Transmission characteristics and reliability of pure-silica-core single-mode fibers

Transmission characteristics and reliability for pure-silica-core single-mode fiber with matched cladding are presented. On account of the "pure" silica core, without any additives, the fiber features the low attenuation and improved chemical stability under the existence of hydrogen and γ-ray radiation. High mechanical reliability and good splicing behavior of the fibers were also confirmed. More than 2000 km of pure-silica-core fiber have been fabricated, exhibiting median attenuation of 0.35 dB/km at 1.3 μm and 0.21 dB/ km at 1.55 μm. The achieved minimum attenuation was 0.154 dB/km at1.55-1.56 mum, which is the lowest attenuation ever reported.     

Low-loss and low-dispersion-slope highly nonlinear fibers

In recent technologies, various optical signal processing systems have been reported. In many of these applications, highly nonlinear fibers (HNLFs) are used as key parts. Especially, low loss and low dispersion slope are critical features of the HNLFs. In this paper, their design and characteristics, packaging technology, and applications are introduced.     

高速传输系统用低损耗单模光纤的研究

介绍了国际上低损耗单模光纤的研究进展,从理论上分析了低损耗单模光纤实现的技术途径。通过对石英玻璃物理特性的研究,探索出石英玻璃光纤的退火工艺,以降低光纤的内应力从而降低光纤的衰减。采用自主知识产权的专利技术制造的光纤在1 310、1 550和1 625nm波长的衰减典型值分别为0.320、0.182和0.195dB/km。该光纤的技术指标优于ITU-T国际标准和GB/T规定的光纤指标值。     

Low-loss fluoride optical fibers for midinfrared optical communication

Attempts to improve transmission loss characteristics in fluoride fibers are described. Optical loss in current fibers is dominated by two major extrinsic loss factors, defect scatterers and impurities. Scatterer analysis using a Raman microprobe has revealed that the majority of them are ZrO2crystallites. These crystallites dominate the fiber scattering characteristics, having both wavelength independent and Rayleigh wavelength^-4dependencies according to their size. Excess loss due to OH groups which causes absorption at around 2.9 μm is quantified as 2000-5000 dB/km/ppm, depending on glass composition. These results suggest that further efforts in glass synthesis should concentrate on eliminating oxide and hydroxide impurities, and on the further purification of the raw materials. The key for realizing high-quality, low-loss, and long-length fluoride fibers is currently related to whether or not oxide scatterers can be completely eliminated.     

低损耗单模光纤的研制及其传输试验研究

分析了 低损耗单模光纤(SMF)的实现途径,并采用自主知识产权的专利技术制造出低损耗SMF,其在 1310、1550和1625nm波长 的衰减典型值分别为0.317、0.182和0.195dB/km, 技术指标优于ITU-T国际标准规定的光纤指标值。100Gbit/s高速传 输试验表明 ,本文研制的低损耗SMF与常规SMF相比可增加近18.8%的传输距离, 有分布拉曼放大(DRA)的传输链路可比无 DRA链路传输距离增加30%。高速通信试验与分析表明,本文研制的低损耗SMF具备良好的高 速长跨距传输特性,能够满足我国100Gbit/s高速光纤通信系统的发 展需求。     

Low-loss on-chip transmission lines with micro-patterned artificial dielectric shields

Low-loss coplanar waveguide (CPW) transmission lines integrated on a standard (5 -10 Omega ldr cm) silicon substrate are realised by using an artificial dielectric shield with a very high in-plane dielectric constant. The shield consists of a 30 nm-thick Al₂O₃ film sandwiched by two 100 nm-thick aluminium layers patterned into lattices of mum-size elements. The individual metallic elements are micro-patterned to suppress the flow of eddy currents at microwave frequencies. Inserted below the CPW, the shield blocks the electric field of the line from entering the silicon substrate. The resulting line attenuation (measured up to 25 GHz) is comparable to that of identical CPWs built on a high-resistivity silicon wafer.     

Low-loss slow-wave propagation along a microstructure transmission line on a silicon surface

We report observations of relatively low-loss propagation in the frequency range of 1.0 to 12.4 GHz using a micrometer-size coplanar MIS transmission line fabricated on a heavily doped N + silicon surface. This low-loss mode of propagation is found to be accompanied by significant wavelength reduction which suggests that such lines may be useful as transmission media for distributed components in silicon monolithic microwave integrated circuits (MMICs).     

AoIP和AES67及其对未来音频系统的影响

随着数字音频信号传输技术的不断发展,网络化传输已成为当今业界最为流行并被普遍接受的传输手段之一.对普通数字音频和网络音频进行了简单的对比,简单介绍了网络音频AoIP的发展现状,概述了AES67标准的主要内容,并分析了其对未来音频系统发展趋势的影响.     

色散补偿光纤传输系统的最佳补偿方案

研究了采用色散补偿光纤传输系统的最佳补偿方案,经研究发现,混合补偿方案可以大大减小光纤非线性效应的影响,提高系统传输距离.此外,还对非归零码(NRZ)和归零码(RZ)的传输性能进行了比较.     

高速DWDM通信技术及进展

综述了高速DWDM(密集波分复用)系统中的关键技术,包括QPSK(四相相移键控)、8QAM(8进制正交幅度调制)和16QAM(16进制正交幅度调制)等新型调制格式、超低损耗光纤/拉曼放大和新型光集成器件,并分析、比较了这些关键技术对DWDM系统传输产生的不同影响。在此基础上,介绍了近年来DWDM大容量传输的一些成功试验。试验表明,这些关键技术有着广阔的应用前景。     

The analysis of crosstalk in multichannel wavelength divisionmultiplexed optical transmission systems and its impact on multiplexerdesign

An analysis of crosstalk in multichannel wavelength-division multiplexing (WDM) systems is presented, deriving new expressions for system degradations and taking into account both receiver design and the practical limitations of regenerator electronics. This theoretical study is corroborated by measured results obtained on a commercially available digital transmission system and is then used to determine the optimum multiplexer design for multichannel wavelength division multiplexed systems. From this study, the optimum multiplexer design for giving acceptable transmission performance is determined     

Polarization-maintaining fibers and their applications

Polarization-maintaining fibers and their applications are reviewed. The classification of high-birefringent fibers and low-birefringent fibers and their fabrication methods and characteristics are discussed in Section II. Analytical methods and numerical methods for fiber design on the birefringence are presented in Section III. Degradation factors of polarization maintenance expressed as crosstalk or mode-coupling parameters caused by internal origins such as structural imperfections, wavelength, and nonlinear effects, and by external origins such as temperature fluctuations, mechanical perturbations, and electromagnetic effects, are discussed in Section IV. Characterization methods on beat length, mode coupling, stress distribution, and mechanical strength are presented in Section V. Applications to the fiber devices and nonlinear effects, and splicing methods for the polarization-maintaining fibers are described in Sections VI and VII.     

RF transmission over multimode fibers using VCSELs-comparing standard and high-bandwidth multimode fibers

Fiber-optic radio-frequency links have been assembled using oxide-confined vertical-cavity surface-emitting lasers (VCSELs) and multimode fibers. Links with single and multimode VCSELs and with standard and high-bandwidth fibers have been evaluated and compared in the frequency range of 0.1-10 GHz. The best results were obtained for links with a multimode VCSEL and a high-bandwidth fiber. For a 500-m-long link, a spurious free dynamic range of 104 dB/spl middot/Hz/sup 2/3/ at 2 GHz and 100 dB/spl middot/Hz/sup 2/3/ at 5 GHz were obtained while allowing for a VCSEL-fiber misalignment of /spl plusmn/12 /spl mu/m. Corresponding numbers for the intrinsic link gain and noise figure are -29 and -33 dB, and 39 and 42 dB at 2 and 5 GHz, respectively. Inferior performance was observed for the standard fiber link due to a larger variation in modal group velocities. This paper also presents a detailed link analysis to identify performance limitations and to suggest modifications for improved performance.     

Multiple antenna systems: their role and impact in future wireless access

Multiple antennas play an important role in improving radio communications. In view of this role, the area of multiple antenna communication systems is in the forefront of wireless research. This article reviews two key related aspects of multiple antenna communication systems: multiple access interference mitigation at the receiver via multi-user beamforming; and space-time modulation and coding for MIMO systems. It is shown that both multi-user and MIMO receivers share similar signal processing and complexity tradeoffs.. Following that, a general unified framework for assessing different types of space-time modulation for MIMO systems is introduced. These space-time modulation methods are then compared in terms of Shannon capacity over multipath channels. Key MIMO system performance and implementation issues are also highlighted.     

Hierarchical transmission and COFDM systems

Draft European terrestrial digital video broadcasting (DVB-T) standard will pose problems for in the selection of the most beneficial and cost effective modes of operation within this flexible standard. This paper describes possible implementations of coded orthogonal frequency division multiplexing (COFDM) transmission schemes. Particular emphasis is placed on practical transmission aspects such as: radio frequency characteristics of the COFDM signal, field trials, and the more common digital television (DTV) measurements. Selection of the best system by broadcasters will involve compromises between costs and system parameters. The unique feature of Hierarchical transmission is described illustrating coverage benefits     

Energy and momentum transport velocities on transmission systems

It has been noted in the literature that the power-energy relation for electromagnetic fields may be written in the form of a flow continuity equation, and thereby a velocity of electromagnetic energy flow may be defined. The force-momentum field relation may be used in the same way to define a velocity of momentum flow, and it is shown that the flow velocity for both momentum and energy is the group velocity.     

Optical transmission loss in liquid-core hollow fibers

Multimode optical fibers consisting of glass cladding and liquid core have been constructed. For a cladding index of refraction of 1.52 and a core of bromobenzene, index of 1.560, a loss of 0.140 dB/m has been measured over lengths of about 50 m. The loss measured with incoherent light is higher due to the presence of higher order modes. Strong absorption in the near infrared occurs in narrow wavebands associated with overtones of the C-H fundamental vibration frequency.     

The impact of CSO/CTB distortion on BER characteristics by hybridmultichannel analog/QAM transmission systems

This article describes the measurements of composite second order (CSO), composite triple beats (CTB) frequency spectrum and time-varying distortion in the basic bandwidth (BB) (0-4 MHz) of the 64-QAM digital channels by multichannel AM/64-QAM optical and coaxial transmission systems. For any regular standard frequency plans (Europe, USA, NCTA, etc.) there is, for the I and Q components in the BB of the QAM channels, the harmonic series of the CSO/CTB with the first harmonic f ₁. It has been shown that for all the same laser-optics or coaxial transmission systems the CSO/CTB distortions spectrum form in the QAM BB 60-80 μs duration bursts of a series pulse with a pulse period T=1/f₁ and a pulse duration τ≈0.4/f_m, where f_m is the CSO/CTB harmonic with maximum amplitude in the QAM BB. The bursts result in the essential unevenness of error bits in time domain distribution. These bursts can deteriorate essential error correction by the interleaver-deinterleaver and Reed-Solomon (RS) forward error correction (FEC) code of the transmission systems also with a relative low bit error rate (BER) of about 10^-5 before FEC. There is, white Gaussian noise like, intermodulation distortion from interaction of digital-, digital-analog channels too, that have added white Gaussian noise     

The impact of CSO/CTB distortion on BER characteristics by hybridmultichannel analog/QAM transmission systems

The FEC limit (uncorrectable errors) with CSO/CTB (composite second order/composite triple beats) distortion presence in a channel is not for modulated lasers only, but for coaxial networks with amplifiers too. The system quality reserve depends not only on CNR, but is more limited on CSO/CTB. It is important, for the definition of the system quality reserve, to calculate the CSO/CTB spectrum caused by analogue channels within analogue and digital QAM channels and also to calculate the changing of CNR from the intermodulation interaction between analog and digital channels in a CATV network