A method of processing glass filament comprises: providing a length of glass filament from which a portion is to be separated from the remainder of the filament; directing energy onto the filament in order to cause a decrease in a width of the filament at a desired location for separation of the portion; and causing relative longitudinal movement between the portion and the remainder of the filament to separate the portion from the remainder of the filament at the desired location.

A method for manufacturing a preform for a multicore fiber, including stacking (S1) a plurality of core rods and a plurality of silica-based filler rods in a tube; collapsing (S2) the tube around the stack of core rods and silica-based filler rods, forming a collapsed stack; depositing (S3) a layer of silica around the collapsed stack; removing (S4) at least part of the deposited layer of silica. The preferential process for depositing a layer of silica around the collapsed stack and removing at least part of the deposited layer of silica is Advanced Plasma and Vapor Deposition.

The present disclosure provides a method for modification of surface of an initial optical fiber preform. The initial optical fiber preform is manufactured using at least one preform manufacturing process. The surface of the initial optical fiber preform is treated with 50-70 liters of chlorine per square meter of the surface of the initial optical fiber preform. The surface of the initial optical fiber preform is flame polished using a flame polishing module. The treatment of the surface of the initial optical fiber preform with chlorine and flame polishing of the surface of the initial optical fiber preform collectively converts the initial optical fiber preform into a modified optical fiber preform.

A method of manufacturing a filter that includes providing a tube having a cylindrical wall and a hollow interior. The method forms a first indentation within the tube in which a first portion of the of the cylindrical wall concaves into the hollow interior, and forms a second indentation within the tube in which a second portion of the cylindrical wall concaves into the hollow interior. The first and second indentations create 1) a first chamber and a second chamber in the tube that are separated by both indentations and 2) a path within the hollow interior formed between the first and second indentations that fluidly couples both chambers together.

A rare earth-doped double-clad optical fiber includes a rare earth ion-doped fiber core, an inner cladding layer, and an outer cladding layer. A cross section of the inner cladding layer is a non-circular plane including at least two arcuate notches. According to the provided optical fiber, optical processing can be performed on a preform without changing a preform preparation process and a drawing process. The inner cladding is designed to have a non-circular planar structure having a cross section with at least two arcuate notches. While maintaining the same light absorption efficiency of pump light within the cladding layer, a preform polishing process is simplified, a risk of cracking the preform during polishing of multiple surfaces and a risk of contamination of the preform caused by impurities are reduced, wire drawing control precision is better, and comprehensive performance of the optical fiber is improved.

The present disclosure provides a method for modification of surface of an initial optical fiber preform. The initial optical fiber preform is manufactured using at least one preform manufacturing process. The surface of the initial optical fiber preform is treated with 50-70 liters of chlorine per square meter of the surface of the initial optical fiber preform. The surface of the initial optical fiber preform is flame polished using a flame polishing module. The treatment of the surface of the initial optical fiber preform with chlorine and flame polishing of the surface of the initial optical fiber preform collectively converts the initial optical fiber preform into a modified optical fiber preform.

A method for preparing a doped optical fibre preform includes formulating, a rare earth material or a functional metal material and a co-doping agent into a doping solution, mixing a high-purity quartz powder with the doping solution, drying same at a temperature of 100 C.-150 C. for 12-48 hours, crushing and screening the same to obtain a doped quartz powder; depositing the doped quartz powder onto the surface of a target rod to form a doped core layer; replacing the doped quartz powder with the high-purity quartz powder, and depositing the high-purity quartz powder onto the surface of the doped core layer to form a quartz outer cladding; and removing the target rod, and gradually collapsing the entirety formed from the doped core layer and the quartz outer cladding at a high temperature to obtain the doped optical fibre preform.

A rare earth-doped double-clad optical fiber includes a rare earth ion-doped fiber core, an inner cladding layer, and an outer cladding layer. A cross section of the inner cladding layer is a non-circular plane including at least two arcuate notches. According to the provided optical fiber, optical processing can be performed on a preform without changing a preform preparation process and a drawing process. The inner cladding is designed to have a non-circular planar structure having a cross section with at least two arcuate notches. While maintaining the same light absorption efficiency of pump light within the cladding layer, a preform polishing process is simplified, a risk of cracking the preform during polishing of multiple surfaces and a risk of contamination of the preform caused by impurities are reduced, wire drawing control precision is better, and comprehensive performance of the optical fiber is improved.

A method of manufacturing a filter that includes providing a tube having a cylindrical wall and a hollow interior. The method forms a first indentation within the tube in which a first portion of the of the cylindrical wall concaves into the hollow interior, and forms a second indentation within the tube in which a second portion of the cylindrical wall concaves into the hollow interior. The first and second indentations create 1) a first chamber and a second chamber in the tube that are separated by both indentations and 2) a path within the hollow interior formed between the first and second indentations that fluidly couples both chambers together.

The single-mode optical fibers have a core region that includes an inner core region having a delta value .sub.1 and a radius r.sub.1 immediately surrounded by an outer core region of radius r.sub.2 and a delta value .sub.2<.sub.1, wherein .sub.1-.sub.2 is in the range from 0.3% to 2%. A cladding region of radius r.sub.3 immediately surrounds the core region. The inner and outer regions define an annular width r=r.sub.2r.sub.1. At least one of r.sub.1, r.sub.2, r and r.sub.3 changes with a period p in the longitudinal direction between first and second values each having a corresponding level distance d.sub.F. The change occurs over a transition distance d.sub.T such that d.sub.T/d.sub.F<0.1. The Brillouin frequency shift f changes by an amount [f] that is least 10 MHz over each period p, thereby allowing for Brillouin frequency-shift management in fiber-based sensor systems.