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AbstractThis article introduces a novel high-sensitivity pressure and temperature sensor utilizing a tapered no-core fiber (NCF) structure created by splicing the NCF with a single-mode fiber (SMF) to form a “SMF-NCF-SMF” structure, tapering the NCF, and applying a polydimethylsiloxane (PDMS) film on the tapered NCF surface. The experimental results show that the device with a diameter of 10 μm has a pressure sensitivity of 86.63 nm/MPa within one to two atmospheres. Furthermore, the temperature sensitivity is −1.97 nm/°C from 30 °C to 60 °C. The sensor exhibits excellent stability and repeatability, and the PDMS film enhances the mechanical strength of the device, indicating promising potential for high-sensitivity pressure and temperature applications. [ABSTRACT FROM AUTHOR]

Free space optical technology promises to revolutionize point-to-point communications systems. By taking advantage of their vastly higher frequencies, coherent optical systems outperform their radio counterparts by orders of magnitude in achievable data throughput, while simultaneously lowering the required size, weight, and power (SWaP), making them ideal for mobile applications. However, the widespread implementation of this technology has been largely hindered by the effects of atmospheric turbulence, often necessitating complex higher-order adaptive optics systems that are largely unsuitable for deployment on mobile platforms. By employing tip/tilt beam-stabilization, we present the results of a bespoke low-SWaP optical terminal that demonstrated single-mode fiber (SMF) coupling. This was achieved by autonomously acquiring and tracking the targets using a combination of aircraft transponder and machine vision feedback to a root-mean-square (RMS) tracking error of 29.4 µrad and at angular rates of up to 0.83 deg/s. To the authors' knowledge, these works constitute the first published SMF coupled optical link to a full-sized helicopter, and we describe derived quantities relevant to the future refinement of such links. The ability to achieve SMF coupling without the constraints of complex adaptive optics systems positions this technology as a versatile quantum-capable communications solution for land-, air-, and sea-based platforms ranging across commercial, scientific, and military operators. [ABSTRACT FROM AUTHOR]

We demonstrate the use of laser diodes and multijunction photovoltaic power converters to efficiently deliver watts of electrical power for long-distance or cryogenic applications. Transmission through single-mode and multi-mode fibers at the wavelengths of 808 nm and 1470/1550 nm are studied. An electrical output power of ~0.1 W is obtained after a 5 km transmission through a standard single-mode SMF28 fiber fed with 0.25 W of optical power. An electrical output power of ~1 W is demonstrated after a 5 km transmission with a standard OM1 multi-mode fiber fed with ~2.5 W. Photovoltaic conversion efficiencies reaching Eff ~49% are obtained with an output voltage of ~5 V using commercial multijunction laser power converters. For low-temperature applications, an ultra-sensitive silicon photomultiplier (SiPM) is used to detect the residual light leaked from fibers as the temperature is decreased. Our study demonstrates that specific fiber types enable low-loss transmission compatible with cryogenic requirements and without light leakage triggering of the SiPM. A cryogenic power-over-fiber system at ~1470 nm is demonstrated with ~2 W of electrical power converted over a 10 m distance having a conversion efficiency of Eff > 65% at 77 K. [ABSTRACT FROM AUTHOR]

We propose a power-over-fiber system with a new photovoltaic converter voltage control technology consisting of intermittent operation of a light source based on capacitor voltage estimation to achieve high energy efficiency. This efficiency is made possible by ensuring the photovoltaic converter voltage stays within an appropriate range. However, detecting and controlling the voltage on the photovoltaic converter side would waste power. In our system, a controller on the light source side estimates the voltage of photovoltaic converter side from our circuit model and controls the photovoltaic converter voltage by controlling light source activation/deactivation. Therefore, it is possible to maintain high photoelectric conversion efficiency without wasting power on the photovoltaic converter side. We show that this method can significantly improve energy efficiency from 11.0% to 22.4% compared to a method that controls the voltage on the photovoltaic converter side. We also demonstrate that an optical switch with a power consumption of 130 mW can be driven with 5-mW optical input. Our power-over-fiber system is practical because its optical power is low and safe enough to be used in existing optical access networks.

In this paper, to the best of our knowledge, a new type of hollow-core anti-resonant fiber (HC-ARF) design using hybrid silica/high-index material (HIM) cladding is presented for single-polarization, high-birefringence, and endlessly single-mode operation at 2 μm wavelength. We show that the inclusion of a HIM layer in the cladding allows strong suppression of $x-$polarization, while maintaining low propagation loss and single-mode propagation for $y-$polarization. The optimized HC-ARF design includes a combination of low propagation loss, high-birefringence, and polarization-extinction ratio (PER) or loss ratio of 0.02 dB/m, 1.2 $\times \, 10^{-4}$, and >550 respectively, while the loss of the $x-$polarization is >20 dB/m. The proposed fiber may also be coiled to small bend radii while maintaining low bend-loss of $\approx$0.01–0.1 dB/m, and can potentially be used as polarization filter based on the different gap separations and bend conditions.

Introduction: Optical coherence tomography (OCT) is a pivotal imaging modality in ophthalmology for real-time, in vivo visualization of retinal structures. To enhance the capability and safety of OCT, this study focuses on the development of a micro intraocular OCT probe. The demand for minimal invasiveness and precise imaging drives the need for advanced probe designs that can access tight and sensitive areas, such as the ocular sclera.Methods: A novel OCT probe was engineered using a piezoelectric tube with quartered electrodes to drive Lissajous scanning movements at the end of a single-mode fiber. This design allows the probe to enter the eyeball through a scleral opening. Structural innovation enables the outer diameter of the endoscopic OCT probe to be adjusted from 13G (2.41 mm) to 25G (0.51 mm), accommodating various imaging field sizes and ensuring compatibility with different scleral incisions.Results: The fabricated micro intraocular OCT probe successfully performed preliminary imaging experiments on in vivo fingers. The Lissajous scanning facilitated comprehensive coverage of the target area, enhancing the imaging capabilities.Discussion: The integration of a piezoelectric tube with quartered outside electrodes into the OCT probe design proved effective for achieving precise control over scanning movements and adaptability to different surgical needs. The design characteristics and practical applications demonstrated the probe’s potential in clinical settings.

Free space optical technology promises to revolutionize point-to-point communications systems. By taking advantage of their vastly higher frequencies, coherent optical systems outperform their radio counterparts by orders of magnitude in achievable data throughput, while simultaneously lowering the required size, weight, and power (SWaP), making them ideal for mobile applications. However, the widespread implementation of this technology has been largely hindered by the effects of atmospheric turbulence, often necessitating complex higher-order adaptive optics systems that are largely unsuitable for deployment on mobile platforms. By employing tip/tilt beam-stabilization, we present the results of a bespoke low-SWaP optical terminal that demonstrated single-mode fiber (SMF) coupling. This was achieved by autonomously acquiring and tracking the targets using a combination of aircraft transponder and machine vision feedback to a root-mean-square (RMS) tracking error of 29.4 µrad and at angular rates of up to 0.83 deg/s. To the authors’ knowledge, these works constitute the first published SMF coupled optical link to a full-sized helicopter, and we describe derived quantities relevant to the future refinement of such links. The ability to achieve SMF coupling without the constraints of complex adaptive optics systems positions this technology as a versatile quantum-capable communications solution for land-, air-, and sea-based platforms ranging across commercial, scientific, and military operators.

Optical fibers with a modified radial profile of acoustic refractive index (ARIP) have been considered. The use of two-component doping of the core in the silica optical fiber makes it possible to create simultaneously various profiles of refractive indices for an optical wave and a hyper-sound wave generated due to electrostriction, which can be applied for efficient reduction of the maximum of the amplification coefficient (gain) of the stimulated Brillouin scattering (SBS). The use of phosphor oxide (P2O5) and fluorine (F) with this purpose, when maintaining optically single-mode operation, makes it possible to realize a high-contrast ARIP by optimizing the shape of it, it is possible to effectively involve a great number of guided acoustic modes to the SBS process. This creates a broad multiband SBS gain spectrum and leads to a reduction of the absolute value of its maximum proportional to the number of acoustic modes. In this work, for the optical fibers with such a step-index profile of optical refractive index (ORIP), we have studied theoretically the dependence of the absolute maximum of the SBS gain at the ARIP parameters providing its ultimately possible reduction owing to the multimode acoustics on the value of the contrast Δn of the optical refractive index between the fiber core and its cladding. Among others, the real technological limitations on the maximum codoping of silica glass with P2O5 and F (in particular, for the method of the modified chemical vapor deposition, MCVD) are considered. In addition, an approximate analytical model of the optimal ARIP (and, respectively, the radial distributions of the P2O5 and F concentrations) is presented. The results have made it possible to come to the conclusion that the maximum SBS gain suppression (up to 15 dB) in the P2O5–F–SiO2 fibers can be achieved at Δn < 0.0045, while at 0.0045 < Δn < 0.0075, these limits are objectively restricted by 6 dB; at Δn > 0.0075, it is necessary to use other glass compositions or methods. [ABSTRACT FROM AUTHOR]

Theoretical analysis of the modulation of anti-dark vector solitons is conducted in this work. The simulation depends on a single-mode optical fiber out-cavity modulation system model that works at 1 μ m. The anti-dark vector soliton's initial state is assumed to be polarization-/group-velocity-locked, with same/different central wavelengths in orthogonally polarized directions. After soliton parameter modulation, modulated anti-dark vector solitons at the output port will demonstrate different properties in orthogonal directions. For example, two symmetrically located frequency peaks always exist for output orthogonal modes when the input state is polarization-locked. And a dual-wavelength anti-dark vector soliton with temporal pulse oscillation can be generated by changing the projection angle with the help of a polarization beam splitter, when the input vector soliton's group-velocity is locked. These modulation results are instructive for the study of out-cavity modulating optical fiber vector soltions with different pulsed properties. [ABSTRACT FROM AUTHOR]

We experimentally investigate the problem of monitoring the Kerr-nonlinearity coefficient $\gamma$ from transmitted and received data for a single-mode fiber link of 1600 km length. We compare the accuracy and speed of three different approaches. First, a standard split-step Fourier method is used to predict the output at various $\gamma$ values, which are then compared to the measured output. Second, a recently proposed nonlinear Fourier transform (NFT)-based method, which matches solitonic eigenvalues in the transmitted and received signals for various $\gamma$ values. Third, a novel fast version of the NFT-based method, which only matches the highest few eigenvalues. Although the NFT-based methods do not scale with link length, we demonstrate that the SSFM-based method is significantly faster than the basic NFT-based method for the considered link of 1600 km, and outperforms even the faster version. However, for a simulated link of 8000 km, the fast NFT-based method is shown to be faster than the SSMF-based method, although at the cost of a small loss in accuracy.

The lack of access to broadband services and speeds that allows urban and rural populations to meet the minimum requirements of today’s society creates a lack of economic opportunities and digital inequality. In contrast, regions with adequate broadband infrastructure can attract investors and become the home of tech workers while boosting the local economy. To level the field and promote the expansion and improvement of broadband infrastructure, federal and state agencies in the U.S. provide funding through programs such as the Rural Digital Opportunity Fund, and The Enabling Middle Mile Broadband Infrastructure Program among others. Here, counties assess their broadband infrastructure, identify the funding opportunity, and compete for that funding by submitting grant applications. In this research paper, we present the problems, challenges, and lessons learned during the process of assessment of the broadband infrastructure for Polk County, Florida, USA. In addition, connectivity technologies and physical layer options for broadband internet infrastructure were reviewed and we present our recommendation in terms of technology for the upgrading and expansion of the current network. In particular, we discuss the challenges in determining actual network coverage by contrasting official data of the Federal Communications Commission (FCC) with several crowd-sensing datasets such M-Lab (Measurement Lab), Ookla Open Datasets, and results from the Polk County community broadband survey. We discuss the advantages and limitations of using these publicly available datasets and open-source tools. Finally, we provide guidelines and best practices in terms of data analysis and visualization that may be used by city planners and researchers.

Dip coating technique has the potential to provide a simpler and more cost-effective means of forming an optical fiber microcollimator composed of parabolic Polymethyl methacrylate microlenses for various applications. The effects of dip-coating operating parameters such as withdrawal speed on the thickness of a microlens were investigated in this work. Zemax® software was used to validate the analytical results and to assess the efficiency of the optical coupling. The obtained waist and working distance values, make possible the optimization of the optical coupling between a microcollimator and a laser beam, as well as between a microcollimator and an optical fiber. The simulation results of the coupling between the microcollimator and the laser beam show that the optical coupling efficiency η is about 99% with an optimal microlens radius R = 19.14 μm, a waist size W1 = 2.49 μm and a working distance Zw = 41.78 μm. However, the optimal microlens for the coupling between the microcollimator and the optical fiber has a minimum curvature radius about 28.78 μm. We believe that these results are of a big interest in many applications in optical experiments and laser-optical fibers applications. [ABSTRACT FROM AUTHOR]

Coupled to endoscopic techniques, Mueller polarimetry has been proven to be promising for early detection of certain diseases which affect biological tissues of inner organs. However, the depolarization power which is one of the most informative polarimetric characteristics cannot be directly measured through a fiber endoscope. For evaluating this quantity, we propose a method based on the Lu–Chipman decomposition of the averaged sum of the Mueller matrices of neighboring pixels. The principle is well supported by numerical simulations. Depolarization powers of Spectralon and of different areas of a biological sample are also successfully evaluated. [ABSTRACT FROM AUTHOR]

Nowadays, forward Brillouin scattering in optical fibers has attracted massive research interests worldwide, owing to its great potential for applications in sensing, filtering, lasing, and all‐optical signal processing, etc. The manipulation of spectrum properties of forward stimulated Brillouin scattering (FSBS) turns out to be particularly important for various application scenarios. However, the manipulation approaches are still very limited by now. Herein, for the first time to the best of one's knowledge, a thorough investigation on the fiber geometry dependence of FSBS effect in optical fibers is presented, where the dependencies of FSBS on fiber core diameter and cladding diameter are investigated, revealing the characteristics of FSBS in terms of linewidth, frequency interval, and nonlinear coefficient, etc. It is indicated in the result that changing the size of the fiber core/cladding might give rise to considerable modification of the FSBS spectrum. The investigation paves the way to engineer FSBS in optical fibers, where acousto‐optic interaction can be manipulated and the FSBS spectrum can be tailored by adjusting the geometric size of the fiber for various applications.

Chromatic dispersion is an important fiber attribute affecting transmission performance over optical fibers. Various chromatic dispersion measurement methods have been developed primarily for single-mode fibers. In the literature, measurement techniques were also developed to characterize few-mode fibers and multi-mode fibers. These methods are often subject to some limitations. In this paper, a simple and robust measurement method for chromatic dispersion measurement of single-mode fibers, polarization--maintaining fibers, and few-mode fibers is presented using a frequency domain instrument and a vector network analyzer. The method is applied to all three types of fibers through one measurement methodology uniformly. Using a vector network analyzer, the measurement instrument obtains the complex transfer function of fiber transmission. The inverse Fourier transform of the measured complex transfer function is used to determine the group delays for each mode of the fiber. Although the sampling is highly under-sampled for the whole fiber link, through proper treatment of the data, we can de-alias the signals and obtain accurate values of the group delays of each mode. By measuring the group delays over different wavelengths, the data can yield the chromatic dispersion of each mode over the wavelength window. [ABSTRACT FROM AUTHOR]

In order to study the relationship between the macro-bending loss characteristics of the single-mode fiber and the temperature change, the thermo-optical effect and thermal expansion effect are corrected according to the theoretical formula proposed by Faustini L. Based on this formula, the macro-bending loss of SMF28 and 1060XP single-mode fiber with core-cladding-infinite coating structure under the influence of temperature is simulated and analyzed. The influence of temperature, wavelength, bending radius and other factors on the macro-bending loss of SMF28 single-mode fiber is explored, and the linear fitting results between the temperature and the two kinds of single-mode fibers are obtained. The results show that the macrobending loss increases with the decrease of bending radius, and the increase of wavelength. The loss also decreases with the increase of temperature. Under certain bending radius and wavelength, the macro-bending loss and temperature are in monotonic relationship, which means increasing the number of bending turns can effectively increase the sensitivity to temperature.

In order to study the relationship between the macro-bending loss characteristics of the single-mode fiber and the temperature change, the thermo-optical effect and thermal expansion effect are corrected according to the theoretical formula proposed by Faustini L. Based on this formula, the macro-bending loss of SMF28 and 1060XP single-mode fiber with core-cladding-infinite coating structure under the influence of temperature is simulated and analyzed. The influence of temperature, wavelength, bending radius and other factors on the macro-bending loss of SMF28 single-mode fiber is explored, and the linear fitting results between the temperature and the two kinds of single-mode fibers are obtained. The results show that the macrobending loss increases with the decrease of bending radius, and the increase of wavelength. The loss also decreases with the increase of temperature. Under certain bending radius and wavelength, the macro-bending loss and temperature are in monotonic relationship, which means increasing the number of bending turns can effectively increase the sensitivity to temperature.

• High-efficiency Raman soliton tunable from 1600 nm to 2040 nm was demonstrated using few-mode EYDCF and telecom fibers. • Raman soliton of 3 nJ at 1700 nm and 6 nJ at 1820 nm were generated. • The proposed architecture offers an easy-to-build, stable femtosecond laser source for multi-photon imaging. We demonstrate here high-efficiency self-frequency-shifted soliton generation in standard single-mode fiber (SMF). Pulse with 80.96-MHz repetition rate passing through a length of 5.5-m fiber, Raman soliton with an energy of as much as 4.8 nJ was generated by pump pulse with an energy of 5.7 nJ, corresponding to an efficiency of nearly 85 %. Wavelength shifting of Raman soliton is fully investigated by controlling the input pulse energy, fiber length, and polarization state, resulting over 440 nm wavelength tuning range 1600–2040 nm. As the length of SMF is shortened to 0.5 m, Raman soliton pulses with energy and pulse duration of 3 nJ, 80 fs at 1700 nm and 6 nJ, 75 fs at 1820 nm are generated respectively, and the output average power keeps stable with a root-mean-square value of 0.7 % in four hours measurement. The proposed demonstration provides an easy-to-build, stable, high efficiency tunable laser source for multiphoton imaging. [ABSTRACT FROM AUTHOR]

In this paper we report our findings on the design, manufacturing and testing of low numerical aperture active step-index optical fibers with very large mode area, operating in a truly single-mode regime. Our approach to efficiently filter higher-order modes in the core relies on applying curvature in a specific direction at a given diameter on a specially designed fiber containing boron-doped silica rods on both sides of the core. The fabricated ytterbium-doped fibers exhibit a mode field diameter of 32 μ m , a cladding pump absorption of 10 dB/m and were designed for use in a compact monolithic configuration due to its all-solid nature and its 14 cm targeted bend diameter. [ABSTRACT FROM AUTHOR]

When two parallel waveguides are close to each other, the power of the two adjacent waveguides will be periodically converted to form a directional coupled waveguide system (). The transverse coupling between two parallel waveguides can be described by mode coupling theory. However, in practical application, due to the limitation of equipment or manual computing capacity, it is impossible to quickly calculate the coupling efficiency of two optical fibers through the current specific formula. Through the form of MATLAB programming, it can determine whether the fiber is a single-mode fiber, solve the characteristic equation to obtain the propagation constant, integrate the coupling coefficients K12 and K21, solve the coupling efficiency in the fiber, and finally output in the form of graphics. The results show that for the directional coupler composed of two fibers, if the core radius and core refractive index change, the mismatching phase constant and coupling efficiency will change correspondingly, and the calculated results are in good agreement with the predicted results. On this background, this paper proposes the form of MATLAB programming to calculate coupling efficiency. The coupling efficiency of fiber directional couplers is analyzed. The theory gives accurate results within the actual parameters.

Coupled to endoscopic techniques, Mueller polarimetry has been proven to be promising for early detection of certain diseases which affect biological tissues of inner organs. However, the depolarization power which is one of the most informative polarimetric characteristics cannot be directly measured through a fiber endoscope. For evaluating this quantity, we propose a method based on the Lu–Chipman decomposition of the averaged sum of the Mueller matrices of neighboring pixels. The principle is well supported by numerical simulations. Depolarization powers of Spectralon and of different areas of a biological sample are also successfully evaluated.

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A novel setup for a Double-Taper Mach-Zehnder Interferometer (DTMZI) is presented to measure axial strain and torsion. An epoxy section is added between the two tapers as a fixture to ensure torsion sensing. The modal filtering effect of the epoxy upon the interferometry response is experimentally verified. The transmission spectrum of DTMZI under strain and torsion is modelled and further analyzed through the differential accumulated phase between the beating modes.The experimental spectral observation confirms our estimate. The relationships between the spectral shifts in wavelength and applied displacements are obtained. The sensor shows a very high sensitivity against the applied strain and twists. [ABSTRACT FROM AUTHOR]

Nonlinear optical effects in optical waveguides play an important role in the development of fiber and integrated optics systems for optical communication and information processing. On the one hand, nonlinear effects impose restrictions on the radiation power that can be transmitted through an optical fiber or light guide. In this paper, the problem of the occurrence of the phenomenon from the stimulated Brillouin scattering (SBS) effect is investigated using two optical sources of rays in a single-mode optical fiber at joint waves of 1310 nm and 1550 nm. Due to the fact that in all trunk fiber-optic lines, the intensity and energy of input signals is limited due to the influence of SBS, methods are currently being sought to reduce the influence of this phenomenon. It was found that the energy of the input beam in the combined propagation of the compound did not reach the value of the threshold of SBS in the values of 25 dBm and 27 dBm due to the discrepancy between the experimental results and the results of the model. The SBS effect was not observed when the threshold threshold of 15 dBm and 27 dBm – SBS was reached when combining a dual beam along a single optical fiber in one direction. As a result, by double integration, the value of the SBS threshold was raised, and the direction for future scientific research was determined. If the possibility of increasing the threshold of SBS is proved, then increasing the distance of amplifiers in the main networks, respectively, its economic effect increases. In addition, it can be noted that there are no scientific papers devoted to the study of the effects of optical nonlinear effects by combining and distributing these two compounds along a single optical fiber. This article discusses the issues of improving the capacity and determination of the threshold for stimulated Brillouin scattering. To increase the power threshold is invited to consider the dependence of the phase modulation frequency of the spectral width of the laser radiation. In addition, the fact that the SBS threshold did not reach the value at an energy of 27 DB in the case of the double-beam distribution can be proved by discrepancies in comparison with the results of experimental studies and the results of the model that determines the SBS effect [ABSTRACT FROM AUTHOR]

Chromatic dispersion is an important fiber attribute affecting transmission performance over optical fibers. Various chromatic dispersion measurement methods have been developed primarily for single-mode fibers. In the literature, measurement techniques were also developed to characterize few-mode fibers and multi-mode fibers. These methods are often subject to some limitations. In this paper, a simple and robust measurement method for chromatic dispersion measurement of single-mode fibers, polarization--maintaining fibers, and few-mode fibers is presented using a frequency domain instrument and a vector network analyzer. The method is applied to all three types of fibers through one measurement methodology uniformly. Using a vector network analyzer, the measurement instrument obtains the complex transfer function of fiber transmission. The inverse Fourier transform of the measured complex transfer function is used to determine the group delays for each mode of the fiber. Although the sampling is highly under-sampled for the whole fiber link, through proper treatment of the data, we can de-alias the signals and obtain accurate values of the group delays of each mode. By measuring the group delays over different wavelengths, the data can yield the chromatic dispersion of each mode over the wavelength window.

The paper reviews the factors limiting the accuracy of locating a fiber optic cable fault when using an optical time domain reflectometer (OTDR) and describes an error estimation method for typical use cases. The primary source of errors lies in the complex relationship between the length of the optical fiber (measured by OTDR), its routing, cable design depending on cable design and type of installation (i.e. duct, directly buried, aerial) as well as the spare lengths used for service purposes. The techniques which considerably improve the accuracy of the fault localization processes are presented, the importance of accurate documentation of the network and of referencing the fault location to the nearest splice instead of end of the line are discussed, as is the absence of cable helix factor in data sheets

A novel interrogation method is presented in the application of strain sensing with a double taper Mach-Zehnder interferometer (DTMZI). The proposed sensing setup comprises a laser source and an optical power meter, which significantly lowers future integration cost and complexity. An analytical coupling model is established to study the sensor's strain-related modal behaviour. The design parameters of the DTMZI device are conditioned to satisfy a single-wavelength measurement. The spectral responses of several fabricated sensors are examined. Our experiments confirm the direct mapping between different strain values and particular transmission measures for the single wavelength case. [ABSTRACT FROM AUTHOR]

The paper reviews the factors limiting the accuracy of locating a fiber optic cable fault when using an optical time domain reectometer (OTDR) and describes an error estimation method for typical use cases. The primary source of errors lies in the complex relationship between the length of the optical fiber (measured by OTDR), its routing, cable design depending on cable design and type of installation (i.e. duct, directly buried, aerial) as well as the spare lengths used for service purposes. The techniques which considerably improve the accuracy of the fault localization processes are presented, the importance of accurate documentation of the network and of referencing the fault location to the nearest splice instead of end of the line are discussed, as is the absence of cable helix factor in data sheets. [ABSTRACT FROM AUTHOR]

In this scientific research article, the new Kudryashov method and the tanh-coth method, which have not been applied before, are employed to construct analytical and soliton solutions of the (2+1)-dimensional Hirota–Maccari system. The (2+1)-dimensional Hirota–Maccari system is a special kind of nonlinear Schrödinger equation (NLSEs) that models the motion of isolated waves localized in a small part of space, and is used in such various fields as fiber optics telecommunication systems, nonlinear optics, plasma physics, and hydrodynamics. In addition, the Hirota–Maccari system defines the dynamical characters of femtosecond soliton pulse propagation in single-mode fibers. Analytical solutions of the model are successfully acquired with the assistance of symbolic computation utilizing these methods. Finally, 3D, 2D, and contour graphs of solutions are depicted at specific values of parameters. It is shown that the new Kudryashov method and the tanh-coth method are uncomplicated, very effective, easily applicable, reliable, and indeed vital mathematical tools in solving nonlinear models.

It is known that the high bandwidth demands are accomplished by deploying the concept of wavelength division multiplexing in optical networks which involves the transmission of multiple wavelength signals spaced very close to each other. Due to closely spaced wavelengths, the signal power of one channel phase modulates the adjacent channel which in turn produces nonlinear effects such as cross-phase modulation (XPM), self-phase modulation (SPM) and four-wave mixing (FWM). Thus, in this paper, PC-DCF (pre-compensating dispersion compensating fiber) technique has been demonstrated and evaluated in the transmission link to compensate the XPM effects, and this result seems to significantly enhance w.r.t. transmission performance and system capacity considering performance metrics such as Optical Signal to Noise Ratio (OSNR), bit rate, Q-factor and bit error rate (BER). It is evident from the simulation results as well as through mathematical modeling that the proposed technique (PC-DCF) provides optimum results at the channel spacing of 100 GHz, bit rate of 10 Gbps and input power of 5 mW which collectively provides a 5 dB increase in OSNR as compared to the existing compensating technique. [ABSTRACT FROM AUTHOR]

In free-space optical communication (FSOC), it is necessary to couple optical fibers for application in optical-fiber technology and devices. However, propagation through atmospheric turbulence degrades the single-mode-fiber coupling efficiency (CE). This degradation can be compensated by an adaptive optics (AO) system. In this paper, we analyze the influence of spatial and temporal characteristics of turbulence on the CE. Experiments along a 1 km urban link demonstrate that the CE increases from 5% without AO to 10%–25% in the AO closed loop at different times of day. We obtain an increase by factor 4 in the CE under weak turbulence conditions. [ABSTRACT FROM AUTHOR]

Ascorbic acid (AA) works as an antioxidant and plays a key role in the regulation of immune system and health maintenance. Low level of AA causes disease like scurvy whereas, its higher-level induces stomach throes in human body. So, for the detection of AA, a sensitive sensor probe is fabricated by splicing a short section of highly germanium (Ge)-doped photosensitive fiber (PSF) to a single-mode fiber. In the present study, PSF’s core is easily expanded by etching with hydrofluoric acid because PSF’s core is 5-times Ge-doped. It also helps in partial removal of cladding. Thereafter, gold nanoparticles (AuNPs) are immobilized over the sensing probe for localized surface plasmon resonance (LSPR) phenomena. Further, graphene oxide (GO) is decorated over the AuNPs-coated sensor probe. The AuNPs and GO helps to increase the sensitivity and biocompatibility of sensor probe. Ascorbate oxidase from Cucurbita species has been used to increase the specificity of the sensor. The developed sensor probe has been characterized by the UV-Visible spectrophotometer, high-resolution transmission electron microscope (HR-TEM), TEM - Energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), field emission scanning electron microscope (FE-SEM), and SEM-EDS. The sensor exhibited a wide linear range of detection from $1~\mu \text{M}$ to 1 mM, with 3.5 %/mM of sensitivity. A detection limit of proposed sensor is found to be $15.12~\mu \text{M}$ , which is lower than the physiological AA level in serum of healthy human body (40 – $120~\mu \text{M}$). The selectivity of sensor probe has been verified by performing the experiments with various other biomolecules present in serum. The proposed LSPR sensor has many advantages such as low cost, less fragile probe, remote sensing, low electromagnetic interference, online monitoring, detection from micro-droplets, low detection limit, fast response, highly sensitive, and high specificity. [ABSTRACT FROM AUTHOR]

Fabrication and experimental validation of a newly developed copper oxide nanoparticles (CuO-NPs) and silver nanoparticles (AgNPs) immobilized SM-MM-SM-MM-SM (SMSMS) in-line Mach–Zehnder interferometer (MZI) fiber structure-based sensor using localized surface plasmon resonance (LSPR) technique are reported in this article. The AgNPs and CuO-NPs are used to improve the biocompatibility and sensitivity of the sensor. The nanoparticles (NPs) and immobilized probe were characterized by UV-Vis spectrophotometer, HR-TEM, SEM, and EDX, revealing superior performance over the existing uric acid (UA) sensors. The proposed optimized structure-based optical fiber sensors (OFSs) exhibit excellent specificity, sensitivity, and limit of detection (LoD) for the detection of UA. Moreover, the developed sensor exhibits linear profile over a very wide range: 1) $10~\mu \text{M}$ –1 mM for detection over UA presents in serum, while the normal range of UA in serum is 100– $400~\mu \text{M}$ and 2) 0.4–10 mM for detection over UA presents in urine, while the normal range of UA in urine is 1.5–4.4 mM. In addition, the developed sensor has a distinguished advantage, such as multicompatibility over the detection of UA presents in both serum and urine along with its high selectivity, reusability, reproducibility, and lowest LoD. The proposed AgNPs and CuO-NPs immobilized and the uricase functionalized SMSMS structure-based LSPR sensor has better compatibility and are potent candidates for medical applications. [ABSTRACT FROM AUTHOR]

A label-free highly sensitive tapered Single-Mode-Multimode-Single-Mode (TSMS) structure-based optical fiber sensors (OFSs) is presented in this study for the detection of L-cysteine (L-Cys). Well studied biocompatible nanomaterials (NMs) including silver nanoparticles (AgNPs) and graphene oxide (GO) were synthesized and immobilized over the surface of the sensing probe using self-assembly method. Configurations involving the excitation of localized surface plasmon resonance (LSPR) phenomena proposed in the work are investigated in detail. Further, a comparative study with tapered multimode fiber (TMMF) OFSs and pioneering investigations on previously reported sensors in this area over the last few years (notable advances only) is also presented in this study. The characterization of NMs and sensing probe are observed using in house high-resolution transmission electron microscope (HR-TEM), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), and atomic force microscopy (AFM) facilities. The proposed method improves the performance of the L-Cys in various fronts, namely: (i) sensitivity, (ii) linearity range, (iii) correlation coefficient, and (iv) limit of detection (LoD). The calibration curve is found to be linear over the range of 10nM to1 mM with an LoD of $63.25~\mu \text{M}$ and sensitivity of 7.0 nm/mM for the proposed TSMS/AgNPs/GO/OFSs. [ABSTRACT FROM AUTHOR]

This study presents a label-free and efficient method for the diagnosis of collagen-IV by using an optical fiber-based Mach-Zehnder interferometer (MZI) structure. The structure of MZI is fabricated by splicing a 2.3 cm long segment of single-mode fiber (SMF) between two ~ 45 cm strands of multi-mode fibers (MMF). Owing to the mismatch of core diameters, cladding of SMF guides the light. SMF’s cladding is partially etched by using 40% hydrofluoric (HF) acid so that a part of propagating energy is released that can interplay with the surroundings. The etched region is immobilized with ~ 10 nm size of gold nanoparticles (AuNPs) and ~ 50 nm size of copper oxide nanoparticles (CuO-NPs) to initiate the influence of localized surface plasmon resonance (LSPR) phenomenon. For a comparative study, two different probes are developed and analyzed. In one probe, CuO NPs are immobilized over the etched part of SMF and named as CuO-NPs probe. In other probe, a monolayer of AuNPs is sandwiched between fiber surface and CuO-NPs and termed as AuNPs/CuO-NPs probe. The characterization of NPs and developed sensor probe are performed using UV-Vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), and energy distribution spectroscopy (EDS). The sensor probes are made very specific towards collagen-IV by functionalizing them with collagenase enzyme obtained from Clostridium histolyticum. A wide range of Collagen-IV solutions of concentrations from 2 $\mu \text{g}$ /ml to 40 $\mu \text{g}$ /ml are sensed through the collagenase functionalized probe. The specificity of the probes are analyzed by sensing other biomolecules present in the human body. [ABSTRACT FROM AUTHOR]

A fiber refractometer with large dynamic range from 1.316 to 1.61 RIU has been realized using a hybrid configuration of a single-mode fiber (SMF) coupled to a stripped-cladding multimode fiber (MMF) as sensing element. An extended analysis of the diffraction principle of a Gaussian beam is specifically developed for this sensor configuration to determine the injected power density into the MMF which, when subsequently combined with ray optics, analytical wave optics and Fresnel equations, enables the sensor response to be comprehensively estimated. Simulation results have been experimentally corroborated to very high agreement for a 2-cm and a 5-cm decladded section of multimode fiber used as the sensing element. The results show, for the shorter sensor (2 cm), a very high sensitivity of ~ −250 a.u./RIU being achieved in the Zone II operating regime, i.e. for indices between the cladding and core indices together with a resolution of $2.76\times 10^{-{6}}$ RIU being attained. In addition, the developed models have been used to accurately predict the response of sensing elements of various lengths, hence demonstrating the potential capability of this research to be exploited for optimizing bespoke design of fiber refractometers of any arbitrary sensing lengths or dimensions. As an example, we present the design of a refractometer achieving a maximum sensitivity of 300 a.u./RIU with a potential resolution of $2.26\times 10^{-{6}}$ RIU. [ABSTRACT FROM AUTHOR]

A newly developed localized surface plasmon resonance (LSPR) phenomenon-based cholesterol (Cho) sensor is reported in this article. Functional test of the proposed sensor over an ultra-wide-range of Cho concentration (0.1–10 mM) which covers the Cho concentration in human serum (∼5.17 mM), revealing great performance is executed. Further, different structures such as multimode-photosensitive-multimode (MPM) and single-photosensitive-single (SPS), also called core mismatch fiber structure are presented here for the effective detection of Cho. The proposed sensors are immobilized with different sizes of gold nanoparticles (AuNPs) (∼10 nm and ∼30 nm) followed by zinc oxide NPs (ZnO-NPs). The characterization and functional test of nanomaterials (NMs) and immobilized probes are observed using a UV-Vis spectrophotometer, HR-TEM, AFM, SEM, and EDS. A noticeable improvement is recorded in the all-important sensing parameters of proposed sensors, such as i) sensitivity (0.6898 nm/mM), ii) linearity (0.1–10 mM), iii) limit of detection (LoD) (0.6161 mM), and iv) correlation coefficient (0.9754) on the course of the immune binding of Cho to a specific cholesterol-oxidase (ChOx) functionalized probe, exhibiting great potential for future practical applications. [ABSTRACT FROM AUTHOR]

This paper proposes the theoretical design of a polarized interferometric fiber-optic gyroscope (IFOG). The polarized IFOG utilizes a coherent light source and polarization elements (Faraday rotators and polarizing beam splitter) to obtain maximum visibility of an interference signal and to compensate for the birefringent effect of a single-mode fiber coil in an IFOG. [ABSTRACT FROM AUTHOR]

An optofluidic chip of the single-mode fiber variable optical attenuator (VOA) is proposed. This chip has a simple structure, and it utilizes microfluid and air to regulate the optical attenuation, where air acts as a shutter. Here, the single-mode characteristics of the VOA chip are discussed at 1310 nm and 1550 nm. The experiment results indicate that it is feasible to regulate optical attenuation using the proposed chip. The VOA with this chip has a large optical attenuation range (82 dB) and a very wide operation waveband from visible to near infrared wavelengths. The measured insertion loss is 0.68 dB at 1310 nm and 0.92 dB at 1550 nm, and the measured return loss is 47.8 dB at 1310 nm and is 47.67 dB at 1550 nm.

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Featured Application: The research results in this paper are helpful for researchers to analyze and design the adaptive optics (AO) systems for atmospheric laser transmission and detection systems, such as free space optical communication and gas sensing lidar. The method in this paper can be used to study the residual margin allocation of AO system under different coupling efficiency thresholds. In this study, Zernike polynomials and optical fiber field theory are applied to build a mathematical model of coupling efficiency (CE) and spatial mode of aberrations. The theory built in this paper can be used to quickly calculate the CE affected by a single aberration as well as the aberrations caused by atmospheric turbulence. The aberrations are classified based on Zernike polynomials and the effects of aberrations on CE of different types and different spatial frequencies are analyzed. The influence of the effects of AO system residual errors is also analyzed. Adaptive optics (AO) equipment is applied to build a system on which the proposed theory was tested; the experimental results validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

Highlights • An ACBS fiber is proposed based on a FS laser micromachining system. • Reflecting power for a FS laser fabricated reflector is calculated and verified. • The results show that the ACBS fiber enhances the backscattering of the SMF. • We show backscattering traces of ACBS fibers using different FS laser pulse energy. Abstract An artificially controlled backscattering (ACBS) fiber is theoretically proposed and experimentally verified using a femtosecond (fs) laser micromachining system. The backscattering power of the ACBS fiber per unit length is similarly defined as the one of the single mode fiber (SMF). We have calculated the relative reflecting power per unit length from a fiber with a reflector fabricated on an SMF core at 5576 m by the fs laser beam. The impact of the pulse energy of the fs laser and the reflector position on the performance of the ACBS fiber are then compared via observing the backscattering trace. The results show that the proposed ACBS fiber can enhance the backscattering of the SMF. High backscattering fibers (HBSFs) can be achieved via appropriate selection of fabrication parameters, offering an efficient way to shorten the fiber length and form a random distributed feedback fiber laser. [ABSTRACT FROM AUTHOR]

A new design of all-glass microstructured fibers with a large mode area is presented. The numerical analysis of the fibers was performed using the finite element method. Confinement losses for the fundamental modes and for those of a higher order were calculated in the spectral range of 0.8 to 1.4 microns. Simulation results show that the proposed design allows us to obtain single-mode guidance of these fibers in the spectral range of 0.87 to 1.11 microns for straight and bent fibers with a bending radius of 0.25 m. [ABSTRACT FROM AUTHOR]

A waveguide-coupled surface plasmon resonance (WCSPR) sensor consisting of two D -shape single-mode fibers is designed and analyzed by the finite element method (FEM). The optical field of the surface plasmon polaritons (SPPs) mode is confined in the dielectric cavity between the dual metallic thin films. Therefore, the effective refractive index of the SPP mode depends largely on the refractive index of the analyte and an anomalous dispersion relationship is observed between the SPP mode and x-polarized core-guide mode of the dual D -shape fiber. The excitation mechanism of surface plasmon resonance (SPR) in the coupling region is attributed to phase matching of the two modes. Further analysis shows that the narrow bandwidth peak in the loss spectrum of the core mode is determined by the sensor dimensions contributed jointly by the thicknesses of the silver film, dielectric layer, and titanium dioxide film. Compared to the single-fiber structure, the optimized dual D -shape WCSPR sensor achieves a maximum wavelength sensitivity of 52,200 nm/RIU with a full-width at half-minimum (FWHM) of 9.47 nm and a figure of merit (FOM) of 346.6 RIU−1 in the analyte refractive index range of 1.32–1.42. [ABSTRACT FROM AUTHOR]

This article presents an extrinsic fiber-optic acoustic sensor applied for partial discharge (PD) detection in air. A Fabry–Perot (F-P) cavity consisting of a single-mode fiber (SMF) and a graphene oxide (GO) film, whose thickness and effective vibration diameter are approximately 500 nm and 4.377 mm, respectively, is used as this sensing core, and the manufacturing process of GO diaphragms and this sensing probe is illustrated to be simple and controllable. Performance tests indicate that this proposed sensor maintains a linear acoustic-pressure response and a flat frequency response in the range of 200 Hz to 20 kHz, while being an omnidirectional sensor and having high working stability during a ten-day test period. Additionally, PD detection results show that the minimum PD size detected by this proposed sensor in air was approximately 100 pC, which demonstrates that this proposed sensor can achieve high-sensitivity PD detection in air.