Article

Cross talk analysis in multicore optical fibers by supermode theory

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  • Bury & Bury European and Polish Patent and Trademark Attorneys
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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.

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... 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. ...
Preprint
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]. ...
Article
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. ...
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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]. ...
Article
Full-text available
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. ...
Article
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. ...
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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. ...
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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. ...
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... 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 . ...
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... 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. ...
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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.
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