COMPARATIVE ANALYSIS OF SINGLE-MODE AND MULTI-MODE FIBRE OPTIC CABLES FOR VIBRATION SENSING

Distributed fiber optic sensors (DFOS) are viewed as a promising technology for efficient, cost-effective, and non-intrusive real-time monitoring for a variety of applications. The chemical passivity, non-magnetic interference behavior, and ability to acquire continuous measurements at high-spatial resolution have made DFOS very attractive for in-situ measurement of temperature, strain, vibration, etc. The accuracy of the measured parameter by the DFOS is highly dependent on the strength and quality of the optical signal returning from the point of interest. The signal degradation in DFOS results from optical losses due to attenuation, absorption, scattering, bending, dispersion, and coupling. This study analyzes the degradation observed in both the single-mode and multimode fibers installed in a 1574 mdeep wellbore for acquiring distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) data, respectively. The degradation was unexpected as it was observed within three years of DFOS installation in an experimental, non-producing well that contains non-corrosive fluids and operates in a low-temperature (<54.4 °C) and low-pressure (<3500 psi or 24131 kPa) environment. A root-cause analysis was performed to investigate the cause of this degradation using time-lapse optical loss measurements acquired at different wavelengths using an optical time-domain reflectometer. Degradation of the multimode fiber was also examined by the time-lapse analysis of the Raman backscatter that is used for DTS measurement. Based on the investigation, microbending was found to be the main cause of the observed degradation. Its impact on the quality of the DAS and DTS measurements was also analyzed both qualitatively and quantitively. Recommendations for minimizing degradation are presented.

Grating-based Fiber Optic Sensors (FOSs), i.e. relying on Bragg Gratings (BGs), Long Period Gratings (LPGs), Tilted Fiber BGs (TFBGs), have seen a popularity in recent years for sensing applications, however, most of these are inscribed on Single-Mode Fibers (SMFs). Multi-Mode Fibers (MMF), on the other hand, offer new and different properties in grating design and performance characteristics compared to SMFs, since the spectral response may be tuned by core size, refractive index profile, numerical aperture, and mode coupling characteristics of the gratings. Also, MMFs can be readily coupled with inexpensive light sources and other optical components due to their large core and, thus, gratings in MMFs are preferred to yield lower cost systems. Moreover, in terms of sensing region, MMFs have a greater mode field surrounding the fiber when compared with SMFs, due to the larger core diameters of MMFs and, thus, even greater mode fields can be accessed with a smaller reduction of the fiber diameter which would have better mechanical robustness, when compared with gratings inscribed in SMFs. In this talk we present our latest research in BG structures inscribed in multi-mode optical polymer and glass fibers.

The advent of fiber optic technology in geophysics exploration has grown in its use in the exploration, production, and monitoring of subsurface environments, revolutionizing the way data are gathered and interpreted critically to speed up decision-making and reduce expense and time. Distributed Acoustic Sensing (DAS) has been increasingly utilized to build relationships in complex geophysics environments by utilizing continuous measurement along fiber optic cables with high spatial resolution and a frequency response of up to 10 KHz. DAS, as fiber optic technology examining backscattered light from a laser emitted inside the fiber and measuring strain changes, enables the performance of subsurface imaging in terms of real-time monitoring for Vertical Seismic Profiling (VSP), reservoir monitoring, and microseismic event detection. This review examines the most widely used fiber optic cables employed for DAS acquisition, namely Single-Mode Fiber (SMF) and Multi-Mode Fiber (MMF), with the different deployments and scopes of data used in geophysics exploration. Over the years, SMF has emerged as a preferred type of fiber optic cable utilized for DAS acquisition and, in most applications examined in this review, outperformed MMF. On the other side, MMF has proven to be preferable when used to measure distributed temperature. Finally, the fiber optic cable deployment technique and acquisition parameters constitute a pivotal preliminary step in DAS data preprocessing, offering a pathway to improve imaging resolution based on DAS measurement as a future scope of work.

&lt;span&gt;This paper presents a design of 3D modeling of Multimode and Single Mode Fiber using SolidWorks. Fiber technology is essential that presents optical fiber is the fastest optical cable laid by Internet Service Providers in network communication. The current design of both fibers has less detail animation on technical specifications of light propagations and cladding. Thus, characterization difficulties occur between this two fiber optics cables. It also has less promotion in media publications such as 3D model design as guidance to users. This paper presents details on 3D modeling of multimode mode and single mode fiber specifications held in the industry market. A 3D design with SolidWorks and comparison of both fiber characteristics are presented. Based on the 3D designed model, users are analyzed on their perspective and searching information which benefits telecommunication’s company. Technical calculations like core-cladding diameter ratio in microns are animated. The propagation of light in 3D single mode and multimode fiber is simulated using SolidWorks animator that presents it real fiber conditions. Result presents 10 most country searching used of both fiber cables and the difference in users search for both cables. A number of user’s search presents 3% more of multimode than single mode fiber search cases. This research is significant in presenting an animator of single and multimode fiber to users of network infrastructure development especially network developers and Telecommunications Company which can present it lively with animator transitions.&lt;/span&gt;

Multi-channel SPR sensor based on the cascade application of the Single-mode and multimode optical fiber

This paper demonstrates the possibility of determining the equivalent, in terms of the coincidence of differential mode delay diagram, refractive index profile of the multimode optical fiber by direct method and responses to pulse action, which are measured at the output through single-mode optical fiber. As an example, by using the measured data of the refractive index profile of the sample of multimode optical fiber and based on Gaussian approximation model impulse responses at the output of a short length single mode fiber, which was jointed with multimode fiber, were calculated. Multimode and single mode fibers were jointed with axial misalignment. Responses to impulse action were calculated for several values of axial misalignment of single-mode and multimode fiber. From the responses by the direct method the equivalent refractive index profile was determined. Comparison of the results of calculations of the differential-mode delay diagram for the investigated and the equivalent refractive index profiles showed their good agreement.

Numerical and experimental study of a multimode optical fiber sensor based on Fresnel reflection at the fiber tip for refractive index measurement

This paper proposes a fiber optic acoustic sensor (FOAS) based on a single-mode fiber - multimode fiber - single-mode fiber (SMS) structure attached to a thin polymer film used as a diaphragm. The diaphragm was specially developed to enhance the sensitivity towards the acoustic pressure-wave resulted from the partial discharge (PD) events. The sensitivity and signal-to-noise ratio (SNR) characterizations of the FOAS without and with a thin polymer film were performed. Both time-resolved and phase-resolved partial discharge (PRPD) patterns measurements were carried out in air and oil media. The experiment was conducted with three-electrodes using FOAS in conjunction with the conventional PD measurement as per IEC 60270 standard. The sensor achieved a sensitivity up to -31.21 dBm and -30.8 (0 dBm is defined as 1V/μBar) using broadband and tunable light source, respectively. The discharge characteristics pattern of FOAS was verified with IEC 60270 standard, and the patterns of FOAS resembled IEC 60270 standard. The proposed FOAS was capable for detecting the PD using both broadband and tunable laser lights. The use of the thin polymer film had a significant impact on the acoustic sensitivity. With the simple, low-cost design structure and free from electromagnetic interference, FOAS is found to be suitable as an in-situ sensor for detecting the acoustic signals of partial discharge and can be utilized inside the transformer.

Visualization of organs and cells in the interior of living beings is a challenging task due to the light absorption and multiple light scattering occurring in biological tissue that prevents the di-rect transmission of images. A standard visualization approach is based on the use of endo-scopes which is accomplished through apertures in the body. Since their invention, the light transmission capability of optical fibers has enabled fiber optic based endoscopy with devices based on bundles of optical fibers that can directly relay images. Due to their small diameter, fiber optic endoscopes are standard in minimally invasive applications either with a white light illumination or as a fluorescent imaging device. The principle behind fluorescent endoscopy consists on the scanning of light intensity over a fluorescent sample, which is achieved by se-quential illumination of each one of the fiber bundles or by mechanical scanning of a single-mode double-cladding fiber. Collecting the fluorescent signal through the light guiding medium, an image can be reconstructed. The main drawback of fiber bundle endoscopes is the pixelated limited resolution given by the presence of thousands of cores that conform the bundle. In the double cladding fiber endoscopes, there is a limit to the miniaturization of the endoscope due to the requirement of mechanical elements at the tip of the fiber to scan the illumination over the sample. In this thesis, methods for focusing and digital scanning of optical light pulses through multimode optical fibers without any distal mechanical element are developed. Such techniques are based on spatial light modulation. Spatial phase modulation allows the control of light propagation in scrambling media, as in a multimode fiber, enabling the generation of intensity light foci or arbitrary intensity profiles. The high intensity of the transmitted pulses permits multi-photon imaging through multimode optical fibers, resulting in imaging probes of higher resolution than in the case of fiber bundles. We demonstrate in a working prototype that this approach provides all the advantages of multi-photon microscopy at the tip of an ultra-thin probe, such as a reduced photo bleaching of the sample, optical sectioning and enhanced image contrast. The developed methods can also be employed for material processing that requires high in-tensity light pulses. In specific, we demonstrate additive manufacturing, also known as 3D printing, at the tip of an ultra-thin needle. The working principle is based on two-photon polymerization, which is accomplished by scanning intense light pulses on a photosensitive material that hardens when exposed to light. All other additive manufacturing methods require very large nozzles or components in close proximity to the structure that they build, up to now. With an ultra-thin 3D printing probe we enable micro-fabrication through very small apertures, in places of difficult access or in the interior of living beings. We call it, endofabrication.

For several decades silica-based optical fibres have been used for telecommunication and sensor purposes. The single-mode fibre is frequently employed in long-distance networks, whereas the multi-mode fibre is the preferred means of signal transport in campus and in-building networks. Because of the huge bandwidth of optical fibres in comparison to its electrical wireless and copper-based counterparts, the demand for optical fibres keeps increasing. In a competitive market, fibre manufacturers aim to produce ever better fibres that are as cheap and easy to employ as possible. As fibre research, development and manufacturing is a mature discipline, improvements in fibre design can only be achieved through the construction of robust, accurate and efficient numerical fibre models for the computation of those quantities that determine the behaviour of the fibre. We have developed a modular software code, based on Maxwell’s equations, to compute these quantities in a vectorial full-wave way for both single-mode and multi-mode optical fibres. Key is the refractive-index profile, or, more specifically, the dopant profile, as it defines the propagation, splicing and bending-loss characteristics of the fibre. For the single-mode fibre, the fibre quantities that we have concentrated on are dispersion, dispersion slope, mode-field diameter, effective area, bending loss, effective and theoretical cut-off wavelength and MAC-value. We highlight one fibre quantity in particular, viz. the computation of the bending loss in a single-mode fibre. Many approximate modelling techniques have been developed to estimate this loss in a fast way. Our numerical scheme, however, is the first rigorous one, as we have performed a vectorial full-wave analysis of the bent optical fibre. In this context, triple integrals involving products of Bessel functions with large, complex order and argument appear. Due to cancellations in the pertaining computation, a high relative accuracy is needed for the computation of each product. As a result, it takes weeks on a contemporary computer to compute the bending loss as a function of the radius of curvature. We have used the vectorial full-wave bending-loss results to determine the most appropriate approximate method. Subsequently, we have extended that approximate method to compute the bending losses of higher-order modes, since the required effective cut-off wavelength depends on the bending loss of the first higher-order mode. The selected approximate method has been used in the ensuing bending-loss calculations. Since the fibre properties are often conflicting, it is a challenging task to adapt the radial dopant profile to meet a set of predefined design goals. A design goal is a combination of desired values for (some of) the aforementioned fibre quantities, and can mathematically be translated into a cost function. The minimisation of this cost function provides us with the optimal dopant profile for that specific set. For the single-mode fibre, we have performed this minimisation for piecewise-linear profiles, by employing various global and gradient-based local optimisation strategies to speed up the design step considerably. Frequently,these optimisation strategies lead to counter-intuitive dopant profile designs that could not have been contrived otherwise. We have selected a deliberate mix of several optimisation routines and have compared their performances. Perhaps the most important conclusion is that there still appears to be room for improvement in the design of the radial dopant profile of commercially available fibres. For the multi-mode fibre, vectorial full-wave optimisation is not feasible yet because of the long computation times for the large number of propagating modes. Still, our numerical scheme allows for a manual fine-tuning of the popular power-law profile to minimise differential mode delay. Further, we have included mode coupling and differential mode attenuation in our model to obtain intensity patterns that match closely with measurements. We have also analysed the influence of profile variations, e.g. on-axis dips and kinks, on the intensity pattern. A selective excitation of different mode groups in a multi-mode fibre, offers the possibility to create several independent transmission channels, and thus a higher information capacity. Recently, the feasibility of this so-called mode group diversity multiplexing technique has been demonstrated. Simulations provide us with a means to better understand its operation and possibly increase its efficiency. The channel separation may be enhanced by employing a lens between the fibre and the detector, which is called mode-selective spatial filtering. Our numerical simulations of a mode group diversity multiplexing link, with and without mode-selective spatial filtering, are in agreement with the measurements. The above discussion makes clear that the developed software code has a wide range of applicability. Moreover, it is built in a modular way and thus extensions, like the inclusion of more fibre quantities or different profile dopants, are straightforward.

Fiber optic sensors offer a high-performance alternative because they provide a low-cost solution, resistance to electromagnetic interference, multiplexing capabilities, and high integration. The performance of fiber optic sensors applies to measuring physical parameters such as pressure, bending, and temperature. This study aims to determine the optimal value of using optical fiber types in landslide early detection sensors. The method used is bending in the form of deflection on the optical fiber. The deflection values used are 0 mm - 15 mm, 0 mm - 20 mm, and 0 mm - 25 mm. The optical fiber is placed horizontally in the middle of the bending tool. This bending affects the deflection of the optical fiber, resulting in the attenuation of light in the optical fiber. The deflection phenomenon results in light attenuation in the optical fiber. The sensitivity level of a single-mode fiber optic sensor is higher than a multimode. It shows the greater linearity value in each deflection treatment. Single-mode optical fiber linearity data on deflection variations of 0 - 15 mm, 0 - 20 mm, and 0 - 25 mm, respectively, are 0.9833, 0.9871, and 0.9847. At the same time, the linearity data of multimode optical fiber is 0.8926, 0.9841, and 0.9687. Single-mode optical fiber is more sensitive than multimode optical fiber. It is caused by the core diameter of single-mode optical fiber, which is much smaller than that of multimode optical fiber. The difference in core diameter results in differences in light propagation in the optical fiber. The small diameter of the core has a low dispersion level so that more light intensity is reflected into the core. Light attenuation occurs in a single-mode optical fiber due to macro bending treatment. Meanwhile, the attenuation of light in Multimode fiber optics is due to the bending and dispersion of light. Therefore, a landslide early detection sensor design is more optimal by using a single-mode optical fiber.

Data center (DC) and high performance computing (HPC) applications have traditionally used a combination of copper, multimode fiber and single-mode fiber interconnects with relative percentages that depend on factors such as the line rate, reach and connectivity costs. The balance between these transmission media has increasingly shifted towards optical fiber due to the reach constraints of copper at data rates of 10 Gb/s and higher. The percentage of single-mode fiber deployed in the DC has also grown slightly since 2014, coinciding with the emergence of mega DCs with extended distance needs beyond 100 m. This trend will likely continue in the next few years as DCs expand their capacity from 100G to 400G, increase the physical size of their facilities and begin to utilize silicon-photonics transceiver technology. However there is a still a need for the low-cost and high-density connectivity, and this is sustaining the deployment of multimode fiber for links ≤ 100 m. In this paper, we discuss options for single-mode and multimode fibers in DCs and HPCs and introduce a reduced diameter multimode fiber concept which provides intra-and inter-rack connectivity as well as compatibility with silicon-photonic transceivers operating at 1310 nm. We also discuss the trade-offs between single-mode fiber attributes such as bend-insensitivity, attenuation and mode field diameter and their roles in capacity and connectivity in data centers.

We report on an approach for reducing the effects of temperature in a fiber optic distributed sensor. This technique employs a sensing fiber and a Brillouin optical time domain reflectometer (BOTDR). The BOTDR has been proposed for measuring both strain and optical loss distribution along optical fibers by accessing only one end of the fiber. The BOTDR analyzes changes in the Brillouin frequency shift caused by strain. This device can measure distributed strain with an accuracy of better than plus or minus 60 X 10-6 and a high spatial resolution of up to 1 m over a 10 km long fiber. However, temperature fluctuations have an adverse effect on the accuracy with which the Brillouin frequency shift can be measured because the shift changes with temperature as well as with strain. This has meant that both spatial and temporal fluctuations in temperature must be compensated for when a fiber optic distributed sensor is used for continuous strain measurements in massive civil structures. We describe a method for the simultaneous determination of distributed strain and temperature which separates strain and temperature in a fiber optic sensor.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Cascaded multiple Fabry–Perot interferometers fabricated in multimode fiber with a waveguide

Multi-parameter harsh environment sensing using asymmetric Bragg gratings inscribed by IR femtosecond irradiation