Characterization of Space-Division Multiplexing Fibers using Swept-Wavelength Interferometry

Abstract

Swept-wavelength interferometry can rapidly characterize the amplitude and phase transfer matrices of multi-mode fibers and components. We will show measurements of short (meter) and long (kilometer) few-mode, multi-mode, and coupled multi-core fibers.Space-division multiplexing (SDM) uses multiple spatial paths in novel fibers and components to provide capacity increases compared to single-mode fiber (SMF) systems. Integrating these paths into the same fiber can lead to reduced costs and size. Spatial paths include the cores in a multi-core fiber (MCF), the spatial modes in few-mode fibers (FMF) and multi-mode fibers (MMF). Successful transmission results have been obtained in all these fibers including >305-Tb/s over 19-core fiber [1], 1.01-Pb/s over 52-km of 12-core fiber [2], 177-km of FMF supporting six spatial modes [3], and 305-km of 50-µm core graded index MMF using 3 spatial modes [4]. In addition to these fibers, SDM requires new characterization tools to measure mode dependencies and transfer matrices. Fig. 1(a) shows a SDM system that includes N transmitters and N receivers, and a spatial multiplexer and demultiplexer to connect the single-mode transmitters and receivers to the spatial paths of the SDM fiber span. The span contains optical amplifiers, and switching elements. An array of coherent receivers measures the full phase and amplitude of each demultiplexed mode and digital signal processing (DSP) fixes transmission impairments. Transmission Fig. 1: (a) SDM system. (b) SDM fibers with multiple spatial paths. SWI configurations for (c) a single polarization and (d) both polarizations. Using time-delays to measure all spatial paths simultaneously (e) transmission measurement and (f) reflection measurement.

Few-mode fiber, splice and SDM component characterization by spatially-diverse optical vector network analysis

“…The columns of the unitary input and output matrices V (ω) and U(ω) are the input and output eigenvectors of the system and describe the 2N-dimensional polarization rotation (also referred to as mode-mapping, -mixing or -scrambling in the literature) between the launched input modes and the eigenmodes ofH(ω), and the latter and the received output modes respectively. Note that the singular values λ i (ω) are the gains or losses associated with each eigenmode and their squares are equal to the eigenvalues of the phase-conjugate round-trip propagation matrixH(ω)H * (ω) [8,11].…”

“…dmd may be derived fromH(ω) by means of principle state of polarization analysis [11,21,29] where the principle delays are approximated by the eigenvalues ofH(ω + ∆ω)H −1 (ω) or by directly analyzing the impulse responsesh k ,l (t) [22,25,30]. In the latter case, distinct peaks for different mode groups h k ,l (t) will be observed and dmd may be derived from the ratio of their respective spacing and the fiber length.…”

“…The transmission span may be a simple fiber link, but may also include more complex subsystems such as switches, and amplifiers [11]. Additionally, a fusion splice every few km will be unavoidable in practical sdm systems.…”

“…More recently, spatially diverse optical vector network analyzer (sdm-ovna) setups have been introduced, allowing measurement of the temporal and spectral response of fmfs [11,22], as well as characterization of sdm system components [14,23,24]. The mode-mixing at fiber splices and their impact on system il and mdl was investigated by the authors in [17,25], based on analysis of the impulse response and comparison of measurements with different splices.…”

Full-set high-speed mode analysis in few-mode fibers by polarization-split segmented coherent detection method: Proposal and simulation of calculation error

“…There have been several mode analysis methods, which can be categorized into two groups. One consists of methods that analyze the modes of output light based on information on the modal pattern of the electromagnetic field, such as prism-coupled mode analysis using an oblique section of an optical fiber [3] and a tapered fiber [4], the low-coherence interferometry method [5], the eigenmode expansion technique [6], the spatial and spectral (S2) imaging method [7,8,9], the swept wavelength interferometry method [10], and so on. The other consists of time-of-flight (ToF) methods such as the OTDR method [11,12].…”