Tianwai Bo

Image processing based common phase estimation for coherent optical orthogonal frequency division multiplexing system

A novel common phase error estimation method based on image processing technique is proposed. Both numerical simulations and experiments prove its feasibility to compensate phase noise with improved spectral efficiency than the pilot-subcarrier aided method.

Common Phase Estimation in Coherent OFDM System Using Image Processing Technique

In a coherent orthogonal frequency division multiplexing system, the possible rotation of the rectangular signal constellation, due to common phase error, is shown to be effectively compensated by applying an skew compensation technique adopted in image processing area. We further propose an improved technique to further reduce the complexity of the algorithm and investigate the effect of the number of required test phases, via numerical simulations. The proposed improved algorithm is also compared with the conventional blind phase searching algorithm. It is shown that by employing only two bits of overhead, it can achieve a comparable performance to that of the traditional pilot aided method.

A Pilot-Correlated PMD Monitoring Scheme for Direct Detection Optical OFDM System

A polarization mode dispersion monitoring scheme is proposed and demonstrated for direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems. A pair of data-assisted pilot subcarriers is inserted at two spectral edges of the OFDM signal spectrum. Simple data correlation technique is used to estimate the powers of the pilot subcarriers and thus retrieves the DGD value at the monitoring unit, without the need of demodulation of the pilot subcarriers. Experiments show a DGD monitoring range of 0 to 45 ps in a typical radio-frequency tone-assisted DDO-OFDM system. The robustness of the proposed scheme to optical signal-to-noise ratio and accumulated chromatic dispersion is further experimentally investigated. Besides, simulations and experiments are performed to demonstrate the feasibility of using photodiodes with narrow bandwidth. By inserting one more data-assisted pilot subcarrier, the proposed scheme becomes insensitive to the input angle of the state of polarization. The proposed scheme provides an effective monitoring solution for the optical OFDM signals across intermediate nodes in flexible optical network.

Modulation Format Recognition for Optical Signals Using Connected Component Analysis

We investigate and characterize the blind modulation format recognition method based on connected component analysis for general-purpose optical receivers. A converted binary graph is generated by projecting a part of the received data in Stokes space onto a 2-D plane. We further characterize three key parameters, namely, the threshold of density filter, the size of averaging filter, and the required number of data points for successful format recognition. In addition, we compare the computation complexity of the proposed method with other format recognition methods in Stokes space. Our results show that there exists a common set of parameters such that the proposed method can recognize a number of common optical modulation formats, proving its good robustness and practicality.

Pump-phase-noise-tolerant wavelength conversion for coherent optical OFDM using coherent DFB pumping

We experimentally demonstrate an OWC scheme for CO-OFDM using coherent DFB pumping. The tolerance against pump phase noise with coherent pumping enables the use of low-cost 2MHz-linewidth DFB as pump to realize OWC of 12Gbps QPSK-CO-OFDM with 1dB penalty.

Common phase error estimation in coherent optical OFDM systems using best-fit bounding box

A new spectral-efficient image processing based scheme is proposed to blindly estimate the common phase error of coherent optical orthogonal frequency division multiplexing system. The scheme provides new perspective for compensating laser phase noise effect through simple image processing techniques used in computer vision. It shows comparable performance with conventional pilot aided method but much improved spectral efficiency.

Optical performance monitoring in elastic optical OFDM networks

Optical performance monitoring (OPM) is a crucial element in network management, in order to assure the quality of the optical signals at various intermediate and destination nodes. In future elastic optical network, the network operation is more adaptive and reconfigurable. The OPM monitoring information retrieved at each intermediate node would be useful for optimal network control. Common OPM parameters in an optical transmission system, include optical signal-to-noise ratio (OSNR), accumulated chromatic dispersion (CD) and polarization mode dispersion (PMD). In this paper, we present our OPM techniques for these three parameters, based on signal correlation procedures on one or a few pilot subcarriers inserted in the spectrum of an optical OFDM signal, which is one of the promising signal format to support the future elastic optical networks.

Common phase error estimation for coherent optical OFDM system using best-fit bounding box

A new spectral-efficient image processing based scheme is proposed to blindly estimate the common phase error of coherent optical orthogonal frequency division multiplexing system. The scheme provides new perspective for compensating laser phase noise effect through simple image processing techniques used in computer vision. It shows comparable performance with conventional pilot aided method but much improved spectral efficiency.