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An in-band optical signal-to-noise-ratio (OSNR) monitoring technique that utilizes the polarization orthogonality and heterodyne mixing is proposed. The technique is not only insensitive to polarization-mode dispersion but also robust to nonlinear polarization scattering induced by interchannel cross-phase modulation. Moreover, the technique places no special requirements on the signal properties, such as modulation format and bit rate. The monitoring technique is demonstrated experimentally in both linear and nonlinear systems

Several polarization mode dispersion (PMD) models were developed to help understanding PMD effects and simplify the analysis regarding their impact on the system performance. Whether or not a PMD model can be used to accurately predict the system impairments depends on how well it approximates fiber PMD. In this paper, we assess the accuracy of six commonly used first- and second-order PMD models by comparing them with an all-order PMD model. Both PMD induced pulse broadening and optical-signal-to-noise-ratio (OSNR) penalties are determined, analyzed, and compared for each PMD model. To separate first- and higher-order PMD effects, we investigate the system performance with and without PMD compensation. We find that, compared with the all-order PMD model, all the known first- and second-order PMD models overestimate the PMD distortions, and the PMD models that do not contain higher than second-order PMD generate the largest deviation. Our results show that the first-order PMD model can be used to approximate the all-order PMD model when no PMD compensation is used, but none of the known PMD models can generate results close enough to those of the all-order PMD model for a PMD compensated system. This indicates that to accurately evaluate the performance of PMD mitigation techniques, the all-order PMD model has to be used.

We demonstrate two 160-Gb/s modulation formats that posses the same intensity pulse profile but differ regarding their phase coding. We analyze the nonlinear transmission properties of both coherent modulation formats by experimental and analytical investigations. The results show that the pairwise alternating phase coded carrier suppressed return-to-zero (PAP-CSRZ) signal outperforms the conventional CSRZ format. Our modulation technique is even applicable at higher speed as demonstrated with the generation of the first CSRZ signal at a record rate of 320 Gb/s.

This paper describes the demonstration of a novel method for detecting optical duobinary signals. Oversampling in combination with maximum-likelihood estimation-based data processing of the optical-to-electronic converted signal results in a record sensitivity for an optically preamplified receiver. The concept is investigated at 10 Gb/s and allows data recovery at bit-error rates of 1/spl times/10/sup -9/ and 1/spl times/10/sup -3/ with a receiver sensitivity of better than -39.5 dBm and an optical signal-to-noise ratio (OSNR) of only 7.8 dB, respectively.

This work presents a high-resolution (13.2 GHz) channel-blocking optical filter, suitable for use as a reconfigurable optical add/drop multiplexer (ROADM), which seamlessly supports data rates from 2.5 to 160 Gb/s. The filter consists of a linear array of 64 MEMS micromirrors and a high-dispersion echelle grating. The demonstrated device had an insertion loss of 9 dB, a loss ripple of 1.2 dB, and a group delay ripple of 15 ps. Data transmission through the device with various mixed data rate scenarios ranging from 2.5 to 160 Gb/s showed negligible penalty, except at 40 Gb/s where a maximum penalty of 1.5 dB was observed due to a phase coherence with the blocker filter ripple.

We investigate using alternate-polarization (APol) on-off keying formats, in which adjacent bits have orthogonal states of polarization, to suppress intrachannel nonlinear impairments in dispersion-managed (DM) optical fiber transmission systems. Simple methods to generate the APol formats are discussed, and the transmission performance of the APol formats for both 40-Gb/s DM systems and 10-Gb/s DM-soliton systems is experimentally studied. We show that the APol formats can significantly improve the performance of 40-Gb/s DM transmission systems, while the improvement of 10-Gb/s systems is smaller.

We demonstrate a novel 160-Gb/s modulation format that employs phase inversion of every four consecutive bits in a group. This format enables a very simplified clock recovery by optical filtering of 40-GHz spaced tones. The recovered clock shows a low timing jitter of 270 fs. In addition, we investigate its enhanced nonlinear transmission property by comparing it with carrier-suppressed return-to-zero (CSRZ) and pairwise-alternating-phase CSRZ signals through analytical studies and numerical simulations. We experimentally verify its good performance relative to CSRZ through a data transmission over a 38-km single-mode fiber.

We experimentally demonstrate broad-band mitigation of polarization-mode dispersion (PMD) in the presence of polarization-dependent loss (PDL) by using distributed fast polarization scramblers in systems adopting forward-error correction. The combined penalty of PMD and PDL is smaller than the sum of the individual penalties, which shows the robustness of the PMD mitigation scheme against PDL and the enhancement of PMD tolerance improvement in the presence of PDL. The desired number of scramblers and their distribution are also discussed.

The performance of a one-stage polarization-mode dispersion (PMD) compensator with different feedback signals is studied and compared with that of a pure first-order PMD compensator. We show that the performance of the one-stage PMD compensator has a strong dependence on feedback signals, and that the efficiency of some feedback signals depends on modulation formats. With proper choice of feedback signals, the one-stage PMD compensator can achieve better performance than the first-order PMD compensator.

We study the effect of transmitter response amplitude and group delay ripples on the performance of systems using duobinary coding. We demonstrate an improved 10-Gb/s transmitter with very low required optical signal-to-noise ratio in back-to-back and transmission over about 4300 ps/nm (258 km of single-mode fiber at 1550 nm) with about 2-dB penalty (at bit-error rate BER=10/sup -3/).

We show that a narrow bandwidth optical filter at the receiver side can greatly improve the receiver sensitivity of a nonreturn-to-zero (NRZ)-duobinary system. We propose to use the narrow bandwidth filtering at the receiver side of a return-to-zero (RZ)-duobinary system to convert RZ-duobinary to NRZ-duobinary, so that the system tolerance to residual chromatic dispersion can be increased while its resistance to nonlinearity in transmission is still maintained. The idea is demonstrated with experiments.

We study the feasibility of achieving 0.8-b/s/Hz spectral efficiency at 160 Gb/s. We generate phase-correlated return-to-zero (RZ) signals by utilizing the Kerr shutter effect in a highly nonlinear fiber. The 160-Gb/s RZ signal is then filtered with a 200-GHz bandwidth filter. Error-free operation is obtained by properly shifting the central wavelength of the filter. We also investigate the filtering performance of phase-uncorrelated signals generated by conventional optical time-division multiplexing means.

We demonstrate a receiver, which improves the back-to-back (b-t-b) performance of optical duobinary signals at 10 Gb/s. The required optical signal-to-noise ratio for a bit-error rate of 1/spl times/10/sup -3/ was found to be as low as 10.8 dB in b-t-b operation. We tested the receiver with two commercially available 10-Gb/s duobinary transmitter samples. Excellent chromatic dispersion tolerance was maintained with the novel receiver design.

We report a hierarchical optical add-drop multiplexer (OADM) network that supports 10-, 40-, and 160-Gb/s data rates with the same bandwidth efficiency. The data rates can be upgraded without hardware modification in the OADM. This hierarchical OADM network is equipped with high capacity (1.6 Tb/s) for traffic growth, while providing different granularities for diverse bandwidth requirements as fine as 12.5 GHz in optical domain. We investigate the transmission penalty through the waveband OADMs, and compare the performance between all-through traffic and add-drop traffic of neighboring wavebands at 40-Gb/s rate.

We demonstrate a switch fabric architecture that allows multicasting and broadcasting and record fast channel access in the nanosecond range. The 10-Gb/s receiver modules are based on a heterodyne detection technique, which is tolerant to moderate wavelength drifts of the local oscillator. A gain clipped electrical amplifier is used as rectifier for bandpass signal recovery.

We describe a novel technique for generating ultrahigh-speed bit-by-bit optical phase correlated data signals based on cross-phase modulation induced nonlinear polarization rotation between a pump and a continuous-wave light. As an illustration of this method, we demonstrate, for the first time, the generation of a 160-Gb/s carrier-suppressed return-to-zero data signal.

We investigate 40-Gb/s return-to-zero signal transmission in a transparent optical network equipped with wavelength-selective optical cross connects (WSOXCs). The investigation is performed in a recirculating loop setup consisting of 4100-km spans of transmission fiber. A WSOXC is placed inside the loop to mimic cascaded WSOXCs with a spacing of 400 km. We study various degradation effects in the system, particularly those of node loss and optical filtering. Q value measurements of the received signal were carried out at different transmission distances and WSOXC loss conditions. A Q value of 15.5 dB was measured at 1200-km distance with two cascaded WSOXCs of which the node loss is 17 dB.

The polarization-mode dispersion (PMD) tolerance of different modulation formats is studied, including ON-OFF keyed (OOK), differential phase-shift keyed (DPSK), and carrier-suppressed return-to-zero (CSRZ) formats. It is shown that, generally, for PMD uncompensated systems, the modulation formats with larger pulsewidth have larger penalty, while the modulation formats with smaller bandwidth perform better in PMD compensated systems. It is also shown that DPSK can tolerate more PMD than OOK for both PMD uncompensated and compensated systems, and that CSRZ, because of its specific spectrum characteristics, has a different feature from return-to-zero formats.

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.

We study the influences of transmitter characteristics on polarization mode dispersion (PMD) impairments in optical transmission systems with both experiments and simulations. We show that transmitter imperfection, such as timing and amplitude jitters and pulse shape distortion, can significantly increase PMD impairments, especially when the differential group delay in the systems is large. Our simulation further shows that the increased PMD impairments due to transmitter imperfection will considerably reduce the effectiveness of using large system optical signal-to-noise ratio margin to combat PMD.

The interaction of intrachannel effects and polarization mode dispersion in 40-Gb/s transmission systems can support signal propagation by reducing the nonlinear impairments. The phenomenon is experimentally observed in a 400-km ON-OFF keying transmission. Simulations predict its impact in ultra-longhaul intensity and phase modulated systems.

We have developed a technique for emulating higher order polarization mode dispersion (PMD) that utilizes a three-section interferometrically stable configuration. Using this approach, we are able to study the impact of higher order PMD on 10-Gb/s nonreturn-to-zero and carrier-suppressed return-to-zero signals when first-order PMD is zero, which is a typical condition that occurs in one-stage optical PMD compensators.

We study several new techniques for reducing polarization-mode dispersion (PMD) induced system outage probabilities for wavelength-division-multiplexed systems. In all cases, we provide equalization of the channel(s) with the worst performance. Realizations based on shared single channel compensators are discussed.

We show a novel higher order polarization-mode dispersion (PMD) mitigation technique for a preamplified system based on narrow optical bandwidth filtering of the signal. Reducing the signal bandwidth results in increased signal immunity against higher order PMD distortions. The method is theoretically explained and experimentally verified.

We demonstrate that the "residual polarization" of two coherent orthogonally polarized channels can be used as an all-optical, bit rate, and format-independent feedback signal to control the two underlying signal polarizations.

A device that can be used for channel individual polarization controlling in wavelength-division-multiplexed (WDM) systems is proposed.

We present a means of synthesizing an arbitrary 2/spl times/2 Jones matrix filter, e.g., the inverse of a PMD fiber characteristic. The described algorithm allows arbitrarily accurate reduction of PMD in a frequency band. A PMD equalization technique for WDM systems is proposed.

We demonstrate for the first time 640-Gb/s single-channel OTDM RZ-DQPSK signaling with record spectral efficiencies of 2.4 bit/s/Hz and up to 3.2 bit/s/Hz. The demonstrated data rate is the highest to date detected with an electro-absorption modulator (EAM) based receiver.

OOK signals with certain phase modulations can show improved performance without incurring much complexity and cost. In this paper we report recent progress on the performance study of high-speed OOK data signals with different phase-modulation schemes.

We first compare different polarization mode dispersion (PMD) models for evaluating PMD impairments. We show that, compared with the all-order PMD model, most of the known first- and second-order PMD models overestimate the PMD induced distortions. Then we discuss various PMD mitigation techniques. We show that modulation formats have a big impact on choosing the most effective PMD compensation techniques. Not only do the benefits of using PMD compensators (PMDCs) depend on modulation formats, but the designing of a PMDC is largely affected by modulation formats as well. Some multi-channel PMD mitigation techniques for wavelength division multiplexing (WDM) systems are also discussed.

We characterize a 200 GHz channel grid, wavelength-selective 4/spl times/1 switch with wide/flat passbands and low chromatic dispersion (|CD

A monitoring technique is demonstrated that utilizes polarization orthogonality and heterodyne mixing to measure the in-band optical-signal-to-noise-ratio. This technique is insensitive to PMD and nonlinear polarization scattering, and operates independently of the optical signal properties.

We demonstrate that distributed fast polarization scramblers in a differential phase-shift keying transmission system with an enhanced forward error correction code outperforms the standard Reed-Solomon code and improves the polarization-mode dispersion tolerance by 140%. (2 pages)

We show that PCD causes larger penalties than depolarization and depolarization induced penalties are also dependent on 1st-order PMD. Moreover, the input polarization states that give maximum and minimum penalties change with the depolarization value. (2 pages)

The field of ultra high-speed (/spl ges/160 Gb/s) transmission has developed rapidly over the past years from proof-of-principle demonstrations towards advanced field trial applications. We review recent trends in 160 Gb/s signal generation and detection techniques.

We compare first-, second- and all-order PMD models for systems with and without first-order PMD compensation. Often the first- and second-order PMD models fail by overestimating PMD distortions, especially when the PMD is large.

We propose and demonstrate a new 160-Gbit/s signal format employing phase inversion of every four consecutive bits in a group. This format enables simple clock recovery by spectral filtering, and increases the nonlinear tolerance compared to CSRZ signals.

We show that DPSK systems can tolerate more PMD than OOK systems, and that CSRZ has a different feature from RZ with respect to PMD, because of its specific spectrum and phase characteristics.

The combined effects of PMD and PDL on pulse broadening are studied. We show that PDL considerably reduces the efficiency of PMD compensation, due to increased higher order PMD in the presence of PDL.

We investigate the retiming and reshaping properties of a 160 Gb/s all-optical wavelength converter based on a semiconductor optical amplifier (SOA) gating delay interferometer (DI) configuration. 160Gb/s operation is performed with as little as -3.5dBm.

Nonlinear polarization rotation between a pump and a probe signal in a highly nonlinear fiber is used as a modulation process to generate 80-Gbit/s return-to-zero differential phase-shift keying signals. Its performance is analyzed and compared with a conventional on-off keying modulated signal.

Interchannel cross-phase-modulation-induced polarization scattering (XPMIPS) and its effect on the performance of optical polarization mode dispersion (PMD) compensation in wavelength-division-multiplexed (WDM) systems are studied. The level of XPMIPS in long-haul WDM transmission systems is theoretically quantified, and its effect on optical PMD compensation is evaluated with numerical simulations. We show that in 10-Gbit/s ultra-long-haul dense WDM systems XPMIPS could reduce the PMD compensation efficiency by 50%, whereas for 40-Gbit/s systems the effect of XPMIPS is smaller.

We describe the design, fabrication, and performance of a high-speed, continuously tunable, and reset-free polarization controller based on nematic liquid-crystal (NLC) microcell wave plates fabricated directly between the tips of optical fibers. This controller utilizes a pulsed driving scheme and optimized NLC materials to achieve a stepwise switching speed of 1 deg/micros, for arbitrary rotation angles with moderately low voltages. This compact microcell design requires no bulk optical components and has the potential to have low insertion loss. We describe the performance of these devices when implemented in polarization mode dispersion compensators for 40 Gbit/s systems. The good optical properties and the nonmechanical, high-speed, and low-power operation suggest that this type of device might be considered for some applications in dynamic compensation of polarization mode dispersion, polarization analysis, polarization division demultiplexing, and polarization scrambling in high-speed optical communication systems.

We have demonstrated a broadband, wavelength sensitive polarimeter suitable for multichannel polarization and PMD monitoring. We were able to measure channel degree of polarisation (DOP), differential group delay (DGD), and principal state of polarisation (PSP) without any signal modulation at the transmitter. The WSP also has reduced polarization sensitivity when measuring channel power.

Summary form only given. The maximum reach of ultra-longhaul on-off keying transmission systems is mainly limited by the three length dependent parameters: CSNR degradation, nonlinear (NL) signal distortion, and fiber polarization mode dispersion (PMD) (in the case of 40 Gb/s per channel systems). The penalty arising from nonlinear effects depends strongly on the link design, while the penalty caused by PMD is related (in the case of linear signal propagation), to the intrinsic fiber PMD and the specific signal modulation format. It is the goal of system engineering to allocate adequate margin for each penalty source such that the system range is maximized under the constraint that the total penalty is covered by the link budget. Here we show for the first time that under certain circumstances the total penalty from nonlinear effects and PMD can be less than the sum of the two individual penalties. Indeed, we demonstrate that a PMD pre-distorted signal suffers less nonlinear signal perturbations. Ultra-longhaul 40 Gb/s systems (per channel) will need PMD compensation even when running over low PMD fiber. Thus, a post compensation of the pre-PMD distortion requires no significant add-ons in the system architecture.

We successfully demonstrated a novel type of RZ data receiver that is based on multi-sampling and logical OR operations (OR-RZ receiver). It has superior performance compared to a standard receiver when the signal is distorted by timing fitter and advantages in case of PMD corrupted signals.

We have demonstrated that optical narrow bandwidth filtering of RZ signals can reduce pulse distortions that result from higher order PMD. The required filter bandwidth is significantly smaller than conventional filter rules predicted for optimal detection in the case of no PMD. Advantageously, this higher order PMD mitigation method requires no active channel adaptation, only a passive filter.

We show that the overall polarization of a WDM signal has to be minimized in order to reduce cross-phase modulation induced polarization scattering (XPMIPS) between channels of a DWDM system which can limit the effectiveness of PMD compensators or polarization demultiplexing mechanisms.

We study the reduction of PMD (polarization-mode dispersion) induced system outage probabilities by equalization of the channel(s) with the worst performance in a WDM signal. Realizations based on shared single channel compensators are discussed. The improved PMD tolerance of a system is quantified.

We demonstrate that the 'residual polarization' of two coherent orthogonally polarized channels can be used as an all optical, bit rate and format independent feedback signal to control the two underlying signal polarizations.