In this paper, we investigate the design of few-mode fibers (FMFs) guiding 2 to 12 linearly polarized (LP) modes with low differential mode delay (DMD) over the C-band, suitable for long-haul transmission. Two different types of refractive index profile have been considered: a graded-core with a cladding trench (GCCT) profile and a multi-step-index (MSI) profile. The profiles parameters are optimized in order to achieve: the lowest possible DMD and macro-bend losses (MBL) lower than the ITU-T standard recommendation. The optimization results show that the MSI profiles present lower DMD than the minimum achieved with a GCCT profile. Moreover, it is shown that the optimum DMD and the MBL scale with the number of modes for both profiles. The optimum DMD obtained for 12 LP modes is lower than 3 ps/km using a GCCT profile and lower than 2.5 ps/km using a MSI profile. The optimization results reveal that the most preponderant parameter of the GCCT profile is the refractive index relative difference at the core center, Δnco. Reducing Δnco, the DMD is reduced at the expense of increasing the MBL. Regarding the MSI profiles, it is shown that 64 steps are required to obtain a DMD improvement considering 12 LP modes. Finally, the impact of the fabrication margins on the optimum DMD is analyzed. The probability of having a manufactured FMF with 12 LP modes and DMD lower than 12 ps/km is approximately 68% using a GCCT profile and 16% using a MSI profile.

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Design of Few-Mode Fibers With M-modes and Low Differential Mode Delay

A new class of hydrophones is currently being developed, which utilize optical beams and interface directly to fiber optic transmission and processing links. Some of these sensors employ an optical fiber itself as the transduction element and possess significant advantages and versatility. The details of these fiber sensors and their advantages are discussed.

Optical fiber acoustic sensor

In this article present results of measurements for refractive index profile of silica graded multimode optical fibers are
presented. The measurement technique is described. Estimation of parameters for profile defects of investigated
samples of multimode optical fibers is received. Analysis data for effect of profile defects of graded multimode optical
fibers (MMF) on differential mode delay (DMD) is presented.

Investigation of defects of refractive index profile of silica graded-index multimode fibers

In this article the problem of image analysis in unmanned aerial vehicle on-board system for objects detection and recognition with the help of energy characteristics based on wavelet transform is described. The approach of salient points extraction based on wavelet transform is proposed. The salience of the points is substantiated with the energy estimates of their weights. On the basis of wavelet transform salient points extraction the method of image contour segmentation is proposed. For further image recognition the salient points descriptors constructed with the help of wavelet transform are used. The objects detection and recognition system for unmanned aerial vehicles based on proposed methods is simulated using the simulation platform.

Image analysis in unmanned aerial vehicle on-board system for objects detection and recognition with the help of energy characteristics based on wavelet transform

Method for mode coupling coefficient estimation of arbitrary order guided modes at the splice of diverse optical fibers
under axial and angular misalignments is proposed. It is based on the well-known overlap integral method and modified
Gaussian approximation been generalized for analysis of the weakly guiding optical fibers with an arbitrary axialsymmetric
refractive index profile. Analytical expressions for the arbitrary order mode coupling coefficients under splice
misalignments were developed. Some results of proposed method approbation are represented.

Mode coupling at the splice of diverse optical fibers

We present results of attempts to apply a conventional fiber parameter field-test equipment for identification of
multimode fibers with high differential mode delay (DMD). Backscattering traces, obtained by optical time domain
reflectometer (OTDR) with the single-mode optical unit, and refractive index profile form, reproduced by image
processing of lighted fiber end-face, were compared with pulse forms, registered by introduced DMD measurement
system. Silica graded-index multimode fibers 50/125 of different generations were considered. Comparing results of high
DMD fiber identification by OTDR, video diagnostics system and DMD measurement system are represented.

Results of conventional field-test equipment application for identification of multimode optical fibers with high DMD

This paper presents algorithm of reconstruction of equivalent refractive index profile of optical fiber by differential mode
delay diagrams. Calculations were performed for profile example of the sample multimode optical fibers.

Reconstruction of equivalent refractive index profile of optical fiber on differential mode delay diagrams

The results of theoretical and experimental study of the vibration sensor based on the few-mode optical fiber are represented in paper. The mode composition of telecommunication single mode fiber working in few-mode regime was obtained by theoretical calculation and experimentally approved. The detection of acoustic influence on few-mode optical fiber was demonstrated and impact of relative mode excitation and state of polarization was registered.

Study of the vibration detection using few-mode optical fiber

In this paper computer simulation and experimental investigation of the vibration influence on the single-mode optical fiber polarization characteristics was carried out. Measurements were made using a standard optical reflectometer and an external module providing sensitivity to polarization. Based on the obtained data, a measurement algorithm with polarization controller was determined and the method for analyzing the polarization reflectograms was proposed. The possibility of detection and localization of multiple fiber segments under vibration action was demonstrated.

Konstantin A. Yablochkin

Papers

Investigation of defects of refractive index profile of silica graded-index multimode fibers

Results of conventional field-test equipment application for identification of multimode optical fibers with high DMD

Reconstruction of equivalent refractive index profile of optical fiber on differential mode delay diagrams

Study of the vibration detection using few-mode optical fiber

Investigation of the vibration influences on the optical fiber polarization characteristics