Annealing effects on optical losses in silica optical fiber drawn from 3D-printed preform were investigated. An irreversible reduction in loss was observed through multiple annealing cycles at a ...temperature <inline-formula> <tex-math notation="LaTeX">T = </tex-math></inline-formula> 800 ° C . Changes in Raman spectroscopy confirm densification of the core as the stresses in glass relax with annealing. The temperature-dependent loss in the 3D printed fiber is consistent with modal field overlap at the core-cladding interface.
We propose an enhanced multiple-pass group delay (GD) measurement scheme of fiber-Bragg grating (FBG) based on optical low-coherence reflectometry (OLCR). The fiber loop embedded with the measured ...FBG is innovatively applied to the OLCR-based system, and the probe signal light can go through the FBG repeatedly. In the multiple-pass propagation of light, the FBG-induced GD or chromatic dispersion is amplified. After the straightforward reduction, the GD of FBG can be recovered accurately. And the triple-pass measurements are demonstrated in detail. Compared to the conventional single-pass scheme, the repeatability of GD in our measurements (<0.4ps) is improved more than 2 times. The multiple-pass scheme can be expected to break the limit of the GD resolution in the existing FBG measurement methods. In addition, using the polarization controllers (PC) in the fiber loop, the weak polarization differential group delay (DGD) or polarization mode dispersion (PMD) of FBG is measured and discussed. It should be interesting to the characterization of the ultraviolet (UV) or mechanical induced birefringence in photosensitive optical fibers. The multiple-pass measurement scheme of FBG could also be expected to realize two-parameter sensing.
This article provides an overview of potential alternatives for providing wireless backhaul in regions that suffer from the lack of fiber optic-connectivity to the core network. These regions can be ...rural and remote locations, low-income neighborhoods in urban and suburban regions, and post-disaster locations suffering from the destruction of cellular infrastructure. For these scenarios, extending fiber optic cables to such locations might be extremely expensive, impractical, or simply not feasible. Hence, in order to enhance the backhaul connectivity in these scenarios, we study the potential and applicability of the integrated access and backhaul (IAB) technique, and a hybrid combination of IAB and non-terrestrial networks (NTN) that includes high/low altitude platforms (HAPs/LAPs) and low earth orbit (LEO) satellites. We conclude this article by discussing the design considerations and potential research problems that would enable efficient deployment of such solutions.
An analytical approach about the general type of step-index optical fiber modes and their variations is presented in this paper. The theoretical model is solved through our analytical method. With ...the boundary conditions, a composite equation set is established and solved. The precise results of all modes are achieved with a high-precision numerical solution. In this paper, the key modal qualities contain electromagnetic fields' distributions, the effective refractive index, and its tendencies. And the modal sensitivity is based on the partial derivative of the effective refractive index (<inline-formula><tex-math notation="LaTeX">\partial</tex-math></inline-formula>n eff /<inline-formula><tex-math notation="LaTeX">\partial</tex-math></inline-formula>n i and <inline-formula><tex-math notation="LaTeX">\partial</tex-math></inline-formula>n eff /<inline-formula><tex-math notation="LaTeX">\partial</tex-math></inline-formula>r i ). The derivative rule of special function allows analyzing the sensitivity of modes. Furthermore, four qualitative deductions are derived during the process, including the qualitative analysis of modes and their variation, several of which are supported with previous experiments. Our work is beneficial for exploiting new fiber and researching relative fiber sensors.
We propose a novel polarization-maintaining supermode fiber containing quasi-elliptically arranged high-index cores. Numerical simulation indicates that such a fiber could support up to 20 distinct ...modes with different polarization states and spatial orientations. At 1550 nm, all the 20 modes are separated from their adjacent modes with effective refractive differences beyond 10- 4 . We also investigate the influence of parameters on mode number and effective area of the proposed fiber. Wavelength-dependent performance is analyzed subsequently ranging from 1500 to 1630 nm. The proposed fiber could guide 20 modes with low dispersion over the entire C-band. This letter illustrates that the proposed fiber might be a promising candidate for mode division multiplexing to enhance optical transmission capacity.
In this letter, we demonstrate the enhancement of the Rayleigh back-scattering signal in germanium-doped-core silica fibers, using high resolution Rayleigh fiber sensor. Experiments are performed to ...estimate the thermo-optic coefficients <inline-formula> <tex-math notation="LaTeX">\text{C}_{\mathrm {T}} </tex-math></inline-formula> for different germanium dioxide (GeO 2 ) concentrations. It was demonstrated that, the thermo-optic coefficients increase with the (GeO 2 ) doped concentrations.
In this letter, a nonlinear semi-analytical model (NSAM) for simulation of few-mode fiber transmission is proposed. The NSAM considers the mode mixing arising from the Kerr effect and waveguide ...imperfections. An analytical explanation of the model is presented, as well as simulation results for the transmission over a two mode fiber (TMF) of 112 Gb/s using coherently detected polarization multiplexed quadrature phase-shift-keying modulation. The simulations show that by transmitting over only one of the two modes on TMFs, long-haul transmission can be realized without increase of receiver complexity. For a 6000-km transmission link, a small modal dispersion penalty is observed in the linear domain, while a significant increase of the nonlinear threshold is observed due to the large core of TMF.
Reflector-less biosensors based on optical fibers enable the detection of the refractive index (RI) variations, in reflection mode, without the need for any reflective element (such as a grating or ...an interferometer). The sensing system works by interrogating the wavelength shift occurring in the Rayleigh scattering signal at each location of a thinned fiber through an optical backscatter reflectometer (OBR); a high-scattering fiber is required in order to compensate for the propagation losses. The approaches reported so far make use of etched fibers, which are however fragile and require tens of minutes of fabrication, and U-bent fibers which are incompatible with in-situ devices. In this article, we present the working principle and main results of reflector-less biosensors fabricated through shallow tapering; this concept allows the fastest fabrication (∼20 seconds through a CO 2 automated laser splicer) reported so far, and allows maintaining a compact and robust form factor as the fiber maintains a diameter >28 μm (>22% of the initial thickness). The fabrication process allows achieving a peak sensitivity up to 1.33 nm/RIU (1.05 nm/RIU average over 5 tapers), using MgO-nanoparticle doped fibers. The tapered biosensors have been functionalized through the silanization method, in order to detect CD44 protein (from 100 fM to 10 nM), a breast cancer biomarker. The results show a successful detection with a low limit of detection (16.4 pM) and high specificity over two controls.
It is essential to carry out real-time position and speed monitoring of trains to ensure the safety of railway operation. In this letter, the phase-sensitive optical-time-domain reflectometry ...(Φ-OTDR) is demonstrated to overcome the drawbacks of the track circuit, which is widely used and has the risk to be damaged by lightening, for the first time. A long sensing cable, buried nearby to two parallel railways, is used to detect the vibration signals generated by trains with Φ-OTDR and the real-time vibration signals of the trains are extracted/quantified by wavelet denoising. With the edge detection by normalized sliding variance, the operation status of two nearby trains, including their relative position and speed, are obtained over a 10.2-km measurement length in real time. This letter offers a new passive way for safety monitoring of railway operation.
Universal fiber is an optical fiber that supports both multimode and single-mode transmission. It is a multimode fiber with a mode field diameter of the fundamental mode roughly matching that of a ...standard single-mode fiber. In today's short-distance communications, both multimode fiber and single-mode fiber are used. Universal fiber can accommodate the needs of single-mode and multimode transmission so that end users can take advantage of the cost and performance benefits of each transmission type. In this paper, we present the design and properties of universal fiber, as well as its transmission performance for 100G systems. We also explore several application scenarios where the fiber can be utilized. In particular, we illustrate how the fiber can be used in 5G wireless fronthaul applications to meet the current needs while providing a path for future upgrades. Testing results and discussions of practical issues are also presented.
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