BER validation of ring-doping cladding-pumped EDFAs for dense WDMapplications

It is shown through BER measurements that ring-doping cladding-pumped EDFAs ensure both low cost and high system performance making them suitable for use in dense WDM systems     

10 gigabit Ethernet long-haul transmission without in-line EDFAs

In this contribution, we present experimental results on optical packet transmission of two 10 gigabit ethernet channels (10Ge) over 252 km link of standard single mode fibre (Ssmf, itu-t Recommendation G.652) and 287 km long link composed of 85 km ofSsmf and 202 km of non-zero dispersion-shifted (Nz DSF, itu-t Recommendation G.655) without deployment of in-line erbium-doped fiber amplifiers (Edfas). All the active components, dispersion compensating fibre (Dcf) modules and optical band-pass filters were placed at the transmitter and at the receiver side of the link. To our best knowledge, this is the first report of pure Ethernet transmission without in-lineEdfas over such a distance. The results are encouraging especially for operators of national research and educational networks who rely on leased dark fibres and prefer as long transmission as possible without deployment of in-line amplifiers.     

长距离海底光缆系统的技术动向

随着全球经济一体化和各国实现自身信息化的需求,国际间的通信和信息流量激增,尤其是以因特网为首的多媒体通信急剧发展,４５Ｍｂ／ｓ、１５５Ｍｂ／ｓ国际数字专用线业务的需求量逐年增加,造成了通信容量不足,因此为海底光缆通信提供了广阔的市场空间。本文将对长距离光放大海底光缆系统的开发现状、主要技术和发展动向进行探讨。     

Reducing pulsewidth broadening in L-band EDFAs by use of a newL-band EDF

Due to a small effective area of erbium-doped fiber (EDF), a short pulse will be broadened because of self-phase modulation when it is amplified in an L-band EDF amplifier (EDFA); hence, it is necessary to develop a new EDF with large Er³⁺ concentration to reduce the EDF length and a large effective area to reduce the nonlinear effect in the L-band EDFA. In this letter, it will be demonstrated that the pulsewidth can be maintained when a short pulse is amplified in an L-band EDFA consisting of a new L-band EDF     

Analysis and measurement of root-mean-squared bandwidth ofcross-phase-modulation-induced spectral broadening

The root-mean-squared bandwidth of spectral broadening induced by cross-phase modulation is derived analytically for a two-channel system consisting of a pump and probe channel. The pump channel is randomly modulated by binary data and the probe channel is a weak continuous-wave channel. The analytical expression is verified by experiments     

Experimental optimisation of central wavelength and bandwidth of reflective FBG for efficiency improvement of low-noise L-band EDFAs

Operation of L-band erbium-doped fibre amplifiers (EDFAs) incorporating a reflective amplified spontaneous emission filter (fibre Bragg grating (FBG)) was emulated with a tunable source. The experimental optimisation of the FBG bandwidth and central wavelength led to a low noise (<5.2 dB) 20 dBm single-pumped WDM EDFA.     

Signal linewidth broadening due to fibre nonlinearities in long-haul coherent optical fibre communication systems

Signal spectral linewidth broadening due to the Kerr effect in long-haul coherent optical fibre communication systems is examined theoretically and experimentally. By recirculating loop experiments, it is shown that linewidth broadening becomes serious in a system of more than a few thousand kilometres.<>     

Spectral broadening due to fibre amplifier phase noise

The authors report, for the first time, measurements of signal spectral broadening caused by phase noise in an erbium-doped fibre amplifier. The spectral broadening was found to be less than 20 kHz. Thus it will not limit the performance of phase or frequency modulated coherent systems employing fibre amplifiers.<>     

线宽展宽L波段掺铒光纤光源特性研究

提出了一种两级级联的掺铒光纤超荧光光纤光源(SFS)的新结构,采用耦合器将一个1 480 nm半导体(LD)泵浦源按照一定的分光比对第二级进行双向泵浦,第一段光纤未泵浦.通过研究两级光纤长度的比例、耦合器的分光比对结构性能的影响,优化结构参数后线宽扩展13 am,输出效率提高6%,并且该结构的中心波长也具有对泵浦功率不敏感的特性.     

DWDM系统中级联EDFA光信噪比计算

本文推导出级联EDFA密集波分复用系统光信噪比表达式,并由EDFA噪声指数的定义推导出级联EDFA系统等效噪声指数的表达式,分析了级联EDFA系统输出端OSNRout与等效噪声指数之间的关系,并通过实验对之加以了验证。     

Link-control gain clamping for a cascaded EDFAs link using differential ASE monitor

We propose a novel scheme for the suppression of gain excursion in a cascaded erbium-doped fiber amplifiers (EDFAs) link. By applying the differential amplified spontaneous emission monitoring method on link-control gain clamping, it is possible to achieve gain clamping for the whole link irrespectively of the control-signal wavelength and characteristics of individual amplifiers. The suggested algorithm/circuitry does not require predefinition of the injected signal power and operates independently of the wavelengths of control/data signals to the EDFA, enabling its application to different amplified links under distinct design parameters.     

Optical coherent broad-band transmission for long-haul anddistribution systems using subcarrier multiplexing

Signal multiplexing techniques for coherent optical transmission are compared, and appropriate application for a coherent subcarrier multiplexing (SCM) system is discussed. Optical frequency modulation (FM) using direct modulation of a distributed-feedback laser diode (DFB-LD) and a heterodyne detection is shown to be feasible. A transmission system using a local laser in the transmitter is unaffected by polarization and is cost effective. Phase noise can be suppressed by a phase-noise-canceling circuit (PNC) in a heterodyne receiver. This circuit can also effectively compensate for the frequency of instability of light sources. A theoretical simulation of a coherent SCM system showed that 100 channels of 30-MHz FM signal or 15 channels of 155-Mb/s signal can be distributed to 10000 subscribers using single-stage or double-stage optical amplifiers     

密集波分复用系统中级联EDFA光信噪比分析

文中推导出级联 EDFA密集波分复用系统光信噪比表达式 ,并由 EDFA噪声指数的定义推导出级联 EDFA系统等效噪声指数的表达式 ,分析了级联 EDFA系统输出端 OSNRout与等效噪声指数之间的关系 ,通过实验对其进行了验证     

密集波分复用系统中级联EDFA光信噪比特性研究

根据级联ＥＤＦＡ密集波分复用系统光信噪比和系统等效噪声指数表达式,分析了各种因素对系统输出端ＯＳＮＲ的影响,并分析了导致信道间输出ＯＳＮＲ产生差别的各种原因。     

Spectral shift and broadening of DFB lasers under direct modulation

The spectrum of DFB lasers, directly modulated at 144 and 622 Mb/s, is found to be considerably wider than the modulating random sequence rate. The broadening, which may be as high as ten times the data bandwidth, is accounted for by frequency changes (chirp) along each bit, incorporating a recently observed short time constant on the order of 10-20 ns. These changes will also introduce a few gigahertz spectral shifts as a function of the bit rate     

Investigations of thermal crosstalk in laser arrays for WDMapplications

Our studies on the thermal crosstalk of laser arrays with integrated thin-film heaters involved theoretical as well as experimental investigations. Comparing the effects of intentional geometrical variations of the device design, we found that the relative thermal crosstalk depends critically on the distance between the active area and the film heater. The most striking result is that a minimization of the thermal resistivity of the device does not always lead to a reduced thermal crosstalk. We demonstrate that an additional heat barrier close to the active region and/or an improved heat transfer between the submount and the heat sink may reduce the relative thermal crosstalk, a result completely unexpected from intuitive considerations     

Serial topology of wide-band erbium-doped fiber amplifier for WDMapplications

We analyze the recently proposed serial topology of a wide-band erbium-doped fiber amplifier (EDFA) covering both the C- and L-bands and compare it with the parallel configuration of C-band and L-band amplifiers. The analysis is based on an application of a comprehensive large-signal numerical model, which takes into consideration propagation of wavelength-division multiplexing (WDM) signals, bidirectional pump, and both the downstream and upstream ASE power spectral components. We have found that in the multiwavelength regime the new topology can provide output power of 3 dBm/channel for 32 C-band and 40 L-band, 0.8-nm-spaced signals with reasonable pump powers to the first and the second stage. In comparison with the usual parallel configuration of C-band and L-band EDFAs, this topology saves about 20% of overall pump power, 10% of the necessary length of erbium-doped fiber (EDF) and achieves lower noise figure for L-band signals     

Segmented-core fiber for long-haul and local-area-networkapplications

Design and experimental results for a segmented-core fiber optimized for long-haul and local-area-network applications are presented. It is compatible with existing dispersion nonshifted fibers above 1300 nm and has high bandwidth (2-4 GHz) over a wide wavelength range in the so-called few mode region near 800 nm. At this wavelength it also provides at least an additional 4.8-dB system margin compared to a single-mode fiber     

Simulation of phase modulation in EDFAs using an extended model

Nowadays, erbium-doped fiber amplifiers are described by the rate equations for the population densities and the evolution equations of the optical power propagation in the fiber. Since only the power is considered, phase effects like phase modulation and dispersion are not addressed. Here, we present an extended model using a slowly varying envelope approximation that takes into account dispersion and phase modulation. The phase modulation shifts the carrier frequency to a higher frequency. Due to this effect the impulse experiences in a single-mode fiber a different dispersion and, therefore, it should be included for numerical simulations