Research On The Beam Combination Of Supercontinuum Generation In Multi-core Photonic Crystal Fiber

In terms of the multi-core photonic crystal fiber(PCF),its advantages are the large-mode-area which could support high beam intensity and disperse heat.However,only the beam profile of far-field and the focal point of in-phase super mode is Gaussian-shaped,whose energy is more concentrated compared with other shapes.And this beam profile feature limits the applications of multi-core PCF.With the development of optics,there is a practical solution to improve beam profile of multi-core PCF by using Kagome fiber.The solution is about coupling the in-phase super mode source,obtained from multi-core PCF,into Kagome fiber to achieve the beam combination of multi-core photonic crystal fiber,which means the beam profile remained to be Gaussian-shaped at any location in optical field.The Kagome fibers have a novel hollow structure and thus there are some new properties such as broad optical transmission bands with relatively low loss,no detectable surface modes and high confinement of light in the core,which are suitable for the beam combination.In this paper,a Ti: Sapphire femtosecond pulsed fiber oscillator,with the center wavelength of 800 nm and output power of 550 m W,was used to pump a piece of seven-core nonlinear PCF,with the efficiency of 19%.The EFL of coupling lens is 18.40 mm and the NA is 0.15.Then the in-phase super mode source was obtained from the 15 m multi-core PCF,with broadband spectrum from 700 nm to 1050 nm.The beam profile of far-field and the focal point of in-phase super mode is Gaussian-shaped and there is seven core shaped pattern at near-field and other locations in optical field.In order to combine the beam of multi-core fiber,in-phase super mode source is coupled into a piece of Kagome fiber,10 cm,by using the coupling lens whose EFL is 13.86 mm.The coupling efficiency is 71% and the output beam profile remained to be Gaussian-shaped at any location in optical field,which means there is no more seven core shaped pattern.It also transmits broadband spectrum with low loss.Moreover,this experiment also proved that this solution can be used for different multi-core PCFs and could have a higher coupling efficiency,80%.It gives a reference for high power applications of multi-core PCF and it could also inspire some other frontier fields in fiber optics.