In this paper, an algorithm based on homomorphic deconvolution is proposed to give an accurate estimation of nonlinear phase in the beat signal in optical frequency domain reflectometry (OFDR). Nonlinearities in the beat signal are obtained by using an auxiliary interferometer. After converting to cepstrum domain and filtering, the nonlinearity can be separated from the beat signal. Then, the deskew filter is used to eliminate the nonlinearity. In the proposed algorithm, no approximations are used, so the estimation is theoretically unbiased. Certain simulations are performed to verify the versatility and effectiveness of the proposed algorithm. The nonlinearities are accurately estimated and eliminated by the method, which improves the spatial resolution of the OFDR system.
A machine learning equalization technique based on KNN for 56Gpbs PAM4-GPONis proposed by nonlinear classification characteristics of KNN. Simulation results show that the proposed method can effectively optimizes the performance of equalization and increase bandwidth of the GPON network.
In 40-Gb/s optical systems, it is impossible to neglect the electronic dispersion of polarization-mode dispersion (PMD).
As the data rate is increased, the maximum useful length of the fiber decreases according to the square of the increase.
With the development of VLSI and DSP technologies, the electronic dispersion compensation for optical network has
aroused greater world attention. In this paper, the performance of decision feedback equalizer (DFE) in PMD-limited
40-GB/s optical links is analyzed by using Matlab/Simulink. A simple equalizer circuit, in fold-cascade traveling-wave
filter topology, is presented and the results based on S-parameter simulations show that a DFE equalizer consisting of a
3-tap feed forward equalizer (FFE) and a 2-tap feed back equalizer (FBE) can mitigate PMD effectively.
Two kinds of electronic compensation of polarization mode dispersion (PMD) are demonstrated in this paper, including
transversal filter(TF) and feed forward equalizer(FFE) + decision feedback equalization(DFE). Compared with the
normalized least-mean-square (NLMS), the least-mean-square (LMS) is the best algorithm to control the equalizers. The
tap weights are adapted using the LMS algorithm until they reach stationary values. Then we focus on the structure of
FFE+DFE and find out the relationship of the number of taps and BER with different structures in the same conditions.
From the comparison, the work of 4-tap FFE+2-tap DFE is more effective, which has the most commercial value.
Novel highly birefringent photonic bandgap fibers (PBGFs) are obtained by filling high index material in the air holes of total internal reflection birefringent photonic crystal fibers. The effect of filling high-index material on the transmission characteristics has been theoretically investigated. The photonic bandgap has been achieved by using the plane-wave method. Moreover, the polarization mode dispersion (PMD) has been studied by a full-vector finite-element method. Numerical results show that very high PMD with magnitude of order of 10-10 has been respectively acquired, which is much higher than those of the non-filled fibers. Furthermore, strong coupling between surface modes and the fundamental modes has been found in the bandgap of the birefringent PBGFs.
Tunable photonic bandgap fibers (PBGFs) were theoretically investigated by using the vector plane-wave expansion method and the vector finite element method. The tunable PBGFs are fabricated by filling high index material in the air holes of index-guiding photonic crystal fibers. The wavelength dependence of leaky loss and group velocity dispersion (GVD) has been illustrated. We show the leaky loss in the tunable PBGFs can be strongly depended on the refractive index of filled material due to the photonic bandgap effect. The tunable attenuator which operates at 1550nm is designed based on this PBGFs.
Tunable photonic bandgap fibers (PBGFs) were theoretically investigated by using the vector plane-wave expansion method and the vector finite element method. The tunable PBGFs are fabricated by filling a high-index material in the air holes of index-guiding photonic crystal fibers. The wavelength dependence of leaky loss and group velocity dispersion (GVD) has been illustrated. We show the leaky loss in the tunable PBGFs can strongly depend on the refractive index of filled material due to the photonic bandgap effect. The tunable attenuator which operates at 1550 nm is designed based on this PBGFs.
In this letter, long period gratings fabricated in single-mode microstructure fibers (index-guiding MF and PBG MF) were achieved by putting periodic pressure on the cladding along the fiber length, furthermore, the characteristics of the LPGs were discussed.
We present theoretical analysis of tunable bandgap guidance in virtue of bandgap theory. By means of plane-wave method a novel tunable photonic bandgap microstructure fiber (MF) was investigated by tuning the refractive index of nematic liquid crystal crystal (NLC) filled in the holes of MFs. Moreover, by using a full-vector finite-element method (FEM) with anisotropic perfectly matched layers (PMLs), the dispersion curves of NLC filled MFs have been computed with different value of the refractive index of NLC. Moreover, the leakage loss of the fundamental modes of the NLC filled MFs has been analyzed.
Using a full-vector finite element method, the phase modal birefringence and group modal birefringence to lateral pressure alone slow axis and fast axis versus wavelength in birefringence microstructure fiber was analyzed. In the wave band of our research, 600nm-1700nm, when different direction pressure is applied, the phase modal birefringence (B) and group modal birefringence (G) have different change to wavelength in microstructure fiber. Moreover, the results reveal that the pressure sensitivity of B and G have different change to wavelength when applying different direction lateral pressure. Our research has great signification in designing microstructure fiber and using microstructure fiber in sensing field et.al., especially using in multidimensional sensor.
The soliton transmission system has great potential for providing high speed and long distance communication. However, the polarization-mode dispersion (PMD) of fiber becomes a serious limitation when the bit-rate of systems is over 40 Gbit/s. So it is very urgent to study the influence of PMD on the Soliton communication system.
In this paper, we use numerical simulations to calculate the Nonlinear Schrodinger Equations with the PMD effect. In our simulation, we mainly investigate the transmission properties of the Manakov-soliton in optical fibers with PMD at the wavelength of 1550 nm. We discuss the self-trapping effect for a single pulse of Soliton, which can prevent a soliton pulse with PMD from splitting. Then we take the pulse sequences into account, which is more significance in real transmission link, we discuss the timing jitter problem due to the loss of Soliton energy.
We present a numerical study of the guidance and amplification properties in an Er3+-doped honeycomb photonic bandgap fiber with down-doped core. Our analysis is based on a full-vector plane-wave expansion method and Runge-Kutta iterative algorithm. Overlap integrals between mode profiles and Er3+-doped region varies from 0.973 to 0.350 in guiding range of the fiber. The highly efficient amplifier can be designed by using this fiber.
This paper presents a method of splitting signals from fast and slow axes of polarization maintaining fibers by using a polarization splitter. The new scheme includes a turning connector and a polarization splitter. The polarization splitter will split signals from a fiber and give two separated outputs. It gives some theoretical calculations and the relations between the turning angle and output power from the splitter. It also analyzes the relationship of electrical power spectrum versus differential group delay and relative angles between the axis of a fiber and direction of a polarization splitter. Preliminary experiments are also given in this paper. The scheme has a great potential of becoming an effective method of solving polarization mode dispersion (PMD) problem.
The PMD-induced pulse broadening may cause degradation of receiver sensitivity and has negative effects on the power spectrum of received signals. The paper deals with derivation of the effects of PMD-induced pulse broadening on receiver sensitivity based on the concept of mean square pulse width. It analyzes in detail the effects of PMD on the spectrum of received power. It also discusses the scheme with which the power of a certain frequency component is extracted as a feedback control signal in a PMD compensation system.