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Tang Y.-L.,CAS Shanghai Institute of Optics and fine Mechanics | Xu J.-Q.,CAS Shanghai Institute of Optics and fine Mechanics | Xu J.-Q.,Shanghai JiaoTong University | Chen W.,State Key Laboratory of Optical Communication Technology and Networks | And 2 more authors.
Chinese Physics Letters | Year: 2010

A home-made double-clad Tm3+-doped silica fiber laser with over 150-W output power is reported. Pumped with a diode bar at 793 nm, the fiber laser is operated at 2.04 μm with a slope efficiency of 56.3%. A quantum efficiency of > 140% is achieved owing to the efficient cross-relaxation process in heavily Tm3+-doped fibers. By using different fiber-cooling techniques, the slope efficiency shows a deviation over 10%. The influence of output coupling on the laser characteristics is also investigated. © 2010 Chinese Physical Society and IOP Publishing Ltd.


Deng S.,University of Electronic Science and Technology of China | Yi X.,University of Electronic Science and Technology of China | Deng M.,University of Electronic Science and Technology of China | Luo Z.,University of Electronic Science and Technology of China | And 3 more authors.
IEEE Photonics Technology Letters | Year: 2013

The overhead of cyclic prefix (CP) in coherent optical OFDM (CO-OFDM) tends to be too large for high-speed and long-haul optical fiber transmissions. We discuss and experimentally demonstrate a transmission of reduced guard interval OFDM (RGI-OFDM) with much reduced CP overhead based on digital sub-band demultiplexing. The proposed techniques are used to process a 66.7-Gb/s RGI-CO-OFDM signal (~20-GHz bandwidth) after 5440-km fiber transmission. The experiments show that it can reduce the overhead from 36.7% to 12.5%. We also optimize the digital signal processing in the filter bank for a better performance. © 1989-2012 IEEE.


Yi X.,University of Electronic Science and Technology of China | Chen X.,University of Electronic Science and Technology of China | Sharma D.,University of Electronic Science and Technology of China | Li C.,State Key Laboratory of Optical Communication Technology and Networks | And 4 more authors.
Optics Express | Year: 2014

Digital coherent superposition (DCS) provides an approach to combat fiber nonlinearities by trading off the spectrum efficiency. In analogy, we extend the concept of DCS to the optical OFDM subcarrier pairs with Hermitian symmetry to combat the linear and nonlinear phase noise. At the transmitter, we simply use a real-valued OFDM signal to drive a Mach-Zehnder (MZ) intensity modulator biased at the null point and the so-generated OFDM signal is Hermitian in the frequency domain. At receiver, after the conventional OFDM signal processing, we conduct DCS of the optical OFDM subcarrier pairs, which requires only conjugation and summation. We show that the inter-carrier-interference (ICI) due to phase noise can be reduced because of the Hermitain symmetry. In a simulation, this method improves the tolerance to the laser phase noise. In a nonlinear WDM transmission experiment, this method also achieves better performance under the influence of cross phase modulation (XPM). © 2014 Optical Society of America.


Yi X.,University of Electronic Science and Technology of China | Chen X.,University of Electronic Science and Technology of China | Li C.,State Key Laboratory of Optical Communication Technology and Networks | Luo M.,State Key Laboratory of Optical Communication Technology and Networks | And 3 more authors.
Optics InfoBase Conference Papers | Year: 2014

We experimentally demonstrate digital coherent superposition of optical OFDM subcarrier pairs with Hermitian symmetry to mitigate phase noise, including laser phase noise and cross-phase modulation in a WDM transmission. © OSA 2014.


Zhang J.,University of Electronic Science and Technology of China | Yi X.,University of Electronic Science and Technology of China | Zeng D.,University of Electronic Science and Technology of China | Chen X.,University of Electronic Science and Technology of China | And 4 more authors.
IEEE Photonics Journal | Year: 2015

Digital coherent superposition (DCS) for optical orthogonal frequency-division multiplexing (OFDM) subcarrier pairs with Hermitian symmetry can simultaneously reduce the inter-carrier interference (ICI) from laser phase noise and cancel the fiber nonlinearity to the first order. In this paper, we study an interesting scenario, where we upgrade the conventional OFDM with 4-quadrature amplitude modulation (QAM) to DCS-OFDM with 16-QAM, which have equal spectrum efficiency and require no change on hardware. We conduct a simulation to compare the tolerance to the laser phase noise and fiber nonlinearity, which are the main concerns for such an upgrading. First, the 16-QAM DCS-OFDM relaxes the laser linewidth requirement and performs better with a smaller fast Fourier transform size. Second, the nonlinear tolerance of 16-QAM DCS-OFDM is better when the nonlinear effects appear. The nonlinear tolerance of DCS-OFDM depends on the dispersion compensation scheme. The maximum SNR improvement is 3.4 dB with full post-dispersion compensation, and it can increase to 6.6 dB with symmetrical dispersion compensation at the launch power of 4 dBm. Finally, we verify that the maximum SNR improvement of 16-QAM DCS-OFDM with full post-dispersion compensation is 3.7 dB at the launch power of 6.2 dBm in the experiment. © 2009-2012 IEEE.


Yu Z.,University of Electronic Science and Technology of China | Yi X.,University of Electronic Science and Technology of China | Yang Q.,State Key Laboratory of Optical Communication Technology and Networks | Luo M.,State Key Laboratory of Optical Communication Technology and Networks | And 3 more authors.
Optics Express | Year: 2013

We propose a polarization demultiplexing method for coherent optical PDM-OFDM based on Stokes space, without inserting training symbols. The proposed approach performs well for different modulation formats of OFDM subcarrier, and shows comparable performances with that of conventional methods, but with a fast convergence speed and reduced overhead. The OFDM signal in the time domain cannot satisfy the conditions of SS-PDM accurately. Therefore, we first digitally convert the received OFDM signals to the frequency domain using fast Fourier transform (FFT). Each subcarrier of the OFDM signal has a much lower speed and narrower bandwidth, the polarization effects that it experiences can be treated as flat. Consequently, we can apply the polarization demultiplexing in Stokes space (SS-PDM) on per subcarrier basis. We verify this method in experiment by transmitting 66.6-Gb/s PDM-OFDM signal with 4QAM subcarrier modulation over 5440km SSMF and 133.3-Gb/s PDM-OFDM signal with 16QAM subcarrier modulation over 960km SSMF respectively. We also compare the results with those of training symbols. Finally, we analyze of the convergence speed of this method. © 2013 Optical Society of America.


Deng S.,University of Electronic Science and Technology of China | Yi X.,University of Electronic Science and Technology of China | Deng M.,University of Electronic Science and Technology of China | Yu Z.,University of Electronic Science and Technology of China | And 3 more authors.
Asia Communications and Photonics Conference, ACP | Year: 2013

Using digital sub-band-demultiplexing, we experimentally demonstrate an efficient 66.7-Gb/s RGI-OFDM transmission scheme. Experimental results show that the overhead of cyclic prefix is reduced from 26.9% to 11.1%, which cannot be received by conventional OFDM. © OSA 2013.


Yi X.,University of Electronic Science and Technology of China | Yang Q.,State Key Laboratory of Optical Communication Technology and Networks | Qiu K.,University of Electronic Science and Technology of China
Asia Communications and Photonics Conference, ACP | Year: 2013

We propose digital coherent superposition of optical OFDM subcarrier pairs with Hermitian symmetry to mitigate phase noise. Both in theory and simulation, we show that the inter-carrier-interference resulted from phase noise can be reduced. © OSA 2013.


Yu Z.,University of Electronic Science and Technology of China | Yi X.,University of Electronic Science and Technology of China | Yang Q.,State Key Laboratory of Optical Communication Technology and Networks | Luo M.,State Key Laboratory of Optical Communication Technology and Networks | And 3 more authors.
Optical Fiber Communication Conference, OFC 2013 | Year: 2013

We propose a polarization demultiplexing method in Stokes space for coherent optical PDM-OFDM without inserting training symbols. The experimental demonstration of fiber transmissions shows good performance, comparable with that of using training symbols. © 2013 OSA.

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