Experimental evaluation of nonlinear crosstalk in multi-core fiber

Abstract

Single-wall carbon nanotube deposition on the cladding of optical fibers has been carried out to fabricate an all-fiber nonlinear device. Two different nanotube deposition techniques were studied. The first consisted of repeatedly immersing the optical fiber into a nanotube supension, increasing the thickness of the coating in each step. The second deposition involved wrapping a thin film of nanotubes around the optical fiber. For both cases, interaction of transmitted light through the fiber core with the external coating was assisted by the cladding mode resonances of a tilted fiber Bragg grating. Ultrafast nonlinear effects of the nanotube-coated fiber were measured by means of a pump-probe pulses experiment. © 2011 OCIS codes: 060.3735, 060.4370, 160.4236.Single-wall carbon nanotubes (SWNTs) have found innovative applications in the optical field due to their nonlinear properties in the near IR. Depending on the chirality of SWNTs, they can be either metallic or semiconducting, the latter being the desired behavior for nonlinear optical performance. Many optical applications could benefit from using SWNTs as nonlinear materials, such as noise suppression, wavelength conversion, and passive mode-locking [1][2][3]. A challenge when designing SWNT-based devices is incorporating the nanotubes in such a way as to enhance their interaction with light. One common method involves dispersing SWNTs in a solvent and spraying the solvent onto substrates in order to produce a nanotube film in the middle of a light beam [3]. Some inherent drawbacks in these configurations are the need for alignment and focusing stages, low SWNT burn thresholds, and low nonlinear interaction length. Solutions that overcome these challenges are based on SWNT deposition onto optical fibers. Tapered, D-shaped, and hollow optical fibers have been proposed to take advantage of the evanescent field interaction with SWNTs, distributing that interaction along the fiber length [4-6]. Nevertheless, manufacturing and handling these kinds of fibers is quite complex and delicate. In this work we propose for the first time SWNT deposition on standard optical fiber cladding for nonlinear applications. Interaction of light propagating through the fiber core with the outer SWNT coating is achieved via cladding mode resonances in a tilted fiber Bragg grating (TFBG). Two nanotube deposition methods have been carried out: dip-coating of the optical fiber in a SWNT suspension and wrapping of a SWNT film around the optical fiber. A TFBG is a kind of grating in which the index modulation planes are not orthogonal to the fiber axis but form a particular tilt angle. This inclination enhances the coupling of light from core mode to counterpropagating cladding mode resonances. Consequently, the grating transmission response is a multinotch response consisting of numerous cladding mode resonances in addition to the core mode resonance [see Fig. 1(a)]. The transverse mode profile of cladding modes spreads to the cladding of the fiber and interacts with the outer mediu...

Birefringence effects in multi-core fiber: coupled local-mode theory

“…4(a) when varying the linear birefringence value Δna,j and Δnb,j throughout a 10-day period (j = 1,…,10). Following [12,13] As we can notice from Figs. 5(a1) and 5(a2), the higher the linear birefringence Δnm,j, the lower the iC-XT mean observed in a given core m. The main reason for this comes from the higher phase mismatching between the intra-core PCMs LP01,mx and LP01,my.…”

“…A local mode can be defined as an eigenfunction in a short core segment where the propagation constant and the transversal Bessel function [23] In this way, in contrast with [4][5][6][7][8][9][10][11][12][13] where the longitudinal and temporal MCF perturbations are heuristically inserted in the coupled-mode theory assuming ideal modes, we include the longitudinal and temporal MCF random perturbations in the Maxwell equations considering local modes. The resulting coupled local-mode equations include oscillatory terms and mode-coupling coefficients (MCCs), which are longitudinal and temporal dependent.…”

“…In this topic, the spatial random nature of the crosstalk has been extensively investigated in [8][9][10][11][12][13] considering a single polarization and neglecting the intra-core coupling between orthogonal polarizations induced by the longitudinal random perturbations, which were heuristically inserted in the coupled-mode equations. On the other hand, in [14][15][16][17] the Manakov equations have been extended to multi-mode fibers (MMFs) and multi-mode multi-core fibers (MM-MCFs) to analyze linear and nonlinear propagation in SDM systems modeling intra-and inter-core coupling effects.…”

“…In [18] the bending and twisting of the media were modeled in the coupling matrix (composed by the coupling coefficients of the coupled-mode theory proposed in [20] for anisotropic optical waveguides), and in [19] the spatial random perturbations were included in the propagation matrix of the optical media. In all these previous works [8][9][10][11][12][13][14][15][16][17][18][19], the longitudinal perturbations of the fiber have been described assuming ideal modes but omitting the temporal fluctuations of the SDM fiber perturbations.…”

“…To complete our study, we perform extensive experimental measurements on a four-core fiber, which are found to be in good agreement with numerical simulations based on the proposed CLMT theory. Considering that in previous works [7][8][9][10][11][12][13] the crosstalk in MCF is usually estimated calculating the mean of the random process, our investigations are mainly focused on the behavior of the crosstalk mean between the PCMs.…”