Perot interferometer (EFPI)-based fiber optic sensor for force measurement. The prototype force sensor consists of two EFPIs mounted on a stainless steel rectangular frame. The primary sensing element, i.e., the first EFPI, is formed between the endface of a horizontally-placed optical fiber and a stainless steel buckled beam. The second EFPI, fashioned between a longitudinally-placed optical fiber and a silver-coated glass beam, is arranged to demonstrate the amplification mechanism of the buckled beam structure. When the sensor is subjected to a tension force, the pre-buckled beam will deflect backward, resulting in a longitudinal/axial displacement of the pre-buckled beam. The axial displacement is further transferred and amplified to a horizontal/vertical deflection at the middle of the buckled beam, leading to a relatively-significant change in the Fabry-Perot cavity length. A force sensitivity of 796 nm/N (change in cavity length/Newton) is achieved with a low-temperature dependence of 0.005 N/°C. The stability of the sensor is also investigated with a standard deviation of ± 5 nm, corresponding to a measurement resolution of ±0.0064 N. A simulation is conducted to study the axial displacement and stress distribution of the sensor when it is subjected to a tension load of 250 N. It is demonstrated that the maximum stress of the sensor is tremendously reduced attributed to the buckled design, enabling a long service life cycle of the force sensor. The robust and simple-to-manufacture force sensor has great potential in structural health monitoring, robotics control, and oil/ gas refining systems.

Rapid fabrication of sub-micron scale functional optical microstructures on the optical fiber end faces by DMD-based lithography.

The rapid development of optical fiber application systems puts forward higher requirements for the miniaturization and integration of optical fiber devices. One promising solution is to integrate diffractive optical microstructures on the end faces of optical fibers. However, rapid microfabrication on such tiny and irregular substrates is a challenge. In recent years, Femtosecond laser polymerization technology has become an effective solution to the challenge, which can be flexibly applied for the fabrication of complex 3D microstructures with ultra-high resolution. When the demand for the lithography resolution is not very high, other microfabrication methods with a lower technical threshold may be developed for achieving a balance between fabrication precision, cost and efficiency. In this paper, we report a Digital Micromirror Device (DMD) based lithography method dedicated to the fabrication of functional optical microstructures on the optical fiber end faces. Especially, it's also applicable to single-mode fibers (SMFs). By the projection via a 40x objective lens, the fabrication resolution of 0.405 μm was achieved within an exposure area of 209.92 μm × 157.44 μm. We evaluated the microfabrication results by the photomicrographs and the optical diffraction modulation effects of the functional optical microstructures. This method provides a new idea for fabricating both hybrid optical fiber devices and SMF devices, and it may be an alternative method for resolving the conflict between the precision, the cost and the efficiency.

(INVITED)Miniaturized lenses integrated on optical fibers: Towards a new milestone along the lab-on-fiber technology roadmap

Optical fibers and lenses are key components in many optical systems. Lenses used to couple light into the fiber or to tailor the output beam coming out from the fiber itself typically involve bulk optical schemes and complex packaging that limit the compactness and flexibility of the overall system. In the last years, new technological solutions based on the lab-on-fiber technology have been proposed to directly integrate optical components on the fiber end-face with a monolithic approach. In this review, we provide a detailed state of the art of the miniaturized lenses integrated on the end-face of optical fibers reported so far. The proposed devices have been divided into three main categories (refractive, diffractive and resonant including metasurfaces) according to their working principle. A critical discussion on the different categories of lenses is given, also providing a comparison in terms of ease of design and fabrication, application flexibility, compactness, scientific and technological maturity, and time to market.

Self-powered and high-performance all-fiber integrated photodetector based on graphene/palladium diselenide heterostructures.

An all-fiber integrated photodetector is proposed and demonstrated by assembling a graphene/palladium diselenide (PdSe2) Van der Waals heterostructure onto the endface of a standard optical fiber. A gold film is covered on the heterostructure working as an electrode and a mirror, which reflects back the unabsorbed residual light for further reusage. Owing to the low bandgap of PdSe2, the all-fiber photodetector shows a broadband photoresponse from 650 to 1550 nm with a high photoresponsivity of 6.68×104 AW-1, enabling a low light detection of 42.5 pW. And the fastest temporal response is about 660 µs. Taking advantage of heterostructures, the photodetector can work in self-powered mode with the on/off ratio about 82. These findings provide new strategies for integrating two-dimensional materials into optical fibers to realize integrated all-fiber devices with multi-function applications.

Mechanical Filter-Based Differential Pressure Fiber-Optic Fabry-Perot Infrasound Sensor

A differential pressure fiber optic infrasound sensor based on a mechanical filter was developed, for the detection of infrasound within the frequency range of 0.01--1 Hz. The sensing unit employs a miniature polyphenylene sulfide (PPS) diaphragm which is fixed onto a glass ferrule. An extrinsic Fabry-Perot (F-P) interferometer was fabricated between the optical fiber end face and the PPS diaphragm, and a mechanical filter structure introduced to improve the minimum detectable frequency down to 0.005 Hz. Experimental results indicate that this infrasound sensor shows a favorable frequency response for infrasound signals between 0.01 and 1 Hz, and it exhibits an average minimum detectable pressure (MDP) of 88.85 mPa·Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1/2</sup> . Our platform provides a promising solution for sensors in infrasound signal detection applications.

Intelligent Electrospun Thermochromic Composite Nanofibers for Temperature Measurements

Thermochromic nanofibers (NFs) have emerged as an important class of nanostructured materials and have found a broad range of technologic applications. Herein, an optical fiber temperature sensor composed of coating electrospun thermochromic NFs on the end-face of fiber is reported. A composite coating consisting of an aqueous dispersion of a thermochromic material (cobalt-doped zinc phosphate or also called cobalt-doped hopeite -CoHo), in polyglycerol dendrimer (PGD), was directly electrospun onto the end-face surface of multimode optical fiber for the fabrication of temperature optical fiber sensor. Morphological features and optical properties of the resulting electrospun CoHo:PGD NFs were assessed. The diameter of the electrospun CoHo:PGDNFs deposited on the end-face of optical fiber was 500 ± 14 nm. The spectroscopic absorption of the electrospun CoHo:PGDNFs at 630 nm is measured to determine their relationship with temperature. The results under variable temperature from 25 to 250 °C indicate good linearity and show the potential of using CoHo:PGDNFs sensing applications for control in industrial processes that require a steady or changing temperature. To extract the chromaticity profile of the CoHo:PGDNFs and their temperature dependence, a multilayer feed-forward artificial neural network (ANN) was used. ANN has been successfully employed to extract temperature information from the chromatic changes of CoHo:PGDNFs.

Deep Learning Based Automated Inspection of Weak Microscratches in Optical Fiber Connector End-Face

Surface defects on optical fiber end-face, such as scratches, cause heavy loss and low data-transfer rate. Therefore, the inspection of optical fiber end-face defect cannot be neglected. Most optical fiber defect detection methods ignore the striped pattern of scratches and easily cause incomplete segmentation. In this article, a novel method based on deep convolutional neural networks (DCNNs) for weak microscratches inspection in the optical fiber end-face is proposed. First, a new feature pyramid structure with criss-cross max-pooling (CCMP) block is developed to extract precise boundary features in all directions and generate feature maps. Second, these feature maps are fed into the spatial attention upsample (SAU) module to recover a full-resolution feature map and localize the defects. Finally, multiple scratches with various types can be detected in the images. This article uses many real optical fiber images as experimental images. The experimental results demonstrate that the proposed method yields good comprehensive performance with a mean pixel accuracy (mPA) of 92.70% and a mean intersection over union (mIoU) of 85.35%.

Reflective Highly Sensitive Fabry–Perot Magnetic Field Sensor Based on Magneto-Volume Effect of Magnetic Fluid

A magnetic field measurement method based on the magneto-volume effect of magnetic fluid (MF) and Fabry-Perot (FP) interferometer (FPI) is proposed, which has higher magnetic field sensitivity and shorter response time than the traditional optical fiber methods. The MF is partially injected into the fabricated FP cavity composed of two sections of SMFs and a capillary glass tube (CGT), where the FPI is made up of optical fiber end face and MF end face. When the external magnetic field is applied to the sensor, the volume change of MF will cause the change of air cavity length. Therefore, the reflection spectrum changes with external magnetic field due to the magneto-volume effect of MF. Experimental results show that the magnetic field sensor shows a sensitivity of 268.81 pm/Gs from 15.5 to 139.7 Gs even with a small amount of MF. The response time is 0.2 s at a step magnetic field of 7.7, 31.0, 46.5, and 139.7 Gs. In this work, the magnetic field sensor boasts high sensitivity, good repeatability, short response time, and low cost, which shows a great potential in applications.

Thermo-mechanical dynamics of nanoimprinting anti-reflective structures onto small-core mid-IR chalcogenide fibers [Invited

Thermal nanoimprinting is a fast and versatile method for transferring the anti-reflective properties of subwavelength nanostructures onto the surface of highly reflective substrates, such as chalcogenide glass optical fiber end faces. In this paper, the technique is explored experimentally on a range of different types of commercial and custom-drawn optical fibers to evaluate the influence of geometric design, core/cladding material, and thermo-mechanical properties. Up to 32.4% increased transmission and 88.3% total transmission are demonstrated in the 2–4.3 µm band using a mid-infrared (IR) supercontinuum laser.

An optic-fiber graphene field effect transistor biosensor for the detection of single-stranded DNA.

Herein, a graphene field effect transistor (GFET) was constructed on an optic fiber end face to develop an integrated optical/electrical double read-out biosensor, which was used to detect target single-stranded DNA (tDNA). Two isolated Au electrodes were, respectively, prepared as the drain and source at the ends of an optic fiber and coated with a graphene film to construct a field effect transistor (FET). Probe aptamers modified with fluorophore 6'-carboxy-fluorescein (6'-FAM) were immobilized on the graphene for specific capture of tDNA. Graphene oxide (GO) was introduced to quench 6'-FAM and construct a fluorescence biosensor. Thus, a dual GFET and fluorescence biosensor was integrated on the end-face of an optic fiber. Following synchronous detection by fluorescence and FET methods, results showed satisfactory sensitivity for DNA detection. Compared with conventional biosensors using a single sensing technology, these dual sensing integrated biosensors significantly improved the reliability and accuracy of DNA detection. Furthermore, this proposed technique provides both a new biosensor for single-stranded DNA detection and a strategy for designing multi-sensing integrated biosensors.

Continuous and Accurate Blood Pressure Monitoring Based on Wearable Optical Fiber Wristband

Continuous monitoring of blood pressure has significant clinical value for the cardiovascular disease prevention and diagnosis in daily life. However, conventional blood pressure measurement is unsuitable for long-term monitoring due to its discomfort and poor portability. Wearable device is an ideal solution to overcome this problem, which has attracted increasing interests of many researchers. While, high-performance wearable blood pressure sensor still remains a challenge. Here, we present a wearable blood pressure wristband system based on optical fiber. The end face of optical fiber was coated with a Polydimethylsiloxane (PDMS) + Ag composite diaphragm. The continuous and accurate measurement of the pulse waveform was achieved through the phase variation of the light reflected from the diaphragm. Then, the blood pressure can be estimated from the pulse transit time (PTT) which is extracted from the high-fidelity pulse waveform. The estimation model was established using data from 45 subjects. The clinical experiment was also carried out on 17 subjects to test the performance of the proposed wearable blood pressure wristband. The results show that the errors of systolic pressure (SBP) and diastolic pressure (DBP) are 0.24 ± 2.39 mmHg and 0.12 ± 2.62 mmHg compared with commercial sphygmomanometer, respectively. The measurement errors were within the required range of the Association for the Advancement of Medical Instrumentation (AAMI) and the British Hypertension Society (BHS) Grade A, which indicates that the blood pressure wristband has a good accuracy and practicability. This wearable and user-friendly optical fiber blood pressure monitor is a competitive alternative to current commercial products.

Resist-free nanoimprinting on optical fibers for plasmonic optrodes

Nanostructure patterning on optical fibers enables miniaturized optrodes for photonic and plasmonic applications. Here we report a direct nanoimprint technique to produce high-quality nanostructure arrays on optical fiber endfaces. It has only one single step: imprinting optical fiber tips against a mold with nanostructures at the elevated temperature. This new method abandons resist used in traditional fiber-imprinting methods. Hundreds of fibers can be shaped simultaneously with one mold within minutes. The imprinted nanostructure arrays on optical fibers are transformed into plasmonic optrodes through metal deposition. Variation of imprint depths and mold patterns allows tailoring of the plasmonic resonances of these nanostructure arrays for high-performance refractometric sensing and on-fiber polarization. The sensitivity of 690 nm/RIU and figure of merit of 50 are both among the highest values for similar plasmonic nanostructure arrays. This resist-free nanoimprint paves the way towards a low-cost and high-throughput realization of plasmonic optrodes and their wide applications.

Ultracompact optical fiber acoustic sensors based on a fiber-top spirally-suspended optomechanical microresonator.

Acoustic wave sensors with a high sensitivity and small size are highly desired for a wide variety of important and emerging applications such as photoacoustic gas sensing and bio-imaging. Here we present an ultracompact optical fiber acoustic sensor based on an optomechanical resonator that is directly in situ printed on the end face of a standard single-mode optical fiber by using an optical 3D μ-printing technology. The fiber-top optomechanical microresonator is composed of a microscale suspended polymer micro-disk that forms a Fabry-Perot interferometric cavity, together with the optical fiber end face, and acts as the acoustic wave-sensitive micromechanical resonator simultaneously. The microbeams for suspending the micro-disk are devised with a spiral structure to overcome the small-size imposed low deflection amplitude so as to improve its sensitivity to acoustic waves. The sensor with a high sensitivity of 118.3 mV/Pa and low noise equivalent acoustic signal level of 0.328µPa/Hz1/2 at audio frequency is experimentally demonstrated. Moreover, with a resonance amplification mechanism, the sensitivity can be enhanced by 40.1 times when the frequency of the acoustic wave matches with the natural resonance frequency of the optomechanical resonator. Such an ultrasmall fiber-tip acoustic sensor has not only a miniaturization-induced broad bandwidth, but also a structure-enhanced ultrahigh sensitivity and thus is very promising in various acoustic wave-based sensing, imaging, and testing applications.

Electrochemical plasmonic optical fiber probe for real-time insight into coreactant electrochemiluminescence

Electrochemical surface plasmon resonance (ESPR) is a powerful technique for defining dynamic changes in chemical composition and morphology of functional interfaces by correlating spectral information with voltammetric characteristics of the electrode processes. However, conventional Kretschmann prism-based surface plasmon resonance (SPR) configurations require sophisticated apparatus and complex optics. Here, we present a versatile flow injection ESPR device that incorporates a plasmonic and conductive fiber optic probe, for which a gold nanohole array film is integrated onto the endface of a conventional optical fiber via template transfer. The coreactant-based Ru(bpy)32+ / tripropylamine (TPrA) electrochemiluminescence (ECL) system, was chosen to unravel electrochemically-induced real-time interfacial information, since such an approach is increasingly employed for clinical assay analysis and the associated ECL mechanism is an active area of investigation. The ESPR observations provide novel experimental evidence to support the proposition that the ECL reactions undergo an oxidative-reduction pathway. Moreover, the ESPR peak shift exhibits a broader linear detection range of TPrA concentration (0.02–20 mmol L−1, R2 = 0.996), compared to the ECL and SPR techniques (<10 mmol L−1). This study clearly demonstrates that the novel fiber optic ESPR device presents as a reliable and multimodal spectroelectrochemical platform to gain mechanistic insights into complicated chemical processes and provide sensing capabilities, while offering great simplicity, portability and miniaturization.

Compact plasmonic fiber tip for sensitive and fast humidity and human breath monitoring.

We demonstrate a plasmonic fiber tip for relative humidity (RH) detection by integrating a gold nanomembrane onto the end-face of a multimode optical fiber via a flexible and high-efficiency transfer method. Fast water condensation/evaporation is responsible for the high performance of the fiber tip in response to RH. A high sensitivity of 279 pm/%RH is obtained in the range of $ 11\% \sim 92\% {\rm RH} $11%∼92%RH. Taking advantage of the fast dynamics (response and recovery times of 156 ms and 277 ms), the plasmonic fiber tip offers an excellent detection capability to human breaths at varied frequencies and depths. The compact, easy-fabrication, and fast-dynamics plasmonic platform has versatile potential for practical applications, including environmental and healthcare monitoring, as well as biochemical sensing.

Micro-nano structure transfer method of optical fiber end face based on PDMS

微纳光纤传感器将微纳加工与光纤传感技术有机结合，具有重大的科研意义和产业化潜力。现有加工方法无法达到任意复杂三维结构可制备化，从而限制了微纳光纤传感器的发展。介绍了一种新型微纳加工方法，该方法在聚二甲基硅氧烷（PDMS）薄膜上实现微纳结构的制备，之后将薄膜连同微纳结构一同转移到光纤端面，在光纤端面实现人为定义三维立体微纳结构。通过在扫描电镜下对制备的样品进行检测，确认PDMS薄膜及其上三维结构可被无损转移至光纤端面。该方法具有易制备、低成本且可加工三维微纳结构的特点。

Orbital angular momentum mode of cylindrical spiral wave-guide

The common feature of traditional methods of preparing orbital angular momentum (OAM) light beams propagating along the &lt;i&gt;z&lt;/i&gt; axis is that the wave-front phase is changed and the chief ray of beam is basically unchanged. But it is difficult to obtain a high &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}$m\hbar $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20190997_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20190997_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; OAM. To solve the above problem, we establish a theoretical framework based on the change of the chief ray of beam instead of the change of wave-front phase. The differential geometry theory is used to verify the theoretical assumption that the light transmitted by the cylindrical spiral wave-guide can carry high &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$m\hbar $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20190997_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20190997_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; OAM. To measure the OAM optical fiber output, we use the diffraction method to detect the phase of vortex, that is, we can use a microscope to observe the phase distribution of optical fiber end face. We consider the output of linearly polarized light along the tangent direction of the fiber to observe its diffraction pattern. The transmission of optical fiber around the cylinder is the main light. The diameter of optical fiber is constant, and the light wave transmitting into the optical fiber is Bessel beam. For the linear fiber output, we need to consider only the linear fiber Bessel beam. The output cross section of the wave surface in the fiber is approximately that of plane wave. When &lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}$\theta &gt; {\theta _0}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20190997_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20190997_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, we use the flow coordinates &lt;inline-formula&gt;&lt;tex-math id="M8"&gt;\begin{document}$(\alpha,\beta, \gamma)$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20190997_M8.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20190997_M8.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; to calculate the diffraction pattern of the cross section of the optical fiber when light travels in the optical fiber around the cylinder, which shows the characteristics of vortex. The optical field distribution carries a high-order OAM mode. When &lt;inline-formula&gt;&lt;tex-math id="M9"&gt;\begin{document}$\theta = {\theta _0}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20190997_M9.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20190997_M9.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, cylindrical orbital optical fibers transit to linear orbital optical fibers. We calculate the diffraction pattern of the cross section of the optical fibers propagating in a straight line. It is an Airy spot, namely a circular aperture diffraction spot. The optical field distribution has no higher-order OAM mode. When the order of the output beam is small, the output shows certain uniformity and symmetry, when the order of the output beam increases gradually, the output beam shows some inhomogeneity and asymmetry.

Interference-Type High-Sensitivity Temperature Sensor Based on the Photosensitive Fiber Microsphere

A high sensitive temperature sensor based on photosensitive optical fiber is proposed in order to detect the special environment temperature in real time. After cutting the end faces of a single-mode fiber and a photosensitive fiber (PF) into flat, put them into a fiber fusion machine for manual discharging. Because of the tension effect of the fiber surface, an optical fiber end face will be fused into an optical fiber microsphere at the moment of discharging, and then two optical fiber microspheres will be fused into an optical fiber peanut structure through manual discharging. The optical fiber peanut structure has the same functions as fiber beam splitter and combiner in an interferometer. Considering that the refractive index of the core and cladding of the PF is different, result in the difference of optical paths propagating between in the core and in the cladding, which causes that the interference will occur when the two beams are coupled. While boron and germanium are doped in the core of the PF, the thermo-optical coefficient and thermal expansion coefficient of the core increase. When the ambient temperature changes, the interference spectrum will drift. Experimental results show that, in the temperature range of 45 °C;-65 °C;, the sensor sensitivity is -386.96 pm/°C, and the linear fitting degree is 99.76%. The sensor has the advantages of high sensitivity, fast response and simple fabrication process. In addition, it has a certain application prospect in marine environmental measurement and in other fields.

Artificial compound eye-tipped optical fiber for wide field illumination.

In this Letter, we present a novel, to the best of our knowledge, component with beam delivering and wide field beam homogenizing functions by grafting an artificial compound eye (ACE) micro-structure onto the polymer optical fiber (POF) end face. The 3D ACE mold is fabricated by femtosecond laser-assisted micro machining, and the ACE micro-structure is transferred onto the end face through high accuracy nano-imprinting. The resultant POF end face integrates over 400 spherical micro-lenses, enabling a 40% enhancement in both the acceptance angle and the effective numerical aperture. Meanwhile, the integrated ommatidia array serves as an outstanding beam homogenizer, shaping the output beam into quasi flat-top distribution, which demonstrates promise in wide field homogeneous illumination, by reflection and transmission imaging experiments in both visible and near infrared bands.