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

Abstract

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 few-mode fiber and excites bend dependent amounts of each of the six linearly polarized (LP) modes guided in the few-mode 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 requiring both large and small curvature measurements.

Optimized active multicore fiber bending sensor

“…Minimum operational curvature radii, i.e. maximum losses, of demonstrated MCF bending sensors are in the range of tens of cm: 54 cm [7], 23 cm [8] and 19 cm [3]. Fig.…”

Probing micron-scale distributed contortions via a twisted multicore optical fiber

“…Among the EM waveguide designs, optical fibers represent a highly attractive platform for developing contortion sensors, owing to a variety of available design parameters and configurations, a shielded transport of EM radiation, and an opportunity for ultralong length distributed sensing operation. [27][28][29] The optical-fiber contortion sensors may employ gratings, [29][30][31][32][33][34][35][36][37][38][39] modal interference, [40][41][42][43][44][45] radiationlosses, [46][47][48][49][50][51][52] or nonlinear effects to detect and measure the probed contortions. 10,26,53,54 In the past, optical fiber sensors for a distributed measurement of such parameters as temperature, pressure, strain, etc., have been extensively studied.…”

“…The measurement of a bend radius and curvature as well as shape and position using optical fiber sensors has also been demonstrated previously. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]53 While fiber shape sensing is comparable to our application, it is typically applied to systems in which a fiber experiences macro bends and displacements on a length scale greater than a few millimeters. Moreover, while sensors based on fiber microbends have been demonstrated, 55 these typically rely on the overall transmitted intensity or spectrum measured through a fiber core.…”

Symmetry selective cladding modes coupling in ultrafast-written fiber Bragg gratings in two-mode fiber

“…Fiber-optic bend sensors are ideally suited for this task because they can be integrated seamlessly and in large numbers. In the past decades, a few modal-interference-based bend sensors have been demonstrated [1][2][3][4][5], and, in most cases, fiber mismatches/discontinuities (like lateral-offset splicing [6] and tapers [7]) or specialty fibers with asymmetric structures [2,[8][9][10] are introduced to recognize different bending planes. Simpler directional bending schemes have also been reported by adding additional fiber waveguides [11,12].…”