Improving Alignment of Free-Space Coupling of Multi-Mode Fibres using Off-Axis Digital Holography

Off-axis digital holography is employed to align multi-mode fibers in a free-space optical setup that can be used for space-division multiplexing (SDM) transmission. We show that alignment based on power coupling measurements alone does not guarantee a low mode-dependent loss, limiting the system capacity. The alignment method we proposed previously enables reliable fiber coupling with low mode-dependent loss and cross-talk for few-mode to multimode fiber alignment, by using digital holography to capture the full complex optical field at the output of the fiber of interest. After capturing the full complex field, by means of digital demultiplexing, we can calculate relevantparameters such as mode-dependent loss and cross-talk. Here we extend these results with few-mode to few-mode fiber alignment measurements and look at alternative optimization metrics such as the cross-talk between the mode groups of interest and all guided modes. The proposed method allows for precise (automated) alignment of space-division multiplexing components, devices and subsystems

Alignment of Free-Space Coupling of Few-Mode Fibre to Multi-Mode Fibre using Digital Holography

Off-axis digital holography is used to align a few-mode fiber to a multi-mode fiber in a free-space optical setup. Alignment based on power coupling measurements alone cannot guarantee low mode-dependent loss. The proposed alignment method enables reliable fiber coupling with low mode-dependent loss and crosstalk

30×30 Mimo Transmission Over 15 Spatial Modes

We transmit over all 30 spatial and polarization modes of a 22.8-km multimode fiber. 15-mode photonic lanterns enabled low-loss coupling into and out of the fiber and a time-multiplexed coherent receiver facilitates measurement of all 30 signals

Optical Trapping And Manipulation Of Multiple Microparticles Using Sdm Fibers

We demonstrate optical trapping and dynamic manipulation of microparticles using multicore and few-mode fibers. Tuning of the input state of polarization of the trapping beam allows for particle rotation and adjustable trapping distances

Bending sensor combining multicore fiber with a mode-selective photonic lantern

A bending sensor is demonstrated using the combination of a mode-selective photonic lantern (PL) and a multicore fiber. A short section of three-core fiber with strongly coupled cores is used as the bend sensitive element. The supermodes of this fiber are highly sensitive to the refractive index profiles of the cores. Small bend-induced changes result in drastic changes of the supermodes, their excitation, and interference. The multicore fiber is spliced to a fewmode fiber and excites bend dependent amounts of each of the six linearly polarized (LP) modes guided in the fewmode fiber. A mode selective PL is then used to demultiplex the modes of the few-mode fiber. Relative power measurements at the single-mode PL output ports reveal a high sensitivity to bending curvature and differential power distributions according to bending direction, without the need for spectral measurements. High direction sensitivity is demonstrated experimentally as well as in numerical simulations. Relative power shifts of up to 80% have been measured at radii of approximately 20 cm, and good sensitivity was observed with radii as large as 10 m, making this sensing system useful for applications req

Off-axis digital holography for analysis of fibre tapping of few mode fibres

Off-axis digital holography is used to analyse the impact of fibre tapping in few mode fibres. Mode dependent loss and cross talk are analysed under fibre tapping with a measured MDL increase of 2.5 dB

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Video showing the rotation of the 8 um borosilicate microparticles by using a photonic lantern spliced to a 2-LP few-mode fiber and adjusting the polarization of the signal at one of the photonic lantern inputs corresponding to the LP11a spatial mode