Chuanchuan Yang

Orthogonal Basis Expansion-Based Phase Noise Estimation and Suppression for CO-OFDM Systems

In coherent optical orthogonal frequency-division-multiplexing systems, the laser phase noise which induces common phase error (CPE) and intercarrier interference (ICI) is a major impairment to the systems performance. In this letter, we propose an orthogonal basis expansion-based phase noise suppression algorithm which can mitigate CPE as well as ICI effectively. The proposal can significantly reduce the bit-error-rate floor caused by ICI.

Phase noise suppression for coherent optical block transmission systems: a unified framework.

A unified framework for phase noise suppression is proposed in this paper, which could be applied in any coherent optical block transmission systems, including coherent optical orthogonal frequency-division multiplexing (CO-OFDM), coherent optical single-carrier frequency-domain equalization block transmission (CO-SCFDE), etc. Based on adaptive modeling of phase noise, unified observation equations for different coherent optical block transmission systems are constructed, which lead to unified phase noise estimation and suppression. Numerical results demonstrate that the proposal is powerful in mitigating laser phase noise.

A CO-OFDM System With Almost Blind Phase Noise Suppression

We propose a high spectral efficiency coherent optical orthogonal frequency division multiplexing system utilizing a novel and almost blind phase noise compensation method. With the aid of pseudo pilots instead of pilots, laser phase noise can be suppressed effectively while the overhead of system is reduced successfully. Numerical results show that the performance of the proposed pseudo pilot-aided phase noise compensation scheme can approach that of the pilot-aided counterpart, yet achieve higher spectral efficiency even when the phase noise is severe.

Time-Domain Maximum-Likelihood Channel Estimation for PDM CO-OFDM Systems

We propose an efficient channel estimation method based on time-domain maximum likelihood (TDML) algorithm for polarization-division-multiplexed coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. Compared with the conventional channel estimation approach, although with overhead reduction, TDML demonstrates similar system robustness against transmission impairments, such as optical noise, chromatic dispersion, and polarization-mode dispersion. More importantly, TDML demonstrates enhanced tolerance against laser phase noise. The theoretical analysis is validated by numerical simulation of quadrature-phase-shift-keying CO-OFDM system.

Orthogonal Basis Expansion-Based Phase Noise Suppression for PDM CO-OFDM System

In this letter, we develop an orthogonal basis expansion (OBE)-based phase noise suppression method for polarization-division-multiplexed (PDM) coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. Compared with the conventional phase noise suppression approach, the OBE method not only significantly promotes the system tolerance of laser phase noise, but also improves the system robustness against nonlinear phase noise. The theoretical analysis is validated by numerical simulations of PDM CO-OFDM systems with 16-quadrature-amplitude-modulation format.

The application of cost-effective lasers in coherent UDWDM-OFDM-PON aided by effective phase noise suppression methods

Digital coherent passive optical network (PON), especially the coherent orthogonal frequency division multiplexing PON (OFDM-PON), is a strong candidate for the 2nd-stage-next-generation PON (NG-PON2). As is known, OFDM is very sensitive to the laser phase noise which severely limits the application of the cost-effective distributed feedback (DFB) lasers and more energy-efficient vertical cavity surface emitting lasers (VCSEL) in the coherent OFDM-PON. The current long-reach coherent OFDM-PON experiments always choose the expensive external cavity laser (ECL) as the optical source for its narrow linewidth (usually<100 KHz). To solve this problem, we introduce the orthogonal basis expansion based (OBE) phase noise suppression method to the coherent OFDM-PON and study the possibility of the application of the DFB lasers and VCSEL in coherent OFDM-PON. A typical long-reach coherent ultra dense wavelength division multiplexing (UDWDM) OFDM-PON has been set up. The numerical results prove that the OBE method can stand severe phase noise of the lasers in this architecture and the DFB lasers as well as VCSEL can be used in coherent OFDM-PON. In this paper, we have also analyzed the performance of the RF-pilot-aided (RFP) phase noise suppression method in coherent OFDM-PON.

Cost-Effective and Spectrum-Efficient Coherent TDM-OFDM-PON Aided by Blind ICI Suppression

Digital coherent orthogonal frequency division multiplexing passive optical network (OFDM-PON) is a strong candidate for the 2nd-stage-next-generation PON (NG-PON2). However, as an OFDM system, especially for long-symbol duration OFDM system, it is very sensitive to laser phase noise. The common phase error (CPE) and intercarrier interference (ICI) caused by the laser phase noise severely cut down the performance of the coherent OFDM-PON. To correct the phase noise as well as guarantee high spectral efficiency, in this letter, we propose an advanced pseudo pilot-aided orthogonal basis expansion-based (A-PS-OBE) blind ICI suppression method over both constant and nonconstant modulus modulation, and deployed it in coherent optical time division multiplexing (TDM) OFDM-PON. The numerical results demonstrate the A-PS-OBE method can make the application of the cost-effective lasers possible in the coherent TDM-OFDM-PON and high-order modulation can also be adopted though the laser linewidth is large to 700 kHz.

Nonlinear performance of multi-granularity orthogonal transmission systems with frequency division multiplexing.

Orthogonal transmission with frequency division multiplexing technique is investigated for next generation optical communication systems. Coherent optical orthogonal frequency division multiplexing (OFDM) and single-carrier frequency division multiplexing (SCFDM) schemes are compared in combination with polarization-division multiplexing quadrature phase shift keying (QPSK) or 16-QAM (quadrature amplitude modulation) formats. Multi-granularity transmission with flexible bandwidth can be realized through ultra-dense wavelength division multiplexing (UDWDM) based on the orthogonal technique. The system performance is numerically studied with special emphasis on transmission degradations due to fiber Kerr nonlinearity. The maximum reach and fiber capacity for different spectral efficiencies are investigated for systems with nonlinear propagation over uncompensated standard single-mode fiber (SSMF) links with lumped amplification.

Phase Noise Estimation and Mitigation for DCT-based Coherent Optical OFDM systems

In this paper, as an attractive alternative to the conventional discrete Fourier transform (DFT) based orthogonal frequency division multiplexing (OFDM), discrete cosine transform (DCT) based OFDM which has certain advantages over its counterpart is studied for optical fiber communications. As is known, laser phase noise is a major impairment to the performance of coherent optical OFDM (CO-OFDM) systems. However, to our knowledge, detailed analysis of phase noise and the corresponding mitigation methods for DCT-based CO-OFDM systems have not been reported yet. To address these issues, we analyze the laser phase noise in the DCT-based CO-OFDM systems, and propose phase noise estimation and mitigation schemes. Numerical results show that the proposal is very effective in suppressing phase noise and could significantly improve the performance of DCT-based CO-OFDM systems.

New optical compensator for higher-order polarization mode dispersion in optical fiber channels

We propose a new optical compensator for both first-order and higher-order polarization mode dispersion PMD effects in an optical fiber channel. The compensation scheme needs just one more polarization controller and one more variable differential group delay DGD element than first-order optical compensators with adjustable DGD ele- ments. And the control algorithm for this compensator is easier and more stable than that for the typical higher-order optical polarization mode dispersion compensators. By an advised control method, the proposed compensator can al- ways have better performance than first-order optical com- pensators. Numerical results are given to prove the effi- ciency of the proposed compensation scheme.