有线电视网双向传输系统

文章概述了有线电视网双向传输的几种接入技术，阐明了有线电视网双向传输光系统的特点，重点描述了光发射机、光放大器、光接收机和有线电视回传信道的应用。本文为某有线电视台双向网改造的实用实例，可为其他有线电视台的双向网改造提供参考。     

Bidirectional fibre-optical transmission using a multiple-quantum-well (MQW) modulator/detector

We demonstrate a simple architecture for bidirectional optical fibre transmission which uses an MQW device as both modulator and photodetector. We achieved transmission of 50 Mbit/s and 600 Mbit/s in both directions over one 3.34 km-long single-mode fibre at 860 nm wavelength. Coherent Rayleigh interference was found to be a limiting factor in single-source bidirectional systems.     

Time-Shared Two-Wire Digital Subscriber Transmission System and Its Application to the Digital Telephone Set

Adopting digital techniques in the local network area will enhance the possibility of extending digital operation capability to the subscriber's equipment. The problem is to convey digital signals at a bit rate of at least 64 kbits/s in both directions over existing two-wire subscriber loops. This paper describes a time-shared two-wire digital subscriber transmission system in which the directional separation of two signals (GO and RETURN) is accomplished by the time division bidirectional transmission method in burst-mode, and also reports results of investigations on the feasibility of an all digital telephone subscriber loop system.     

Wavelength-interleaving bidirectional transmission system using unidirectional amplification in a 5/spl times/100 km recirculating loop

This investigation presents a novel 50-GHz interleaved bidirectional transmission system with eight wavelengths that uses four-port interleavers in a bidirectional recirculating loop. This bidirectional configuration shares optical components in the fiber network and an interleaver is utilized to enable unidirectional amplification in an erbium-doped fiber amplifier to block noise associated with Rayleigh backscattering. After bidirectional transmission through 500-km LEAF fibers in the recirculating loop, power penalties of less than 2.5 dB were achieved at 10 Gb/s for all channels.     

Low-cost 2 Mbit/s optical local line transmission system using single-mode fibre

A laboratory demonstration is reported in which low-cost optoelectronic devices are used for transmission over 9/125 ?m single-mode fibre at 2 Mbit/s. This novel system has been designed for application in local network and office systems where optical device cost constraints present severe restrictions on the technology options.     

Bidirectional unrepeatered 43 Gb/s WDM transmission with C/L band-separated Raman amplification

A novel wavelength arrangement using C- and L-band-separated Raman preamplification is proposed for application to bidirectional unrepeatered transmission systems operating with multiple 43 Gb/s channels. The proposed wavelength allocation makes it possible to greatly mitigate Raman gain depletion by the counter-propagating signals. The authors have achieved bidirectional unrepeatered transmission of 32 /spl times/ 43 Gb/s channels (= 1.28 Tb/s) over 200 km with Raman preamplifiers using the proposed technique. They found that the system performance of bidirectional transmission with C/L band-separated Raman preamplification is degraded by nonlinear interactions between the high power Raman pump lights and the WDM signals. The root cause can be described in terms of nondegenerate four-wave mixing induced by beating between the WDM signals and two longitudinal modes of the Raman pump light. A solution avoiding ND-FWM was demonstrated in a 32 /spl times/ 43 Gb/s transmission experiment.     

Digital Optical Receiver Sensitivity Degradation Caused by Crosstalk in Bidirectional Fiber Optic Systems

Receiver sensitivity degradation caused by Rayleigh backscattering and coupler reflections is investigated for bidirectional digital transmission systems. Experimental values for APD receiver sensitivity degradation in a system operating at a bit rate of 10 Mbits/s and at a wavelength of 830 nm were found to be within 2 to 3 dB (optical) of the values predicted by a simple theoretical model.     

Bidirectional higher order cascaded Raman amplification benefits for 10-Gb/s WDM unrepeated transmission systems

Benefits provided by higher order bidirectional Raman pumping schemes in 10-Gb/s unrepeated wavelength-division-multiplexing transmission systems are experimentally quantified in terms of BER performances at 10 Gb/s. By keeping under control double-Rayleigh-scattering-noise-induced transmission penalties, which can degrade system performance at very high ON-OFF Raman gain, as well as nonlinear propagation effects such as Brillouin scattering, self- and cross-phase modulations, four-wave-mixing, and Raman-induced crosstalks, we show a total unrepeated system reach enhancement up to 3.5 dB with respect to first-order bidirectional pumping. As confirmed by theory, the maximum reach enhancement is mainly limited by pump-to-signal relative intensity noise transfer induced by higher order copumping.     

Bidirectional multimode-fiber communication links using dual-purpose vertical-cavity devices

This paper describes the development of novel multimode-fiber (MMF) communication links that achieve half-duplex bidirectional transmission over a single fiber through the use of 850-nm dual-purpose GaAs vertical-cavity optoelectronic devices. The dual-purpose devices are fabricated by focused-ion-beam micromachining (FIBM) of standard vertical-cavity surface-emitting lasers (VCSELs) and are able to be switched between operation as either efficient laser sources or as resonant-cavity-enhanced avalanche photodetectors. An avalanche multiplication factor of 10 is achieved at a reverse-bias voltage of 12.3 V. A 1.25-Gb/s half-duplex bidirectional data communication link is demonstrated and shown to allow error-free transmission of binary data over 500 m of standard 50-/spl mu/m-core-diameter MMF. Receiver sensitivities for transceivers based upon these devices are predicted for the first time to be comparable with conventional data communication transceivers. Furthermore, a half-duplex analog bidirectional system is constructed, which permits the transmission of advanced RF modulation formats over MMF. Link characterization by error-vector magnitude (EVM) is described. The dual-purpose vertical-cavity devices are employed for bidirectional transmission of 32-symbol quadrature-amplitude-modulated (32-QAM) signals on a carrier frequency of 2 GHz, relevant to many current wireless local-area network and cellular standards. EVM as low as 1.3% rms is observed for a 600-m link of 62.5-/spl mu/m-core-diameter MMF.     

Millimeter-wave broad-band fiber-wireless system incorporating baseband data transmission over fiber and remote LO delivery

We present the first demonstration of a millimeter-wave (mm-wave) broadband fiber-wireless system which incorporates baseband data transmission in both the downstream (622 Mb/s) and upstream (155 Mb/s) directions. The local oscillator (LO) required at the remote antenna base station for up- and downconversion to/from the mm-wave radio frequency (RF) is delivered remotely via a modulation scheme that is tolerant to the effects of fiber chromatic dispersion on the detected LO carrier power. The technique employs a single dual electrode modulator located at the central office (CO) and the data and an RF signal at a frequency equal to half the LO frequency, are applied simultaneously to the device. The modulation scheme was optimized as a function of the modulator operating conditions. Simultaneous bidirectional radio transmission in the mm-wave fiber-wireless network was implemented using specially designed mm-wave diplexers located at the base station (BS) and customer unit, and a single Ka-band printed antenna array at the BS operating simultaneously in transmit and receive mode. Error-free data transmission was demonstrated for both down(34.8 GHz) and uplinks (37.5 GHz) after 20 km of single-mode optical fiber and a bit error rate (BER) of 10/sup -6/ was achieved after the inclusion of a 2-m radio link.     

Shared access packet transmission systems for compressed digitalvideo

The problem of designing shared access packet-transport-based transmission systems for compressed video signals is studied. The feasibility of using conventional link-level and transport-level protocol services to transmit compressed video is examined by focusing on two practically important scenarios for compressed video transmission: (1) multipoint-to-multipoint video transmission using a 200 Mb/s implicit token passing (ITP) fiber-optic local area network (LAN); and (2) point-to-multipoint broadcast video distribution using a 90 Mb/s packet time-division multiplexing (packet-TDM) direct-broadcast satellite channel. To evaluate the performance of such shared-access broadband packet video systems accurate simulation models were developed that were driven by realistic `broadcast quality' compressed video sources for the ITP-LAN and packet-TDM systems. The models were used to determine design tradeoffs between channel throughput, video quality (measured by clipping probability), and the transport-level and media-access-level protocol features and parameters implemented in the packet video network interface unit     

Bandwidth-efficient digital transmission over unshieldedtwisted-pair wiring

Describes techniques for achieving data rates up to 155 Mb/s over unshielded twisted-pair (UTP) wiring for local area network (LAN) applications in premises distribution systems. Duplex operation at these high data rates is achieved over two pairs of UTP wiring and with a bandwidth utilization that is less than 30 MHz, thus avoiding potential problems with radiation limits. The transmission scheme used for these LAN applications is carrierless AM/PM (CAP), which is a bandwidth-efficient two-dimensional passband encoding scheme. The paper also discusses in some detail a technique called NEXT equalization, which allows several users to share the same cable     

A fiber-optic line-switching network with a 150 Mb/s user data rate

The authors describe ImNet/2, a fiber-optic local area network, which has been specially developed for rapid image transport in picture archiving and communications systems (PACS). A comprehensive analysis of image communication requirements in hospitals led to the conclusion that current LANs would not be satisfactory under routine workload. ImNet/2 is optimized for the transmission of large datafiles. It applies line switching by means of active switch modules in a multistar topology. Once established, a link between two image equipment units continuously transfers data at a speed of 140 mB/s. Each switch unit has a total data throughput of 1.12 Gb/s. Asynchronous parallel network ports and a simple lightweight high-speed protocol make it easy to interface the network to image workstations and PACS servers. The mechanisms and components of ImNet/2 are described in detail     

A simple broad-band coherence multiplexed optical access networkand its scalability

This paper proposes a novel and simply configured broad-band optical access network that uses coherence multiplexing (CM) and half-duplex bidirectional transmission. It allows the on-demand use of broad bandwidth on existing fiber-to-the-home (FTTH) access lines. The design of the proposed CM network considers degradation factors in CM systems. This paper introduces two analyses. The first one is a numerical simulation to optimize the tradeoff between available user number and fiber dispersion degradation, and the second estimates acceptable access-line loss in the network. These analyses show that 16 users×100 Mb/s (or 12 users×155 Mb/s) bandwidth Is possible on a standard single-mode fiber access line whose loss and length are under 9 dB and 10 km (and 7 km), respectively. The feasibility and scalability of the proposed network are verified by an experiment in which eight-channel 155-Mb/s half-duplex optical packet transmission is successfully demonstrated on a 7-km standard fiber access line with bit error rates better than 1×10^-9. This study shows that the capacity of existing FTTH access lines that employ star couplers can be significantly enhanced     

An introduction to local area networks

Within a restricted area such as a single building, or a small cluster of buildings, high-speed (greater than 1 Mbit/s) data transmission is available at a small fraction of the cost of obtaining comparable longhaul service from a tariffed common carrier. Local area networks use this low-east, high-speed transmission capabality as the basis for a general-purpose data transfer network. There are two basic issues in local area network design. First, how should the hardware realizing the network be organized to provide reliable high-speed communication at minimum cost? With the low cost of the raw transmission capability, care is required to keep the associated hardware costs correspondingly low. Second, what protocols should be used for the operation of the network? While many protocol problems are common to local area networks and long-haul networks such as the ARPANET, new protocols are required to exploit the extended capabilities of local area networks. This paper addresses these two basic issues. It also considers the interconnection of local area networks and long-haul networks and presents a case study which describes in detail the host computer interface hard-ware required for a typical local area network.     

Bidirectional WDM passive optical network for simultaneous transmission of data and digital broadcast video service

We have demonstrated an easily upgradable bidirectional passive optical network for the simultaneous transmission of wavelength-division-multiplexing channels and digital broadcast video signals. The proposed network could transmit 15 2.5-Gb/s downstream channels, 15 155-Mb/s upstream channels, and one broadcast signal consisting of more than 70 digital video channels.     

Optimization of spatially adaptive reciprocal multipoint communication networks

A mathematical framework for a duplex multiple-input-multiple-output, multipoint network is presented and used to develop uplink and downlink network objective functions based on information theoretic "waterfilling" capacity arguments. It is shown that these objective functions possess equal local optima in reciprocal networks where the internode channel responses between uplink and downlink reception nodes are reciprocal, e.g., in time-division duplex networks. This mathematical framework can be used to develop locally enabled global optimization algorithms that use only local information available at each transceiver. A numerical experiment reveals an order-of-magnitude capacity improvement over conventional single-antenna systems, and/or a several-orders-of-magnitude improvement in required transmission power.     

Present Status of Mechanical Connectors for Optical Fiber

Trunk transmission network systems connecting exchange offices were the first transmission systems using optical fiber cables. Subscriber network systems connecting the exchange office with each subscriber including local area networks or CATV network systems are under development at present. Two main techniques are newly required to be developed for making optical fiber mechanical connectors for optical fiber subscriber network system realization. The first is to realize a new connector with a high return loss and a low connecting loss. The second is to cut the joining cost of optical fibers. The newly developed "optical contact connector" realized a high return loss of more than 25 dB and a low connecting loss of 0.15 dB average value. A newly developed "multifiber connector" which can connect many optical fibers at the same time can save time and space for joining fiber cables, and also a "plastic molding technique" can save the cost of the connector. The performance of all these connectors is the same as that of the "optical contact connector." This paper describes the present status of the technique to obtain a high return loss connector, a multifiber connector, and a plastic molded connector for the subscriber network system.     

Evaluation of light beams for short and medium range wireless communications

Technological improvements in free space optical communication systems have reduced the cost and alternatives to fiber optic transmission. The advantages of the free space optical link over fiber optic cabling are primarily economic. In line with the demand for gigabyte link from 10 Mbit/s to 10 Gbit/s in the market, the uses of free space optical communication systems have increased exponentially from 1995 to 2008. However, free space optics is subject to atmospheric effects such as attenuation and scintillation which can reduce link availability and may introduce errors not seen in fiber transmission. In this paper we argue that optical wireless communication is an alternative to fiber optic transmission in short and medium range wireless communications and we discuss that the liability and availability of the free space optical link is mainly determined by the local atmospheric condition, this is to say that the transmission quality may be affected by weather conditions. For the evaluation we constructed an experimental communication network with a free space system. One way to characterize the strength of the turbulence fluctuation is by examining the Rytov variance for a plane wave. This Rytov variance physically represents the intensity fluctuation induced by atmospheric turbulence.     

Repeated Bidirectional Transmission Using Two 4-Port Optical Circulators and a Bidirectional EDFA without Isolators

By using a newly designed bidirectional erbium-doped fiber amplifier, we demonstrated a 2 × 2.5 Gb/s repeated bidirectional transmission over a 100-km single-mode fiber. Two tunable optical bandpass filters were used to suppress the Rayleigh backscattering and amplified spontaneous emission in the bidirectional transmission system. The bit error rate performances were measured for both directions. A negligible power penalty of 0.2 dB for the 2 × 2.5 Gb/s transmission due to backreflections was observed when comparing the bidirectional transmission with single-channel, unidirectional transmission.