掺铒光纤中方波信号高次谐波的快慢光特性

Superluminal and slow light of high-order harmonic for rectangle signal in erbium-doped fiber

光纤中方波信号的慢光技术在全光通信和光纤传感等领域具有重要的应用前景.提出了谐波相对延时量的度量方法,分别采用速率方程和相干布居振荡理论,对掺铒光纤中方波信号的基波和高次谐波的快慢光特性进行了研究.在无抽运光输入情况下,改变入射光功率,入射探测光的基波最大相对延时量能达到20%,且存在实现最大相对延时量的入射光功率为8 mW;在有抽运光输入的情况下,改变信号光增益,入射探测光的基波相对超前量同样能达到-20%,且随着信号光增益的增大而增加.N次谐波(N=1,3,5,7,···)在频率f/N(f为基波信号最大延时量对应的调制频率)处有最大相对延时量,且它们的最大延时量相同,频率处于相干布居振荡引起的光谱烧孔带宽内.

The slow light technology of the rectangle signal propagating in erbium-doped fiber（EDF） has potential applications in the fields of all optical communication and optical fiber sensing. The method of using harmonics fractional delay to evaluate the slow/fast light of rectangle signal propagating in the EDF is proposed, and the characteristics of phase delay for fundamental and high order harmonics components are analyzed for the first time based on the rate equations and the theory of the coherent population oscillations（CPO）. We experimentally demonstrate the dependences of fundamental fractional delay on input power and optical gain. The maximum fractional delay 20% is obtained when the input power is about 8 mW without pump. The negative fractional delay-20% is also achieved and it will increase with the rising of the optical gain. The Nth-order fractional delays（N = 1, 3, 5, 7） of rectangle signal propagating in EDF without pump are investigated. Their maximum fractional delays are all about 0.07 and the corresponding fundamental modulation frequencies are 22, 7, 5 and 3 Hz, respectively. What is more, the Nth-order fractional delays（N = 1, 3, 5, 7） with pump are also investigated. Their maximum fractional delays are all about-0.135 and the corresponding fundamental modulation frequencies are 175, 58, 35 and 25 Hz, respectively. The experiments indicate that the maximum Nth-order fractional delays are equal and they will be achieved at the frequency f/N（the fundamental harmonic fractional delay is maximum at the modulation frequency f）. The results show good agreement with CPO and the frequency is also located in the spectral burning hole.