Special optical fiber for measuring 3D curved shape, manufacturing method thereof, and system for measuring 3D curved shape by using special optical fiber

A method of manufacturing an optical fiber for measuring a three-dimensional curved shape, wherein the optical fiber comprises an optical fiber core transmitting an optical signal, an inner cladding covering the optical fiber core, and an outer cladding covering the inner cladding, the method comprising:

• preparing the outer cladding;
• forming an insertion hole in the outer cladding into which the inner cladding is to be inserted;
• preparing the optical fiber core;
• preparing the inner cladding in the form of a tube having an inner space into which the optical fiber core is to be inserted, wherein the inner cladding has a cut-open portion formed in a longitudinal direction of the inner cladding;
• inserting the optical fiber core into the inner space of the inner cladding;
• filling the cut-open portion of the inner cladding with a material having the same refractive index as that of the optical fiber core or the outer cladding;
• and
• inserting the inner cladding into which the optical fiber core has been inserted into the insertion hole of the outer cladding.

A method of manufacturing an optical fiber for measuring a three-dimensional curved shape, wherein the optical fiber comprises an optical fiber core transmitting an optical signal, an inner cladding covering the optical fiber core, and an outer cladding covering the inner cladding, and wherein the optical fiber core has a refractive index n1, the inner cladding has a refractive index n2, and the outer cladding has a refractive index n3, and wherein the refractive index n1, the refractive index n2, and the refractive index n3 are set in a relationship of n1≥n3>n2, the method comprising:

• preparing the outer cladding;
• forming an insertion hole in the outer cladding into which the inner cladding is to be inserted;
• preparing the optical fiber core;
• coating the optical fiber core in a C-shape using a rod-in-tube process of partially coating the optical fiber core with a material for constituting the inner cladding;
• filling a cut-open portion in the C-shape of the inner cladding with a material having the same refractive index as that of the optical fiber core or the outer cladding;
• and
• inserting the optical fiber core coated with the inner cladding into the insertion hole of the outer cladding.

A method of manufacturing an optical fiber for measuring a three-dimensional curved shape, wherein the optical fiber comprises an optical fiber core transmitting an optical signal, an inner cladding covering the optical fiber core, and an outer cladding covering the inner cladding, and wherein the optical fiber core has a refractive index n1, the inner cladding has a refractive index n2, and the outer cladding has a refractive index n3, and wherein the refractive index n1, the refractive index n2, and the refractive index n3 are set in a relationship of n1≥n3>n2, the method comprising:

• preparing the outer cladding;
• forming an insertion hole in the outer cladding into which the inner cladding is to be inserted;
• preparing the optical fiber core;
• coating the entire outer surface of the optical fiber core with a material for constituting the inner cladding;
• exposing a portion of the optical fiber core by cutting or etching a portion of the inner cladding along a longitudinal direction of the optical fiber core;
• and
• inserting the optical fiber core covered with the inner cladding into the insertion hole of the outer cladding.

A system for measuring a three-dimensional curved shape using an optical fiber, the system comprising:

• a LD for outputting an optical signal having a predetermined peak and a predetermined width to an input side of the optical fiber core;
• a PD1 for measuring a power of the optical signal output from the LD and input to the optical fiber core;
• a TDC part for detecting a peak of a reflected signal formed by the optical signal being scattered at a bending location of the optical fiber core and being returned to the input side of the optical fiber core;
• a PD2 for measuring a power of the reflected signal;
• and
• an FPGA for controlling operations of the LD, the PD1, the TDC part, and the PD2, and calculating the bending location of the optical fiber core and a curvature of the bending location, based on the peak of the optical signal output from the LD, the power of the optical signal measured by the PD1, the peak of the reflected signal detected from the TDC part, and the power of the reflected signal measured by the PD2.