Fast fiber mode decomposition with a lensless fiber-point-diffraction interferometer

Abstract

Recently, the growing interest in few-mode fibers in telecommunications and high-power lasers has stimulated the demand for fiber mode decomposition (MD). Here we present a fast fiber MD method with a lensless fiber-point-diffraction interferometer. The complex amplitude at the fiber end is achieved by the polarization phase-shifting technique and the lensless imaging technique. Then, the eigenmode coefficients are determined by the mode orthogonal operations of the complex amplitude. In the experiment, the SMF-28e fiber containing 10 linear polarized modes at the wavelength of 632.8 nm is studied for MD. The decomposition of the 50 * 50 pixels interferograms takes only 0.0168 s. The similarity of the intensity patterns of the testing light is larger than 97% before and after the MD. This new, to the best of our knowledge, method can achieve fast and accurate 10-mode MD without using any imaging systems.

Simultaneous determination of polarization states and mode coefficients of fiber LP modes with four-channel off-axis holography

“…In Fig. 8, the area circled by the solid yellow line is the four-channel off-axis holographic system [18], which is ultra-compact within 50 mm× 30 mm× 30 mm. The holograms taken by the polarization camera (PHX050S, Lucid) are analyzed by personal computer (Lenovo Y7000P, CPU: i7-10875H, RAM: 16G).…”

“…( 5) is lowresolution. To solve this problem, the virtual transmission method based on 4F system is used to obtain the enlarged complex amplitude distribution E p (x,y) at the conjugated position of the end surface of the fiber core in each channel [18]. The coefficient c mp of mth-order mode on pth channel can be calculated by the cross-correlation degree [23].…”

“…Fig. 6(a) shows the calculated light intensity distribution of the fiber end in the 0° polarization channel using the virtual transmission method [18]. Light intensity varies in each polarization channel due to the different polarization states of LP modes.…”

“…So far, a variety of mode decomposition (MD) techniques which calculates the mode coefficients have been proposed, such as the spatial spectroscopy method [6][7][8], correlation analysis method [9][10][11], numerical analysis method [12][13][14][15][16], digital holography method [17,18] and the matrix analysis method [29] etc. Both mode weights and phase differences can be determined simultaneously using these methods.…”

Speckle backpropagation for compensation of nonlinear effects in few-mode optical fibers

“…It is noteworthy that no standards for MDM receiver operation principles have been established yet, and not every spatial demultiplexing scenario would be appropriate for conventional MM-DBP schemes. In particular, demultiplexing may refer to utilization of bulky optics [28] , physical mode separation [29] , or implementation of numerical algorithms [30][31][32][33] . The latter is mostly given by the technique referred to as intensity-only mode decomposition (MD), which implies separation of modes, based on the near-field intensity distributions of multimode signals captured by a digital camera.…”