Loss Optical Fibers Research Articles

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.

Improved evaluation model for macro-bending loss and power variation in single-mode fiber

It is challenging to calculate the macro-bending loss of optical fiber when the bending radius is reduced to sub-millimeter levels, based on Marcuse's theory and its derivative theories. Furthermore, these theories are limited in their ability to assess the distribution and changes of the optical field within the fiber, focusing solely on the analysis of loss. To overcome these limitations, we proposed an evaluation model which can simultaneously provide results for both macro-bending loss and power variation in a bent single-mode fiber. Our model achieves this by conformally transforming the fiber's refractive index profile of the axis section according to the bending radius. The ratio of output power to input power exhibits oscillation with changes in the bending radius, thereby resolving the issue of inability of Marcuse's theory to obtain an oscillation loss curve for sub-millimeter bending radii. The proposed model was validated by finite element method. We also obtained the internal power variation along the axial distance of the bent fiber through this model. This research improves the current fiber macro-bending loss evaluation model and lays a foundation for further studies on bend-insensitive fibers and the design of sub-millimeter bending sensors.

Intelligent Improvement Techniques for Fiber Optic Losses

The optical fiber systems have grown in response to the increasing demand for ultra-high-speed data transmission in fiber telecommunications system. Yet, the problem of the losses in optical fiber has limited the fiber system performance such as, dispersion, dispersion slope, and non linearities. This study proposes a mitigation techniques for fiber-optic system losses based on artificial intelligent algorithms. In this study, the proposed method produces a good system performance with maximum compensation for fiber linear and nonlinear losses.

Radiation Monitoring with Radiosensitive Pure-Silica Core Ultra-Low Loss Optical Fiber

Radiation Monitoring with Radiosensitive Pure-Silica Core Ultra-Low Loss Optical Fiber

Evaluation of in-situ optical loss of polyimide-coated optical fiber under hydrothermal environments

When distributed fiber optic sensing (DFOS) devices are deployed in a geothermal borehole, the optical fiber as the key element, must be able to withstand the harsh environment because the temperature of the geothermal boreholes is higher than 250 °C in most cases. Understanding the deterioration behavior of optical fibers in hydrothermal conditions higher than 250 °C is important for predicting the lifetimes of DFOSs in operation.Geophysical equipment using optical fiber sensing was developed for in-situ measurement of the optical loss of optical fibers under hydrothermal conditions, and a survey method was established. Using this optical fiber sensing, we characterized the deterioration behavior of single-mode polyimide-coated optical fibers. Our experiments with carbon / polyimide-coated fibers under subcritical water from 250 to 350 °C revealed that the polyimide layer and silica cladding easily dissolved in water in that environment.

Embedding Fiber Bragg Grating Sensors in Carbon Composite Structures for Accurate Strain Measurement

Fiber Bragg Grating (FBG) sensors written by femtosecond laser pulses in polyamide-coated low bending loss optical fibers are succesfully embedded in carbon composite structures, following laminating and light resin moulding processes which optimize the size of each ply to address aesthetic, drapability and structural requirements of the final components. The sensors are interrogated by a tunable laser operating at around 1.55 μm and their response to temperature and strain variations is characterized in a thermally controlled chamber and by bending tests using suspended calibrated loads and a laser scanning system. Experimental results are in good agreement with simulations, confirming that the embedding process effectively overcomes potential issues related to FBG spectral distortion, birefringence and losses. In particular the effects of the composite material non homogeneity and FBG birefringence are investigated to evaluate their impact on the monitoring capabilities. A bi-material mechanical beam model is proposed to characterize the orthotropic laminates, pointing out better accuracy in estimating the applied load with respect to the classical homogeneous beam model. A comparative analysis, performed on different instrumented carbon composite samples and supported by theory, points out the repeatability of the FBG sensors embedding process and the effectiveness of the technology for real time accurate strain measurement. Based on such measurements damages and/or changes in local stiffness can be effectively detected, allowing for structural health monitoring of composite structures for applications in specific industrial fields like automotive and aerospace.

Sensitivity of confinement losses in optical fibers to modeling approach.

A prime objective of modeling optical fibers is capturing mode confinement losses correctly. This paper demonstrates that specific modeling choices, especially regarding the outer fiber cladding regions and the placement of the computational boundary, have significant impacts on the calculated mode losses. This sensitivity of the computed mode losses is especially high for microstructure fibers that do not guide light by total internal reflection. Our results illustrate that one can obtain disparate mode confinement loss profiles for the same optical fiber design simply by moving the boundary to a new material region. We conclude with new recommendations for how to better model these losses.

Disentanglement induced by combined effects of polarization mode dispersion and polarization-dependent loss in optical fibers

Disentanglement induced by combined effects of polarization mode dispersion and polarization-dependent loss in optical fibers

300 km ultralong fiber optic DAS system based on optimally designed bidirectional EDFA relays

Optical fiber distributed acoustic sensing (DAS) based on phase-sensitive optical time domain reflectometry (φ-OTDR) is in great demand in many long-distance application fields, such as railway and pipeline safety monitoring. However, the DAS measurement distance is limited by the transmission loss of optical fiber and ultralow backscattering power. In this paper, a DAS system based on multispan relay amplification is proposed, where the bidirectional erbium-doped fiber amplifier (EDFA) is designed as a relay module to amplify both the probe light and the backscattering light. In the theoretical noise model, the parameters of our system are carefully analyzed and optimized for a longer sensing distance, including the extinction ratio (ER), span number, span length, and gain of erbium-doped fiber amplifiers. The numerical simulation shows that a bidirectional EDFA relay DAS system can detect signals over 2500 km, as long as the span number is set to be more than 100. To verify the effectiveness of the scheme, a six-span coherent-detection-based DAS system with an optimal design was established, where the cascaded acoustic-optic modulators (AOMs) were used for a high ER of 104 dB. The results demonstrate that the signal at the far end of 300.2 km can be detected and recovered, achieving a high signal-to-noise ratio of 59.6 dB and a high strain resolution of 51.8pε/Hz at 50 Hz with a 20 m spatial resolution. This is, to the best of our knowledge, a superior DAS sensing distance with such a high strain resolution.

Assessment of Scattered-Bend Loss in Polymer Optical Fiber (POF) Displacement Sensor

Assessment of Scattered-Bend Loss in Polymer Optical Fiber (POF) Displacement Sensor

Measurement of resonant bend loss in anti-resonant hollow core optical fiber: erratum.

An error on the part of the authors in drafting resulted in Eq.(3) being incorrect in the published paper [Opt. Express25, 20612 (2017)10.1364/OE.25.020612]. We present a corrected version of the equation. It should be noted that this does not affect the presented results or conclusions of the paper.

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.

Anti-icing Performance Evaluation of OPGW Based on BOTDA and OTDR

Under certain icing load, the optical fiber of OPGW is seriously affected by stress, which will not only affect the operation quality of line communication, but also threaten its own and line safety, such as cable breaking, tower falling and other accidents. At present, OTDR is mainly used to test the optical path loss of the optical fiber in the OPGW after icing, but that can’t reflect and judge the damage state of the OPGW accurately. In this paper, a method combining BOTDA and OTDR is proposed to detect the damaged state of OPGW after icing. Based on this, the anti icing performance is divided into healthy state, sub-health state and fault state.

Loss in hollow-core optical fibers: mechanisms, scaling rules, and limits

Over the past few years, progress in hollow-core optical fiber technology has reduced the attenuation of these fibers to levels comparable to those of all-solid silica-core single-mode fibers. The sustained pace of progress in the field has sparked renewed interest in the technology and created the expectation that it will one day enable realization of the most transparent light-propagating waveguides ever produced, across all spectral regions of interest. In this work we review and analyze the various physical mechanisms that drive attenuation in hollow-core optical fibers. We consider both the somewhat legacy hollow-core photonic bandgap technology as well as the more recent antiresonant hollow-core fibers. As both fiber types exploit different guidance mechanisms from that of conventional solid-core fibers to confine light to the central core, their attenuation is also dominated by a different set of physical processes, which we analyze here in detail. First, we discuss intrinsic loss mechanisms in perfect and idealized fibers. These include leakage loss, absorption, and scattering within the gas filling the core or from the glass microstructure surrounding it, and roughness scattering from the air–glass interfaces within the fibers. The latter contribution is analyzed rigorously, clarifying inaccuracies in the literature that often led to the use of inadequate scaling rules. We then explore the extrinsic contributions to loss and discuss the effect of random microbends as well as that of other perturbations and non-uniformities that may result from imperfections in the fabrication process. These effects impact the loss of the fiber predominantly by scattering light from the fundamental mode into lossier higher-order modes and cladding modes. Although these contributions have often been neglected, their role becomes increasingly important in the context of producing, one day, hollow-core fibers with sub-0.1-dB/km loss and a pure single-mode guidance. Finally, we present general scaling rules for all the loss mechanisms mentioned previously and combine them to examine the performance of recently reported fibers. We lay some general guidelines for the design of low-loss hollow-core fibers operating at different spectral regions and conclude the paper with a brief outlook on the future of this potentially transformative technology.

An L-band emitter with quantum memory in silicon

Fluorescent centres in silicon have recently attracted great interest, owing to their remarkable properties for quantum technology. Here, we demonstrate that the C-centre in silicon can realise an optically readable quantum register in the L-band wavelength region where the transmission losses in commercial optical fibres are minimal. Our in-depth theoretical characterisation confirms the assignment of the C-centre to the carbon-oxygen interstitial pair defect. We further explore its magneto-optical properties, such as hyperfine and spin-orbit coupling constants from first principles calculations, which are crucial for tight control of the quantum states of the triplet electron spin. Based on this data, we set up quantum optics protocols to initialise and read out the quantum states of the electron spin, and realise a quantum memory by transferring quantum information from the electron spin to proximate 29Si nuclear spins. Our findings establish an optically readable long-living quantum memory in silicon where the scalability of qubits may be achieved by CMOS-compatible technology.

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.

ZnO/Cu2O heterojunction integrated fiber-optic biosensor for remote detection of cysteine

Indium tin oxide, semiconductor nanomaterial ZnO, and Cu2O were first loaded on the surface of the optical fiber to form an optical fiber probe. Large-volume macroscopic spatial light is replaced by an optical fiber path, and remote light injection is implemented. Based on the optical fiber probe, a photoelectrochemical biosensor was constructed and remote detection of cysteine was realized. In this tiny device, the optical fiber probe not only acts as a working electrode to react with the analyte but also directs the light exactly where it is needed. Simultaneously, the electrochemical behavior of cysteine on the surface of the working electrode is dominated by diffusion-control, which provides strong support for quantitative detection. Then, under the bias potential of 0 V, the linear range of the fiber-optic-based cysteine biosensor was 0.01∼1 μM, the regression coefficient (R2) value was 0.9943. In spiked synthetic urine, the detection of cysteine was also realized by the integrated biosensor. Moreover, benefiting from the low optical fiber loss, the new structure also possesses a unique remote detection function. This work confirms that photoelectrochemical biosensors can be integrated via optical fibers and retain comparable sensing performance. Based on this property, different materials can also be loaded on the surface of the optical fiber for remote detection of other analytes. It is expected to facilitate the research on fiber-optic-based integrated biosensors and show application prospects in diverse fields such as biochemical analysis and disease diagnosis.

Strength, crack resistance and optical losses of heat-treated silica fibers coated with non-ferrous metal

Metallic coatings currently provide the highest performance for silica fibers. The purpose of the present works predict of crack resistance, in determining the hardness and strength of uncoated and copper-coated optical fibers, as well as in the study of changes in strength parameters and optical losses after thermal effects on the studied optical fibers. The hardness and crack resistance values of silica fibers are measured by indentation. Crack resistance K1c is calculated using a semi-empirical Niihara relationship that relates the indentation size, radial crack length, and crack resistance. It was found that copper coating of silica fibers increases crack resistance 4 times, probably due to the affect of compressive stresses. The tensile strength of the fibers is determined by axial tension and two-point bending methods at a constant loading rate. Using a scanning electron microscopy, the initial crack length is calculated and the size of the characteristic defect is determined.

Optical Loss in Copper-Coated Multimode Optical Fibers of Different Diameters

Optical Loss in Copper-Coated Multimode Optical Fibers of Different Diameters

Femtosecond laser welding for robust and low loss optical fiber bonding.

Driven by the increasing demand for faster high-performance computing (HPC) networks and higher data center fabric transmission bandwidth, to favorite the needs of machine learning, data training, and computing, the adoption of co-packaged optics (CPO) and near-packaged optics (NPO) is one of the innovations to mitigate the slowing down of Moore's law. Because of the high temperature generated by the next generation of high-speed chips like switch ASICs, CPUs, and GPUs, coupling fibers to photonic integrated circuit (PIC) with traditional epoxy-based fiber arrays is becoming more challenging and problematic. Therefore, an epoxy-free bonding method using femtosecond laser welding borosilicate glass 3.3 and optical fibers is proposed and demonstrated. Then, a low loss and polarization independent fiber to fiber coupling was demonstrated to show the reliability of bonding. In the experiment, a V groove is used for aligning and positioning two fibers. After welding, the minimum coupling loss and polarization dependent loss is 0.347 dB and below 0.1 dB respectively. The average shear force limit of the welded samples with 0.5 mm welding length is measured to be as high as ∼0.719 N. This technology could be used for epoxy-free based edge coupling the high density multi-fibers with PIC and has potential of scalable manufacturability through automation.