Calculating the CSO/CTB spectrum of CATV amplifiers and opticalreceivers

The discrete CSO/CTB intermodulation distortion has a big influence on the CATV net quality. This article describes a new method to calculate the composite second order (CSO) and composite triple beat (CTB) intermodulation distortion spectrum for the full frequency range of a coaxial cable CATV amplifier for any input frequency plan. The calculation takes into account the output level ripple and preemphasis, using frequency dependent intermodulation coefficients. These coefficients have been established through CSO/CTB measurements on multichannel test systems for standard frequency plans at 5-8 intermodulation frequencies or on distortion arrays for the two (three) oscillator measuring test system. The defined intermodulation coefficients are unrelated to the frequency plan and the input/output level ripple. It is also possible to calculate the CSO/CTB spectrum caused by analogue channels within digital QAM channels. The results equally apply to optical CATV receivers. Simulation results have been verified using extensive data from multichannel measurement systems     

A hybrid CATV/256-QAM/OC-48 DWDM system over an 80 km LEAF transport

A hybrid dense-wavelength-division-multiplexing (DWDM) system for CATV, 256-QAM and OC-48 trunking is proposed and demonstrated. It used two wavelengths for AM-VSB CATV, one wavelength for 256-QAM digital passband signals and four wavelengths for OC-48 (2.5 Gb/s) digital baseband signals transport. Good performances of carrier-to-noise ratio (CNR) /spl ges/ 50 dB, composite second order (CSO) /spl ges/ 67 dB and composite triple beat (CTB) /spl ges/ 65 dB were obtained for AM-VSB CATV; and low bit error rate (BER < 10/sup -9/) had been achieved for 256-QAM and OC-48 digital signals over an 80 km large effective area fiber (LEAF) transport.     

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     

CSO/CTB performances improvement in a bi-directional DWDM CATV system

We proposed and demonstrated a four-wavelength bi-directional dense-wavelength-division-multiplexing (DWDM) CATV system that uses chirped fiber gratings (CFGs) as the dispersion compensation devices to reduce the fiber dispersion and cross-phase modulation (XPM)-induced crosstalk simultaneously. Our proposed system not only reduces the required number of fibers, but also offers the advantages of capacity doubling. Excellent performances of carrier-to-noise ratio (CNR) /spl ges/ 50 dB, composite second order (CSO) /spl ges/ 72 dB and composite triple beat (CTB) /spl ges/ 69 dB were obtained over a 50-km single-mode fiber (SMF) transport.     

光子晶体光纤在有线电视传输系统中的应用

文章介绍了一种利用光子晶体光纤作为宽带色散补偿装置的直接幅度调制残留边带(AM-VSB)有线电视传输系统,测试结果表明,与未加补偿的外调制方式相比,本系统具有更高的载噪比(CNR),更优的复合二阶失真(CSO)和复合三阶差拍性能(CTB).将光子晶体光纤用作色散补偿,不但可以应用到CATV系统中,还可以广泛应用于其它宽带高速长距离光纤通信领域.     

Multichannel 64-QAM transmission in AM/digital and all-digitalhybrid-fiber-coax based video dial-tone systems

A hybrid-fiber-coax (HFC) system is operated with a combination of 63 AM and 21 64-QAM subcarriers as well as with the 21 64-QAM subcarriers alone. The 64-QAM subcarriers are 6-MHz wide, decorrelated, and of the type intended for compressed digital video. The AM signal levels (over both the optical and coaxial links) are set to produce standard carrier-to-noise ratios (CNRs), composite second order distortion (CSO), and composite triple beat (CTB). The optical modulation depth (OMD) is independently varied and transmission tests are carried out over the optical link alone, as well as over the entire system (including two coaxial amplifiers, or actives). The relative degradation of the system due to the optical link versus the actives is investigated. For an OMD of 24% or less and with the raw bit-error ratio (BER) set to 10^-5 (as anticipated for use with forward error correction (FEC) systems), the performance is limited by the actives. There is an approximate 3.5 dB penalty in the necessary CNR for 64-QAM reception, due to the presence of the AM signals. On the other hand, when the system is operated with all-digital subcarriers, the optical modulation depth may be increased from 24% to 37% with no penalty in the required digital CNR     

Performance characteristics and applications of hybrid multichannelANI-VSB/M-QAM video lightwave transmission systems

The performance characteristics and applications of hybrid multichannel amplitude modulation vestigal sideband (AM-VSB)/M-quadrature amplitude modulation (QAM) video lightwave transmission systems operating at either 1310 or 1550 nm are reviewed. These systems can transport up to 80 AM-VSB video channels and more than 30 64/256-QAM digital video channels over a standard single-mode fiber (SMF) using a single laser transmitter. Five main transmission impairment mechanisms for these systems are reviewed as follows: (a) clipping-induced impulse noise, (b) bursty nonlinear distortions, (c) multiple optical reflections, (d) stimulated Brillouin scattering, and (e) self-phase modulation. For AM-QAM video lightwave trunking applications, the in-line erbium-doped fiber amplifier (EDFA) selection is discussed using a frequency-domain simulation model. Such lightwave trunking systems can provide an AM carrier-to-noise ratio (CNR) greater than 50 dB with composite second order (CSO) and composite-triple-beat (CTB) distortions less than -65 dBc, and nearly error-free transmission (BER⩽10^-9) for the 64-QAM channels with signal-to-noise ratio (SNR) of 30-dB or better. Comparison between 64-QAM and 256-QAM video channel transmission and the effect of the QAM channels on the AM-VSB channels are also presented. The implications of these results and others in hybrid multichannel AM-QAM video lightwave trunking systems are discussed     

Performance comparison between DCF and RDF dispersion compensation in fiber optical CATV systems

An architecture of an externally modulated AM-VSB CATV 77-channel erbium-doped fiber amplifier (EDFA)-repeated system which use the combination of a single-mode fiber (SMF) and reverse dispersion fiber (RDF) as a dispersion compensation device is proposed and demonstrated. Compared to the conventional externally modulated fiber optical CATV systems with or without a dispersion compensation fiber (DCF), excellent performance of composite second order (CSO) /spl ges/ 78 dB accompanied by satisfied carrier-to-noise ratio (CNR) /spl ges/ 50 dB and composite triple beat (CTB) /spl ges/ 65 dB was obtained in the proposed system.     

Radio-on-hybrid WDM transport systems based on mutually injection-locked Fabry–Perot laser diodes

A radio-on-hybrid wavelength-division-multiplexing (WDM) transport system employing mutually injection-locked Fabry–Perot laser diodes (F–P LDs) is proposed and demonstrated. System performances evaluated by carrier to noise ratio (CNR), composite second order (CSO), composite triple beat (CTB), bit error rate (BER), and third-order intermodulation distortion to carrier ratio (IMD₃/C) for simultaneous transmission of CATV/LAN/ITS are improved. Our proposed systems are relatively simple and potentially low cost due to the use of mutually injection-locked F–P LDs as broadband light source (BLS).     

Signal distortion and noise in AM-SCM transmission systemsemploying the feedforward linearized MQW-EA external modulator

In subcarrier multiplexing (SCM) optical video distribution systems, the nonlinear signal distortion generated by the combined action of laser chirp and fiber dispersion limits the transmission distance. This paper for the first time shows that low-chirp MQW (multiquantum well)-EA (electroabsorption) external modulators are applicable to AM-SCM transmission systems. The feedforward linearization technique is used to compensate the signal distortion due to the nonlinearity in the modulator's L-V (light power versus voltage) characteristic. The effectiveness of this type of modulator for suppressing dispersion-induced distortion is clarified experimentally. A feedforward linearized transmitter with composite second order (CSO) intermodulation distortion <-62 dBc, composite triple beat (CTB) intermodulation distortion <-59 dBc and a carrier-to-noise ratio (CNR) >50.5 dB is successfully constructed. It is shown that the transmitter can achieve a CSO <-59 dBc, a CTB <-57 dBc and a CNR >49.5 dB for a 32 channel AM signal and 10 km transmission. Furthermore, estimations of the signal distortion cancellation and the noise characteristic achieved with feedforward circuit modeling are shown. The results obtained here emphasize that MQW-EA external modulators are applicable to AM-SCM transmission systems     

全数字有线电视光网络系统指标浅析

数字电视是有线电视发展的方向,分析了全数字有线电视系统的总指标需求和全数字有线电视城域网络系统对光网络指标的要求,比较了全数字有线电视网络和传统有线电视网络的关键指标,传统的模拟光传输设备指标远超出全数字有线电视网络的需求,建议采用低成本有线电视光传输设备进行数字电视整体平移。     

入射偏振态偏离TE模对光纤AM CATV外调制发射机性能影响的研究

从理论上分析了入射到调制器的偏振态偏离ＴＥ模时对外调制光发射机组合二次失真（ＣＳＯ）和组合三次差拍（ＣＴＢ）的影响。得出在ＴＥ，ＴＭ模插入损耗相同时，传输５９个ＰＡＬ－Ｄ频道，在保证ＣＳＯ＝－７０ｄＢｃ时，偏离ＴＥ模的角度应小于６°。单频传输的实验结果和理论分析一致     

Reduction of dispersion-induced distortion in SCM transmissionsystems by using predistortion-linearized MQW-EA modulators

The application of low-chirp MQW (multiquantum well)-EA (electro-absorption) modulators to subcarrier multiplexing (SCM) optical transmission systems is studied. The authors show that a third-order predistortion circuit is feasible for compensating the nonlinearity of this type of modulator. The degree of frequency chirping per optical intensity modulation depth of the modulator is theoretically determined to be about 1.4 MHz. A 42-channel AM-SCM signal transmitter with the predistortion circuit realizes both composite second-order distortion (CSO) and composite triple beat distortion (CTB) values under -57 dBc after 200-km-long transmission. The authors confirm dispersion-induced distortion of the MQW-EA modulator is as small as that of the LiNbO₃ modulator. Carrier-to-noise ratios (CNRs) of 45.2 dB for channel 1 and 43.8 dB for channel 42 were measured after 100 km transmission. It is found that the deterioration of a CNR is caused by the cascaded erbium doped fiber amplifiers (EDFAs), Rayleigh backscattered power and the optical phase noise. Theoretical CNRs show that the output power of the modulator should be higher to improve CNR     

Multichannel single-sideband SCM/DWDM transmission systems

To understand the transmission limitation of multiple narrow single-sideband subcarrier-multiplexed (SSB/SCM) signals, this paper first presents a closed-form analysis to predict Mach-Zehnder intensity modulator-induced composite triple beat (CTB), and linear-fiber-dispersion-induced composite second-order (CSO) and CTB distortions. To combine SSB/SCM with dense-wavelength-division-multiplexing (DWDM) systems, analytical and numerical tools, which are not constrained by any wavelength spacing and modulation frequencies, are used to analyze cross-phase modulation-induced crosstalk. All the analytical and numerical results are verified by computer simulations. Several multichannel SSB/SCM/DWDM systems with transport capacities of 10 or 20 Gb/s per wavelength, with a wavelength spacing of 25, 50, and 100 GHz, are also studied in this paper to understand the fundamental transmission limitations.     

Design and demonstration of hybrid AM-VSB/digital WDM videotrunking system with cascaded EDFAs

The authors have analysed and designed a five-channel (one AM-VSB and four 2.5 Gbit/s baseband digital) hybrid WDM system, with cascaded in-line EDFAs for high capacity video trunking applications. Simultaneous transmission of high quality AM-VSB signals with CNR >50.5 dB and four 2.5 Gbit/s digital channels with negligible power penalty over 105 km of standard singlemode fibre is demonstrated     

光纤CATV系统和光调制度

光纤ＣＡＴＶ系统的一个主要设备是ＡＭ光发送、接收端机。本文从分析ＡＭ光发送、接收端机的内部机理出发，说明了一个重要的内部参数－光调制度，它与光纤ＣＡＴＶ系统的性能指标ＣＮＲ（载噪比）、ＣＴＢ（组合三次差拍）、ＣＳＯ（组合二次差拍）等的关系，再从内部参数转为频道数与ＣＮＲ、ＣＴＢ、ＣＳＯ等的关系。为实际光纤ＣＡＴＶ系统设计给出了一个理论依据。本文同时出讲述了光调制度的控制方法、具体测量方法，以及ＡＭ     

光发射机中MZ型波导调制器产生CTB的分析

AM－CATV外调制光发射机中的MZ型波导调制器，其转移特性呈正弦曲线。当多路信号同时调制时，将产生组合二次失真（CSO）和组合三次差拍（CTB）。本文对CTB进行了理论分析，并对我国450、550MHz二种CATV系统调制时的CTB进行了计算。这对非线性补偿电路的设计具有一定的指导价值。     

拉曼放大对长跨距有线电视网中QAM信号的影响

论文研究了在目前的数字CATV网络中使用光纤拉曼放大器改善QAM数字信号的性能,重点分析了数字CATV网络中数字频道和模拟频道的相互影响。分析结果表明:模拟频道的非线性失真指标CSO/CTB对QAM信号的误码率将产生重要影响,从而可以通过采用拉曼放大来改善系统非线性失真指标,进而改善系统的误码率性能。     

Multichannel AM video transmission using a high-power Nd:YAG laserand linearized external modulator

A high-power Nd:YAG laser with a linearized external modulator-based system is demonstrated for a transmission of 50 channels of vestigal sideband amplitude modulated (VSM AM) video. The 1320-nm diode-pumped Nd:YAG laser is an attractive source for AM video transmission due to the high output power (~200 mW) and low relative intensity noise (<-170 dB/Hz). However, the required external modulator generates third-order distortion products, which limit the performance of such a system. A predistortion linearization technique is described. It reduces the modulator generated third-order distortion products by 16.4 dB, allowing a modulation index of 3.37% per channel. When combined with the Nd:YAG laser, this yields a 50-channel video transmission system with a 12 dB optical power budget for video carrier-to-noise ratios of 52 dB and composite distortion products (CSO and CTB) of less than -60 dBc. The demonstrated power budget is sufficient to allow four-way power splitting, with the remaining margin comparable to the test results obtained with DFB (distributed-feedback) laser-based AM transmission systems     

Second- and third-order harmonic distortion in DFB lasers

The second- and third-order harmonic distortion in distributed feedback (DFB) lasers is simulated using a time domain large signal dynamic model. The effects of the longitudinal spatial hole burning, nonlinear gain, spontaneous emission, and current leakage are included in the model. Composite second-order (CSO) and composite triple beat (CTB) are calculated for an 80 channel 60-540 MHz system with 3% modulation depth in each channel. The simulation results are compared with the experimental harmonic distortion measurements