Yajie Li

Beijing Jiaotong University, Peping, Beijing, China

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Publications (11)10.99 Total impact

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    ABSTRACT: To extend the buffer depth of a fiber loop optical buffer, we have experimentally demonstrated an enhanced semiconductor optical amplifier (SOA)-based dual-loop optical buffer (DLOB) for storing variable-length optical packets. We have theoretically derived constraints governing the buffer depth of the DLOB, in which the SOA not only provides a nonlinear phase shift in the loop to implement the buffer function but also compensates for the fiber loop attenuation during long-time storage. It is found that the maximum allowable length of a stored packet to avoid the counter-propagation packet collision inside the SOA depends on the SOA bias position as well as the length of the fiber loop. To demonstrate the effectiveness of the proposed enhanced configuration, we have successfully demonstrated the storage of 2.5-Gbps variable-length packets even when the length of the input packet exceeds the corresponding length of the fiber loop. Another unique advantage of the proposed enhanced DLOB configuration is that it can also overcome the problem of power leakage of the stored packet due to a directional gain difference of single SOA and gain saturation. Index
    Journal of Lightwave Technology 03/2008; 26(4-26):425 - 431. DOI:10.1109/JLT.2007.912516 · 2.97 Impact Factor
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    Songnian Fu · P. Shum · Guo Ning · Chongqing Wu · Yajie Li ·
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    ABSTRACT: In this paper, we theoretically investigate the dual-wavelength packet signal storage in the semiconductor optical amplifier (SOA)-based dual-loop optical buffer (DLOB). The loadable function of the DLOB is implemented by the cross phase modulation induced by the SOA. The influence of the nonlinear phase shift on the chirp and distortion of the stored packet pulse is examined for the case of the dual-wavelength loadable operation. It is found that, when the overlapping area of the stored dual-wavelength pulse is less than half of the pulse width, the distortion of output pulse after storage is negligibly small. However the most severe distortion appears when the dual-wavelength pulses overlap completely. The peak power of output packet pulse is reduced by approximately 30%. The obtained results can provide helpful insight for experimental implementation.
    Optics Communications 11/2007; 279(2-279):255-261. DOI:10.1016/j.optcom.2007.07.049 · 1.45 Impact Factor
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    ABSTRACT: It is essential to extend the optical buffer depth to meet the burst-mode packet requirement. In this paper, we propose to incorporate the Mach-Zehnder interferometer (MZI) into our successful SOA-based dual loop optical buffer (DLOB) configuration. The maximum packet length for the DLOB storage is evaluated theoretically, and the fiber loop utilization can be greatly enhanced with our modified configuration. Then we have successfully demonstrated the 2.5 Gbps variable-length packet loadable function with the MZI-DLOB configuration. The waveform of variable-length packet is little degraded after optical storage. Meanwhile an effective polarization stable method is also experimentally implemented to reduce the instability of MZI-DLOB. All the obtained results confirm the feasibility of our configuration to apply in variable-length optical packet switching.
    Proceedings of SPIE - The International Society for Optical Engineering 10/2007; 6783. DOI:10.1117/12.743510 · 0.20 Impact Factor
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    ABSTRACT: In this paper, a theoretical study and experimental demonstration are applied to achieve power equalization for semiconductor optical amplifier (SOA)-based dual-loop optical buffers (DLOBs). It is found that, due to the gain saturation and limited linewidth-enhancement factor of the SOA, the peak power of a packet pulse with an optically controlled delay of 9.9 mus is 4.83 dB lower than that of a packet pulse without storage. In order to eliminate the 4.83-dB output power fluctuation of the DLOB, a simple power-equalization method based on the optimization of an optical control pulse is proposed. By injecting a negative optical control pulse, the output power fluctuation of a packet pulse can be effectively reduced to zero. We have also investigated the peak power level of the optical control pulse required to fulfil the buffer function. It is found that the SOA with larger linewidth-enhancement factor and larger small-signal gain should be used to reduce the peak power of the optical control pulse. It is also theoretically found that, due to the negative optical-control pulse injection, the packet signal with Gaussian profile has some distortion after storage. However, the distortion effect is mitigated when the shape of the input pulse is more similar to the square profile. Finally, the proposed method for achieving power equalization in an SOA-based optical buffer has been justified by carrying out a 2.5-Gb/s 2times2 exchange-bypass optical switch experiment. We believe that this power-equalization method can be also applied to other SOA cross-phase modulation-based applications
    IEEE Journal of Quantum Electronics 07/2007; 43(6-43):508 - 516. DOI:10.1109/JQE.2007.897915 · 1.89 Impact Factor
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    ABSTRACT: We demonstrate two aligned principal states of polarizations for the bias current variation or optical control pulse injection, thus power equalization is achieved for the SOA polarization rotation based subsystem with less than 0.3 dB fluctuation.
    Lasers and Electro-Optics, 2007. CLEO 2007. Conference on; 06/2007
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    Zhi Wang · Yongjun Wang · Yajie Li · Chongqing Wu ·
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    ABSTRACT: The mode index and mode field of a triple-core waveguide are simulated by the compact supercell method and the FEM method. The coupling property of LP(11) mode is analyzed, for the first time to our knowledge, which is similar to that of LP(01) mode except the different coupling length. Both LP(01) and LP(11) modes can be separated based on their different coupling lengths in the waveguide. When both modes are put into the central port, they will come out on different ports by optimizing the coupler length, and the mode extinction ratio can approach 30dB.
    Optics Express 11/2006; 14(22):10324-31. DOI:10.1364/OE.14.010324 · 3.49 Impact Factor
  • Bin Wei · Chongqing Wu · P. Shum · S. N. Fu · Yajie Li ·
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    ABSTRACT: The survivability is one of the important issues in Resilient Packet Ring (RPR) networks. This article analyzes a new failure scenario and put forward a new restoration mechanism named as C-steering. The mathematical model has been established to investigate the survivability of the RPR network in three operation methods. The throughput-delay performance and link utilization are discussed theoretically and experimentally.
    Proceedings of SPIE - The International Society for Optical Engineering 10/2006; DOI:10.1117/12.688142 · 0.20 Impact Factor
  • Yajie Li · Chongqing Wu · P. Shum · Songnian Fu · Bin Wei ·
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    ABSTRACT: A precise measurement method for linewidth enhancement factor of SOA by Sagnac interferometer when considering XGM is presented. It needs neither spacial interference nor optical spectrum analysis, has simple configuration and better measurement stability than existing methods.
    Proceedings of SPIE - The International Society for Optical Engineering 10/2006; 6351. DOI:10.1117/12.688603 · 0.20 Impact Factor
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    ABSTRACT: This paper reports the progress of the 863 high-technology project of China "Optical Resilient Packet Ring (O-RPR) Based on All-optical Buffering Techniques". In this ring network, for the packet through an intermediate node the conversion of O/E/O is not needed in order to overcome the bottleneck of O/E/O. In all-optical node a Dual Loop Optical Buffer (DLOB) is used to revolve the collision between the packet, which pass through the node, and add packet from local user to ring. The principle of DLOB is introduced. The bit-rate of head of optical frame is lower than the bit-rate of payload in a packet, in order to increase the efficiency of transmission link. This paper will introduce the network topology, layers and the structure of optical node. It includes an optical splitter, optical delay line as input buffer, a SOA as optical switch, which switch the packet dropping down form the ring or pass through the node, a DLOB and an electric buffer. An ARM is used for regulation of different buffers. The experiment results of a demonstrate network including 3 nodes are given.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2006; 6025. DOI:10.1117/12.667052 · 0.20 Impact Factor
  • Yajie Li · Chongqing Wu ·
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    ABSTRACT: This paper analyzes the performance of DLOB and discusses the influence of SOA's linewidth enhancement factor and XGM on the performance of DLOB, gets the relation between linewidth enhancement factor and extinction ratio, transfer ratio. Then discusses the influence of state of polarization (SOP) on buffer's output power and finds their evolution regularity. Many useful conclusions are drawn.
    Proceedings of SPIE - The International Society for Optical Engineering 11/2005; 6019. DOI:10.1117/12.635406 · 0.20 Impact Factor
  • Songnian Fu · Chongqing Wu · Yajie Li · Xianzi Dong ·
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    ABSTRACT: This paper firstly introduces the principle of distributed sensing system based on Polarization sensitive Optical Time-Domain Reflectometer (P-OTDR). As known, the change of State of Polarization (SOP) in fiber is sensitive to environment, consequently this sensing method can extract very little perturbation of extra temperature or strain; another significant advantage is that the sensing information can be achieved nondestructively at one end. Hence, this technique has become a practical and helpful tool in distributed optical fiber sensing system. However backscattered light in single-mode fiber is very weak, and the optical pulse width limits the spatial resolution, so there is a compromise between SNR and sensor spatial resolution. We investigate two signal-process methods to extract the state polarization (SOP) evolution from backscatted signal. From the experiment results, we find that both the digital average and deconvolution can be used for enhancing SNR and system spatial resolution. And we also find hundred of digital average is enough, the more time we average the less improvement of SNR we get. At the same time, we view that the SOP of backscattered signal is the response of sensing system. By mean of deconvolution the actual SOP evolution is not lost, and the spatial resolution of POTDR System doesn"t degrade with a wider pulse. Compared with previous deconvolution case, the deconvolution method can effectively improve the system spatial resolution without decreasing the transmitting pulse width. Finally we give some experiment results with strain perturbation, our system can detect the point where the environment changes, which is suitable for smart structure and optic-fiber sensor application.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2005; DOI:10.1117/12.569706 · 0.20 Impact Factor