Study on the Controllable Slow-Light Phenomenon in an Optical Fiber
|School||Shanghai Jiaotong University|
|Keywords||Stimulated Brillouin scattering (SBS) Fiber Brillouin amplifier (FBA) resonator optical buffer optical delay line slow light all-optical communication|
It is a significant technique to control the speed of light in an optical fiber for the information processing and the all optical communication systems. In the present communication systems, optic-electric convertions are needed in many places, which will bring unfavorable factors to the systems, such as increase the system complexity and reduce the signal quality. Such system is not fit for high speed application. To address the problem, men have been dreaming of the coming of all-optical communication for many years.Tunable optical buffers (TOB) are key components in future all-optical routers (AOR). The lack of feasible AOR is a well-known bottleneck of developing all-optical communication network. To realize the TOB, one needs to optically control the group velocity of light. Investigation of slow-light technique aims at realizing controllable optical delay or optical buffer with high precision. In addition, slow light technique can also be applied to information processing and optical storage.We have studied the slow-light technique, in particular the slow-light technique that based on stimulated Brillouin amplification both theoretically and experimentally.We first proposed and demonstrated a controllable optical buffer based on a high power Brillouin amplifier. An experimental investigation is performed of the characteristics, gain, gain saturation and noise figure (NF) of a high-power fiber Brillouin amplifier (FBA) for the requirement of slow-light buffer application. Among these features, gain saturation is highlighted because it is a fundamental limitation for FBA based slow-light buffer. An analysis on how the performance of the high power FBA affects FBA based buffer is presented. The results show that for a -30dBm input signal, up to around 20ns delay enhancement can be obtained by using high-power FBA.Up to now, in all experiments of SBS slow light, no public reports have evidently shown that the delay time exceeded one bit period. The physics origin of this limitation has not been clarified. We, taking into account pulse broadening, proposed a detailed analysis on the buffer ability of slow-light buffers based on the FBA. Our analysis shows that for continuous wave (CW) or quasi-CW pump the maximum storage bits is dominated by the available net gain, which is limited by both the saturation gain and pulse broadening for bit streams in optical communication systems. We show the real storage capacity of SBS based slow light buffer is around one bit (0.5 for RZ data and 1 for NRZ data) for CW or quasi-CW pump. Detailed analysis shows that for pulse sequence with given peak power, the optimum data bit rate to achieve the best storage capacity can be obtained by using our method.Broadband application of all-optical buffers is a developing trend for high speed communication requirements. The storage performance of broadband Brillouin slow-light buffer is still unknown until now. We propose a theoretical analysis of broadband tunable Brillouin slow light with variable pump bandwidth. It is shown that the storage capacity is around 1.2 bit for data of RZ code. The value is twice as we obtained in the narrow band amplification case.In addition, we studied the slow light based on resonator. We investigated several important characteristics of the resonator, in particular the delay and dispersion performance with a high amplitude loss coefficient. It is shown that delay and dispersion will mutate when the product of amplitude loss coefficient and amplitude coupled ratio is around 1.