Optical Dispersion Compensation Research Articles

960-km transmission over G.652 fiber at 10 Gb/s with a laser/electroabsorption Modulator and no optical dispersion compensation

We report, what is to our knowledge, the longest unregenerated reach achieved for a 10-Gb/s intensity modulated direct detection system on standard dispersion fiber with a laser/electroabsorption modulator and no optical dispersion compensation. The total amount of chromatic dispersion compensated with the proposed scheme is 17 245 ps/nm.

Four-stage Mach-Zehnder-type tunable optical dispersion compensator with single-knob control

We present a concept for colorless tunable optical dispersion compensators consisting of a series arrangement of generalized interferometers and adjustable lenses. The designs require only one control knob to adjust the dispersion, making the control simple and low power. We demonstrate a four-stage all-two-arm version in silica waveguides that achieves 460-ps/nm tuning range on a 100-GHz grid for 40-Gb/s signals.

Optical fibers and fiber dispersion compensators for high-speed optical communication

In order to meet the requirements necessary for advanced optical fiber transmission schemes that enable larger transmission capacity, higher efficiency and/or lower transmission costs per bit, optical fiber technologies are still evolving toward ultimate performance. Recent developmental activities have realized a number of improved performance optical fibers, such as ultra-low loss or ultra-low nonlinearity fibers and various types of dispersion-modified fibers. Fiber-based dispersion compensators or dispersion compensating fibers have also become one of the most essential optical components that support high-speed large capacity optical transmission. Very recently, the dispersion compensating fibers have further evolved into dispersion-managed optical transmission lines, which are now being actually deployed in transoceanic submarine optical cable networks.

Practical Considerations for Optical Polarization-Mode Dispersion Compensators

For transmission systems at 10 Gb/s and beyond, polarization-mode dispersion (PMD) is one of the limiting factors. Optical PMD compensators aim at increasing the PMD value tolerated by the system; however, they do not cancel out its effects. Therefore, the performance of a PMD compensator is assessed statistically. Requirements for optical PMD compensators include a response time in the range of 1 ms in order to follow polarization fluctuations over the line. The system design should account for the interaction of other transmission impairments with the PMD compensator operation. For instance, transmitter chirp and residual chromatic dispersion have a deleterious impact on the compensator performance. While self-phase modulation is harmless, cross-phase modulation greatly reduces the compensator efficiency. System design rules have been applied to a one-year field trial, showing the compensator's efficiency and reliability. However, reducing their cost is the next challenge that will bring optical PMD compensators to be used in installed systems.

Effect of cross-phase-modulation-induced polarization scattering on optical polarization mode dispersion compensation in wavelength-division-multiplexed systems.

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.

최적의 2차 편광모드분산 보상에 관한 이론적 고찰

본 논문에서는 피드포워드(feedforward) 방식의 2차 편광모드분산 보상에 있어서 보상 장치에서 발생시켜야 할 최적의 보상 벡터를 펄스 폭 증가율을 최소화함으로써 이론적으로 유도하였다. 최적의 2차 보상 벡터는 전송 선로의 편광모드분산 벡터의 단순한 Taylor전개식과는 달리, 편광모드분산 벡터와 출력 신호 편광의 주파수 평균들의 선형 조합으로 표현됨을 밝혔다. 최적의 2차 편광모드분산 보상에서의 펄스 폭 증가율을 해석적으로 계산하였으며, 계산 결과를 전산 모의 실험에 의한 결과와 비교하여 일치함을 확인하였다. 본 논문에서 유도한 최적의 2차 보상 벡터에 관한 공식은 피드포워드 방식의 2차 편광모드분산 보상에 반드시 필요한 정보를 제공한다. In this paper, the optimal performance of optical second-order polarization mode dispersion (PMD) compensation has been investigated theoretically in terms of minimization of the root-mean-square (RMS) pulse broadening. The optimal compensation vector in feedforward-type second-order PMD compensation has been derived, and the RMS pulse broadening factor after the optimal second-order PMD compensation has been analytically calculated. The calculated result has been compared with the previously reported simulation result where numerically optimized feedback scheme was adopted. They are in good agreement, which verifies the validity of the derivation. The investigation in this work will form the basis for the implementation of the feed-forward-type second-order PMD compensation.

Semiconductor mirror for optical noise suppression and dynamic dispersion compensation

We report on a monolithic Gires-Tournois semiconductor interferometer used for both suppression of low-intensity spontaneous noise in a high-power fiber amplifier and to generate a tunable delay. The potential of the noise suppression technique was demonstrated using a two-stage amplifier system. Gain improvement by a factor of five illustrates the capability of semiconductor gates to greatly enhance energy extraction from optical amplifiers. We demonstrate also that controllable saturable absorption in an optically pumped multiple-quantum-well semiconductor reflector provides promising means for rapidly changing the group delay of the reflector and represents a new form of dynamic dispersion compensator.

Design of a tunable optical chromatic dispersion compensator with simplified control of a Mach?Zehnder lattice, and dispersion slope mitigation

Planar lightwave circuits composed of Mach–Zehnder interferometers are suitable for compensating chromatic dispersion in optical fiber communication. The number of externally controlled phase shifts is halved if the power equidistribution between the branches is monitored and controlled in each Mach–Zehnder section. Suitably chosen delays yield increased tunability and, in multichannel compensators, a selectable dispersion slope.

Pulse compression of nanojoule pulses in the visible using microstructure optical fiber and dispersion compensation

Experimental results on the pulse compression of 1-nJ, 150-fs pulses from a tunable, 76-MHz Ti:sapphire laser oscillator operating at around 750 nm are reported. The length of the pulses can be compressed to nearly one tenth by applying a high-delta, single-mode microstructured optical fiber exhibiting zero group-delay dispersion at 767 nm, and by a prism-pair/chirped-mirror compressor. The experimental results are verified by theoretical investigations modeling the pulse propagation taking into account non-linear self-phase modulation and fiber dispersion.

Group velocity and dispersion model of coupled-cavity waveguides in photonic crystals.

A theoretical model of the group velocity, dispersion parameter, and dispersion slope of coupled-cavity waveguides in photonic crystals is reported. Results arising from closed-form expressions show a good agreement with simulation results obtained by employing a plane-wave expansion method. Coupled-cavity waveguides present interesting dispersion properties that may be employed in applications such as optical signal processing, dispersion compensation, and optical delay lines.

Effects of nonlinear crosstalk in optical PMD compensation

We report on the effects of nonlinear crosstalk on the optical polarization-mode dispersion (PMD) compensation in wavelength-division-multiplexing (WDM) systems. An analytical model is presented to describe the effect of nonlinear crosstalk on the first-order PMD compensation. We also experimentally show that the performance of WDM systems could be degraded by nonlinear birefringence, even when the first-order PMD is completely compensated.

Polarization mode dispersion compensator field trial and field fiber characterization

Two high-PMD long distance routes were characterized and used to test an optical polarization mode dispersion compensator (PMDC) under field conditions. For this trial, 110 km routes with mean PMD values of 25 and 26.5 ps were provisioned with commercial WDM transport equipment and tested for several weeks. The route was comprised of three spans of characterized fiber that followed railroad tracks. We show the temporal variation of the output polarization state and the evolution of first- and second-order PMD spectra over 7 days. The deployment of a variablelength PMDC on these links allowed error-free transmission of an OC-192 signal. Splitting the output to receivers with and without PMDC demonstrated specific PMD events that caused errors in the absence of a PMDC.

Improving the Spectral Efficiency of DWDM-DST Systems through Line Coding and Optimized FBGs

In this contribution we show that by using the dense wavelength division multiplexing (DWDM) and the dispersion supported transmission (DST) techniques, together with compressed bandwidth data formats and optimized fiber Bragg grating (FBG) filters, it is possible to implement optical fiber communication systems with very high spectral efficiencies and long fiber spans. This is achieved by using fiber gratings with a Gaussian apodization together with a non-uniform average index perturbation, acting simultaneously as optical demultiplexers and group velocity dispersion compensators. For a be 32 x 20 Gsymbol/s WDM-DST system, we demonstrate spectral efficiencies of 0.7 bit/s/Hz for the binary and duobinary data formats, at distances of 65 km and 100 km, respectively, over standard single-mode fiber. Using 4-level coding, 1.28 Tbit/s (32 x 40 Gbit/s) can be packed in approximately 10 nm of optical bandwidth, corresponding to a spectral efficiency of 1 bit/s/Hz, and transmitted over a fiber span with 45 km.

Performance limits of first-order PMD compensators using fixed and variable DGD elements

In this letter, we analyze optical polarization-mode dispersion compensators using a single differential-group-delay (DGD) element that is either fixed or variable. We evaluate the upper-bound performance limits, and quantify the compensator performance under dynamic operations. We show that the variable-delay compensator can reduce the risk of feedback loops trapping a locally optimized state. Moreover, the variable-delay approach provides superior performance as compared to a fixed-delay compensator by increasing the optimal system tolerance for a 10-Gb/s nonreturn-to-zero signal from 28 to 33 ps of average link DGD.

PMD compensation up to second order by tracking the principle states of polarization using a two-section compensator

This paper presents a theoretical analysis of an optical polarization mode dispersion compensator comprised of two adjustable delay sections with a polarization controller in between. Not only the differential group delay of the fiber but also the rotation of the principle states of polarization within a bandwidth can be compensated by tracking the trajectory of the fiber output principle states of polarization around the carrier frequency. The theoretical analysis of the two-section compensator shows how to adjust its parameters. Based on numerical simulations applying a 10 Gbit/s NRZ transmission, we show the enlarged bandwidth of compensation in comparison to a simple first-order compensator.

Analysis of signal degree of polarization degradation used as control signal for optical polarization mode dispersion compensation

The basic property of degree of polarization (DOP) degradation of optical signal induced by polarization mode dispersion (PMD) in high-speed optical fiber transmission is investigated in detail. The DOP of the optical signal reflects the degree of waveform degradation caused by PMD, therefore, it is proposed to be used as the control signal judging the best compensation point for the optical adaptive PMD compensation techniques. However, the signal DOP is not only affected by PMD, but also by various factors, such as the modulation format, modulator chirp, fiber nonlinearity, amplified spontaneous emission (ASE), and so on. We use numerical simulations and experiments to explore the basic DOP property to detect PMD with these factors. We also show that using the signal DOP as control signal is especially useful for the optical duo-binary modulation because of its high sensitivity and wide PMD detection range.

The analysis of an optical fibre communication system using laser rate equations.

Fibre dispersion has been the main limitation to high-speed data transmissions employing optical fibres. Various techniques and methods for combating this limitation have therefore been proposed. Such techniques include electrical and optical dispersion compensation, optical and electrical pulse shaping, and modifications of the fibre dispersion profiles. Some of these techniques and methods have resulted into very effective but expensive systems, and it has been difficult to adopt them. Others have resulted into inexpensive systems with moderate performance, and some of these have been adopted. In the present paper, the effect of electrical pulse shaping on dispersion-induced pulse distortion is investigated by computer simulation techniques. The results show that the detrimental effects of the dispersion can be greatly reduced without incurring very high costs. Moreover, this method is applicable to systems employing standard optical fibres, the major component in the already installed systems. Tanzania Journal of Science Volume 27 (2001), pp. 73-86

Maximum-channel-number Investigation of Limiting-Amplified Multiwavelength Dispersion Compensator Incorporating Chirped Fiber Gratings

We theoretically investigate the design of an optical limiting-amplified multiwavelength dispersion compensator (LDC) incorporating multiple chirped fiber gratings (CFGs) and a common bidirectional erbium-doped fiber (EDF) amplifier. The LDC provides simultaneous dispersion compensation and limiting amplification of multiple dense wavelength division multiplexing (DWDM) signals. The design criteria for multiwavelength LDC are to provide high constant channel output power and low interchannel differential power by optimization of the EDF length. The influence of the CFG's rejection ratio on the LDC is addressed. The dynamic range and maximum channel number of the LDC are studied. The multiwavelength LDC may facilitate easier DWDM system design flexibility and network implementation.

Simultaneous filtering and dispersion compensationin WDM systems using apodised fibre gratings

The authors demonstrate the use of apodised fibre Bragg gratings with a negative index change mean value, acting simultaneously as optical filter demultiplexers and efficient group velocity dispersion compensators in wavelength division multiplexing systems. The optimum mean value is obtained by simulation.

Small-signal analysis for nonlinear and dispersive optical fibres and its application to design of dispersion supported transmission systems with optical dispersion compensation

The exact general analytical solution of the small-signal analysis for nonlinear and dispersive optical fibre is derived and discussed. Exact solutions in case of particular situations are also presented, and compared with other authors' results. An approximated solution obtained from the physical description of fibre nonlinearity effect on the small-signal conversions is derived, numerically compared with the general solution, and shown to be less accurate for larger fibre nonlinearity effect, larger modulation frequencies and/or fibre dispersion. It is shown quantitatively that, at low-medium frequencies and for moderate optical powers at fibre input, the fibre nonlinearity affects the intensity modulation fibre transfer function (IM-FTF) primarily through the IM-IM conversion. Furthermore, it is shown that the fibre nonlinearity can provide perfect compensation of IM-FTF distortion in case of an external modulator with positive chirp parameter. The performance of various optical dispersion compensation (DC) configurations in dispersion supported transmission systems is compared and discussed using the IM-FTF, from the viewpoint of amplitude and delay distortion and bandwidth available. It is shown that under- and post-optical DC leads to an equalised IM-FTF with smaller amplitude and delay distortions and larger bandwidth.