The statistics of polarization-dependent loss in a recirculating loop

In this paper, we study the statistical distribution of the accumulated polarization-dependent loss (PDL) in a recirculating loop. The distribution is studied both via numerical simulations and with analytical theory and very good agreement is found between the two. In addition, we have experimentally obtained the probability density distribution for the PDL and, even in this case, we find good agreement with the predicted one. The mean accumulated PDL is found to grow linearly with the number of circulations N in contraposition to a straight-line system. Moreover, the statistical distribution tends to become uniformly distributed as N is increasing. Finally, the statistics of the PDL for a recirculating loop, when considering small values of PDL, is found to be equal to the statistics of the differential group delay for recirculating loops.     

Statistics of polarization-dependent loss, insertion loss, and signal power in optical communication systems

We present analytical solutions to describe the statistics of signal power and insertion loss due to polarization-dependent loss (PDL) concatenation in communication systems. Using the methods of stochastic differential equations, we show that a system with a large number of low-PDL elements yields a Gaussian distribution for the signal power when it is expressed in units of decibels.     

Limitations imposed by polarization-dependent gain and loss onall-optical ultralong communication systems

The performance degradation of an all-optical ultralong system due to polarization dependent loss and polarization dependent gain is analytically analyzed. In particular, both the mean and the standard deviation of the performance are calculated. The analytical predictions are compared against a computer simulator, which includes the effects of nonlinearity and polarization mode dispersion. The result show that polarization dependent gain is the major source of degradation for the mean performance, while both polarization dependent loss and gain affect the standard deviation from the mean performance. Finally, the performance improvement due to polarization scrambling is evaluated     

Pulse distortion induced by polarization-mode dispersion and polarization-dependent loss in lightwave transmission systems

The combined effects of polarization-mode dispersion (PMD) and polarization-dependent loss (PDL) on pulse broadening in optical transmission links for both PMD uncompensated and compensated systems are investigated by numerical simulation. It is shown that, when PDL is large, PDL considerably reduces the efficiency of PMD compensation, which, we find, is mainly due to the increased higher order PMD caused by the combined effects of PMD and PDL, as well as nonorthogonal principal states of polarization.     

Accurate spectral characterization of polarization-dependent loss

Building on previous work, a rapid automated nonmechanical measurement system for spectral characterization of polarization-dependent loss (PDL) has been developed. A deterministic fixed-states Mueller-Stokes method in conjunction with realtime calibrated spectral information is used to derive wavelength-dependent Mueller matrix elements. Voltage-modulated liquid-crystal variable retarders set the input polarization states. A narrow voltage-tuned filter provides a wavelength sweep following a broadband source; the sweep wavelength is calibrated in realtime by hydrogen cyanide reference lines. This rapid measurement system can measure PDL over a wavelength range of 15 nm in 5 s. A complete uncertainty analysis has been conducted for PDL in the range of 0.05 to 0.3 dB with an expanded uncertainty of 0.0098 dB over the range of 1535 to 1560 nm. Performance was verified using a Fresnel reference. Finally, design and performance results from all-fiber artifact calibration standards are presented.     

Transient dynamics of stimulated Brillouin scattering in opticalcommunication systems

Dynamic aspects of stimulated Brillouin scattering (SBS) and criteria for its occurrence in optical communications are studied numerically. SBS is shown to cause sharp amplitude modulations in phase-shift keying (PSK) modulated systems close to or above the SBS threshold. It is shown that the convolution method to high accuracy yields correct relative gains for different modulation sequences. The transient change of backscattered radiation caused by abrupt changes in the modulation format is studied and it is demonstrated that the transition can occur on different time scales     

Nonlinear crosstalk and two countermeasures in SCM-WDM opticalcommunication systems

We investigate, theoretically and experimentally, crosstalk between wavelengths in subcarrier-multiplexed (SCM) wavelength-division multiplexed (WDM) optical communication systems. Crosstalk arises mainly from interactions between subcarriers on one wavelength and the optical carrier of another wavelength. In a dispersive fiber, crosstalk can be attributed to stimulated Raman scattering (SRS) and cross-phase modulation (XPM) combined with group velocity dispersion (GVD). We investigate the phase relationship between SRS-induced and XPM-induced crosstalks. Crosstalks induced by SRS and XPM add in the electrical domain and can interfere constructively or destructively. Experimental results show that the combined crosstalk level can be as high as 40 dBc after 25 km of SMF with two wavelengths and 18 dBm per wavelength of transmitted power. We propose two crosstalk countermeasures. The first countermeasure uses parallel fiber transmission. We show theoretically that both SRS-induced and XPM-induced crosstalks can be cancelled to the first order. We present an experimental demonstration of concept which has achieved 15 dB of crosstalk cancellation over 200 MHz. The second countermeasure uses optical carrier suppression. We show, theoretically and experimentally, that by suppressing the optical carrier, we can significantly reduce crosstalk while maintaining the same link budget and carrier-to-noise ratio (CNR) at the receiver, 20 dB of crosstalk reduction over 2 GHz has been demonstrated experimentally     

Performance degradation induced by polarization-dependent loss in optical fiber transmission systems with and without polarization-mode dispersion

The performance degradation caused by polarization-dependent loss (PDL) in optical fiber transmission systems in both the absence and presence of polarization-mode dispersion (PMD) is studied. First a simple theory is given to show how PDL affects the system performance and then extensive simulation results are presented. We show that PDL causes a much larger fluctuation of optical-signal-to-orthogonal-noise ratio (OSNR/sub ort/) than that of optical-signal-to-parallel-noise ratio (OSNR/sub par/), but OSNR/sub par/ has a much larger impact on the system performance than OSNR/sub ort/. We find that when there is no PMD, the system performance degradation induced by PDL can be effectively reduced by suppressing OSNR/sub par/ fluctuation. However, the presence of PMD in the system could significantly reduce the efficiency of the PDL mitigation technique, especially the mitigation technique that suppresses the OSNR/sub par/ fluctuation.     

Importance sampling for analysis of direct detection opticalcommunication systems

Analytical solutions of the performance of optical communication systems are difficult to obtain and often, Monte Carlo simulations are used to achieve realistic estimates of the performance of such systems. However, for high performance systems, this technique requires a large number of simulation trials for the estimates to be in a reasonable interval of confidence, with the number of trials increasing linearly with the performance of the system. We apply an importance sampling technique to estimate the performance of direct detection optical systems, where the “gain” of importance sampling over Monte Carlo simulations is shown to increase linearly with the system performance. Further, we use this technique to study the performance of optical communication systems employing avalanche photodetectors as well as fibre-optic code division multiple access systems (FO-CDMA). We also show that the quick simulation technique developed can be used for a wide variety of coding schemes, and for the first time, we present a comparative analysis of the performance of FO-CDMA systems employing optical orthogonal codes and prime sequences. In all cases, it is shown that importance sampling simulations require less than 50-100 trials for estimating error probabilities of 10^-10 and below     

基于FBG偏振相关损耗的二维力测量

采用耦合模理论分析了光纤布拉格光栅(FBG)反射偏振相关损耗(RPDL)峰位置与轴向力和侧向力的关系,进而通过相关灵敏度系数矩阵,应用单根FBG实现对轴向力和侧向力的同时测量,从而得到结构体内部二维力及二维应变信息。实验测得,(RPDL)左峰和右峰的轴向力灵敏度分别为0.986 2nm/N和0.986 7nm/N,侧向力灵敏度分别为0.007 1nm/N和0.000 5nm/N,轴向力和侧向力测量精度分别为±0.01N和±0.51N。本文方法核心传感元件简单,稳定性好,精度高,易于实现,为检测材料内部结构变化提供了新方法。     

Robustness of polarization-mode-dispersion compensation in the presence of polarization-dependent loss

The robustness of polarization-mode dispersion (PMD) compensation utilizing radio-frequency feedback in the presence of polarization-dependent loss (PDL) is investigated using a closed-loop dynamic model. Simulations using mean PMD of 30% of the bit period show that mean PDL of up to 2 dB increases the Q-penalty after PMD compensation by less than 0.1 dB. We find that the compensator can become trapped in secondary optima at high PDL, incurring significant additional penalty.     

Silicon bipolar integrated circuits for multi-Gb/second opticalcommunication systems

The authors discuss several important circuits for fiber-optic transmission, implemented in an advanced silicon bipolar integrated circuit technology. Specifically, the authors discuss the design considerations and measured performance of a 2:1 multiplexer, front end receiver, limiting amplifier, and decision circuit IC. Also discussed are three hybrid circuit modules: a 2:1 multiplexer, 1:2 demultiplexer, and parallel processing decision circuit. These ICs and hybrid circuit modules operate at multi-Gb/s data rates. The performance of these ICs indicates that advanced silicon bipolar integrated circuits with their high speed, functionality and low cost potential could play an important role in alleviating the electronic bottleneck in future multigigabit optical communication systems     

A Clifford algebra analysis of polarization-mode dispersion and polarization-dependent loss

We present an overview of Clifford algebra and its application to polarization-mode dispersion and polarization-dependent loss. We demonstrate that the Jones matrix corresponds to a Lorentz transformation in this algebra and obtain its frequency-dependent evolution through the Magnus expansion. We also comment on the application of Clifford algebra methods to partially polarized light.     

Fiber-optic parametric amplifiers in the presence of polarization-mode dispersion and polarization-dependent loss

Polarization-mode dispersion (PMD) and polarization-dependent loss (PDL) associated with various optical components affect the quality of pump beams even before they enter a fiber-optic parametric amplifier (FOPA). A vector theory of the underlying four-wave mixing process is developed to study the impact of PMD and PDL on the amplification of signal and idler fields. It is shown that the use of high-quality polarizers just before the input end of the fiber can improve the performance of a dual-pump parametric amplifier considerably.     

Wavelength-switchable erbium-doped fiber ring laser using spectral polarization-dependent loss element

We propose a wavelength-switchable erbium-doped fiber ring laser that uses a spectral polarization-dependent loss element. The element was fabricated by inscribing a long-period grating on a polarization-maintaining fiber. Dual-wavelength switching operation was accomplished by rotating the polarization plane of the fiber laser cavity. The amplitude variation of both laser lines was measured to be less than 1 dB and the signal-to-amplified spontaneous emission ratio was more than /spl sim/40 dB.     

Statistical distribution of polarization-dependent loss in thepresence of polarization-mode dispersion in single-mode fibers

The statistical distribution of polarization-dependent loss in single-mode fibers is studied via Monte-Carlo simulations. In the presence of polarization-mode dispersion, it is found that the probability density function of polarization-dependent loss is a combination of Rayleigh and Maxwell distributions     

Theoretical analysis of reflectometric measurements in optical fiber links affected by polarization-dependent loss

The theory of reflectometric measurements of polarization-dependent effects in optical fiber links is generalized to the case of links with polarization-dependent losses. The results are a clean generalization of the no-loss case. In particular, a new technique for the reflectometric measurement of the mean polarization-dependent loss is proposed. Furthermore, the possibility of characterizing the local birefringence and the local dichroism of the link is discussed.     

Analysis of optical amplifier noise in coherent opticalcommunication systems with optical image rejection receivers

A detailed theoretical analysis of optical amplifier noise in coherent optical communication systems with heterodyne receivers is presented. The analysis quantifies in particular how optical image rejection receiver configurations reduce the influence of optical amplifier noise on system performance. Two types of optical image rejection receivers are investigated: a novel, all-optical configuration and the conventional, microwave-based configuration. The analysis shows that local oscillator-spontaneous emission beat noise (LO-SP), signal-spontaneous emission beat noise (S-SP), and spontaneous-spontaneous beat noise (SP-SP) can all be reduced by 3 dB, thereby doubling the dynamic range of the optical amplifier. A 2.5-dB improvement in dynamic range has been demonstrated experimentally with the all-optical image rejection configuration. The implications of the increased dynamic range thus obtained are also discussed from a systems point of view     

First-order PMD compensation in nonlinearly dispersive opticalcommunication systems via transmission over the principal states ofpolarization

Soliton propagation in the presence of polarization mode dispersion (PMD) is studied with an analytical approach. It is shown that there exist two peculiar initial states of polarization that may prevent the soliton to undergo shape distortions. These states coincide with the states that, in the absence of chromatic dispersion and nonlinearity, are usually referred to as principal states of polarization. This fact is used to show that it is possible to improve the performance of an optical transmission system operating in the presence of chromatic dispersion, PMD and Kerr nonlinearity by coupling the input pulses to one of the principal states of polarization