With the rising output power of industrial lasers, how to safely, efficiently, long-distance and flexibly transmit high-energy lasers has become the key to promote the in-depth application and development of laser technology in the fields of industry, scientific research and medical treatment. The large core diameter laser energy transmission fiber technology is undoubtedly an effective way to unlock the "last meter" of the laser to accurately reach the application scene.
What is a large core diameter? That is, the core diameter is greater than 50 μm, compared with the traditional single-mode fiber core diameter is usually 9 ~ 10 μm. why use a large core diameter? Large core diameter can effectively increase the fiber mode field area, reduce nonlinear effects and improve beam quality; most importantly, the fiber can withstand the optical power and mode field size is proportional to the size of the core diameter can effectively improve the fiber damage threshold, so the energy transfer optical fiber with a large core diameter structure has become inevitable. The following is a brief introduction to several major large-core diameter laser energy transmission fiber.
Conventional large core diameter fiber
Conventional large core diameter fiber, structure and traditional single-mode fiber, by the core and cladding two parts of the composition, the core size is larger, for high-purity quartz glass, cladding materials can choose plastic or high-purity fluorine-doped (F) quartz glass. Plastic cladding high tensile strength, radiation resistance; F-doped glass cladding has a higher bandwidth, and lower loss.
Industrially, conventional large core diameter fibers are the most common type of laser energy transmission fibers, and are widely used in the fields of material surface heat treatment, laser welding, and laser cutting. Medically, large core diameter fiber can be applied in endoscopic laser lithotripsy and prostate treatment due to its characteristics of high energy transmission, insulation and bendability.
Picture of conventional large core diameter fiber structure and its cross-section (Source: Wuhan Changyingtong Optoelectronics)
Large Core Diameter Special Structure Homogenized Fiber
Compared with the conventional large core diameter optical fiber, large core diameter special structure homogenization optical fiber, mainly the structure of the core changes, no longer the traditional round, such as rectangular core, square core, hexagonal core, octagonal core, toroidal core and so on, can meet the needs of different application scenarios. Its unique core structure, to achieve a homogenized flat-top beam output, compared to conventional large core diameter fiber output of energy concentrated in the center of the Gaussian beam, can make the laser and the role of the material is more uniform, while the uniform distribution of energy of the laser also improves the damage threshold of the fiber as a whole, in the high-end laser welding, heat treatment, surface cleaning, photolithography and semiconductor wafer processing and so on, is very advantageous.
Picture part of the cross-section of large core diameter special structure homogenization fiber (source: Wuhan Changyingtong Optoelectronics)
Microstructure fiber
Also known as photonic crystal fiber, its cross-section has a complex refractive index distribution, usually a periodic arrangement of doped glass materials or air holes, there are two major categories of solid core and empty core. Here we focus on hollow-core microstructured optical fibers, mainly three kinds of hollow-core Bragg fibers, hollow-core photonic bandgap fibers and hollow-core antiresonant fibers, of which hollow-core Bragg fibers are mainly used in the field of sensing, while hollow-core photonic bandgap fibers and hollow-core antiresonant fibers, which not only show extraordinary potential in the field of sensing, but also have been widely used in a number of cutting-edge scientific and technological fields, such as energy transmission and high-speed communications.
Compared with solid-core fibers, hollow-core fibers have an air core, a characteristic that gives them the advantage of low dispersion and low nonlinear effects, thus ensuring that good spot output quality is maintained during transmission. At the same time, its high damage threshold provides solid support for various high-power laser applications.
