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Research Work
 
 
    I. Introduction  
    The constant development of the information-intensive society give a persistent driving fource of optical communication development. As we can see aroud us, many new emerged applications, such as HD vedio sharing, P2P file share, IPTV, etc., consume a huge bandwidth of transmission networks and lead to a reapid growth of the internet traffic. The growth of the Internet traffic does not appear to be leveling off any time soon and it is projected to continue to grow exponentially in the years to come. Commercial optical systems operating at 40 Gb/s based on two-level modulation formats and wavelength-division multiplexing (WDM) with channel spacing set to 50 GHz can provide a maximum spectral effciency SE= 0.8 bit/s/Hz. The increasing demand for data transmission capacity is however requiring to better exploit installed optical links operating in the C-band, fostering the search for transmission techniques with higher spectral efficiencies.
    II.Research Summary  
(1)OPT's Work: Lamda-based ultra-high speed Optical Circuit Swithing Networks (2004-2010)
     I stayed in Xian Institute of Optics and Precision Mechanics (CAS) for more than six years (2004-2010). During that time, I completed my Ph.D. study and then worked as a research assistant in there for another year. In here, I had been doing research works on key technologies for the next generation ultra-high speed optical transmission and switching optical networks continuously. My research interests focus on picosecond optical pulse generation, all-optical signal processing based on semiconductor optical amplifier (SOA) and high nonlinear optical fiber (HNLF), and optical switching system realization. We proposed several methods to obtain high quality ultra-short optical pulses using SOAs[1,2] . We do an extensive research about optical wavelength conversion based on SOA[3]. Error-free optical demultiplexing operations were achieved by using SOA or HNLF[4]. We also did some format conversion work between RZ and NRZ signals[5], which can be used for WDM to OTDM conversion. Based on these key technologies, we demonstrated an 80Gbit/s multiple-ports optical circuits switching networks successfully. In the experimental demo, optical wavelength was used as address label. A ultra-high speed optical wavelength converter with a subsequent wavelegnth router were acted as the circurt switcher. The swtiching opeation was controled by labview software with GPIB interface. Belowing figure shows the setup of the 80Gbit/s multiple-node all-optical wavelength routing network.

Fig.1 Optical Switching Network with a simple optical wavelength converter

(2) PolyU's Work: high spectral efficient optical transmission networks (2011.1 to now)
    All my research works in Xi'an use RZ-OOK signal and direct detection method. As we all know, These signals experience great system degradation due to dispersion, PMD and nonlinear effects, especially for high-speed OTDM signals. Recent years, more and more researchers are exploring new signal format and introduce coherent detection in optical transmission system. In addition, advances in integrated circuits and DSP technologies make coherent communication more close to practical application. So in 2010, I decide to move my research forcus to coherent optical communication, such as M-PSK and M-QAM systems.
    In Jan. 2011, I joint the Hong Kong polytechnic university and work with Prof. Lu and Alan Lau for spectral efficient optical transmission networks.In the Hong Kong polytechnic university, I took charge in a series of cooperation projects, funded by Huawei Technologies, Ltd. The main aim of the research is to explore the potential transmission capacity in optical fiber by using high-order modulation formats and digital signal processing technologies. With state-of-the-art transmission device and components, we setup a coherent transmission testbed. The design testbed consisted of multiformat transmitters, 100G integrated coherent receivers, versatile signal format analyser for offline processing, a direct transmission link with pure EDFA amplification and an optical recirculating loop. The versatile signal format analyser have the capability to handle variable optial signals, such as QPSK, 16QAM, 64QAM, with a series of self-developed DSP algorithms. Belowing figure shows the interface of our designed mult-format signal analyser.

    We develped novel 16/64 QAM signal generation techniques using a dual-drive IQ modulator with simple drive signals. WDM transmission systems are setup to verify our proposed generation techniques and the digital signal processing algorithms. The 16/64 QAM transmitters based on our proposed techniques use all commercially available components, and simplfy the driver circuits design by decreasing the levels of the driving signals. The test results showed the proposed transmitters have comparable performance with other generation techniques. The research works will be presented in OFC 2012 and OFC 2013.
updated in 7/1/2013
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