为了提高光纤放大器单纤输出功率,设计了一种新型折射率掺镱双包层光纤,纤芯直径30μm,包层直径125μm。采用一种改良的高温气相掺杂技术和改进的化学气相沉积法制作,纤芯折射率分布为凹陷型结构,掺杂区为低折射率区。对光纤的荧光特性、模场特性以及放大特性进行了测试。试验结果表明,该新型折射率分布设计有利于纤芯对抽运光吸收,荧光输出平坦,对光纤进行弯曲处理可实现平坦模场的能量输出,5m光纤实现了40dB高功率飞秒信号光放大,输出功率30kW。

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.