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What is the Bend Loss Sensitivity of a DTG® Sensor Versus Bend Radius?


In general, bending losses in the DTG-LBL-1550 can be considered to be negligibly small.  To illustrate this, some measured bending-induced optical losses are presented in the table below. As can be seen, the attenuation per winding for millimeter-sized radii is less than 1 dB..



Table: Bending loss of DTG-LBL-1550 fiber



The limiting factor for the operational minimal bending radius will rather be governed by the bending-induced strain in the fiber glass. Coiling an optical fiber over a small bending radius gives rise to bending strain in the fiber.  For large strain values, it can lead to a damage in the optical fiber or even breakage.  The strain due to bending is largest at the optical fiber surface. The surface strain can be calculated as a function of the bending radius and optical fiber diameter. The figure below shows the surface strain as function of the bending radius for an 80µm and a 125µm diameter optical fiber.


Figure: Surface strain as function of the bending radius for a fiber cladding of 80µm diameter and a fiber cladding of 125µm diameter fiber.


In order to prevent fiber breakage on the long term, the strain should be as small as possible. As can be observed, the smaller the fiber diameter, the lower the surface strain for an identical bending radius. In case smaller bending radii are needed, it is recommended to use smaller fiber diameters.   

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