A double clad Yb-doped fiber in a new refractive index profile

In order to increase output power of a single fiber amplifier,a double clad Yb-doped fiber in a new refractive index profile was designed with a core diameter of 30μm and a cladding diameter of 125μm.The fiber,prepared with modified chemical vapor deposition(MCVD)process and improved high temperature vapor deposition,has a hollow refractive index profile with lower refractive index in the doped area.The fluorescence,mode field and amplification characteristics of the fiber were tested.The test results show that the pump power can be absorbed effectively and fluorescent spectrum curve becomes smooth for this new kind fiber.It is realized that smooth mode field energy can output by bending the fiber.40dB high power fs signal light was amplified in a 5m fiber with output power up to 30kW.