Single-mode Telecommunication Fiber Research Articles

Technology and research on the influence of liquid crystal cladding doped with magnetic Fe3O4 nanoparticles on light propagation in an optical taper sensor

The results obtained for new dual-cladding optical fiber tapers surrounded by liquid crystal (LC) doped with Fe3O4 nanoparticles in a specially developed glass cell are presented. The created structures are sensitive to changes in refractive index values in the surrounding medium caused by modifying external environment parameters. In this investigation, cells are filled with nematic LCs 6CHBT and with the same mixture doped with 0.1 wt% and 0.5 wt% of magnetic nanoparticles (Fe3O4 NPs). The taper is made on a standard single-mode telecommunication fiber, stretched out to a length of 20.0 ± 0.5 mm, and the diameter of the tapers is approximately 15.0 ± 0.3 μm, with a loss lower than 0.5 dB @ 1,550 nm. Measurements are carried out in a wide range covering the visible and infrared ranges in two setups: 1) without a magnetic field, with steering only by voltage and 2) with an applied magnetic field. The presented spectrum results are divided into two ranges according to the parameters of optical spectrum analyzers: 350–1,200 nm and 1,200–2,400 nm. For all investigations, a steering voltage is chosen from the range of 0 to 200 V, which allows for establishing the influence of dopants on transmitted power and time response at different arrangements. Due to the sensitivity of LCs to temperature changes, this paper focuses on measuring at room temperature the effect of the magnetic field on propagation in a fiber optic taper. The proposed solution demonstrates the technology for creating advanced components as a combination of fiber optic technology, LCs, and nanoparticles. The presented results show the possibility of creating new sensors of various external factors such as magnetic or electric fields in miniaturized dimensions.

Cryogenic temperature 3D mapping via a distributed temperature sensor with centimeter resolution

We conduct 3D mapping of cryogenic temperatures via a Raman-based distributed temperature sensor, employing standard telecom single-mode fibers and polarization-independent superconducting nanowire single photon detectors (SNSPDs). By coiling a test fiber around various stages of a liquid helium cooled cryostat, our device demonstrates a lower temperature sensing limit of (48 ± 2) K, below the nitrogen boiling point. This achievement is made possible by the low dark count rates of SNSPDs, as validated by theoretical simulations. Furthermore, we utilize our device to map cryogenic temperatures on the 350 cm2 surface of a specially designed hollow cylindrical aluminum sample, accommodating approximately 2 m of standard single-mode optical fiber. During nitrogen cooling, we monitor the temporal evolution of the spatially dependent temperature gradient on the metallic sample with a temporal sampling down to one minute. Fiber-based distributed temperature sensing with centimetric spatial resolution can be effectively applied for 3D mapping at cryogenic temperatures of superconducting, quantum computing and aerospace instrumentation.

Analog Wavelength Locking in an Optical Single-Sideband Transmitter of a Millimeter-Wave Radio-Over-Fiber Link Featuring a Micro-Ring Resonator and a Heat-Pump-Controlled Laser

This paper presents a novel approach to addressing the issue of temperature-induced instability in an optical, single-sideband transmitter based on a micro-ring resonator (MRR) suitable for millimeter-wave (mmW) radio-over-fiber (RoF) communications. We propose utilizing the drop port of the MRR to provide a feedback signal to the closed-loop control (CLC) system. The latter serves to maintain the optimal alignment between the laser’s carrier and the MRR’s resonant wavelength, thus mitigating the adverse effects of chromatic-dispersion-induced power fading at the receiving end. Since the feedback information is extracted from the otherwise-wasted resonant energy at the drop port, the control system does not compromise the delicate optical signal at the through port. A CLC was synthesized, designed, and prototyped to provide real-time wavelength tuning of the heat-pump-controlled laser based on the feedback signal. Experimental evaluations demonstrate that the wavelength of the laser could be successfully locked to the MRR’s resonance with a wavelength dither of less than 0.004 nm (~491 MHz). This allowed us to limit the power-penalty deterioration to less than 2 dB for a RoF link with a 2.5-km standard telecommunication single-mode fiber (SMF), a modulation frequency of 37.8 GHz, and a carrier wavelength of 1563.97 nm (~191.820 THz). The proposed solution offers an alternative approach for the carrier and the MRR’s resonant wavelength interlocking without the need for complex photonics like thermo-optic or electro-optic structures to control the temperature or phase velocity, respectively.

Pilot-scale testing of natural gas pipeline monitoring based on phase-OTDR and enhanced scatter optical fiber cable

In this paper, we present the results of lab and pilot-scale testing of a continuously enhanced backscattering, or Rayleigh enhanced fiber cable that can improve distributed acoustic sensing performance. In addition, the Rayleigh-enhanced fiber is embedded within a tight buffered cable configuration to withstand and be compatible for field applications. The sensing fiber cable exhibits a Rayleigh enhancement of 13 dB compared to standard silica single-mode fiber while maintaining low attenuation of ≤ 0.4 dB/km. We built a phase-sensitive optical time domain reflectometry system to interrogate the enhanced backscattering fiber cable both in lab and pilot-scale tests. In the laboratory experiment, we analyzed the vibration performance of the enhanced backscattering fiber cable and compared it with the standard single-mode telecom fiber. Afterward, we field validated for natural gas pipeline vibration monitoring using a 4-inch diameter steel pipeline operating at a fixed pressure level of 1000 psi, and a flow rate of 5, 10, 15, and 20 ft/s. The feasibility of gas pipeline monitoring with the proposed enhanced backscattering fiber cable shows a substantial increase in vibration sensing performance. The pilot-scale testing results demonstrated in this paper enable pipeline operators to perform accurate flow monitoring, leak detection, third-party intrusion detection, and continuous pipeline ground movement.

Resonant Couplings in U-Shaped Fibers for Biosensing

U-shaped tight curvatures in optical fibers lead to resonant couplings between the fundamental and higher order modes that are sensible to different parameters, such as strain or temperature, for example. The optical response of the sensor consists on the shift of the resonant wavelength of the coupling. In the case of singlemode fibers, the coupling involves a so-called “cladding mode” and, due to its evanescent field, the curved region will be sensible to changes in the external medium, as well. In this paper, we present the fabrication and characterization of a robust, easy-to-make, U-shaped fiber sensor based on singlemode telecom fiber and its application for biosensing. The resonant nature of the sensing mechanism presents the advantage of large dynamic ranges for RI variations without the ambiguity of other techniques such as interferometry. We studied the performance of the U-shaped fiber sensor for different bending radii, to optimize its sensitivity and detection limit at 1550 nm operation wavelength, as well as the effect of temperature on its response. The shift of the resonant wavelength was measured in detail as a function of the external RI within the range [1.33-1,37]; the detection limit was established in (3.71±0.03)×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> RIU. Furthermore, the device was successfully tested as a proof of concept biosensor, using a system model antigen-antibody (BSA-aBSA.)

Continuous variable quantum key distribution with a shared partially characterized entangled source

Locking the sophisticated and expensive entanglement sources at the shared relay node is a promising choice for building a star-type quantum network with efficient use of quantum resources, where the involved parties only need to equip low-cost and simple homodyne detectors. Here, to our best knowledge, we demonstrate the first experimental continuous variable quantum key distribution with an entanglement source between the two users. We consider a practical partially characterized entangled source and establish the security analysis model of the protocol under realistic conditions. By applying a biased base technology, the higher key rate than that of the original protocol is achieved. The experimental results demonstrate that the distance between two users can reach up to 60 km over telecom single-mode fiber, implying the feasibility for high-rate and secure communication with a shared entangled source at metropolitan distances.

Zastosowanie światłowodowego interferometru różnicowego w pomiarach natężenia prądu elektrycznego

The article presents an electric current sensor built of a fiber-optic differential interferometer using the Faraday effect in a single-mode fiber. It was applied to measure current waveforms with large amplitudes and mains frequency. The optical sensor does not introduce additional resistance and inductance into the measured circuit, which is a desirable phenomenon in this type of measurements. The magnetosensitive element is an optical fiber coil made of a quartz single-mode telecommunications fiber. The optical fiber, in which the core is twisted around its axis, is characterized by a small influence of disturbing quantities, i.e., mechanical vibrations and pressure changes, on the working of the differential interferometer by inducing linear birefringence in the glass fiber. The methods of elimination of the quantities influencing the operation of the optical fiber current sensor were proposed by reducing the linear birefringence induced in the optical fiber from these quantities. The dependence of the normalized light intensity was plotted. The results of experimental research on a design solution of a differential interferometer based on the Faraday effect, operating at a wavelength of 1550 nm, are presented. The sensor was used for measurements of sinusoidal current with a frequency of 50 Hz and amplitudes ranging 100–1500 A. The uncertainty of measurement of the electric current amplitude was determined in the range of the measured values, which was estimated at no more than 1.5 %.

The SARS-CoV-2 specific IgG antibodies biophotonic sensor.

In this paper, we present the design and the principle of operation of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific immunoglobulin G (IgG) biophotonic sensor, which is based on the single-mode telecommunication fiber. We fabricated the sensor head at the face of the single mode fiber-28. Due to the process of bio-functionalization, our sensor has the ability to selectively detect the SARS-CoV-2 specific IgG antibodies. The results of preliminary tests allowed us to correctly determine the presence of antibodies in less than 1 min in 5 μl in a volume sample of concentration of 10 μg/ml, which according to studies, corresponds to the concentration of IgG antibodies in human serum. Additionally, the tested sample can be smaller than 5 μl in volume.

Optical Properties of a Tapered Optical Fiber Coated with Alkanes Doped with Fe3O4 Nanoparticles

The presented research shows the possibilities of creating in-line magnetic sensors based on the detection of changes of light propagation parameters, especially polarization, obtained by mixing Fe3O4 nanoparticles with hexadecane (higher alkane) surrounding a biconical optical fiber taper. The fiber optic taper allows to directly influence light parameters inside the taper without the necessity to lead the beam out of the structure. The mixture of hexadecane and Fe3O4 nanoparticles forms a special cladding surrounding a fiber taper which can be controlled by external factors such as the magnetic field. Described studies show changes of transmission (power, loss) and polarization properties like azimuth, and ellipticity, depending on the location of the mixture on sections of tapered optical fiber. The taper was made of a standard single-mode telecommunication fiber, stretched out to a length of 20.0 ± 0.5 mm and the diameter of the tapers is around 15.0 ± 0.3 μm, with the loss lower than 0.5 dB @ 1550 nm. Such a taper causes the beam to leak out of the waist structure and allows the addition of the external beam-controlling cladding material. The presented research can be used to build polarization switches or optical sensor. The results show that it can be a new way to control the propagation parameters of a light beam using tapered optical fiber and magnetic mixture.

Distributed temperature sensor combining centimeter resolution with hundreds of meters sensing range.

We present a Raman distributed temperature sensor based on standard telecom single mode fibers and efficient polarization-independent superconducting nanowire single photon detectors. Our device shows 3 cm and 1.5 °C resolution on a 5 m fiber upon one minute integration. We show that spatial resolution is limited by the laser pulse width and not by the detection system. Moreover, for long fibers the minimum distance for a measurable temperature step change increases of around 4 cm per km length, because of chromatic dispersion at the Stokes and Anti-Stokes wavelengths. Temperature resolution is mainly affected by the drop in the laser repetition rate when long fibers are tested. On a 500 m fiber, a trade-off of 10 cm and 8 °C resolution is achieved with 3 minutes integration. Fiber-based distributed temperature sensing, combining centimetric spatial resolution with hundreds of meters sensing range, could pave the way for a new kind of applications, such as 2D and 3D temperature mapping of complex electronic devices, particles detectors, cryogenic and aerospace instrumentation.

Filament-arrayed Bragg gratings for azimuthally resolved displacement sensing in single-mode fibers.

Filament arrays were inscribed off-axis in the core of standard single-mode telecommunication fiber, using femtosecond laser pulses. The flexible line-by-line writing formed uniform, parallel filaments, permitting Bragg grating sensing of the photoelastic response from inside of the narrow grating plane. Active monitoring of the Bragg resonance wavelength while driving a lateral fiber tip displacement directly informed on the fiber mechanics when coupled with opto-mechanical modelling. Overlaying of parallel and orthogonal gratings further provided a strongly contrasting azimuthal sensitivity, which paves the way for multi-dimensional displacement sensing with improved precision.

Thermal Stability of Type II Modifications Inscribed by Femtosecond Laser in a Fiber Drawn from a 3D Printed Preform

Fiber drawing from a 3D printed perform was recently discussed to go beyond the limitations of conventional optical fiber manufacturing in terms of structure and materials. In this work, the photosensitivity of silica optical fibers to femtosecond laser light, and fabricated by 3D printing a preform, is investigated. The writing kinetics and the thermal performance of Type II modifications are studied by varying the laser pulse energy and investigating the birefringence response of the femtosecond (fs)-laser written structures. Compared with a conventional telecom single mode fiber (SMF28), the fiber made by 3D printing is found to have similar writing kinetics and thermal performance. Additionally, the thermal stability of the imprinted fs-laser induced nanostructures is investigated based on the Rayleigh–Plesset equation, describing a model of nanopores dissolution underpinning Type II modifications with thermal annealing.

Phase-Sensitive Optical Time Domain Reflectometry With Rayleigh Enhanced Optical Fiber

In this paper, a phase-sensitive optical time domain reflectometry ( $\Phi $ -OTDR) based on Rayleigh enhanced optical fiber is proposed to improve the system signal-to-noise ratio (SNR). In the experiment, the vibration performance of the Rayleigh enhanced optical fiber is analyzed and compared with standard single-mode telecom fiber. The results demonstrate that the measured SNRs of peaks in frequency spectra have been improved by 14 dB (at 1 kHz vibration frequency) at the end of the 2 km specialty sensing fiber. A wide range of vibration frequencies from 50 Hz to 15 kHz are demonstrated experimentally. The proposed method overcomes the inherent limitations of the conventional $\Phi $ -OTDR system and significantly enhances the vibration sensing performance.

Distributed High Temperature Monitoring of SMF under Electrical Arc Discharges Based on OFDR.

The distributed high temperature measurement of an optical fiber subjected to electric arc discharges based on optical frequency-domain reflectometry is experimentally demonstrated. The distributed temperature profile is attained in an open glow regime of a few milliamps with maximum detectable temperature up to 2100 ± 20 °C. The discharge arc-induced softened length of the fiber and mechanical stress are measured and statistically analyzed in terms of the correlation of the Rayleigh spectra. The large wavelength scanning range of OFDR enables much higher accuracy for the delay time measurement with a minimum measured delay of 40 fs. The delay shift over the entire heating range for a single discharge duration is statistically calculated by using a temporal correlation method. The reliability of the thermal sensitivity coefficient as 10 pm/°C for telecom single mode fiber (SMF, @1550 nm) is quantitatively analyzed and evaluated by the correlation coefficient. Lastly, a spectral mapping method is employed in spectrum monitoring for discharge dynamic impact on the optical path length (OPL) and local Rayleigh scatter.

A Digital Twin Approach to Study Additive Manufacturing Processing Using Embedded Optical Fiber Sensors and Numerical Modeling

One of the major challenges for metal-powder-based additive manufacturing is measuring and mitigating residual strain induced during the manufacturing processes. This article reports distributed fiber optic sensors embedded in Inconel alloy components as experimental means to validate numerical models of additive manufacturing process. Electroplating was used to deposit a metal protective jacket onto standard telecom single-mode fibers for strain measurements, Fiber sensors were embedded in an Inconel alloy substrate using the laser engineered net shaping (LENS) process. Using a Rayleigh-scattering optical frequency domain reflectometer (OFDR), temperature changes, and residual strain in the metal substrate were monitored with 5 mm spatial resolution during the LENS process. Using finite element analysis, temperature and strain profiles induced by the LENS deposition processes were also numerically studied. Discrepancies between the simulated temperature and strain profiles and those measured directly were less than 10%. Results presented in this article demonstrates a digital twin approach to fuse modeling results with distributed fiber sensor measurement data to study additive manufacturing process toward design and fabrication process optimization.

ZnO indiffused MgO:PPLN ridge waveguides.

We have demonstrated the first MgO:PPLN ridge waveguides based on ZnO indiffusion and dicing. The fabrication process utilizes ductile regime dicing of a planar waveguide layer producing second harmonic generation (SHG) devices with a near-symmetric sinc2 spectral profile, indicating highly uniform 40 mm long devices. A near circular pump mode is also obtained enabling efficient coupling to single mode telecommunication fibers. A conversion efficiency of 145%/W, for 1560-780 nm SHG, has been measured.

Line-by-line fiber Bragg grating fabrication by femtosecond laser radiation

We report on the fabrication of second order and fourth order fiber Bragg gratings (FBGs) in standard single mode telecom fiber through the polymer coating made line-by-line technique using femtosecond laser radiation. Measurement of spectral characteristics were performed in the reflection mode of the input signal of tunable laser.

Two-photon direct laser writing of beam expansion tapers on single-mode optical fibers

Small misalignments between two standard telecom single-mode fibers in a physical contact connection can lead to large optical losses. It is known that by expanding the mode field diameter of the fiber, the misalignment tolerances can be relaxed. One of the approaches to obtain this beam expansion is to use tapers. We propose an air-clad taper structure to transmit the fundamental mode of a single-mode fiber adiabatically to a 3 times larger mode field area in physical contact expanded beam connectors. This results in a 241.4 μm long linear taper. The taper itself is fabricated on top of a cleaved fiber facet by means of the two-photon polymerization direct laser writing technique. Experimental results for lateral misalignment show excellent agreement with simulated values and give an increase in lateral misalignment tolerance of 1 μm (−1 dB) and 1.8 μm (−3 dB). Total insertion losses down to 0.76 dB are measured, showing the trade-off between achievable insertion loss and misalignment tolerance relaxation. Finally, we show that the use of additive manufacturing techniques in fiber beam expansion applications make it possible to fabricate taper structures with full 3D design freedom and to upscale the process to multi-fiber components.

High Sensitive Z-Shaped Fiber Interferometric Refractive Index Sensor: Simulation and Experiment

A robust fiber-optic interferometer, which is formed by introducing two bends (i.e., z shape) to the standard telecommunication single mode fiber, is designed and analyzed theoretically and experimentally for the refractive index (RI) sensing. The first (second) bend couples (re-couples) the core (cladding) mode to the cladding (core) modes. The RI-sensitive phase difference between the core and cladding modes gives rise to the modulation of the transmitted intensity. The experimental results show that the z-shaped interferometric sensor possesses an RI sensitivity as high as 196 nm/RIU and fit well with the theoretical predictions. An investigation of the effect of perturbations of bent angle reveals that the sensor possesses relative high sensitivities as the bent angle ranges from 13° to 17° with the difference between the maximum and minimum sensitivities only 2.5% indicating the structure has a good fabrication tolerance to the inaccuracy of the bent angles. In addition, the sensor has advantages of low cost, simple structure, and an ease of fabrication, showing great potential in many sensing applications.

Fabrication of Bragg Gratings in Random Air-Line Clad Microstructured Optical Fiber

Fiber Bragg gratings (FBGs) are written using an infrared (IR) femtosecond laser and a phase mask into pure silica microstructured optical fiber having a cladding region comprised of random air-lines (RAL). Scanning electron microscopy measurements of the IR irradiated RAL fiber samples shows the presence of subwavelength nanograting structures associated with thermally stable type II Bragg gratings. High temperature annealing testing shows that although the RAL FBGs have a high degree of stability even at 1000 °C, they are less stable than similar FBGs made in single mode telecom fiber (SMF-28).