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Cross talk analysis in multicore optical fibers by supermode theory
Abstract
We discuss the theoretical aspects of core-to-core power transfer in multicore fibers relying on supermode theory. Based on a dual core fiber model, we investigate the consequences of this approach, such as the influence of initial excitation conditions on cross talk. Supermode interpretation of power coupling proves to be intuitive and thus may lead to new concepts of multicore fiber-based devices. As a conclusion, we propose a definition of a uniform cross talk parameter that describes multicore fiber design.
... In a massive mode multiplexing, it is challenging to avoid cross talk between the modes during preparation and distribution [33][34][35], which can reduce or even destroy logarithmic negativity of entangled pairs and undermine applicability of shared entanglement. It was, in particular, shown that cross talk effects in the multimode homodyne detection can undermine security of mode-non-discriminating CV QKD [36][37][38]. ...
... , 2 = −0.5 ), right: high loss unbalanced channels ( 1 = −9 , 2 = −10 ). The thin horizontal lines represent the asymptotes for 0 → ∞ given by (26) for the decoupling method, (34) and (36) for the homodyne and heterodyne measurement method, and (6) for the no cross talk case. ...
... Both of the methods increase the amount of entanglement, that can be transferred, and remove the necessity to optimize the initial entanglement. The lines corresponding to interference method (purple) and to the conditional measurement (green and yellow) continue to the right approaching the asymptotes given by (26), (34), (36), and the lines corresponding to the ideal case without cross talk (blue) approach the asymptote (6). We also compare the methods in Fig. 8 for the same initial entanglement in the large region of transmittance values and in the presence of unbalancing. ...
Two-mode squeezed states are scalable and robust entanglement resources for continuous-variable and hybrid quantum information protocols at a distance. We consider the effect of a linear cross talk in the multimode distribution of two-mode squeezed states propagating through parallel similar channels. First, to reduce degradation of the distributed Gaussian entanglement, we show that the initial two-mode squeezing entering the channel should be optimized already in the presence of a small cross talk. Second, we suggest simultaneous optimization of relative phase between the modes and their linear coupling on a receiver side prior to the use of entanglement, which can fully compensate the cross talk once the channel transmittance is the same for all the modes. For the realistic channels with similar transmittance values for either of the modes, the cross talk can be still largely compensated. This method relying on the mode interference overcomes an alternative method of entanglement localization in one pair of modes using measurement on another pair and feed-forward control. Our theoretical results pave the way to more efficient use of multimode continuous-variable photonic entanglement in scalable quantum networks with cross talk.
... A high value of ISO has a great impact on the isolation effect [32]. Fig. 13 also illustrates, with the increase of frequency ISO as well as is increased. ...
... In signal transmission of MCFs, crosstalk is a disturbance caused by magnetic or electric fields of one core to another adjacent core. The crosstalk of one core to another core or one mode to another mode is mathematically evaluated through equation (13) and expressed by XT [32]. ...
In this letter, a hollow core ring based circular photonic crystal fiber (PCF) is explored and proposed with stably supporting terahertz (THz) orbital angular momentum (OAM) states transmission. The proposed PCF is discussed, investigated, analyzed and simulated with optical properties in a terahertz frequency spectrum ranging from 0.20 THz to 0.55 THz. The OAM and THz communication-based parameters of the fiber are deliberated extensively under various conditions through using the full vector finite element method (FEM). Some significant parameters of PCF like effective refractive index difference, dispersion profile, confinement loss, effective mode area, numerical aperture, power fraction and isolation effects are numerically discussed for the first time with their effects and applications on the THz OAM transmission. The mentioned PCF has supported 48 OAM modes with a large effective refractive index difference up to 10−3. The confinement loss of the PCF around 10−10 dB/cm, and the average dispersion profile variation is 1.0055 ps/THz/cm. Besides, the highest numerical aperture and power fraction of the PCF are 0.35 and 99.7882%, respectively. Also, a higher isolation power effect around 267 dB, and crosstalk less than −14 dB are obtained for the PCF. Moreover, this kind of PCF would be a robust candidate for efficient THz OAM transmission, high capacity and high feasibility of optical fiber communications.
... Based on the coupled mode theory, in a single optical fiber with more than one core, or multi-core fiber (MCF), power exchange happens between these cores. To represent this core-to-core crosstalk, supermode theory was proposed and the theoretical analysis on modes in standard multimode fiber can be applied in the same manner on these supermodes in MCF [29]. Thus, the coupling between supermodes also happens in MCF due to the difference of propagation constants. ...
... Thus, bending will induce the change on the refractive index of these two cores in opposite direction. Since supermode is demonstrated to be highly sensitive to unidentical refractive index change of cores [29], under different curvatures, n s and n a will change dramatically, leading to large wavelength shift in optical spectrum. In experiment, the experimental setup used to characterize the bending is shown in Fig. 10(a), in which the BLS and OSA are used for the spectrum monitoring. ...
Twin-core fiber (TCF)-based sensor was proposed for non-invasive vital sign monitoring, including respiration and heartbeat. The TCF was homemade and the corresponding sensor was fabricated by sandwiching single-mode fiber (SMF) on both ends. The offset distance between SMF and TCF was optimized while the length of TCF was identified from preliminary vital sign measurement results. Then, the TCF-based sensor was attached under a mattress to realize non-invasive vital sign monitoring. Both respiration and heartbeat signal can be obtained simultaneously, which is consistent with the reference signals. For further application, post-exercise physiological activitity characterization were realized based on this vital sign monitoring system. In discussion, mode coupling in TCF was analyzed and utilized for curvature sensing with achieved sensitivity as high as 18 nm/m-1, which supported its excellent performance for vital signs monitoring. In conclusion, the TCF-based vital signs monitors can be a promising candidate for healthcare and biomedical applications.
... The design flexibility of PCF in terms of changing the number, size, shape, and arrangement of holes allows tailoring unique characteristics that cannot be achieved by conventional optical fibers [7,8]. PCF can serve in a wide range of applications [7], such as endlessly single-mode operation [5,9], bend-loss edge at short wavelength [5]. Controlled effective-core-area at the single-mode region and anomalous group-velocity dispersion at visible and nearinfrared wavelength [4,5,10], all of which make photonic crystal fibers an ideal candidate for a variety of applications in optical communication systems [1,7]. ...
... Recently, developments have revealed that multicore photonic crystal fiber [12], which has attracted interest from researchers for the flexibility of its design, easy manufacturing process, and many research interests are shown towards MPCF couplers [7], the coupling properties of MPCF with adjacent identical cores, useful for coupling [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15], splitter [16], switching [17][18]. Besides, it possesses the possibility of realizing a multiplexerdemultiplexer (MUX-DEMUX) [5]. ...
Multicore photonic crystal fibers (MPCF) with identical and non-identical cores
are analyzed numerically using Comsol Multiphysics software. Investing
coupling between cores limiting by parameters, such as the slight change in
central core diameter; the separation distance between cores and the
wavelength were investigated. Controlling these parameters allows predicting
the mode propagation. Moreover, anisotropy in all cores diameters of multicores
photonic crystal fibers, as a result, the change of all core diameters
simultaneously lead to different of coupling behavior, suppresses the coupling
between the core modes by inducing a small mismatch between the modes such
that the core modes to be uncoupled through this change. Then this leads to the
light mode propagate independently of their neighbors and gives rise to the
mode to primarily remain in a certain region of the MPCF array. These
properties suggest that multicore PCFs could be a novel candidate for both
multiplex or de-multiplex.
... The sensor principle is based on the crosstalk (XT) between the MCF cores. XT is defined as the relative amount of power transferred from the excited core to another core [27]. Fig. 1 depicts the crosstalk between the different cores in the proposed sensor. ...
Multicore optical fibers are of great interest in the optical sensing field. Their core diversity and spatial distribution enable the development of sensing mechanisms that are not possible in single-core fibers. In this paper we study the use of the inter-core crosstalk phenomena for the implementation of a surrounding refractive index (SRI) sensor. The selective inscription of a tilted fiber Bragg grating (TFBG) intentionally increases the inter-core crosstalk between the inscribed cores and makes it sensitive to the SRI. With this technique we simplify the measurement of the SRI and improve the identification and tracking of the excited cladding modes, as compared with the analysis of the transmission spectrum of a TFBG in single-core fibers. The proposed device is also sensitive to temperature. Temperature is obtained from the crosstalk wavelength shift with a measured sensitivity of 9.75pm/oC. The SRI is obtained from the measurement of the crosstalk optical power. For increasing SRIs the cladding modes gradually fade, reducing the crosstalk optical power. We observed that the higher the tilt, the higher the sensor sensitivity. For a 7o TFBG the SRI sensitivity obtained is -74.2 dB/RIU from 1.31 to 1.39 and -250.8 dB/RIU from 1.39 to 1.44.
... Multicore fibers (MCFs) are another kind of fiber attracting lots of attention recently. According to coupled-mode theory (CMT), the guiding modes of MCFs are supermodes [17,18], which are formed due to the coupling of every individual core mode. In the formation of supermode, the propagation constant is also modulated, which further leads to a change in its dispersion. ...
A trench-assisted multicore fiber (TA-MCF) with single-supermode transmission and nearly zero flattened dispersion is proposed herein. By adding a simplified microstructure cladding with only one ring of low-index inclusions on the basis of the multicore fiber, the microstructure cladding and mode-coupling mechanism were jointly employed into the TA-MCF to modulate light transmission. This guarantees that the TA-MCFs had sufficient capability for wideband dispersion management when only pure, germanium-doped, and fluorine-doped silica glass with low index differences were chosen to form the TA-MCF. Analyses also revealed that the TA-MCFs have the merits of shorter cut-off wavelength and flatter-top optical intensity distribution compared with traditional multicore fibers. After the investigation of the structural parameters’ influences on the dispersion of the fundamental supermode, two TA-MCFs with single-supermode transmission and nearly zero flattened dispersion were designed. For the seven-core TA-MCF, the dispersion varying from −0.46 to 1.35 ps/(nm·km) in the wavelength range of 1.50 to 2.04 μm, with bending loss as low as 0.085 dB/km and 35-mm bending radius at 1550 nm was achieved with index difference less than 0.015. The TA-MCFs proposed herein have the advantages of being a quasi-single material, with an all solid scheme and simplified structure.
... In this paper, the supermode theory is applied to the analysis of the MSC [20][21][22][23][24][25][26][27]. It is shown that all characteristic parameters of the MSC can be obtained using only the propagation constants of the supermodes supported by the MSC structure. ...
In this paper, the mode selective coupler (MSC) is analyzed using the supermode theory. It is shown that all characteristic parameters of the MSC can be obtained using the propagation constants of the supermodes supported by the MSC structure. Simulation results show that the characteristic parameters calculated by the supermode theory match well with those calculated by the traditional coupled mode theory (CMT) near the phase matching point of the MSC structure. In practice, the propagation constants of the supermodes can be obtained using common finite element software directly, avoiding the complex double integral in the traditional CMT. This analysis based on the supermode theory gives a deeper insight into the characteristics of the MSC, providing a fast and accurate method for the analysis of MSCs, which is helpful for their design, fabrication and applications.
... In the optical fiber communications by MCFs, the crosstalk is a problem that is caused for the various adjacent cores [53]. The crosstalk of one mode to another mode or one core to another core is calculated by Eq. (13) [54]. It is defined through the XT. ...
This article introduced a double guided ring-based spiral photonic crystal fiber (S-PCF) supporting both the orbital angular momentum (OAM) and linear polarization (LP) mode simultaneously with the efficient transmission. The outcomes exhibition that the designed S-PCF have good optical features such as less confinement loss (4.05342 × 10⁻¹² dB/m for the EH9,1 mode), better mode quality and ISO (up to 98.87% and 126 dB, respectively), supported a decent amount of modes which is numerically 64 OAM and 6 LP modes, maintaining the large refractive index differences (>10-4) of all the eigenmodes, and a relatively flat dispersion variation (0.0743 ps/km-nm for the EH1,1 mode). Also, we obtained the crosstalk less than −12 dB and the power fraction is approximately 93%-99% of the S-PCF. All the optimizing properties are obtained using the full-vector finite element method (FEM) and also the perfectly matched layer (PML) as a boundary condition. Thus, the above mentioned optimizing propagation characteristic based S-PCF has effective applications like reliable long-distance communication into the space division multiplexing (SDM) process of the large-capacity fiber communication systems.
... Thus, we can define this theory as the overlap of even and odd field distributions. This analysis requires that both even and odd super modes be excited simultaneously [54], [56]. Hence, the coupling length (L c ) is defined as the length of the fiber where a complete power transfer occurs between core A and core B . ...
We present the design of a porous-core PCF with elliptical holes in the core that achieved low-loss, high birefringence and flattened dispersion for guiding terahertz waves. The finite element method is used to study the properties of the designed waveguide in detail: Effective Material Loss (EML), birefringence, confinement losses, and dispersion. Simulation results show that the proposed structure exhibits simultaneously high modal birefringence of 1.32 × 10 −2 and a flattened dispersion over a broadband of 1.28 THz. Then, polarization splitters, based on both symmetric and asymmetric porous-core PCF structures, are designed and evaluated at 1 THz. We show that this kind of devices exhibits a strong polarization-dependent coupling behavior. The numerical results show that the configuration based on dual-core waveguide with asymmetric cores can achieve a 10.9 cm long splitter with a broadband of 0.306 THz for x-polarization and 0.23 THz for y-polarization. Finally, this work offers an effective method to design an ultra-wideband polarization beam splitter to operate in the THz region, which might be relevant for future applications in technical areas, such as spectroscopy, sensing, and high-speed data transmission.
... This central core allows the stability of the system to be controlled by monitoring, for example, fluctuations in the power of the light source. Furthermore, the appropriate design of the air-hole structure in the MCF ensures practically no crosstalk between the cores, which guarantees the independent propagation of the signal through each core [24]. Fig. 2 illustrates the experimental setup employed throughout the measurements. ...
In this article we present an all-fiber vector bend sensor by means of a self-fabricated micro-structured multicore optical fiber. The reported solution is based on differential intensity variations of the light transmitted along the cores whose changes are influenced by the bending angle and orientation. The unique asymmetric structure of the air-holes in the optical fiber provides each core with different confinement losses of the fundamental mode depending on the bending radius and orientation, making each of the cores bend-sensitive in a range of at least 80°. It has been experimentally demonstrated that the reported sensor enables the bending angle and orientation to be detected in a full range of 360° without any dead-zones, and the possibility of end point detection with millimeter precision. Additionally, a reconstruction of the bending vector has been carried out theoretically, and a good match can be observed between the experimental and theoretical data.
The coupled-mode theory (CMT) is a powerful approach routinely used to calculate the effects of spatial mode interactions in perturbed structures, such as optical waveguides. One of its basic hypotheses requires that perturbations are weak. This is usually not the case for devices fabricated with modern semiconductor-based technologies. In this paper, the CMT is studied in these critical cases to assess its validity. Attention will be focused on the quite common case of parallel coupled waveguides. For these structures, results can in fact be compared to the exact ones, obtained using super-modes. The study will show that not all the possible expressions of the coupling coefficients are equivalent, and which one can be pragmatically used to obtain results with minimum errors with respect to exact solutions.
Space division multiplexing is calling for devices that fully replace their single mode fiber counterparts. Fast optical switches represent one such type of key devices. In this paper, we present a free-space optical add drop multiplexer for multicore fiber optical communications. Micro electromechanical mirrors were used as the optical switching element. We detail the implementation steps leading to the proposed device and then characterize its performance in terms of crosstalk and insertion loss. Overall average crosstalk is around -38 dB while insertion losses remain large. The device investigated here is another step towards the practical adoption of space division multiplexing for optical networks based on multicore fibers.
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.
We examine single-mode optical fiber transmission using the angular spectrum method. We find excellent agreement with the theoretical solutions for the cylindrical single-mode optical fiber. Next, we examine fiber coupler configurations with 1 × 2, 1 × 3, and 1 × 5 designs. The input within the central fiber core is broadcast equally into the surrounding fiber cores and then returns with propagation distances as expected. Then we examine supermode theory for the 1 × 3 case. The initial energy is sent into different combinations of fiber cores where their phase relationship governs the output. Surprisingly, we find evidence of an unexpected mode in some of the multicore designs. We expect these results might be useful for exploration of more complicated fiber core arrays. However, computational times are short using this algorithm.
The use of two separated, compact modal interferometers (MIs) with an adequate phase shift is proposed for precision optical fiber sensing. The output spectrum of interferometers with such features is a well-defined peak. Changes in the wavelength position or amplitude of the peak caused by a measurand can be detected with high precision. The advantages of phase-shifted interferometers for optical sensing include sensitivity enhancement, easy implementation, simple interrogation, and compactness, among others. The concept is demonstrated by placing two supermode interferometers in series that were built with multicore fiber to sense vibrations with low frequencies and low amplitudes. The sensing architecture proposed here can also be implemented with other types of optical fiber interferometers, and the advantages mentioned above can be achieved.
In this paper we discuss optical fiber sensors protected by metal coatings and their industrial applications. In particular, we focus on gold-coated temperature sensor for application in temperature up to 900°C based on dual-core fiber.
In this study, the coupling properties of multicore photonic crystal fibers (MCPCFs) are analyzed numerically using COMSOL Multiphysics 5.5, based on the finite element method. The dependence of the coupling properties on the structure of the MCPCFs and the wavelength are investigated to realize applications such as multiplexers-demultiplexers for wavelength division multiplexing. The effective mode indexes and transverse electric field distributions of multiple cores are evaluated for different spatial configurations of identical and non-identical cores. A slight change in the central core diameter relative to adjacent cores leads to non-identical cores that lead to wavelength-dependent coupling properties, such as the coupling lengths and strength of the coefficients. The results show that the coupling lengths become longer and the strength coefficients become smaller as the wavelength decreases for non-identical cores than the identical cores. The introduction of anisotropy to all core diameters shows that the coupling lengths become longer and the strength of the coefficients become smaller as the wavelength decreases as well, and both values become lower than the ones for non-identical cores. These results prove that coupling lengths of MCPCF couplers are significantly shorter in μm compared to conventional multicore optical fiber couplers.
This paper reviews the characteristics of coupled and uncoupled multicore fibers for enhancing the capacity of optical fiber communication system by utilizing both the space and mode division multiplexing technologies. Various limitations in realizing efficient few mode multicore fiber (FM-MCF) design are analyzed in this paper. For both types of fibers, achievable spatial channel count, crosstalk and dispersion behavior, nonlinear effects and overhead at the receiver side are discussed. Some of the reported coupled MCF and uncoupled MCF designs are also summarized from the view point of mechanical reliability and transmission characteristics of the fiber. The constraints of the state of the art fiber designs are discussed. Also the advantages and drawbacks of both types of the fibers were reviewed. It has been observed from the existing MCF designs that, improvement in one transmission characteristics costs the other required characteristics to degrade. Finally it is outlined in this paper that, in order to make the space and mode division multiplexing more efficient and realistic in all aspects simultaneously, still better optimization in the MCF system design is required and the same can be achieved with the development of novel FM-MCF fibers, active and passive devices, data modulation techniques and signal processing algorithms.
COMSOL MULTIPHYSICS software based on the finite element method is being used to simulate the random anisotropy in diameters of the cores formed in multicore photonic crystal fibre structures, and this may affect the coupling properties between the cores’ modes. Consequently, this leads to a reduction in the coupling efficiency between the cores with different structures. This anisotropy in diameters of the cores leads to the creation of a small mismatch between the modes of these cores and is sufficient to inhibit coupling. The coupling properties are affected hugely depending on the amount of the change in core diameter and increasing the number of cores coupled inside the multicore structure. We also found an improvement in the coupling efficiency when increasing the number of cores within the structure of the multicore photonic crystal fibres; otherwise, the independent light propagation of each core inside the multicore structure, with/without a little penetration with other adjacent cores. As the coupling efficiency of seven-core coupled is better than three-core, and the latter may be better than two-core in which the cores appear decoupled and independent in their propagated for the adjacent other cores. It can be considered this study a novel characteristic of multiplexing-demultiplexing applications.
Two-mode squeezed states are scalable and robust entanglement resources for continuous-variable and hybrid quantum information protocols that are realized at a distance. We consider the effect of a linear cross talk in the multimode distribution of two-mode squeezed states propagating through parallel similar channels. First, to reduce degradation of the distributed Gaussian entanglement, we show that the initial two-mode squeezing entering the channel should be optimized already in the presence of a small cross talk. Second, we suggest simultaneous optimization of relative phase between the modes and their linear coupling on a receiver side prior to the use of entanglement, which can fully compensate the cross talk once the channel transmittance is the same for all the modes. For the realistic channels with similar transmittance values for either of the modes, the cross talk can be still largely compensated. This method relying on the mode interference overcomes an alternative method of entanglement localization in one pair of modes using measurement on another pair and feed-forward control. Our theoretical results pave the way to more efficient use of multimode continuous-variable photonic entanglement in scalable quantum networks with cross talk.
In this work, a compact all-fiber bend sensor based on a dual-core microstructured optical fiber has been manufactured and characterized. The sensor relies on the unbalanced Michelson interferometric technique realized by attaching a piece of silica fiber to one of the fiber cores acting as the unbalancing element. Three probes with different lengths of the unbalancing element have been experimentally tested for sensitivity tailoring analysis. Additionally, a theoretical model has been developed for comparison and verification of the results. Good linear behavior of the spectral shift with bend has been measured and it has been proven that the sensitivity of the sensor depends on the length of the unbalancing element and the orientation of the cores. Higher sensitivities are achieved for shorter lengths of the unbalancing element and orientation of the core axis parallel to the bend direction. The highest sensitivity reported is 9.97 pm/µm for the case of 34 µm of unbalancing element and orientation of 0 degrees.
Numerical simulation of directional coupler that is based on the finite element method was conducted using the COMSOL Multiphysics software. The distributions of electric field and power flow of light propagates in two cores of directional coupler were analyzed. The results showed the dependencies of coupling length and maximum transfer power between cores on the cores separation and the wavelength, the characteristic of a subwavelength directional coupler can be used for photonic integrated circuits. Asymmetric directional coupler was also designed by changing in the device dimension, as the core width. The variation of coupling length with the core width were analysed. It was found that the power switching between cores is reduced when introducing a small difference in the one core width of directional coupler, followed by increased coupling length. At the same time, the coupling length can be decreased efficiently by increasing the difference in one core width; therefore, a directional coupler with large core width is more convenient to reduce the power switching between cores than the smaller core width. This study is useful for determining the coupling characteristics between the cores that may be used as a platform for future photonic integrated circuits in optical communication systems.
We introduce a new, to the best of our knowledge, type of multicore optical fiber having a quantum-inspired network topology and unique spectral features. Particularly, the connectivity between the cores is generated by unfolding a circular array of coupled quantum oscillators in Fock space. We show that in such a fiber geometry, the eigenvalues of the optical supermodes exhibit partial degeneracy and form a ladder. In turn, this leads to revival dynamics, allowing for a periodic re-imaging of the input intensity. As an example, we present a realistic design with six cores in silica glass platforms.
We demonstrate a force and temperature sensor consisting of a multicore fiber (MCF) spliced between two single-mode fibers. Increasing of the sensitivity to applied force is achieved through etching of the MCF cladding, with an overall increase of $7times $ compared with a 125- $mu text{m}$ MCF device, and $12times $ compared with a standard fiber Bragg grating (FBG). Simultaneous decoupling of force and temperature with high accuracy is demonstrated using two MCF sections with different outer diameters. This device has robust operation up to 1000 °C, making it more suitable than FBGs for extreme environments.
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.
The shape of a multi-core optical fiber is calculated by numerically solving a set of Frenet-Serret equations describing the path of the fiber in three dimensions. Included in the Frenet-Serret equations are curvature and bending direction functions derived from distributed fiber Bragg grating strain measurements in each core. The method offers advantages over prior art in that it determines complex three-dimensional fiber shape as a continuous parametric solution rather than an integrated series of discrete planar bends. Results and error analysis of the method using a tri-core optical fiber is presented. Maximum error expressed as a percentage of fiber length was found to be 7.2%.
In this paper, the concept of supermode is introduced for long-distance optical transmission systems. The supermodes exploit coupling between the cores of a multi-core fiber, in which the core-to-core distance is much shorter than that in conventional multi-core fiber. The use of supermodes leads to a larger mode effective area and higher mode density than the conventional multi-core fiber. Through simulations, we show that the proposed coupled multi-core fiber allows lower modal dependent loss, mode coupling and differential modal group delay than few-mode fibers. These properties suggest that the coupled multi-core fiber could be a good candidate for both spatial division multiplexing and single-mode operation.
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.
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.
We designed and fabricated a multi-core fiber (MCF) in which seven identical trench-assisted pure-silica cores were arranged hexagonally. To design MCF, the relation among the crosstalk, fiber parameters, and fiber bend was derived using a new approximation model based on the coupled-mode theory with the equivalent index model. The mean values of the statistical distributions of the crosstalk were observed to be extremely low and estimated to be less than -30 dB even after 10,000-km propagation because of the trench-assisted cores and utilization of the fiber bend. The attenuation of each core was very low for MCFs (0.175-0.181 dB/km at 1550 nm) because of the pure-silica cores. Both the crosstalk and attenuation values are the lowest achieved in MCFs.
A statistical theory for crosstalk in multicore fibers is derived from coupled-mode equations including bend-induced perturbations. Bends are shown to play a crucial role in crosstalk, explaining large disagreement between experiments and previous calculations. The average crosstalk of a fiber segment is related to the statistics of the bend radius and orientation, including spinning along the fiber length. This framework allows efficient and accurate estimates of cross-talk for realistic telecommunications links.
The Trace transform proposed, a generalization of the Radon
transform, consists of tracing an image with straight lines along which
certain functionals of the image function are calculated. Different
functionals that can be used may be invariant to different
transformations of the image. The paper presents the properties the
functionals must have in order to be useful in three different
applications of the method: construction of invariant features to
rotation, translation and scaling of the image, construction of
sensitive features to the parameters of rotation, translation and
scaling of the image, and construction of features that may correlate
well with a certain phenomenon we wish to monitor
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