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Fiber Bragg gratings in hole-assisted multicore fiber for space division multiplexing
Abstract
In this Letter we present, for the first time to our knowledge, the results of fiber Bragg grating (FBG) inscription in a novel microstructured multicore fiber characterized by seven single-mode isolated cores. A clear Bragg reflection peak can be observed in all of the 7 cores after one inscription process with a KrF nanosecond laser in a Talbot interferometer set up. We furthermore perform a numerical analysis of the effective refractive indices of the particular modes and compare it with the FBG inscription results. An experimental analysis of the strain and temperature sensitivities of all of the Bragg peaks is also included.
... Several types of multiplexing techniques have been proposed for FBG based multipoint/quasi-distributed sensing networks, including time division multiplexing (TDM) [11], wavelength division multiplexing (WDM) [12], a combination of TDM and WDM [13], space division multiplexing (SPD) [14], etc. Among these multiplexing techniques, WDM based quasi-distributed sensing interrogation scheme is the most preferable because of its high speed. ...
... It can be seen from Eqs. (14) and (15), that slow-light sensitivity depends on the product of delay and peak transmissivity at Bragg wavelength which is relevant "figure of merit (FoM)" of slow-light FBG sensors. ...
In this paper, we theoretically analyze the slow-light -phase-shifted fiber Bragg grating (-FBG) and its applications for single and multipoint/quasi-distributed sensing. Coupled-mode theory (CMT) and transfer matrix method (TMM) are used to establish the numerical modeling of slow-light -FBG. The impact of slow-light FBG parameters, such as grating length (L), index change (∆n), and loss coefficient (α) on the spectral properties of -FBG along with strain and thermal sensitivities are presented. Simulation results show that for the optimum grating parameters L = 50 mm, ∆n = 1.510-4, and α = 0.10 m-1, the proposed slow-light -FBG is characterized with a peak transmissivity of 0.424, the maximum delay of 31.95 ns, strain sensitivity of 8.380 με-1, and temperature sensitivity of 91.064 °C-1. The strain and temperature sensitivity of proposed slow-light -FBG is highest as compared to the slow-light sensitivity of apodized FBGs reported in the literature. The proposed grating have the overall full-width at half maximum (FWHM) of 0.2245 nm, and the FWHM of the Bragg wavelength peak transmissivity is 0.0798 pm. The optimized slow-light -FBG is used for quasi-distributed sensing applications. For the five-stage strain quasi-distributed sensing network, a high strain dynamic range of value 1469 με is obtained for sensors wavelength spacing as small as 2 nm. In the case of temperature quasi-distributed sensing network, the obtained dynamic range is 133 °C. For measurement system with a sufficiently wide spectral range, the -FBGs wavelength grid can be broadened which results in substantial increase of dynamic range of the system. The additional advantage of slow-light -FBG in quasi-distributed sensing networks over the conventional apodized FBG sensing networks is that slow-light peaks are free from the side-lobes.
... Several types of multiplexing techniques have been proposed for FBG based multipoint/quasi-distributed sensing networks, including time division multiplexing (TDM) [11], wavelength division multiplexing (WDM) [12], a combination of TDM and WDM [13], space division multiplexing (SPD) [14], etc. Among these multiplexing techniques, WDM based quasi-distributed sensing interrogation scheme is the most preferable because of its high speed. ...
... It can be seen from Eqs. (14) and (15), that slow-light sensitivity depends on the product of delay and peak transmissivity at Bragg wavelength which is relevant "figure of merit (FoM)" of slow-light FBG sensors. ...
In this paper, we theoretically analyze the slow-light-phase-shifted fiber Bragg grating (-FBG) and its applications for single and multipoint/quasi-distributed sensing. Coupled-mode theory (CMT) and transfer matrix method (TMM) are used to establish the numerical modeling of slow-light-FBG. The impact of slow-light FBG parameters, such as grating length (L), index change (n), and loss coefficient (˛) on the spectral properties of-FBG along with strain and thermal sensitivities are presented. Simulation results show that for the optimum grating parameters L = 50 mm, n = 1.5×10 −4 , and ˛ = 0.10 m-1 , the proposed slow-light-FBG is characterized with a peak transmissivity of 0.424, the maximum delay of 31.95 ns, strain sensitivity of 8.380-1 , and temperature sensitivity of 91.064 • C-1. The strain and temperature sensitivity of proposed slow-light-FBG is the highest as compared to the slow-light sensitivity of apodized FBGs reported in the literature. The proposed grating have the overall full-width at half maximum (FWHM) of 0.2245 nm, and the FWHM of the Bragg wavelength peak transmissivity is of 0.0798 pm. The optimized slow-light-FBG is used for quasi-distributed sensing applications. For the five-stage strain quasi-distributed sensing network, a high strain dynamic range of value 1469 is obtained for sensors wavelength spacing as small as 2 nm. In the case of temperature of quasi-distributed sensing network, the obtained dynamic range is of 133 • C. For measurement system with a sufficiently wide spectral range, the-FBGs wavelength grid can be broadened which results in substantial increase of dynamic range of the system.
... In recent years, emerging methods for multiplexing have been implemented, having a much more specific implementation, which are designed for a particular type of sensor or for specific hardware. SDM has been implemented in multicore fibers, with the capability of resolving inline FBGs [14] and Fabry-Perot interferometers [15], and allows for implementing up to three-dimensional-shape sensing with a single fiber [16]. CDM has been reported for broadband sensors with a quasi-periodic spectrum, such as interferometers [17]. ...
Fiber-optic ball resonators are an attractive technology for refractive index (RI) sensing and optical biosensing, as they have good sensitivity and allow for a rapid and repeatable manufacturing process. An important feature for modern biosensing devices is the multiplexing capacity, which allows for interrogating multiple sensors (potentially, with different functionalization methods) simultaneously, by a single analyzer. In this work, we report a multiplexing method for ball resonators, which is based on a spatial-division multiplexing approach. The method is validated on four ball resonator devices, experimentally evaluating both the cross-talk and the spectral shape influence of one sensor on another. We show that the multiplexing approach is highly efficient and that a sensing network with an arbitrary number of ball resonators can be designed with reasonable penalties for the sensing capabilities. Furthermore, we validate this concept in a four-sensor multiplexing configuration, for the simultaneous detection of two different cancer biomarkers across a widespread range of concentrations.
... Here, it is worth mentioning that writing gratings in MCF turns out to be more complicated than in SMF, due to the geometric difference in spatial position between cores of the MCF, which adds some technical challenges in fabrication, e.g., due to the lens effect of the fiber, the grating strength may have variations between cores, and it may also lead to different transmission/reflection profiles of the FBGs [39,62,76,[88][89][90][91]. Currently, the most widely used way to write gratings in MCF is to use UV light irradiation, and this method will normally bring in gratings in all cores of the MCF. ...
In recent years, multicore fiber (MCF) has attracted increasing interest for sensing applications, due to its unique fiber structure of multiple parallel cores in a single fiber cladding, which offers a flexible configurable platform to establish diverse functional fiber devices for sensing applications. So far, a variety of discrete fiber sensors using MCF have been developed, among which one of the major categories is the MCF grating sensors. The most distinct characteristic of MCF that differs from the normal single mode fibers is that the off-center cores of a MCF are sensitive to bending, which is caused by the bending induced tangential strain in off-center waveguides through either compression or stretching. The bending sensitivity has been widely developed for bending/curvature sensing or measuring physical parameters that are associated with bending. In this paper, we review the research progress on MCF-based fiber grating sensors. MCF-based diverse fiber grating sensors will be introduced, whose working principles will be discussed, and various types of applications of the MCF grating sensors will be summarized. Finally, the challenges and prospects of MCF grating for sensing applications will be presented.
... The multiplexing technology uses the same interrogation system to query the measurement information of multiple sensors, which not only greatly simplifies the complexity of the system, but also ensures the measurement accuracy and reliability of the system [4]. The multiplexing technologies that have been developed are mainly time division multiplexing (TDM), frequency division multiplexing (FDM), wavelength division multiplexing (WDM), code division multiplexing (CDM), and space division multiplexing (SDM) [5][6][7][8]. ...
Optical fiber sensor networks (OFSNs) provide powerful tools for large-scale buildings or long-distance sensing, and they can realize distributed or quasi-distributed measurement of temperature, strain, and other physical quantities. This article provides some optical fiber sensor network technologies based on the white light interference technology. We discuss the key issues in the fiber white light interference network, including the topology structure of white light interferometric fiber sensor network, the node connection components, and evaluation of the maximum number of sensors in the network. A final comment about further development prospects of fiber sensor network is presented.
... Today a diversity of MCF fibres from different manufacturers is available on the market. I order to avoid cross-talk between cores different methods can be used to increase the signal to noise ratio [4]. Such multicore fibres have also become attractive for multiplexed fibre sensor systems. ...
Fibre Bragg gratings in multicore optical fibres are attractive sensing elements for multiplexed measurements (e.g. shape sensing). In order to achieve optimized uniformity in the grating inscription, a setup with control of orientation was applied.
... The fiber Bragg grating (FBG) sensor, in particular, is widely employed to sense strain, temperature or pressure changes by monitoring the shifting of the reflected optical carrier in the wavelength. The FBG-based sensor systems have many advantages, such as electromagnetic interference immunity, lightweight, compact size, easy fabrication, broad wavelength-tunability, excellent multiplexing capability, etc. Numbers of large-scale FBG sensor networks have been experimentally demonstrated based on timedivision multiplexing (TDM), wavelength-division multiplexing (WDM) and spatial-division multiplexing (SDM) techniques [11][12][13][14][15][16][17][18][19][20][21]. Nevertheless, as the amount of sensing information is increased, maintaining the resilience of optical fiber sensor networks becomes a challenge because the probability of failure in connecting fibers is increased and the amount of affected sensing traffic is generally greater when a fiber failure occurs. ...
An all-passive optical fiber sensor network is proposed based on a novel single-line bidirectional optical add-drop multiplexer (SBOADM). By reasonably employing fiber Bragg gratings (FBGs) and optical circulators (OCs) to compose the self-developed SBOADM, single-line bidirectional transmission can be easily achieved by the SBOADM without the assistance of a power supply or optical switch. When the SBOADM is employed to bridge a hybrid tree-based and ring-based optical fiber sensor network, self-healing functionality can be easily embedded into the network. Once an interruption occurs in the network, the only thing that the system maintainer needs to do is to adjust one optical switch pre-installed in the remote node of the sensor network. That is to say, it will reduce the system's complexity to achieve self-healing functionality to immediately recover the connection of optical signals as soon as the optical fiber interruption occurs. The advancement of the self-developed SBOADM is experimentally demonstrated, and the self-healing functionality of the proposed all-passive optical fiber sensor network is simulated. Great results show that the proposal can easily overcome any one fiber-link failure without adjusting the network deploying setting or employing complex control management.
... expand the sensing range, and thus various multiplexing FBGs techniques have been proposed and demonstrated [4]- [6]. In particular, wavelength division multiplexing (WDM) [5], time domain division multiplexing (TDM) [6], frequency domain multiplexing (FDM) [7] and their combinations [8] are most widely adopted. ...
We combine wavelength-division multiplexing (WDM) and frequency shifted interferometry (FSI) to interrogate a large-scale ultra-weak Fiber Bragg Grating (FBG) array. Based on Sagnac interference, FSI can location resolve sensors without using pulses or fast detection, therefore considerably lowers the system cost. By combining FSI with WDM, higher spatial resolution can be achieved. We demonstrated simultaneous interrogation of 363 FBG sensors, grouped into 121 identical units of 3 FBGs of different central wavelengths and spaced two meters apart. Based on the performance of the 363 grating system, we show the potential for interrogating 3207 sensors with good signal-to-noise ratio. Stability test and temperature sensing were carried out, and the obtained temperature resolution was ± 0.4 oC. The results indicate the proposed scheme can greatly enhance the multiplexing capacity and meet the requirements of large-scale optical fiber networks.
... The latter is particularly useful in large civil engineering structures and in oil and gas exploration and distribution systems. In order to reduce the system cost and multiplex a large number of FBGs for multipoint measurements, many multiplexing schemes have been developed, including optical time-domain reflector (OTDR) [7], optical frequency-domain reflector (OFDR) [8], space-division multiplexing (SDM) [9], wavelength-division multiplexing (WDM) time-division multiplexing (TDM) and combinations thereof [10,11]. However, except for a recent few demonstrations [12][13][14], FBG multiplexing usually has capacities limited to a few or tens of gratings. ...
We demonstrate interrogation of a large-capacity sensor array with nearly identical weak fiber Bragg gratings (FBGs) based on frequencyshifted interferometry (FSI). In contrast to time-division multiplexing, FSI uses continuous-wave light and therefore requires no pulse modulation or high-speed detection/acquisition. FSI utilizes a frequency shifter in the Sagnac interferometer to encode sensor location information into the relative phase between the clock-wise and counter-clockwise propagating lightwaves. Sixty-five weak FBGs with reflectivities in the range of -31 ∼-34 dB and with near identical peak reflection wavelengths around 1555 nm at room temperature were interrogated simultaneously. Temperature sensing was conducted and the average measurement accuracy of the peak wavelengths was ± 3.9 pm, corresponding to a temperature resolution of ± 0.4 °C. Our theoretical analysis taking into account of detector noise, fiber loss, and sensor cross-talk noise shows that there exists an optimal reflectivity that maximizes multiplexing capacity. The multiplexing capacity can reach 3000 with the corresponding sensing range of 30 km, when the peak reflectivity of each grating is -40 dB, the sensor separation 10 m and the source power 14 mW. Experimental results and theoretical analysis reveal that FSI has distinct cost and speed advantages in multiplexing large-scale FBG networks.
Fiber Bragg gratings (FBGs) are successfully inscribed in the heterogeneous double period array multicore fiber (DPAMCF), in which the spacing between two adjacent cores is approximately equal and the core sizes change periodically. The responses of each grating to the axial strain and temperature are measured.
A novel fiber bending sensor is proposed based on a home-made seven-core fiber (SCF). The sensing head is formed by splicing a piece of a SCF between two sections of single-mode fibers(SMFs). Two super modes with most of mode energy in the central fiber core and in the six outsider fiber cores are exited in the SCF, which ensures the Mach–Zehnder interferometer (MZI) structure of the proposed sensor and form the mode interference spectrum in the lead-out SMF. The relationship between the dip wavelength shift of the interference spectrum and the bending curvature of the SCF is experimentally investigated. The temperature response of the SCF bending sensor is also experimentally investigated Our experimental results show that the MZI sensor exhibits a high bending sensitivity of 2.65 nm/m⁻¹ and a temperature sensitivity of 0.021 nm/°C, respectively. The compact size, low cost and high sensitivity makes the MZI sensor a good candidate for bending sensing application.
We demonstrate a direct inscription of a fiber Bragg grating (FBG) in the active cores of an Yb-doped large mode area multicore fiber (MCF). An ultrashort pulsed laser is used to inscribe the FBG simultaneously in all six cores. In order to validate the FBG reflection and uniformity, the FBG is incorporated as a rear mirror in a fiber laser oscillator setup. The MCF, which has been fabricated in-house, has six cores located in a hexagonal-ring shape, each with a 19 µm diameter and an NA of ∼0.067. A reflection of ∼96% was measured at a center Bragg wavelength of ∼1062nm for the inscribed FBG. The laser performance of the MCF with the femtosecond inscribed FBG at its end shows a similar performance to lasing with a free-space commercial volume Bragg grating as the rear-reflector. A slope efficiency of ∼72.4% and a maximum (pump limited) output power of 51.8 W have been obtained for the FBG setup. An effective M2 of 3.88, indicating a somewhat multimode operation and a narrow bandwidth of ∼0.19nm, has been measured for this fiber laser.
Wide-area and multi-point remote sensing technology plays an important role in the fields of disaster monitoring and locating. We demonstrate a demultiplexing method for quasi-distributed uniform strong fiber Bragg grating (FBG) sensors based on optoelectronic oscillator (OEO). When the FBG sensor is affected by environmental changes, the wavelength of the FBG will shift. An oscillation will be stimulated in the OEO since the laser power is reflected by the FBG. The demultiplexing system utilizes the oscillating frequency of the OEO to encode the location information of grating series. Compared with other schemes, the proposed system has three superior advantages. First, as a digital discrete position encoding system, it has a strong anti-interference ability and does not require continuous sweeping wavelength and rapid digital signal processing, which can achieve high speed and high stability. Second, it can demodulate identical FBGs with strong reflectivity, thus ensuring long-distance and large capacity. Third, it can work in a low-frequency range without using high-frequency devices, which has the potential to be a low cost interrogator in practical applications. The theoretical capacity of the system is 62 multiplexed points in one line and the experimental results show that the sensing area can range from 1 m~1 km with the response time of ~0.61 s and the oscillating frequency stability of < 28 kHz. The linear relationship between the wavelength of the laser and the alarm strain/temperature, corresponding to 1.3
${\mu\varepsilon}$
/pm or 0.1 °C/pm, can be used to set alarm threshold values.
A novel heterogeneous double period array multicore fiber (DPAMCF) is proposed, in which the spacing between two adjacent cores is approximately equal and the core sizes change periodically. The modes in the DPAMCF form two supermode groups, which can be attributed to double period distribution of heterogeneous cores. Two supermode groups are phase mismatched and the coupling crosstalk between them is suppressed. Fiber Bragg gratings (FBGs) are successfully inscribed in the DPAMCF and the responses of each grating to the axial strain and temperature are measured. The proposed DPAMCF offers a platform to integrate a series of FBG units with two sets of different Bragg wavelengths into a plane at the same longitudinal position.
An all-fiber twin-core fiber (TCF) fan-out device is proposed and experimentally demonstrated. The device is capable of simultaneously accessing optical signals from both cores for a variety of TCF types. The device was fabricated via bi-tapering of a fiber bundle consisting of two parallel large-core multimode fibers (LMFs), each of which was tapered-spliced with single mode fibers (SMFs). A commercial fiber fusion splicer was used in the device fabrication process for both tapering and splicing. A series of experiments were conducted in which two different TCF types, featuring different inter-core distances, were connected to test the functionality of the proposed device. The results demonstrate successful accessing of optical signals from the two TCF cores with a low crosstalk of -38.6 dB. The proposed all-fiber TCF fan-out device could be further developed for applications in novel fiber sensors or advanced optical communication systems.
We demonstrated femtosecond laser inscription of fiber Bragg gratings (FBGs) in a twin-core few-mode fiber (TC-FMF) for directional bend sensing. An FBG was selectively inscribed in one core of the TC-FMF by using an 800 nm femtosecond laser through a phase mask. Three resonance peaks at the wavelengths of 1549.05, 1547.65, and 1546.08 nm were observed in the reflection spectrum of the TC-FM FBG, and were generated by the LP01 mode resonance, LP01-LP11 mode cross-coupling resonance, and LP11 mode resonance, respectively. Moreover, the TC-FM FBG exhibited the capability of directional bend sensing and achieved a maximum bend sensitivity of -37.41 pm/m-1. Hence, the proposed TC-FM FBG directional bend sensors could further be developed as promising solutions for detecting vectorial seismic or acoustic waves and 3D shape sensing.
Multicore and microstructured fibers open a new door for designing all-fiber telecom components. In this article we propose a design of an optical power splitter based on the phenomenon of power coupling in the tapered splice between a single-core (SMF-28) and a seven core fiber (MCF-7), which was originally developed for spatial division multiplexing telecommunication systems. Comprehensive numerical analysis is presented and backed up with an experimental demonstration.
In this paper we present possibilities of tuning spectrum of supercontinuum with the use of temperature change. Our study is based on the information about the role of dispersion characteristics in the process of nonlinear effects generation in nanosecond pulse regime. We obtain tunable spectrum effects in microstructured fiber and we show how to optimize its properties. Our experimental results showing nonlinear effects generation in fiber pumped in normal and anomalous dispersion regime enables to determine how the nonlinear effects depend on temperature changes. We show that even small changes of dispersion characteristic of microstructured fibers enable to obtain significant modification of generated spectra when four wave mixing is dominant effect. Controllable generation of tunable supercontinuum can be used in numbers of potential applications such as diagnostics and measurement systems. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
In this paper we present the idea and test results of an all-fiber unbalanced Mach-Zehnder interferometer for fiber Bragg grating shift demodulation. The interferometer design allows to monitor Bragg wavelength changes (caused by temperature or strain variations) as changes of intensity on the output detector. Furthermore the construction is cost-effective and based on simple optoelectronic components, which makes the solution attractive for application as a low cost fiber Bragg grating interrogator. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
The authors designed and fabricated opti cal power splitters, which make an alternative solution to existing commercial products. The proposed solutions use multicore microstructured optical fiber designed for new generation telecommunication networks made in Spatial Division Multiplexing (SDM) system. The splitters presented in this paper aim to have low loss and to be compatible with existing elements of optical networks, and in the same time to eliminate disadvantages of existing splitters. Two designs presented in this paper are made in all-fiber technology in order to ensure high environmental stability. The authors present detailed description and experimental results for both optical power splitters designs. Keywords: splitter, all-fiber technology, optical power splitter, optical fiber splitter, microstructured optical fiber, optical fiber technology, multicore fibers, microstructured fibers 1. INTRODUCTION Optical power splitter is a passive device used to divide signal between several recipients. Due to its role splitters are essential in all types of optical fiber networks, especially FTTH networks. Currently, commercially used splitters are made in two different technologies: fused biconical taper (FBT) [1] and planar lightwave circuit (PLC) [2]. Splitters made in fused biconical taper technology are fabricated by putting closely two or more fibers and stretching them under the heating zone to enable power coupling between the cores. Main disadvantages of this technology are limited number of output ports and the manufacturing process, which cannot run automatically and during the whole fabricating process operator is needed. The PLC splitters, made in planar techno logy, are fabricated in similar way as semiconductors. The PLC splitters have greater number of outputs than FBT splitters and the process of fabricating it is fully automatic. On the other hand, splitters made in this technology have relatively big loss caused by a need to connect planar and fiber optics technology, as well as low resistance to changing conditions of the ex ternal environment (especially temperature variations). In this paper two different designs are presented and characterized. Authors proposed solution which will eliminate main disadvantages of both existing solutions. Proposed splitters are made in all-fiber technology in order to provide high environmental stability and possibility of high temperature range performance. They have 7 outputs but it is possible to fabricate splitters with higher number of outputs by applying similar fiber with different number of cores.
In this letter, the light transfer promoted by long-period gratings (LPGs) inscribed in heterogeneous multicore fibers (HeMCFs) is theoretically analyzed. We determined the power evolution along the LPG in two different four-core HeMCFs. This letter demonstrates the selective switch of optical power between the identical cores of the HeMCFs with less than -40 dB of crosstalk to the other cores, regardless the position of the identical cores. The results show that the proposed technique can be used to produce inline selective core switching for multicore space division multiplexing.
We present an approach to crosstalk limitation and higher order modes suppression in multicore hole-assisted fibers. Our designed and fabricated fiber is compliant with singlemode fiber standards, hence can be utilized in space division multiplexing.
We present multicore fiber based elements created by fine crosstalk management. We show all fiber 1x7 power splitter and WDM splitter.
In this paper we present a fiber Bragg grating shift demodulator with changeable resolution based on an unbalanced fiber Mach–Zehnder interferometer. Preliminary research proves phase sensitivity to Bragg wavelength changes of 6,83 rad/mε. Phase sensitivity can be modified by changing the optical path difference witch is only limited by the coherence length of light reflected by the fiber Bragg grating. This solution can be used as a single sensor or as a part of a more complex system.
Long period fiber gratings (LPGs) in a two-core hollow eccentric fiber (TCHF) have been demonstrated experimentally. Two LPGs have been fabricated into the respective core of the TCHF by a high frequency CO2 laser. The coupling characteristics in the TCHF-LPG have been studied using the coupling mode theory (CMT). The resonant peak is mainly caused by the coupling between the core mode LP01 and cladding mode LP81. The experimental results agree well with the simulation results. Furthermore, the sensing properties of the TCHF-LPG have been investigated with respect to bending, temperature and axial strain. Compared with the LPG in the single mode fiber (SMF), the experimental results indicate that the sensitivity of the TCHF-LPGs to bending curvature is low and even very small at some bending directions. In addition, TCHFLPGs are insensitive to the axial strain while sensitive to the temperature. Therefore, the proposed TCHF-LPGs can efficiently sense the changing temperature that is independent of the strain. Moreover, the TCHF-LPGs can also be applied to two-channel filters without signal crosstalk between two cores.
In presented work, we examined the structures of dual-core fibers paying special attention to the possibility of using them for sensing. In the hole-assisted fiber structure, the character of propagation in the cores was changed fluently, by post-processing the fiber, i.e. tapering with collapsing the holes. Fiber post-processing changed the conditions for supermodes interference and thus the different scale of power transfer between cores was observed. In the paper we investigated the influence of the taper parameters (taper waist, length and ratio) on the properties of the fiber. We have also studied the behaviour of the transmitted signal, while putting post-processed segment of fiber into different external conditions. Presented research shows a great potential of using modified hole-assisted fibers as sensing elements.
The cancellation of the 0th order is described by a low-contrast fused-silica grating. In reported works, the high-contrast grating and complicated structure were applied with reasonable and excellent performance. However, the low-contrast grating is proved that it can also cancel the 0th order with the period more than 2λ in this paper. Grating parameters are optimized by using rigorous coupled-wave analysis, whose physical essence for cancellation of the 0th order can be well explained by modal method. The fabrication tolerance is investigated for production of the low-contrast grating for cancellation of the 0th order, which can be potentially used for writing the fiber Bragg grating.
We present a multicore fiber dedicated for next generation transmission systems. To overcome the issue of multicore fibers' integration with existing transmission systems, the fiber is designed in such a way that the transmission parameters for each core (i.e., chromatic dispersion, attenuation, bending loss, etc.) are in total accordance with the obligatory standards for telecommunication single core fibers (i.e., ITU-T G.652 and G.657). We show the results of numerical investigations and measurements carried out for the fabricated fiber, which confirm low core-to-core crosstalk and compatibility with standard single-core single-mode transmission links making the fiber ready for implementation in the near future.
Optical communication technology has been advancing rapidly for several
decades, supporting our increasingly information-driven society and
economy. Much of this progress has been in finding innovative ways to
increase the data-carrying capacity of a single optical fibre. To
achieve this, researchers have explored and attempted to optimize
multiplexing in time, wavelength, polarization and phase. Commercial
systems now utilize all four dimensions to send more information through
a single fibre than ever before. The spatial dimension has, however,
remained untapped in single fibres, despite it being possible to
manufacture fibres supporting hundreds of spatial modes or containing
multiple cores, which could be exploited as parallel channels for
independent signals.
A new type of optical fiber called heterogeneous multi-core fiber (heterogeneous MCF) is proposed towards future large-capacity optical-transport networks and the design principle is described. In the heterogeneous MCF, not only identical but also non-identical cores, which are single-mode in isolation of each other, are arranged so that cross-talk between any pair of cores becomes sufficiently small. As the maximum power transferred between non-identical cores goes down drastically, cores are more closely packed in definite space, compared to a conventional, homogeneous multi-core fiber (homogeneous MCF) composed of only identical cores.
Fiber Bragg gratings are written across all 120 single-mode cores of a multi-core optical Fiber. The Fiber is interfaced to multimode ports by tapering it within a depressed-index glass jacket. The result is a compact multimode "photonic lantern" filter with astrophotonic applications. The tapered structure is also an effective mode scrambler.
We describe a new multicore fiber (MCF) having seven single-mode cores arranged in a hexagonal array, exhibiting low crosstalk among the cores and low loss across the C and L bands. We experimentally demonstrate a record transmission capacity of 112 Tb/s over a 76.8-km MCF using space-division multiplexing and dense wavelength-division multiplexing (DWDM). Each core carries 160 107-Gb/s polarization-division multiplexed quadrature phase-shift keying (PDM-QPSK) channels on a 50-GHz grid in the C and L bands, resulting in an aggregate spectral efficiency of 14 b/s/Hz. We further investigate the impact of the inter-core crosstalk on a 107-Gb/s PDM-QPSK signal after transmitting through the center core of the MCF when all the 6 outer cores carry same-wavelength 107-Gb/s signals with equal powers, and discuss the system implications of core-to-core crosstalk on ultra-long-haul transmission.
We design and fabricate a novel multicore fiber (MCF), with seven cores arranged in a hexagonal array. The fiber properties of MCF including low crosstalk, attenuation and splice loss are described. A new tapered MCF connector (TMC), showing ultra-low crosstalk and losses, is also designed and fabricated for coupling the individual signals in-and-out of the MCF. We further propose a novel network configuration using parallel transmissions with the MCF and TMC for passive optical network (PON). To the best of our knowledge, we demonstrate the first bi-directional parallel transmissions of 1310 nm and 1490 nm signals over 11.3-km of seven-core MCF with 64-way splitter for PON.
We experimentally characterized a birefringent microstructured polymer fiber of specific construction, which allows for single mode propagation in two cores separated by a pair of large holes. The fiber exhibits high birefringence in each of the cores as well as relatively weak coupling between the cores. Spectral dependence of the group and the phase modal birefringence was measured using an interferometric method. We have also measured the sensing characteristics of the fiber such as polarimetric sensitivity to hydrostatic pressure, strain and temperature. Moreover, we have studied the effect of hydrostatic pressure and strain on coupling between the cores.
The combination of fiber Bragg grating inscription with femtosecond laser sources and the usage of the Talbot interferometer setup not only gives access to the fabrication of Bragg gratings in new types of materials but also allows, at the same time, to keep the high flexibility of an interferometric setup in choosing the Bragg grating wavelength. Since the spatial and temporal coherence properties of the femtosecond laser source differ strongly from those of conventional laser sources, specific limits and tolerances in the interferometric setup have to be considered. Such limits are investigated on the basis of an analytical ray tracing model. The results are applied to tolerance measurements of fiber Bragg grating reflections recorded with a DUV sub-picosecond laser source at 262 nm. Additionally we demonstrate the wavelength versatility of the two-beam interferometer setup for femtosecond inscription over a 40 nm wavelength band. Inscription experiments in Al/Yb doped silica glasses are demonstrated as a prove for the access to non-photosensitive fibers.
The effect of the microstructure on transversely coupled laser light into the core of a photonic crystal fiber is investigated. Computational two-dimensional modeling and direct experimental measurements indicate that there exist angles and positions of the fiber microstructure, relative to a transversely launched laser beam, that preferentially couple laser light into the fiber core. The implications of these observations on long period and fiber-Bragg grating fabrication in photonic crystal fibers are discussed.
We present ArF laser-induced dynamics of Bragg grating (BG) growths in phosphosilicate-doped or germanosilicate-doped core photonic crystal fibers (PCFs). To this end, we have adapted the technique of H2 loading, usually used in conventional fiber, to the case of microstructured fiber, allowing both the concentration of hydrogen in the PCFs to be kept nearly constant for the time of the exposure and the BG spectra to be easily recorded. We compared the characteristics of BG growths in the two types of PCF to those in conventional step-index fibers. We then conducted a study of the thermal stability of the BGs in PCFs through 30 min of isochronal annealing. At the same time we discuss the role played by the microstructuration and the doping with regard to the grating contrast and the Bragg wavelength stability.
A seven-core few-mode multicore fiber in which each core supports both the LP01 mode and the two degenerate LP11 modes has been designed and fabricated for the first time, to the best of our knowledge. The hole-assisted structure enables low inter-core crosstalk and high mode density at the same time. LP01 inter-core crosstalk has been measured to be lower than -60 dB/km. LP11 inter-core crosstalk has been measured to be around -40 dB/km using a different setup. The LP11 free-space excitation-induced crosstalk is simulated and analyzed. This fiber allows multiplexed transmission of 21 spatial modes per polarization per wavelength. Data transmission in LP01/LP11 mode over 1 km of this fiber has been demonstrated with negligible penalty.
The inscription of fiber Bragg gratings during the drawing process is a very useful method to realize sensor arrays with high numbers of gratings and excellent mechanical strength and also type II gratings with high temperature stability. Results of single pulse grating arrays with numbers up to 100 and definite wavelengths and positions for sensor applications were achieved at 1550 nm and 830 nm using new photosensitive fibers developed in IPHT. Single pulse type I gratings at 1550 nm with more than 30% reflectivity were shown first time to our knowledge. The mechanical strength of this fiber with an Ormocer coating with those single pulse gratings is the same like standard telecom fibers. Weibull plots of fiber tests will be shown. At 830 nm we reached more than 10% reflectivity with single pulse writing during the fiber drawing in photosensitive fibers with less than 16 dB/km transmission loss. These gratings are useful for stress and vibration sensing applications. Type II gratings with reflectivity near 100% and smooth spectral shape and spectral width of about 1 nm are temperature stable up to 1200 K for short time. They are also realized in the fiber drawing process. These gratings are useful for temperature sensor applications.
We present KrF excimer laser-induced dynamics of Bragg grating growths in GeO2 doped microstructured optical fibers. The studied fibers all have 6 rings of airholes in a hexagonal lattice and a GeO2 doped region in the center of the microstructure. We compare the growth rates of fiber Bragg gratings in the different microstructured fibers with UV grating inscription. The influence of the doping level, the airhole filling factor, the airhole pitch distance and the fiber orientation are investigated. We expand the range of microstructured optical fibers in which Bragg gratings can be inscribed, achieving reflection strengths that are useable for FBG-based sensing applications, even for doped regions with GeO2 concentrations as low as 1.36 mol% and 0.45 mol%.
Photosensitivity in optical fibres properties of Fibre Bragg gratings inscribing Bragg gratings in optical fibres Fibre Bragg grating theory applications of Bragg gratings in communications Fibre Bragg grating sensors impact of Fibre Bragg gratings.
We describe what is to our knowledge the first use of fiber Bragg gratings written into three separate cores of a multicore fiber for two-axis curvature measurement. The gratings act as independent, but isothermal, fiber strain gauges for which local curvature determines the difference in strain between cores, permitting temperature-independent bend measurement.
The feature of a multicore fiber with one-ring structure is theoretically analyzed and experimentally demonstrated. The one-ring structure overcomes the issues of the hexagonal close-pack structure. The possibility of 10-core fiber with Aeff of 110 μm<sup>2</sup> and 12-core fiber with Aeff of 80 μm<sup>2</sup> is theoretically presented. The fabricated 12-core fibers based on the simulation results realized Aeff of 80 μm<sup>2</sup> and crosstalk less than -40 dB at 1550 nm after 100-km propagation. The MCF with the number of core larger than seven and the small crosstalk was demonstrated for the first time.
We report on a photonic crystal fiber with a large mode area designed for compact high power fiber lasers and amplifiers. The fiber suppresses higher order modes when bent around a 10-cm radius and enables single mode operation in small footprint laser and amplifier architectures. We experimentally confirm the peculiar bending properties of this fiber in its passive version, by reporting on the measurement results of fundamental mode loss in bent and straight fibers, and of the influence of the bending plane orientation on this fiber loss.
A review of optical fiber sensing demonstrations based on photonic crystal fibers is presented. The text is organized in five main sections: the first three deal with sensing approaches relying on fiber Bragg gratings, long-period gratings and interferometric structures; the fourth one reports applications of these fibers for gas and liquid sensing; finally, the last section focuses on the exploitation of nonlinear effects in photonic crystal fibers for sensing. A brief review about splicing with photonic crystal fibers is also included.
We present several applications of microstructured optical fibers and study their modal characteristics by using Bragg gratings inscribed into photosensitive core regions designed into the air-silica microstructure. The unique characteristics revealed in these studies enable a number of functionalities including tunability and enhanced nonlinearity that provide a platform for fiber device applications. We discuss experimental and numerical tools that allow characterization of the modes of the fibers.
We report a compact two-dimensional accelerometer based upon a simple fiber cantilever constructed from a short length of multicore optical fiber. Two-axis measurement is demonstrated up to 3 kHz. Differential measurement between fiber Bragg gratings written in the multicore fiber provides temperature-insensitive measurements.
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