Machine learning for fiber nonlinearity mitigation in long-haul coherent optical transmission systems

Fiber nonlinearities from Kerr effect are considered as major constraints for enhancing the transmission capacity in current optical transmission systems. Digital nonlinearity compensation techniques such as digital backpropagation can perform well but require high computing resources. Machine learning can provide a low complexity capability especially for high-dimensional classification problems. Recently several supervised and unsupervised machine learning techniques have been investigated in the field of fiber nonlinearity mitigation. This paper offers a brief review of the principles, performance and complexity of these machine learning approaches in the application of nonlinearity mitigation

Advanced DSP for coherent optical fiber communication

In this paper, we provide an overview of recent progress on advanced digital signal processing (DSP) techniques for high-capacity long-haul coherent optical fiber transmission systems. Not only the linear impairments existing in optical transmission links need to be compensated, but also, the nonlinear impairments require proper algorithms for mitigation because they become major limiting factors for long-haul large-capacity optical transmission systems. Besides the time domain equalization (TDE), the frequency domain equalization (FDE) DSP also provides a similar performance, with a much-reduced computational complexity. Advanced DSP also plays an important role for the realization of space division multiplexing (SDM). SDM techniques have been developed recently to enhance the system capacity by at least one order of magnitude. Some impressive results have been reported and have outperformed the nonlinear Shannon limit of the single-mode fiber (SMF). SDM introduces the space dimension to the optical fiber communication. The few-mode fiber (FMF) and multi-core fiber (MCF) have been manufactured for novel multiplexing techniques such as mode-division multiplexing (MDM) and multi-core multiplexing (MCM). Each mode or core can be considered as an independent degree of freedom, but unfortunately, signals will suffer serious coupling during the propagation. Multi-input−multi-output (MIMO) DSP can equalize the signal coupling and makes SDM transmission feasible. The machine learning (ML) technique has attracted worldwide attention and has been explored for advanced DSP. In this paper, we firstly introduce the principle and scheme of coherent detection to explain why the DSP techniques can compensate for transmission impairments. Then corresponding technologies related to the DSP, such as nonlinearity compensation, FDE, SDM and ML will be discussed. Relevant techniques will be analyzed, and representational results and experimental verifications will be demonstrated. In the end, a brief conclusion and perspective will be provided

Well-posedness of the fractional Ginzburg-Landau equation

In this paper, we investigate the well-posedness of the real fractional Ginzburg-Landau equation in several different function spaces, which have been used to deal with the Burgers' equation, the semilinear heat equation, the Navier-Stokes equations, etc. The long time asymptotic behavior of the nonnegative global solutions is also studied in details

SNPHunter: a bioinformatic software for single nucleotide polymorphism data acquisition and management

BACKGROUND: Single nucleotide polymorphisms (SNPs) provide an important tool in pinpointing susceptibility genes for complex diseases and in unveiling human molecular evolution. Selection and retrieval of an optimal SNP set from publicly available databases have emerged as the foremost bottlenecks in designing large-scale linkage disequilibrium studies, particularly in case-control settings. RESULTS: We describe the architectural structure and implementations of a novel software program, SNPHunter, which allows for both ad hoc-mode and batch-mode SNP search, automatic SNP filtering, and retrieval of SNP data, including physical position, function class, flanking sequences at user-defined lengths, and heterozygosity from NCBI dbSNP. The SNP data extracted from dbSNP via SNPHunter can be exported and saved in plain text format for further down-stream analyses. As an illustration, we applied SNPHunter for selecting SNPs for 10 major candidate genes for type 2 diabetes, including CAPN10, FABP4, IL6, NOS3, PPARG, TNF, UCP2, CRP, ESR1, and AR. CONCLUSION: SNPHunter constitutes an efficient and user-friendly tool for SNP screening, selection, and acquisition. The executable and user's manual are available at

Theoretical analysis of the non-reciprocal phase shifts due to birefringence and topology in fiber ring interferometers

The non-reciprocal phase shifts in fiber ring interferometers due to the fiber birefringence and the path topology are investigated for the first time. It is shown that the resultant birefringence of the fiber, which is the combination of the linear birefringence intrinsic to the fiber and the circular birefringence induced by the twisting in the fiber coiling, is not reciprocal for both rays in the bidirectional propagation due to the path topology confined by the coiled fiber. Our model indicates that the performance of fiber ring interferometers periodically depends on both the linear and the circular birefringence of the coiled fiber, and the bias error can be reduced by the typical fabrication process of the fiber ring interferometers

Analytical estimation of stress-induced birefringence in panda-type polarization-maintaining fibers

An analytical model for estimating the stress -induced birefringence in true Panda-type polarization -maintaining fibers with imperfect geometry has been developed in this letter. The developed model is simpler and more accurate compared to conventional sophisticated and asymptotic formulas in reported works. Our model provides a clear and simple solution to demonstrate the periodic dependence of the birefringence on the misalignment angle between the two stress-applying parts, and the monotonic dependence on the geometric parameters of stress-applying parts. Our work also reveals the important role of the misalignment angle between the two stress-applying parts in practical Panda-type fibers

Bias error and its thermal drift due to fiber birefringence in interferometric fiber-optic gyroscopes

Polarization-maintaining fibers (PMFs) with intrinsic highly stress-induced birefringence (SIB) are widely employed in interferometric fiber-optic gyroscopes (IFOGs). The performance of which is limited by the refractive index and its thermal fluctuations induced by the temperature variations. The SIB contributes to the refractive index variously along with the temperature. However, the bias error and its thermal drift arising from the SIB in PMFs are never considered. In this paper, we present theoretical analysis on high-performance IFOGs considering the effects of the SIB and its thermal fluctuation incorporated into the early model. The numerical analysis of the proposed model shows that the accuracy of IFOG using PMFs is better than single-mode fibers (SMFs) by a factor of 2,and the high performance with ultimate sensitivity of IFOGs is achievable by the special design of PMFs which depends not only on the pure Shupe effect but also on the effects from intrinsic SIB and its temperature sensitivity

One-stage partial vertebrectomy, titanium mesh implantation and pedicle screw fixation in the treatment of thoracolumbar burst fractures through a posterior approach

OBJECTIVE: To analyze the clinical results of a partial vertebrectomy with titanium mesh implantation and pedicle screw fixation using a posterior approach to reconstruct the spine in the treatment of thoracolumbar burst fractures. METHOD: From January 2006 to August 2008, 20 patients with severe thoracolumbar fractures were treated.For vertebral bodies associated with one injured intervertebral disk, subtotal vertebrectomy surgery and single-segment fusion were performed. For vertebral bodies with two injured adjacent intervertebral disks, partial vertebrectomy surgery and two-segment fusion were performed. RESULTS: All 20 patients were followed up for 12 to 24 months (average of 18 months). There were no complications such as wound infections, hemopneumothorax or abdominal infections in any of the patients. The neurological status of all of the patients was improved by at least one American Spinal Injury Association grade by the last follow-up. The anterior vertebral body height was an average of 50.77% before surgery, 88.51% after surgery and 87.86% at the last follow up; the sagittal Cobb angle was improved, on average, from 26.15° to 5.39° and was 5.90° at the last follow up. The percentage of spinal stenosis was improved, on average, from 26.07% to 4.93%° and was 6.15% at the last follow up. There were significant differences in the anterior vertebral body height pre- and post-surgery and in the sagittal Cobb angle and the percentage of spinal stenosis (

(Z)-N-{(E)-10-[(2,6-Diisopropyl­phen­yl)­imino]-9,10-dihydro­phenanthren-9-yl­idene}-2,6-dimethyl­aniline

The title compound, C34H34N2, adopts a Z,E configuration with respect to the N=C—C=N backbone, with an N—C—C—N torsion angle of 41.1 (4)° The dihedral angle between the benzene rings in the 9,10-dihydro­phenanthrene moiety is 18.0 (1)°

Analytical estimation in differential optical transmission systems influenced by equalization enhanced phase noise

An analytical model is presented for assessing the performance of the bit-error-rate (BER) in the differential m-level phase shift keying (m-PSK) transmission systems, where the influence of equalization enhanced phase noise (EEPN) has been considered. Theoretical analysis has been carried out in differential quadrature phase shift keying (DQPSK), differential 8-PSK (D8PSK), and differential 16-PSK (D16PSK) optical transmission systems. The influence of EEPN on the BER performance, in term of signal-to-noise ratio (SNR), are investigated for different fiber dispersion, LO laser linewidths, symbol rates, and modulation formats. Our analytical model achieves a good agreement with previously reported EEPN induced BER floors, and can give an accurate prediction for the DQPSK system, and a leading-order approximation for the D8PSK and the D16PSK systems