Although high-power, erbium-doped fiber amplifiers (EDFAs) allow trans

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Although high-power, erbium-doped fiber amplifiers (EDFAs) allow trans

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Overcoming Nonlinear Optical Impairments High-Source Laser Launch Powers
Although high-power, erbium-doped fiber amplifiers (EDFAs) allow transmission more, there several effects these power levels that degrade signal quality point being unusable trunking applications. important effects system designer needs concerned with stimulated Brillouin scattering dispersive intensity noise. origins these effects will discussed well techniques used circumventing their influence signal quality. This process implications. First, scattering process lead excess noise link, thereby degrading carrier-to-noise ratio (CNR). This especially pronounced lower channel frequencies CATV band. second consequence apparent from fiber transfer function presence (see Figure Since input/ output power relation sublinear, second-order distortions will result. circumvent effects SBS, technique spreading optical spectrum outside bandwidth MHz) often employed. result this technique illustrated Figure this case, phase modulator used broaden optical spectrum multiples GHz. power phase modulator increased, amount decreases since frequency broadening effectively increases threshold. Using this technique, launch powers accommodated without suffering significant composite second-order (CSO) penalties. increase threshold above this level, more exotic suppression schemes necessary.
Stimulated Brillouin Scattering (SBS)
nonlinear process places relatively limit optical power level that launched into single-mode fiber particular suppression techniques employed. most easily viewed sort collision scattering process involving three waves: incident optical wave, backscattered optical wave, acoustic wave fiber itself (caused unavoidable vibrations within glass). collision process associated bandwidth approximately MHz. This implies that incident optical signals within spectral width participate given scattering process. When incident optical wave sufficient power (i.e., greater than threshold power occur) travels down fiber, scattering that occurs between resulting acoustic wave causes forward wave backscattered towards transmitter. Figure shows consequences this process transmitted power. threshold power level (typically dBm-7 SMF-28 fiber 1550 nm), output power linear replica input power (less normal fiber attenuation). However, occurrence causes fiber's transfer characteristic from input output become severely nonlinear backscattering process.
SMF-28 trademark Corning, Inc.
Note: avoid effects back-scattering, modulation applied phase modulator. lower curve shows full effect with dither applied.
Figure Output Characteristics Length SMF-28 Single-Mode Fiber 1550
Overcoming Nonlinear Optical Impairments High-Source Laser Launch Powers
Dispersion-Induced Intensity Noise
Relative Intensity Noise (RIN)
semiconductor diode lasers used externally modulated 1550 transmitters often have strict noise requirements. most common noise specification RIN, which describes amount amplitude fluctuations present optical field. These fluctuations pass through modulator limit achievable link. typical specification 1550 source lasers -163 dB/Hz.
Benefits High-Power 1550 Transmitters with Advanced Suppression Techniques
Fiber Links
system designer accomplish sufficient suppression ensure levels dispersive intensity noise, high-power source lasers and/or highlaunch power EDFAs greatly expands network performance service operator. With robust, high-power transmitter solutions, network achieve greater performance, increase distances between hubs, possibly lower costs through elimination EDFAs. Currently, commercially available 1550 source lasers typically have output powers dBm. Taking into account modulator loss splicing losses, output powers from outputs 1550 transmitter approximately each. these power levels, transmitter usually followed EDFA with optical power launched into fiber. source laser power increased (without affecting other characteristics such phase noise), system designer options. First, EDFA supplied with higher optical input powers. This will improve overall link since EDFA gain saturation being increased (the output power relatively constant). Figure shows typical link performance.
Phase Noise
addition inherent amplitude noise diode lasers, amount phase noise present must carefully controlled. Since single-mode fiber exhibits high amounts dispersion 1550 link itself acts form frequency discriminator optical field. result that optical phase fluctuations converted amplitude fluctuations signal passes down fiber. This residual noise referred dispersive intensity noise. levels dispersive intensity noise addition inherent RIN) become more pronounced higher frequencies longer fiber lengths. systems move into higher bandwidth longer fiber-span architectures, system designer must more closely scrutinize both phase amplitude noise properties source lasers.
characterize amount phase noise present source laser, laser spectral linewidth often measured. absence external noise sources (i.e., laser noise solely result inherent, spontaneous noise processes within diode), spectral linewidth valid predictor phase noise optical field. Typical supertrunk systems require source laser spectral linewidth MHz. However, required phase-noise levels become smaller applications characterized high-channel count long fiber length, spectral linewidth measurements easily become contaminated low-frequency MHz), extraneous noise sources present system. Therefore, imperative distinguish between actual phase fluctuations, which contribute dispersive intensity noise, residual phase noise, which never affects CATV band. been shown that spectral linewidth measurements often overestimate amount dispersive intensity noise link would suffer. Therefore, serves system designer develop accurate characterization techniques laser phase noise within CATV band such that source lasers screened intended performance.
Figure Performance Launch-Power EDFA, 0.25 dB/km Fiber Attenuation, Noise Bandwidth, Channels Modulation/Channel, Laser dB/Hz, Receiver Noise Current pA/Hz, EDFA Noise Figure input)
Lucent Technologies Inc.
Overcoming Nonlinear Optical Impairments High-Source Laser Launch Powers
Benefits High-Power 1550 Transmitters with Advanced Suppression Techniques (continued)
Fiber Links (continued)
Figure shows, link improves approximately every increase laser power. While this negligible, increasing source laser power levels more require considerable effort. Therefore, another strategy that leverages high-source laser powers greater extent examined. When transmitter output power levels reach higher regime, excluding EDFA from system considered. This advantage only lowering system cost, also improving link performance. Such EDFA-less operation 1550 shown Figure Here, link fiber lengths examined. even source lasers provide superior performance compared EDFA-based transmission. Moreover, dBm-20 level optical power approached, 54.6 achieved without EDFA over fiber. Clearly, designer access such high-power sources, EDFA-less transmitters most effective means leverage this power directly into improved network performance
Figure performance EDFA-less Transmitter Architecture; 0.25 dB/km Fiber Attenuation, Noise Bandwidth, Channels Modulation/Channel, Laser -163 dB/Hz, Receiver Noise Current pA/Hz
Lucent Technologies Inc.
Overcoming Nonlinear Optical Impairments High-Source Laser Launch Powers
Benefits High-Power 1550 Transmitters with Advanced Suppression Techniques (continued)
Fiber Links Over
addition high-power source lasers, capability support high EDFA launch powers into long fiber lengths also opens opportunities network architectures. primary challenge here overcome effects well other nonlinear effects such self-phase modulation) these power levels. additional launch power utilized number ways. distribution networks, additional suppression capability used span longer lengths fiber prior splitting. fiber length increases above
transmitter with capability launch more power into given length fiber than transmitter with capability. Also, transmitter with capability launch certain amount power into longer length fiber than transmitter with capability. fiber links Figure illustrate improved suppression used expand distribution networks. some distribution networks, EDFAs with powers high dBm, example, used followed immediately splitters that limit optical power launched into fiber limit transmitter. However, some distribution networks require launching optical power into length fiber before splitter reached. these networks, suppression capability transmitter limits extent distribution network.
Figure Distribution Network Expansion from Capability Capability; 0.25 dB/km Fiber Attenuation, Noise Bandwidth, Channels Modulation/ Channel, Laser -163 dB/Hz, Receiver Noise Current pA/Hz
Lucent Technologies Inc.
Overcoming Nonlinear Optical Impairments High-Source Laser Launch Powers
received distribution hubs optically amplified, split, distributed. Here, through launch power EDFAs, link improved over launch case. should noted that addition higher suppression, self-phase modulation impairments must also carefully controlled these launch powers.
Benefits High-Power 1550 Transmitters with Advanced Suppression Techniques (continued)
Fiber Links Over (continued)
suppression also allows point-topoint spans using only EDFA, depending fiber attenuation. Launching optical power does allow additional fiber loss link, however, various fiber dispersion mechanisms result much more challenging environment. illustration using higher transmitter capability increase length fiber link shown Figure this case, penalty incurred additional fiber performance. regenerated links greater length envisioned, improved CNRs obtained providing fielddeployed line amplifiers (EDFAs) with greater input powers, thereby reducing overall link CNR. particular case 1550 trunking/distribution, optically regenerated architecture shown Figure this topology, 1550 signals used through network from head receiving nodes. Signals
Summary
summary, higher-power source lasers capability support higher EDFA launch powers greatly expand utility 1550nm externally modulated transmitters. High-source laser powers vicinity dBm-20 allow EDFA-less transmitter designs which achieve superior performance lower cost compared EDFA-based architectures. other hand, having ability launch EDFA powers allows user extend point-to-point links, achieve higher levels through higher received powers, improve performance optically regenerated distribution links. Clearly, raising 1550 power levels will allow service operators squeeze more performance dollar their existing networks.
Figure Increasing Link Length with Higher Transmitter Capability; 0.25 dB/km Fiber Attenuation, Noise Bandwidth, Channels Modulation/ Channel, Laser -163 dB/Hz, Receiver Noise Current pA/Hz
Figure Trunking/Distribution 1550 Link with Improvements from Higher EDFA Launch Powers; 0.25 dB/km Fiber Attenuation, Noise Bandwidth, Channels Modulation/Channel, Laser -163 dB/Hz, Receiver Noise Current pA/Hz Lucent Technologies Inc.
Overcoming Nonlinear Optical Impairments High-Source Laser Launch Powers
additional information, contact your Microelectronics Group Account Manager following: INTERNET: http://www.lucent.com/micro, Optoelectronics information, E-MAIL: docmaster@micro.lucent.com AMERICA: Microelectronics Group, Lucent Technologies Inc., Union Boulevard, Room 30L-15P-BA, Allentown, 18109-3286 1-800-372-2447, 610-712-4106 CANADA: 1-800-553-2448, 610-712-4106) ASIA PACIFIC: Microelectronics Group, Lucent Technologies Singapore Pte. Ltd., Science Park Drive, #03-18 Cintech III, Singapore 118256 Tel. (65) 8833, (65) 7495 CHINA: Microelectronics Group, Lucent Technologies (China) Co., Ltd., A-F2, 23/F, Fong Universe Building, 1800 Zhong Shan Road, Shanghai 200233 China Tel. (86) 6440 0468, ext. 325, (86) 6440 0652 JAPAN: Microelectronics Group, Lucent Technologies Japan Ltd., 7-18, Higashi-Gotanda 2-chome, Shinagawa-ku, Tokyo 141, Japan Tel. (81) 5421 1600, (81) 5421 1700 EUROPE: Data Requests: MICROELECTRONICS GROUP DATALINE: Tel. (44) 7000 368, (44) 1189 Technical Inquiries: OPTOELECTRONICS MARKETING: (44) 1344 (Ascot
Lucent Technologies Inc. reserves right make changes product(s) information contained herein without notice. liability assumed result their application. rights under patent accompany sale such product(s) information.
Copyright 2000 Lucent Technologies Inc. Rights Reserved
October 2000 AP00-068OPTO

Although high-power, erbium-doped fiber amplifiers (EDFAs) allow trans

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