Bending Loss Of Fiber Research Articles

Noninvasive high-resolution deep-brain photoacoustic imaging with a negatively focused fiber-laser ultrasound transducer

Noninvasive high-resolution deep-brain imaging is essential to fundamental cognitive process study and neuroprotective drugs development. Although optical microscopes can resolve fine biological structures with good contrast without exposure to ionizing radiation or a strong magnetic field, the optical scattering limits the penetration depth and hinders its capability for deep-brain imaging. Here, in vivo high-resolution imaging of the whole mouse brain is demonstrated by using a photoacoustic computed tomography system with a negatively focused fiber-laser ultrasound transducer. By leveraging the high flexibility and low bending loss of the optical fiber, a rationally designed negatively focused fiber laser cavity exhibits a low detection limit down to 5.4 Pa and a broad view angle of ∼120 deg, enabling mouse brain imaging with a penetration larger than 7 mm and a nearly isotropic spatial resolution of ∼130 μm. In addition, the negative curvature of the fiber laser reduces the working distance, which facilitates the development of a compact and portable linear scanning imaging system. In vivo imaging of a mouse model with intracerebral hemorrhage is also showcased to demonstrate its capability for potential biomedical and clinical applications. With high spatial resolution and large tissue penetration, the system may provide a noninvasive, user-friendly, and high-performance imaging solution for biomedical research and preclinical/clinical diagnosis.

Deep Learning-Based Simultaneous Temperature- and Curvature-Sensitive Scatterplot Recognition.

Since light propagation in a multimode fiber (MMF) exhibits visually random and complex scattering patterns due to external interference, this study numerically models temperature and curvature through the finite element method in order to understand the complex interactions between the inputs and outputs of an optical fiber under conditions of temperature and curvature interference. The systematic analysis of the fiber's refractive index and bending loss characteristics determined its critical bending radius to be 15 mm. The temperature speckle atlas is plotted to reflect varying bending radii. An optimal end-to-end residual neural network model capable of automatically extracting highly similar scattering features is proposed and validated for the purpose of identifying temperature and curvature scattering maps of MMFs. The viability of the proposed scheme is tested through numerical simulations and experiments, the results of which demonstrate the effectiveness and robustness of the optimized network model.

Anti-Resonant Hollow-Core Fibers with High Birefringence and Low Loss for Terahertz Propagation

A new type of anti-resonant hollow-core fiber for terahertz waveguides is proposed. By introducing central support pillars and an elliptical structure, the fiber achieves high birefringence while maintaining low confinement loss and low material absorption loss. The fiber structure is optimized through simulation using the finite element method. The optimized fiber exhibits a birefringence of up to 1.22 × 10−2 at a frequency of 1 THz, with a confinement loss of 8.34 × 10−6 dB/cm and a material absorption loss of 7.17 × 10−3 dB/cm. Furthermore, when the bending radius of the fiber is greater than 12 cm, the bending loss of the anti-resonant optical fiber at 1 THz is less than 1.36 × 10−4 dB/cm, demonstrating good bending resistance and high practical value. It is expected to play a significant role in optical communication systems.

중요 시설물 감시용 광센서 시스템 구성 및 감시기법 연구

A buried optical fiber sensor that can be detected over a large area per unit length was designed and manufactured, and study was conducted on the signal characteristics according to the load of an external intrusion object. The optical fiber used was designed and manufactured for external intrusion detection that generated bending loss of the optical fiber using a single mode optical fiber for general optical communication with a length of 4 km. This study investigated the change in the output of the optical fiber sensor and the change in the sensor output signal and detection signal owing to the invasion of external intruders according to the width of the pulse pumping light. Therefore, when changing the width of the pulse pumping light, the minimum detectable conditions according to the detection of external intruders were investigated. Finally, a monitoring technique was presented by developing a signal processing algorithm for an optical fiber sensor.

Optoelectronic Pressure Sensor Based on the Bending Loss of Plastic Optical Fibers Embedded in Stretchable Polydimethylsiloxane.

We report the design and testing of a sensor pad based on optical and flexible materials for the development of pressure monitoring devices. This project aims to create a flexible and low-cost pressure sensor based on a two-dimensional grid of plastic optical fibers embedded in a pad of flexible and stretchable polydimethylsiloxane (PDMS). The opposite ends of each fiber are connected to an LED and a photodiode, respectively, to excite and measure light intensity changes due to the local bending of the pressure points on the PDMS pad. Tests were performed in order to study the sensitivity and repeatability of the designed flexible pressure sensor.

OTDR-based optical fiber bending and tensile loss analysis

OTDR-based optical fiber bending and tensile loss analysis

Refractive index profiles and propagation losses in bent optical fibers

A better understanding of stress effects that affect the bending losses in active and passive optical fibers allows us to improve fiber system designs and helps to optimize refractive index profiles in high power, large mode area laser fibers. Bending an optical fiber affects the light in a fiber core by two different phenomena. First, the curved shape of the waveguide changes the light propagation. The second phenomenon is the refractive index change caused by the mechanical stress in a bent optical fiber. The refractive index changes due to bending stresses are estimated by the elasto-optic and stress-optic models. The light propagation in a curved waveguide can be modeled by applying the electromagnetic wave theory together with the conformally transformed refractive index profiles that include the stress effects. The modeled refractive index profiles that include the bending stress-induced index changes are compared with the refractive index profiles that were measured from actual bent optical fibers. We tested if this comparison would allow us to estimate stress-optic coefficient C2 values in stress-optic model. Measured bend loss values are compared to the bend loss values simulated with the modeled refractive index profiles.

Multi-mode step graded index fibers performance parameters (attenuation/dispersion/mode field) measurements by using OptiFiber simulation

Abstract This paper has clarified the positive and negative effects of 3.1% germania and 1% fluorine DS fibers in multi-mode silica profile. The group delay and the total fiber dispersion against operating wavelength for PS and various doped silica (DS) fibers are demonstrated and assured by using OptiFiber simulation. The material, waveguide and total fiber dispersions are demonstrated against wavelength for the PS fiber, 3.1% germania DS (GDS) fiber and 1% fluorine DS (FDS) fiber. Besides the mode field diameter, fiber material loss, fiber bending loss and the dispersion group delay are simulated and clarified against the operating wavelength for PS and different DS fibers. The study gives the effects of the dopant ratio of germania and fluorine on the zero dispersion wavelength shift and DS.

Multi-channel curvature sensor based on fiber bending loss wavelength and SPR.

Fiber Bragg gratings and interferometric curvature sensors are easily disturbed by axial strain and temperature, and cascaded multi-channel curvature sensing is difficult. In this letter, a curvature sensor based on fiber bending loss wavelength and the surface plasmon resonance (SPR) mechanism is proposed, which is insensitive to axial strain and temperature. In addition, fiber bending loss valley wavelength demodulation curvature improves the accuracy of bending loss intensity sensing. Experiments show that the bending loss valley of single-mode fiber with different cut-off wavelengths has different working bands which is combined with a plastic-clad multi-mode fiber SPR curvature sensor to realize a wavelength division multiplexing multi-channel curvature sensor. The bending loss valley wavelength sensitivity of single-mode fiber is 0.8474 nm/m-1, and the intensity sensitivity is 0.0036 a.u./m-1. The resonance valley wavelength sensitivity of the multi-mode fiber SPR curvature sensor is 0.3348 nm/m-1, and the intensity sensitivity is 0.0026 a.u./m-1. The proposed sensor is insensitive to temperature and strain, and the working band is controllable, which provides a new, to the best of our knowledge, solution for wavelength division multiplexing multi-channel fiber curvature sensing.

Polarization-Maintaining Performance of Solid-Core Anti-Resonant Fiber With Nested Circular Tubes in 3 μm Wavelength

We present the structural design and polarization-maintaining performance of solid-core anti-resonant fiber with two nested circular tubes in 3 μm wavelength for the first time, to the best of our knowledge. Numerical simulation results indicated that laser fundamental mode could be obtained by filling the specially designed fiber model with materials of different refractive indices to form the completely solid configuration. We calculated the bend loss of fiber to demonstrate the preferable birefringence performance and outstanding light-confining ability. With the structural deformations from resonant tubes, the birefringence coefficient was enhanced significantly from 2 × 10^−5 to 6.93 × 10^−5, which was of great importance in the polarization sensitive systems. In particular, when nested circular tubes were moved to introduce deformations, the confined loss difference in two orthogonal polarizations was calculated more than two orders of magnitude, which was the desirable result to promote the fabrication of the linear polarizer in 3 μm wavelength.

Experimental investigation on performance monitoring of the combined optical fiber transducer in landslide

An innovative combined optical fiber transducer (COFT) based on the optical fiber bending loss characteristic has been developed for landslide monitoring. To better understand the working principle and improve the monitoring performance of the transducer, the capability of the COFT for exploring subsurface properties of slopes (sliding direction, magnitude, and rate of slope movement) and the deformation compatibility between the COFT and surrounding geo-materials were explained semi-empirically and semi-theoretically, which was also verified by the laboratory shear experiments of the COFTs constructed with two kinds of host materials (expanded polystyrene and polyvinyl chloride) and three kinds ratios of cement mortars (sand to cement 1:4, 1:5, and 1:6) and the related numerical simulation. In the following, model monitoring tests of an artificial slope and field monitoring application of the proposed COFTs in a field slope were carried out and the progressive slope movements were effectively determined, which validated the performance of the proposed COFT in landslide monitoring.

Experimental research on a novel spring-shaped fiber-optic displacement sensor for settlement monitoring

In this paper an innovative spring-shaped fiber-optic displacement sensor (SSFODS) based on optical time domain reflectometer (OTDR) technology with simple construction and cheap cost was proposed for subgrade settlement monitoring. The sensor incorporated a simple spring-shaped fiber bending modulation that increased its sensitivity in bending, light source and detector. The sensing principle between the measured external displacement and bending loss of optical fiber was theoretically explained and its expression was also derived. Sensor calibration was conducted, which showed that the SSFODS was characterized by a large measurement range of 90 mm, minimum displacement resolution of 0.173 mm, maximum hysteresis error of 2.81% and maximum repeatability error of 8.42%, respectively. A soil drainage model test with the SSFODS was performed to study its performance in determining compression deformation of the soil. At last, a simple field monitoring application with two SSFODSs connected in series was conducted and the progressive compaction behavior of the fill slope was accurately captured by two SSFODSs. Additionally, it is possible to connect these SSFODSs in series on one optical link to realize quasi-distributed sensing monitoring. This capability supports a promising application of the sensor in geotechnical engineering for real-time monitoring of the stability of fill slopes, foundation pits and so on.

A Novel Force Sensor Based on Optical Fibers Used for Semicircular Flexure Beam Unit

In this article, a novel force sensor is designed based on the optical fiber bending loss theory utilizing a structure with periodically corrugated semicircular flexure beam units. The fiber bending loss theory composed of the pure bending loss and the transition loss is related to the curvature radius according to the theoretical analysis. Both the optical working modes and the mechanical properties of the designed sensor are discussed. The output voltage attenuation of different curvature radii is tested and the curvature radius of 6 mm is selected for further experiment. The actual sensing results are acquired using a commercial force sensor. The result shows that the nonlinear errors of the forward and the reverse force applying process are 11.82% and 17.86%, respectively. The sensitivity is 13 mV/N and the precision is 160 mN. The experiment under different temperatures ensures the temperature-insensitive characteristics of the sensor.

Design, sensing principle and testing of a novel fiber optic displacement sensor based on linear macro-bending loss

This paper presents a linear fiber optic displacement sensor for the use over a large range based on the macro-bending loss. The sensor incorporates an extremely simple design, light source and detector. A concentric gear shaft is used to bend the fiber and transfer the displacement. The linear relationship between the measured displacement and the bending loss of optical fiber was proved theoretically and its expression was derived. A series of calibration experiments and performance tests were conducted. The experimental results show that the sensor was characterized by a wide measurement range, a high sensitivity and a minimum displacement resolution of 0–200 mm, 0.1668 dB/mm and 0.06 mm, respectively. The stability and repeatability of the sensor was verified by repetitive testes with a maximum measurement deviation of 0.162 mm. The predicted displacements of the sensor were similar to the actual values, and the difference errors of all samples are basically within 10%. These characteristics demonstrate that the sensor can be used for displacement monitoring for large-scale civil structures and has a promising prospect.

Bend loss fiber optics design based on sinusoidal and ellipse configurations

Bending losses in optical fibers comprise one of the extrinsic attenuations that contribute to optical loss and they are essential for optical fiber bending sensor applications. This work investigated the optical loss in a standard single-mode step-index fiber optics due to fiber bending at 1550 nm wavelength. Variations in macro-bending loss with curvature radius and turn number have been measured. Curvature radius and turn number are examined for sinusoidal and elliptical shaped bending configurations. It has been found that the loss increases as the bending radius and number of turns increase. The result also showed that elliptical shaped bending configuration produced more loss in contrast to that of sinusoidal shaped at bending angles of 180° and 360°. The study on the macro-bending loss in terms of curvature radius and turn number for both elliptical and sinusoidal shaped bending configurations is beneficial for future fiber optic sensor applications.

Application and analysis of three-layer-core structure in single-mode large-mode-area fiber with low bending loss

A three-layer-core single-mode large-mode-area fiber with low bending loss is investigated in this paper. The three-layer structure in the core which is comprised of core-index layer, cladding-index layer and depression-index layer, can achieve large-effective-area Aeff while maintaining low-bending-loss without deteriorating cutoff behaviors. The large-mode-area of 100–330 μm<sup>2</sup> can be achieved in the fiber. The effective area Aeff can be further enlarged by adjusting the layer parameters. Furthermore, the bending property can be improved in this three-layer-core structure. The bending loss can decrease by 2–4 orders of magnitude compared with the bending loss of the conventional step-index fiber with the same Aeff. These characteristics of three-layer-core fiber suggest that it can be used in large-mode-area wide-bandwidth high-capacity transmission, or high-power optical fiber laser and amplifier in the optical communications, which can be conducive to studying the basic physical layer structure of big data storage, reading, calculation and transmission applications and so on.

Dispersion-limited versus power-limited terahertz communication links using solid core subwavelength dielectric fibers

Terahertz (THz) band (0.1–10 THz) is the next frontier for ultra-high-speed communication systems. Currently, most of communications research in this spectral range is focused on wireless systems, while waveguide/fiber-based links have been less explored. Although free space communications have several advantages such as convenience in mobility for the end user, as well as easier multi-device interconnectivity in simple environments, fiber-based communications provide superior performance in certain short-range communication applications such as multi-device connectivity in complex geometrical environments (ex., intra-vehicle connectivity) and secure communications with low probability of eavesdropping, as well as secure signal delivery to hard-to-reach or highly protected environments. In this work, we present an in-depth experimental and numerical study of the short-range THz communications links that use subwavelength dielectric fibers for information transmission and define the main challenges and trade-offs in the link implementation. Particularly, we use air or foam-cladded polypropylene-core subwavelength dielectric THz fibers of various diameters (0.57–1.75 mm) to study link performance as a function of the link length of up to ∼ 10 m , and data bit rates of up to 6 Gbps at the carrier frequency of 128 GHz (2.34 mm wavelength). We find that depending on the fiber diameter, the quality of the transmitted signal is mostly limited either by the modal propagation loss or by the fiber velocity dispersion (GVD). An error-free transmission over 10 m is achieved for the bit rate of 4 Gbps using the fiber of smaller 0.57 mm diameter. Furthermore, since the fields of subwavelength fibers are weakly confined and extend deep into the air cladding, we study the modal field extent outside of the fiber core, as well as fiber bending loss. Finally, the power budget of the rod-in-air subwavelength THz fiber-based links is compared to that of free space communication links, and we demonstrate that fiber links offer an excellent solution for various short-range applications.

Recent Advances and Tendency in Fiber Bragg Grating-Based Vibration Sensor: A Review

Vibration sensing is critical to monitor and ultimately preserve the health state of engineering systems. These systems with a large structure are typically working in some harsh environments including strong magnetic fields. However, traditional electrical sensors are difficult to accurately measure the vibration under harsh environments. Besides these instinct advantages of normal fiber optic sensors (FOS) sensors such as compact size, passive sensing, resistance to electromagnetic interference, etc., fiber Bragg grating (FBG) sensors have a capability of distributed sensing based on wavelength demodulation and resistance to light intensity fluctuation and unwanted fiber bending losses. Such merits lead them to be a hot topic in FOS field and excellent candidates for vibration sensing. Three types of FBG-based vibration sensors have been classified based on the difference of vibration-strain coupling way to FBG in this survey, which are pasted FBG-based, axial property of FBG-based and transverse property of FBG-based, respectively. FBG-based vibration sensors' principles and designs have been introduced and discussed. Recent advances in the applications of FBG-based vibration sensors have been investigated. The limitations and prospects of the FBG-based vibration sensing technologies have been analyzed and discussed.

Low-Cost Coil-Shaped Optical Fiber Displacement Sensor for a Twisted and Coiled Polymer Fiber Actuator Unit

This study proposes a low-cost coil-shaped optical fiber (COF) sensor that can be used in the twisted and coiled polymer fiber (TCPF) actuator unit. The TCPF is a thermal-driven artificial muscle with large stroke and large power ratio. To improve its response, several actuator units, which combine the TCPF with a cooling system, were developed. However, the displacement sensors for these units were not established, unlike the encoder for the motor. Although several methods are available to estimate the TCPF displacement, they are based on the resistance of the heating wire and are affected by TCPF actuation and load change. Therefore, to accurately measure displacement, in this study, we focus on the bending loss of optical fiber, which is often used in soft robotics. Because the bending loss of COFs is caused by the change in length of the coil, the displacement can be obtained by measuring the light intensity through the optical fiber. This study experimentally demonstrates that the COF is available, even when driving the TCPF actuator and changing the load.

A U-shaped-wound fiber macro-bending loss crack sensor improved by an optical splitter

Abstract In traditional fiber macro-bending loss crack sensors, temperature can affect the light source and the fiber link between the light source and the optical splitter, thereby reducing the measurement accuracy of the sensor. In this study, by combining a U-shaped-wound fiber bending loss crack sensor and an optical splitter on the fiber link, we reduce the effect of temperature on the light source and the fiber link. Furthermore, the sensing mechanism of the improved fiber crack sensor is analyzed. Additionally, a comparison between the U-shaped-wound sensor and a butterfly-shaped sensor is carried out to compare both fiber crack sensors. The experimental results indicate that the optical splitter efficiently reduce the effect of temperature on the light source and the fiber link between the light source and the optical splitter and the U-shaped-wound fiber bending loss crack sensor has a better measurement accuracy.