Gain Controlling of Erbium-Doped Fiber Amplifier by Samarium Doped Inner-Cladding in the 1.5µm Region

In this work, WDM transmission with 40-Gbit/s per channel bit rate has been experimentally demonstrated over a 500-km link. Different chromatic dispersion conditions have been managed and in-line all-optical wavelength conversion has been carried out with a periodical poled lithium niobate (PPLN) device in a polarization-independent scheme. The link was obtained by connecting the fibers contained in an installed cable between Roma and Pomezia (25 km), encompassing single-mode (G.652) and high-end (G.655, non-zero dispersion with a particular value and flat curve for chromatic dispersion) fibers. Some 40 Gb/s channels were propagated in the link 500 km long and one channel was dropped from the link after 300-km propagation, wavelength converted, and added to the other channels for the next 200 km. The electrical data interfaces exploited a 4 × 10 Gbit/s to 1 × 40 Gbit/s MUX at the transmitter, along with a 1 × 40 Gbit/s to 4 × 10 Gbit/s DMUX at the receiver. Successful transmission of 4 channels, 200-GHz spaced, has been achieved over 500 km along both G.652 and G.655 links. No evidence of penalty comparing converted and unconverted channels has been reported. Transmission experiments of 8 × 40 Gbit/s, with 100 GHz frequency spacing, are also reported. No significant degradation has been observed in the case of the G.652 link.     

In-Field n × 40 Gb/s Transmission Experiments with In-Line All-Optical Wavelength Conversion

In this work, WDM transmission with 40-Gbit/s per channel bit rate has been experimentally demonstrated over a 500-km link. Different chromatic dispersion conditions have been managed and in-line all-optical wavelength conversion has been carried out with a periodical poled lithium niobate (PPLN) device in a polarization-independent scheme. The link was obtained by connecting the fibers contained in an installed cable between Roma and Pomezia (25 km), encompassing single-mode (G.652) and high-end (G.655, non-zero dispersion with a particular value and flat curve for chromatic dispersion) fibers. Some 40 Gb/s channels were propagated in the link 500 km long and one channel was dropped from the link after 300-km propagation, wavelength converted, and added to the other channels for the next 200 km. The electrical data interfaces exploited a 4 × 10 Gbit/s to 1 × 40 Gbit/s MUX at the transmitter, along with a 1 × 40 Gbit/s to 4 × 10 Gbit/s DMUX at the receiver. Successful transmission of 4 channels, 200-GHz spaced, has been achieved over 500 km along both G.652 and G.655 links. No evidence of penalty comparing converted and unconverted channels has been reported. Transmission experiments of 8 × 40 Gbit/s, with 100 GHz frequency spacing, are also reported. No significant degradation has been observed in the case of the G.652 link.     

Recent progress in soliton transmission technology

Recent progress on time-division multiplexed (TDM) and wavelength-division multiplexed (WDM) soliton transmission is described, in which dispersion management plays an important role in increasing the power margin and the dispersion tolerance. The characteristics of the dispersion-managed soliton are compared with those of return to zero and nonreturn to zero pulses. With a small dispersion swing, the system can still be described as an average soliton using the nonlinear Schrodinger equation, while with a large dispersion swing, the solitonlike steady-state pulse becomes a chirped Gaussian pulse, in which the governing equation is closer to a linear Schrodinger equation with a parabolic potential well. We describe an in-line modulation scheme for up to 80 Gbit/s per channel and its two channel WDM transmission over 10 000 km. Finally, we describe 640 Gbit/s (40 Gbit/sx16 channels) WDM soliton transmission over 1000 km with a dispersion-managed single-mode fiber. (c) 2000 American Institute of Physics.     

3000 km transmission of densely-spaced, 2.5 Gbit s-1 directly-modulated channels demultiplexed with a concave grating demultiplexer

WDM transmission and demultiplexing of four directly-modulated DFB lasers at 2.5 Gbit s-1, with very narrow channel spacing (50 GHz) over 3000 km of dispersion-shifted fibre has been performed with a single-span recirculating loop test-bed. A high-performance free-space concave grating demultiplexer is used for the first time in a dense WDM transmission experiment.     

Patterning effects in a WDM RZ-DBPSK SMF/DCF optical transmission at 40 Gbit/s channel rate

Through extensive direct modelling we quantify the error statistics and patterning effects in a WDM RZ-DBPSK SMF/DCF fibre link using hybrid Raman/ EDFA amplification at 40 Gbit/s channel rate. We examine the BER improvement through skewed channel pre-coding reducing the frequency of appearance of the triplets 101 and 010 in a long data stream.     

混沌超宽带信号的光学产生及其链路传输

用光反馈半导体激光器产生混沌超宽带(UWB)信号, 搭建了混沌UWB光载无线通信链路, 实现了360, 720 Mbit/s和1.44 Gbit/s三种不同传输速率下混沌UWB脉冲信号的生成和传输. 在未经任何色散补偿处理的情况下, 1.44 Gbit/s的混沌UWB信号在经过10 km单模光纤和0.6 m无线链路传输后, 在天线接收端被成功解调. 由于混沌UWB信号输出的随机性, 对应的UWB信号频谱中未出现任何离散的谱线. 这意味着利用混沌UWB信号实现的光载无线通信链路, 可以完全避免离散谱线对系统传输性能的劣化.     

Absolute polar duty cycle division multiplexing over wavelength division multiplexing system

The performance of absolute polar duty cycle division multiplexing (AP-DCDM) over wavelength division multiplexing (WDM) system is presented based on the simulation results. The AP-DCDM signal has narrower bandwidth than conventional time division multiplexing (TDM) signal, which makes its implementation in WDM system advantageous. In this paper, characteristics of AP-DCDM and TDM signals in WDM system are compared at the speed of 40 Gbit/s per channel, for the minimum allowed channel spacing and the chromatic dispersion tolerance. The results clearly show that AP-DCDM performs significantly better than TDM. By using AP-DCDM, 1.28 Tbit/s (32 × 40 Gbit/s) was successfully transmitted over 320 km standard single mode fiber. Spectral efficiency of 0.64 b/s/Hz was achieved by using 10 Gbit/s transmitters and receivers without polarization multiplexing.     

The system of L-band 2×10 Gb/s WDM transmission over conventional single mode fibre with 600 km by chirped fibre Bragg gratings dispersion compensation

A chirped fibre Bragg grating according to ITU-T suggested L-band (2nd channel $\lambda _{1}=1570.83$~nm; 80th channel $\lambda _{2}=1603.57$ nm) with more than 1800 ps/nm single channel dispersion compensation is presented in this paper, of which the cladding mode loss, the delay curve ripple and the power fluctuation of the reflected spectrum are less than 0.5 dB, 50 ps and 0.25 dB, respectively. With this new FBG as dispersion compensation device, a $2\times 10$ Gb/s wavelength division multiplexing (WDM) L-band transmission of 600 km based on conventional single mode fibre (G.652 fibre) is performed without forward error correction. The bit error rate (BER) is less than 10$^{ - 12}$ and the power penalties of the 2{nd} and 80{th} channel of L-band are 1.8~dB and 2.0~dB, respectively.     

43 Gbit/s x 54 ch Transmission with Dense 75 GHz Channel Spacing in NRZ Modulation Scheme

We demonstrated 2.16-Tbit/s (43 Gbit/s x 54 ch) WDM transmission over 600 km of standard single-mode fiber with high spectral efficiency 0.53 bit/s/Hz using optimized optical mux/demux filters for 75-GHz channel spacing in a simple NRZ modulation scheme.     

光相位共轭色散补偿波分复用系统的传输带宽

导出了光相位共轭器（DPC）接于常规单模光纤链路中点的色散补偿波分复用（WDM）系统传输带宽的估算公式，并用数值仿真的结果验证了公式的正确性；采用不对称接入光相位共轭器提高传输带宽的方法，导出了光相位共轭器接入位置对传输带宽影响的估算公式，利用公式估算和数值仿真的结果表明，当光相位共轭器处于最佳接入位置时，色散补偿的波分复用系统的传输带可以提高近一倍。     

Simulative analysis of pre- and post-compensation using CRZ format in WDM optical transmission link

This paper reports the effects of pre- and post-compensation using CRZ modulation format in long-haul WDM optical transmission link using wavelengths in three bandwidths viz. 1537.4; 1550; 1562.6 nm at per channel bit rates of 10 Gbit/s. It has been investigated here that optimization of dispersion map results in improved management of nonlinear effects in long-haul light wave systems operating in the quasi-linear regime. In addition, pre- and post-dispersion compensation was applied at the transmitter and receiver depending on the signal wavelength, which resulted in improvement of performance metrics viz. Q² (dB), BER and OSNR over longer transmission distances. It is reported here that optimum values of Q² dB of 17.1 dB, BER of 8.4933e⁻⁰¹⁵ and OSNR of 30.1 dB are obtained at 1550 nm at a transmission distance of 7360 km with pre- and post-compensation using CRZ modulation format.     

Determination of the optimum electrical bandwidth for spectral slicing

The implementation of wavelength division multiplexing (WDM) in communication access networks is dependent upon the availability of low cost optical sources. One possible alternative to lasers is to employ slices of a broadband optical source obtained via optical filters, which may be tuneable. This paper considers the behaviour of such a spectrally sliced optical transmission system as a function of the bandwidth of a realistic receiver electrical filter for the first time. The treatment includes distortion from optical fibre dispersion over several kilometres of fibre. The optimum ratio between the electrical bandwidth and the optical bit rate is found to be ~0.6 for a fifth-order Bessel filter     

4×10 Gb/s 412 km密集波分复用光纤光栅色散补偿的实验

研制了一种多波长啁啾光纤布拉格 (Bragg)光栅 ,波长、波长间隔符合ITU T标准 ,利用这种多波长啁啾光栅可以同时对多信道波长进行色散补偿 ,光栅的每个波长补偿范围满足ITU T对应信道波长波动的要求 ,并进行了 4× 10Gb/s、4 12km波分复用色散补偿实验 ,实验结果比色散补偿光纤模块要好 ,无误码功率代价都小于 2dB。     

Recent Progress of Wavelength Division Multiplexing Technology In Tera-bit/s Transoceanic Undersea Cable Systems

Transmission capacity for optical undersea cable systems is growing remarkably and a more than 500-fold increase has been achieved for commercial systems over the past 10 years. The first optical fiber cable in the Pacific Ocean went into service in 1989 and has a capacity of 280 Mbit/s per fiber pair. The emergence of an Erbium-doped fiber amplifier paved the way for a drastic capacity increase for these cables, and large capacity optical amplifier undersea cable systems with 5 Gbit/s per fiber pair were constructed worldwide in 1995-1996. Recent 10 Gbit/s-based wavelength division multiplexing (WDM) technologies together with new fibers and new amplifiers have allowed a further increase in capacity up to 160 Gbit/s, and these WDM systems will begin commercial service in both the Pacific Ocean and the Atlantic Ocean in 2000. Research interest is now being directed towards the development of undersea cable systems with a transmission capacity of 1 Tera-bit/s or more. This paper reviews the key technologies for next generation 160 Gbit/s optical undersea cable systems and recent progress towards Tera-bit/s systems. Dispersion managed soliton transmission for future higher bit rate WDM is also discussed.     

A long-haul wavelength division multiplexed system using standard single-mode fiber in presence of self-phase modulation

Performance of a long-haul wavelength division multiplexed (WDM) communication system has been evaluated in presence of nonlinear effects using standard single-mode fiber. Different compensation configurations, namely, post-, pre- and bi-end compensation, have been investigated to mitigate the fiber nonlinear effects. Eye-opening degradation due to mutual interplay between self-phase modulation (SPM) and group velocity dispersion for the compensating techniques has been estimated with respect to the transmission length and the residual dispersion in case of WDM system. Maximum threshold power levels at the bit error rate of 10⁻⁹ limited by the SPM effect have been determined. From a comparison among the compensating techniques, bi-end compensation configuration has been found to be the most suitable technique for any fiber length in case of a WDM communication system.     

The analysis of the error statistics in a 5 × 40 Gbit/s fibre link with hybrid amplification

We quantify the error statistics and patterning effects in a 5 × 40 Gbit/s WDM RZ-OOK SMF/DCF fibre link using hybrid Raman/EDFA amplification. By extensive use of a numerical model, we determine how the error statistics change with the transmission distance. This knowledge is used as a basis for a constrained coding technique in order to improve the transmission error rate. We propose an adaptive constrained code for mitigation of the patterning effects and demonstrate that this approach can substantially reduce the bit error rate (BER) even for very large values of the channel BER (BER > 10^− 1). The proposed technique can be used in combination with forward error correction schemes (FEC) to extend the range of channel BERs that an FEC scheme is effective over.     

Numerical Study on the Performance in High bit rate Optical Communication Systems

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Performance comparison between digital back propagation (DBP) and pilot-aided method for fiber nonlinearity compensation in different fiber links

We numerically investigate and compare the performance of fiber nonlinearity compensation using digital back propagation (DBP) method and pilot-aided method in coherent optical transmission systems using different fiber links. Simulations for wavelength division multiplexed (WDM) 112 Gb/s polarization division multiplexed quadrature phase shift keying (PDM-QPSK) systems with dispersion unmanaged (no DM) and dispersion managed (DM) fiber links are implemented. System Q-factor and maximum transmission distance at bit error rate (BER) of 3.8 ÿ 10^?3 are calculated for performance comparison. The results show that, for system with no DM fiber link, DBP method outperforms pilot-aided method, because DBP method has better performance for intra-channel fiber nonlinearity compensation. However, for system with DM fiber link where inter-channel fiber nonlinearity plays an important role, pilot-aided method performs better than DBP method, because of its ability for inter-channel fiber nonlinearity compensation.     

Phase encoded spread in time signals for suppression of propagation non-linearities in 40 Gb/s CDM/WDM communications systems using optical phase conjugation for dispersion compensation

The non-linear degradation along a RZ-WDM 40 Gb/s transmission link is shown to be reduced when a spectral direct sequence bipolar phase shift keying (DS/BPSK) encoding format is used. Standard single mode fibre transmission links are studied which use optical phase conjugation for dispersion compensation in the encoded system. For a WDM system with 100 GHz channel spacing, an improvement of 6 dB is found in the link output power margin at a distance of 300 km after five amplification stages.     

Comparison of various dispersion compensation techniques at high bit rates using CSRZ format

In this paper, the dispersion compensation techniques are compared on the basis of eye opening, eye closure, bit error rate and Q-factor. These techniques are applied to CSRZ system, which operates at bit rates of 2.5, 5, 10, 15 and 20 Gbps bit rates. The technique using fiber Bragg grating (FBG) for dispersion compensation is the best technique as this technique gives larger values of eye opening at 10 and 20 Gbps bit rate, smaller values of eye closure at 10 and 20 Gbps, minimum value of BER at 15 Gbps and maximum value of Q-factor at 15 Gbps when compared with other techniques. The RDF technique is the next best technique since this technique gives maximum value of eye opening when other techniques give almost similar values of eye opening at 15 Gbps, minimum value of eye closure at 15 Gbps, minimum value of BER at 15 Gbps and maximum value of Q-factor at 15 Gbps when compared with other techniques. The DCF is the next best technique as this technique gives maximum and minimum values of eye opening and eye closure at 20 Gbps (next best to FBG at 20 Gbps).