Four-Cores FBG Probe Based on Capillary Self-Assembly Fabrication Technique for 3D Measurement

A three-dimensional (3D) four-cores fiber Bragg grating (FBG) probe is developed by doubling the twin FBG structure to extend the 2D radial tactile capacity of an FBG probe. The measuring principle of the four-cores FBG is thoroughly investigated and the four-cores structure is also found to have a benefit of orthogonal radial decoupling capacity. To avoid the inscription of four-cores FBG and usage of fan-out device, and make the four-cores fiber customizable, a new approach, capillary self-assembly technique of optical fibers, is researched and an external constraint is introduced into a self-assembly system to fabricate square four-cores FBG using four single-core FBGs. The spectrum characteristic and performance of the four-cores FBG probe are thus much improved. Advantages of the probe and fabrication technique are low cost, customizable design, high precision, and high aspect ratio.