New approach to determine the effects of polarization mode dispersion and chromatic dispersion on pulse and RF signals

We present a novel analytical expression relating the output state of polarization (SOP) and the polarization mode dispersion (PMD) vector, including polarization-dependent chromatic dispersion (PCD), in terms of the angle of precession of the output SOP around the PMD vector. We derive a number of new expressions incorporating for the first time this angle of precession. First, a general relation to study the effect of differential group delay, PCD, and chromatic dispersion on pulses of arbitrary shapes is given. From this general relation, we derive expressions for pulse broadening and power penalty for Gaussian pulses. Moreover, a new expression for PMD-induced power fading for single-sideband modulated radio frequency signals is also derived. Measured experimental results are presented to support the derived expressions.     

Dispersion effect and compensation in optical-carrier-suppressed modulation transport systems

We develop new expressions for power fading and average power fading that are induced by first-order polarization mode dispersion, polarization-dependent chromatic dispersion, chromatic dispersion, and chirp under both (i) carrier suppressed modulation and (ii) odd-order optical sideband and carrier suppression. Experimental results show the effectiveness of the theoretical analysis. Further, based on the expressions, we propose a technique for optically compensating the polarization mode dispersion-induced power fading in carrier suppressed modulation.     

A new experimental approach to second-order polarization mode dispersion analysis for optical communications systems

This article analyzes the polarization mode dispersion (PMD) in optical fibers and presents a new approach for its measurement. This approach permits the combined analysis of the first-order PMD and the second-order polarization mode dispersion (SOPMD) in optical systems for different values of temperature. The relation between SOPMD and the differential group delay (DGD) in a single-mode fiber is discussed. The analysis is based on time/wavelength and temperature variations changing/impacting PMD and DGD measured values. We present long-term statistical characteristics of SOPMD acquired by a PMD emulator constructed with some pieces of high birefringence fiber, and the correlation between the SOPMD, depolarization (Depol) and polarization-dependent chromatic dispersion (PCD) was investigated. A new interpretation of SOPMD is presented to analyze the problem of the temperature spectral stability. The actual techniques for SOPMD determination, consequently Depol and PCD, use the variation with time and/or wavelength. In some studies, the results obtained for SOPMD are correlated to first-order PMD. We demonstrate experimentally that the temperature is an important factor for the correlation between SOPMD and PMD and cannot be neglected in the optimization of high-speed optical communications links.     

Performance of a single-input multiple-output decision feedback equaliser for polarisation mode dispersion compensation

To compensate the performance degradation induced by polarisation mode dispersion (PMD) in high-speed optical transmission, a single-input multiple-output (SIMO) decision feedback equaliser (DFE) technique is proposed to combat all orders of PMD-induced distortion. The scheme is based on a new SIMO PMD channel model which utilises information embedded in both polarisation states. The performance analysis of the proposed PMD SIMO DFE scheme is provided along with explicit expressions for the filter coefficients. The analysis results show that the new scheme provides a significant improvement over using a first-order optical compensator and conventional DFE.     

Operator expansions for polarization mode dispersion analysis and compensation

We present analytic third- and fourth-order expansions of the Jones matrix as products of exponentials of individual matrices. In our first formalism, these are polarization mode dispersion (PMD) matrices of definite orders. We then discuss an alternative procedure that instead employs exponentials of general skew-Hermitian matrices with a low-order dependence on the deviation of the optical frequency from a central reference frequency. Our expressions correspond to PMD compensators formed from a succession of relatively simple optical components each of which has the frequency response of a single operator in the product.     

Measurement of the complex polarization mode dispersion vector using Jones matrix analysis

The polarization mode dispersion (PMD) of a nondepolarizing optical system is analyzed. A new method is proposed to calculate the complex PMD vector by measuring two Jones matrices at two different wavelengths.     

Polarization-mode dispersion effect of an acousto-optic tunable filter

The effect of the polarization-mode dispersion (PMD) of an acousto-optic tunable filter (AOTF) is studied both theoretically and experimentally. A coupled-mode method derived from Maxwell's equations is proposed to study the evolution of the polarization of light and hence the deterministic dynamics of the PMD inside an AOTF. It is found that the PMD value of a typical AOTF is around several picoseconds and is adjustable by tuning the strength of the applied sound signal. A set of experimental data acquired by the wavelength scanning method is employed to check the validity of the proposed method. A high degree of similarity is observed between the experimental and the theoretical data.     

Scheme for feed-forward polarization mode dispersion compensation

We propose a feed-forward polarization mode dispersion (PMD) compensator with three segments that is capable of compensating for the first- and second-order PMD in a transmission fiber. All control parameters are analytically obtained by the PMD concatenated rules. The influence of all possible perturbations on the compensation is investigated with Monte Carlo simulations. The main advantage of our PMD compensation module over the models reported so far is that it shows excellent robustness to all possible perturbations.     

First- and second-order polarization mode dispersion generated by a two-stage emulator

A two-stage polarization mode dispersion (PMD) emulator design consisting of two variable delay lines separated by a rotatable half-wave linear retarder is analyzed and shown to generate an adjustable amount of first- and second-order PMD without any higher orders. This two-stage PMD emulator configuration provides a simple easy-to-breadboard solution for second-order PMD emulators. When compared with PMD emulators based on birefringent crystals, this two-stage emulator is simpler to calibrate.     

利用DOP数值搜索的偏振模色散补偿算法

根据光域动态反馈的PMD补偿方案中在线测量的偏振度波动特点,提出了一种基于搜索最优DOP数值的PMD补偿控制算法。此算法在以变步长精确搜索全局最值的基础上,采用近似定步长的搜索策略,避免陷入局部极值区域,得到全局最优DOP数值,从而较好地补偿高速光纤链路中的PMD。将此算法用于人工神经网络训练的仿真中,能够使训练后的网络达到最小网络误差,提高网络的泛化能力。仿真结果验证了该算法的正确性和良好的搜索性能。     

Spectral-domain measurement of chromatic dispersion difference of polarization modes in polarization-maintaining fibers

A spectral white-light interferometric (WLI) technique for measuring the chromatic dispersion difference of the two polarization eigenmodes in polarization-maintaining fibers (PMFs) is presented. The approach is based on the application of a transverse point-like force on the fiber that causes coupling between the two modes and utilizes their spectral interferogram. A Fourier-transform spectral interferogram (FTSI) and a polynomial curve fitting are applied to obtain the phase function. The chromatic dispersion difference of the long PMFs can be obtained by taking the second derivative of the phase function. The experimental results for two kinds of PMFs of 110 and 750?m length are presented, respectively.     

Chromatic dispersion effects in analog polarization-modulated links

The effect of chromatic dispersion on a photonic link employing polarization modulation is studied analytically and experimentally. For analog polarization modulation, dispersion introduces a frequency-dependent rotation to the orientation of modulation about the center of modulation. As a result, the dispersion-limited bandwidth of the link will depend on receiver design.     

Optical post-equalization based on self-imaging

Optical fibre transmission systems operate in the presence of inter-symbol interference (ISI) caused by chromatic dispersion (CD), polarization-mode dispersion (PMD), and other impairments. As the transmission rate increases, ISI mitigation becomes mandatory. Many schemes for dispersion compensation have been proposed. We present and discuss a new optical method for post-compensating the chromatic dispersion in a particular dispersive medium, namely the single mode fibre. This method is based on the self-imaging phenomenon known as the temporal Talbot effect. The main advantage of our method results in using standard optical fibres instead of special fibres. We also have all freedom in subdividing and processing sequences of the dispersed optical signal.     

Impact of second-order PMD in a coherent optical orthogonal frequency division multiplexing system

The second-order, polarization-mode dispersion (PMD) effect for coherent optical orthogonal frequency division multiplexing (CO-OFDM) system in long-haul transmission with single-mode fiber was analyzed in detail. The closed-form expression is presented for the time impulse response of an OFDM signal affected by second-order PMD. Analysis and simulation results show that, compared with polarization-dependent chromatic dispersion (PCD), CO-OFDM system performance is mainly influenced by depolarization rate (DR) which can moderate phase noise induced by chromatic dispersion. For a fiber link of 800 km and DR of 30 ps, the system Q value is improved by about 1.3 dB over the case of no DR.     

Compensation of chromatic dispersion-induced power fading using optimised chirped fibre Bragg grating for millimetre-wave radio-over-fibre system

Compensation of fibre dispersion-induced power fading in an externally modulated sub- carrier multiplexed radio-over-fibre transmission link using the chirped fibre Bragg grating (CFBG) has been investigated. The results show that periodic power fading caused by fibre chromatic dispersion is significantly reduced and the optimum transmission distance can be increased by proper design of grating parameters and optimum selection of apodisation profile. The investigation also reveals that carrier-to-noise ratio and bit-error rate of 156 Mbps DPSK signal are also significantly improved using the CFBG with asymmetric apodisation profile as the dispersion compensator.     

Characterization of chromatic dispersion and polarizationsensitivity in fiber gratings

Fiber gratings have already become key passive components in fiber optic communication systems. We have characterized gratings used in reflection for dispersion compensation and long period gratings used in transmission for gain flattening using a low-loss, low-noise experimental setup having a picometer optical wavelength resolution. Our measurements include reflection or transmission response, group delay and polarization dependent loss. We have scanned the spectrum of our devices using a very narrow linewidth tunable laser. A network analyzer is used for the chromatic dispersion measurements. Time delays corresponding to the design values have been measured within the useful bandwidth of the gratings for dispersion compensation and the devices have been found to have reasonably small ripples that increase in magnitude toward the shorter wavelength range. The long period gratings for gain flattening have very small group delays. Polarization dependent loss has been measured for the first time in these devices. A polarization analyzer was used and Jones matrix analysis was applied to obtain the measurements. The gratings for dispersion compensation have small a polarization dependent loss within their useful bandwidth, while the long period gratings exhibit higher values and a stronger wavelength dependency in the polarization dependent loss     

Chromatic dispersion correction in planar waveguide using one-layer volume holograms based on three-step exposure

We propose a novel method to correct the chromatic dispersion in a planar waveguide with volume holograms fabricated by the three-step exposure technique. The 532 nm green laser is used to illuminate the holographic plate in three groups of different angles for achieving the desired holograms. When it is used in the planar waveguide, the chromatic dispersion of the original display can be corrected and an image with the real color can be obtained. The experiments are performed, and the results are in good agreement with the theory. It is believed that this technique is a good way to correct the chromatic problems in the display systems in the future.     

Design of multi-rate optical code paths considering polarisation mode dispersion limitations

The authors propose an original design based on multi-rate optical code paths (OCPs) for transport in advanced wavelength-division multiplexing/optical code division multiplexing (WDM/OCDM) networks. The authors utilise multi-length optical orthogonal codes (OOC) to obtain multi-rate OCPs. The performance of the proposed scheme is analysed and the impact of multiple access interference (MAI) and polarisation mode dispersion (PMD) over these OCPs is evaluated. Results show that not only multi-rate operation can be achieved but also MAI effects can be reduced, while mitigating PMD effects.     

Impacts of imperfect geometry structure on the nonlinear and chromatic dispersion properties of a microstructure fiber

We numerically investigated the impacts of the imperfect geometry structure on the nonlinear and chromatic dispersion properties of a microstructure fiber (MF). The statistical results show that the imperfect geometry structure degrades the high nonlinearity and fluctuates the chromatic dispersion in a MF. Moreover, the smaller air holes and the larger pitch are more likely to maintain the properties of nonlinearity and chromatic dispersion. Finally, the nonlinearity and chromatic dispersion are more insensitive to air-hole nonuniformity than to air-hole disorder. All of these will provide references for designing and fabricating MF.