When few-mode fibers are employed in mode-division multiplexing (MDM), mode coupling between the propagation modes must be suppressed. In this study, the impulse response for a two-mode fiber (TMF) ...is theoretically described to estimate the mode coupling in the fiber and at a splice point. We then propose a technique for measuring the mode-coupling coefficient in a TMF based on the impulse response technique. The mode-coupling behavior in a fiber and at splice points is measured experimentally using the proposed technique for several fabricated TMFs. We clarify the relationship between the effective-index difference Δ n eff between LP 01 and LP 11 modes and the mode-coupling coefficient h for our fabricated TMFs.
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.
Resonant couplings in U-shaped fibers for biosensing Londero, Carolina; Delgado-Pinar, Martina; Cuadrado-Laborde, Christian ...
Journal of lightwave technology,
07/2023, Letnik:
41, Številka:
13
Journal Article
Recenzirano
Odprti dostop
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 -5 RIU. Furthermore, the device was successfully tested as a proof of concept biosensor, using a system model antigen-antibody (BSA-aBSA.)
A novel multi-core fiber (MCF), having eight cores within a 125-μm-diameter cladding and suitable for short-reach transmissions, is proposed. By optimizing O-band transmission, the proposed MCF ...realized the high-density core packing simultaneously achieving the optical characteristics comparable to those of the standard single-mode fiber in O-band, where low material dispersion can be leveraged. The standard 125-μm-diameter cladding is compatible with conventional cabling/connecting technologies and has the tightly bendable mechanical reliability proven by the widely installed standard optical fibers. An ultra-high-density 12-MCF cable was fabricated with the proposed MCF, and achieved 13.6 cores/mm 2 (96 cores in the 3-mm-diameter cable). The transmission characteristics of the cabled MCF were evaluated using a 100GBASE-LR4 transceiver, and error-free 8-SDM × 4-WDM × 25-Gb/s (800-Gb/s/fiber) signals in O-band were successfully transmitted over the 1.11-km-long cabled MCF.
This paper compares the impact of gamma irradiation on various optical fibers, where the evolution in their optical properties could be identified using long period gratings (LPG) there induced. The ...LPGs were fabricated in broad spectrum of commercially available single-mode optical fibers - from standard to unconventional ones - using the electric arc discharge method. The fused silica fiber material contained such dopant as Ge, F, B/Ge and P. The gamma exposure has been performed with a dose rate of 2.6 kGy/h for 20 h (a total dose of 52 kGy). Subsequently, the recovery effect was monitored during the following 48 h. The wavelength shift and power change of the LPG attenuation bands during irradiation were investigated in real time. Moreover, to identify the impact of gamma treatment on the fiber properties, the thermal response of the gratings was studied before and after the irradiation. Depending on the fiber, significant differences have been observed in the grating responses. The highest radiation-dependent resonance wavelength shift has been found for B/Ge fiber (∼10 nm at maximum dose). Moreover, for these LPGs no response saturation within the applied dose levels has been observed together with very low recovery effect, what differentiate these LPGs from the other tested in this experiment. Finally, concerning the changes in optical power at the resonance wavelength, the LPG induced in P-doped fiber has shown a strong irradiation-induced attenuation reaching 18 dB with a negligible recovery effect. The findings reported in this work are crucial for optical fiber and optical fiber sensors application in environments exposed to radiation.
Radiation-induced attenuation (RIA) in undoped-silica-core optical fibers, of which the preform cores are synthesized in high O 2 excess conditions in the vapor-gas mixture ("high oxygen excess ...fibers, HOE-fibers"), is investigated in the spectral range 1.1-1.7 μm under γ-irradiation from a 60 Co-source. The O 2 excess degree, the F content in the cladding, the drawing speed, and tension are varied among the fibers. RIA is found to strongly depend on the balance between the O 2 excess degree in the core and the F content in the cladding and also on the fiber drawing tension. RIA anticipated in HOE-fibers with optimized O 2 excess and a practicably low drawing tension at λ = 1.55 μm is estimated to be a few times lower than that in the commercial radiation-resistant F-doped-silica-core fibers.
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.
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.
In this letter, a strain sensor with high sensitivity enhancement using a special case of Vernier effect is presented. The sensor configuration is composed of two-fiber loop mirrors in a cascaded ...configuration with opposite strain responses when individually characterized. Thus, the enhanced Vernier effect is explored, which is the most sensitive of three possible cases Vernier effect. Here, the Vernier response depends on the difference between the sensitivities of each Hi-Bi optical fiber. In addition to this, the fundamental and the first harmonic were also explored. The results obtained are a strain sensitivity of (13.3 ± 0.3) pm/<inline-formula> <tex-math notation="LaTeX">\mu \varepsilon </tex-math></inline-formula> for the carrier, (80.0 ± 0.3) pm/<inline-formula> <tex-math notation="LaTeX">\mu \varepsilon </tex-math></inline-formula> or the Vernier envelope of the fundamental case and (120 ± 1) pm/<inline-formula> <tex-math notation="LaTeX">\mu \varepsilon </tex-math></inline-formula> for the Vernier envelope of the first harmonic. The first harmonic could achieve a magnification factor of 8. Considering that the optical interrogation system allows a minimum resolution of 0.02 nm, the minimum measurement step achievable is <inline-formula> <tex-math notation="LaTeX">0.2~\mu \varepsilon </tex-math></inline-formula>. This work proves the possibility of applying the concept of enhanced Vernier effect to fiber loop mirrors, obtaining higher sensitivity than a standard fiber loop mirror alone. Besides, the sensitivity can be increased through the usage of harmonics of the Vernier effect. Moreover, the use of large interferometers allows a better discretization of the envelope, which implies a greater ease of analysis.
