" Nothing is predictable!" It is nearly impossible to forecast day to day with any degree of certainty the stock market or the cost of energy so to predict the direction technology customer requirements and where regulatory and legislative decisions will ultimately lead the telecommunications industry is extremely difficult. But as they say the future waits for no one! Southwestern Bell Telephone (SWBT) has determined that single mode fiber is the preferred medium of choice in the network. SWBT''s initial analysis indicates that a fiber optic distribution network would reduce the provisioning and maintenance expense normally associated with today''s copper network. In addition a fiber based distribution network could be easily upgraded for the delivery of enhanced broadband services if required in the future. However SWBT does not plan to begin a general deployment of fiber into the distribution network until the initial first cost of a fiber deployment is equivalent to (or less than) the initial first cost of a copper deployment. In an effort to evaluate our initial assumptions SWBT has deployed three fiber optic field trials with a fourth trial planned to evaluate aerial rehabilitation. SWBT''s challenge is to move beyond the trial stage and identify architectures that are flexible enough to meet future service requirements and can be deployed for the equivalent first cost of copper. In these four trials SWBT is examining different fiber deployment alternatives an effort to identify those options which might satisfy these requirements. This paper details the information SWBT has obtained from our ongoing Fiber-to-the- Home (FTTH) and Fiber-to-the-Curb (FTTC) fiber field trials. The developing architectures technologies and ONU powering strategies are discussed as they impact the development of a SWBT fiber deployment strategy for the local loop.
The copper based telephone network of today (see Fig. 1) will be evolving over the next twenty years towards a fiber optic based Broadband Integrated Services Digital Network (BISDN). The initial mass deployment phase of placing fiber closer to the residential customer will be based on the economic deployment of narrowband services only. From an architectural point of view the most likely deployment to single family residences would be in the form of a Fiber To The Pedestal (FTTP) ar?hitecture. This is consistent with Bellcore''s Fiber In The Loop (FITL) Architectural Summary Report The form of this FYFP architecture will probably be that of an active double (or single) star or that of a passive optical network (PON). These two architectures will be examined as to their relative technical and economic merits pertaining to initial narrowband deployments all the way through to deployments that are capable of narrowband video and BISDN services.
This paper outlines Raynet's fiber-to-the-subscriber system and its evolution to a fiber-to-the-home system. The Raynet system uses resource sharing to provide a full mix of concurrent POTS, Basic ISDN, AM Video and Broadband ISDN services. A fiber-to-the-subscriber system must be cost competitive with today's copper systems. The requirement to support AM video and digital broadband services must have a very low impact on the system's installed cost. The upgrade must be non-service effecting and must gracefully support a full mix of services on a nonblocking basis.
An overview of the passive components that have been developed by Technologies for subscriber loop applications will be presented. The paper will cover new products and technologies that have allowed to introduce passive components that will allow optical services to be cost-effectively delivered to the subscriber. The types of devices discussed will include the low cost Subscriber Loop Coupler and the new singlemode monolithic multiport coupler arrays. The paper will highlight the volume manufacturing process that is used by to fabricate the Subscriber Loop Coupler as well as the wavelength-flattened non-50/50 splitters that have been developed for passive optical networking. Characterization of the monolithic multiport coupler arrays will also be presented. Specifically the broadband (wavelength-flattened) operation of the monolithic 1 x6 and 1 x7 couplers across the 1 250 to 1 600nm window will be covered. Applications in which the new monolithic coupler arrays and the Subscriber Loop Couplers can be used in the local loop will also be discussed.
The growing deployment of fiber optics which are vulnerable to single point failure creates an urgent need for a means of automatic protection switching test access and reconfiguration in telephone networks. Fiber switching is a technology which is beginning to be used in trunk and subscriber ioop applications to satisfy this need. This paper focuses on several applications of fiber switching in public networks including the economic and technical advantages of this technology.
This paper discusses the use of the acousto-optic tunable filter (AOTF) in a multiwavelength crossconnect that eliminates back-to-back optical-to-electrical and electrical-to-optical conversions in the central office. We show that the ability of the AOTF for multiple wavelength selection can be exploited to reduce the component count in a multiwavelength cross-connect.
A rotary single-mode optical fiber switch has been developed which uses a novel anti-backreflection geometry. As a result the return loss is greater than 50 dB while insertion loss is maintained below 1 dB. This paper will indicate applications in the subscriber ioop then detail the rotary switching concept anti-backreflection enhancement and electromagnetic actuator. The switch will be shown to be rugged under the environmental conditions that may be expected in the outside plant.
NTT'' 5 ISDN primary-rate interface services which employ the CCITT Recommendation I. 431 user/network interface use an economical optical subscriber line transmission system to cover both small and large exchange areas. DSU is miniaturized through LSI techniques and its cost is reduced by mainly using consumer components. Moreover an OCU installed in a subscriber line terminal for direct connection has the same unified internal interface for user information transmission and testing functions as remote terminal connection. In addition the optical line terminating module adopted for the DSU and OCU components is extreniely cost effective: e. g. its circuit adjustment has become easier by enlarging the emission peak wavelength range and optimizing module optical output. Consequently these technologies will facilitate the early and widespread installation of primaryrate interface services.
We demonstrate a four-channel WDM network at 622 Mb/s with 1 .3 xm multifrequency Fabry-Perot laser diodes. A channel spacing of only 15 nm was achieved by using a WDM component consisting of interference filters of special design. Results of laser-filter misalignment measurements suggested that more channels could be implemented without serious power penalties from mode-partition noise. Higher bit rate transmission in such a medium-density WDM system was also shown.
Proposals for fiber-to-the-curb (FTTC) systems have been made in recent years as optical system researchers and telecommunication providers have sought ways to deploy optical technologies close to the home based only on plain-old-telephone service (POTS) revenues. Fiber-to-the-home (FTTH) systems in contrast offer maximum bandwidth per subscriber but at significantly greater cost per subscriber today. One issue to explore with FTTC systems is their ability to support future broadband services since FTTC systems do not bring fiber all the way to customer premises. This paper presents an economic and technical analysis of various FTFC upgrade alternatives from a system supporting only POTS to later-generation systems also capable of broadcast video transport.
A basic objective behind the development of the Synchronous Optical Network (SONET) standards is inter-vendor compatibility. In the simplest case this means the terminals at the ends of a fiber optic link can be made by different manufacturers. In the future this objective means that many SONET Terminals Add/Drop Multiplexers Regenerators Digital Cross-Connects and Digital Loop Carriers will all be interconnected to form a single efficient and flexible network. This paper will discuss the goals of the Bdilcore SONET Compatibility Test Program that is now being developed and implemented. Some details of the test plan and early observations are reported.
Fiber optics is playing an increasing role in transmission of CATV signals. This paper describes the currently evolving architectures which eliminate conventional coaxial trunks and make possible greatly expanded bandwidths. Evolving network architectures enable the extension of fiber deeper into the network structure while improving performance and reducing operating costs. Several different architectures will be examined and their advantages and disadvantages will be discussed as well as their ability to deliver different forms of entertainment video.
Although the cable television industry has seriously proposed the widespread use of optical fiber technology as the foundation of its networks only since 1988 an important financial watershed already has been reached. Based on stunningly rapid AM technology developments and new research by industry engineers the CATV industry has already reached the point where building new optical trunk is cheaper than building conventional coaxial cable plant. Although as recently as 1988 it might have seemed preposterous to suggest that the financial crossover point between optical media and copper media would soon be reached that indeed has occurred. Using a topology dubbed the " fiber trunk and feeder engineers at American Television Communications the second-largest U. S. CATV operator have demonstrated that it is currently feasible to build new optical fiber trunking networks at costs equal to or less than conventional 450-MHz coaxial cable plant. Installation of the first such network already is underway and it is expected that the significant change in fiber economics will further spur the already-heady pace of fiber introduction in the CATV industry. That in turn will create new types of networks with topologies resembling telephone " star" networks more than conventional " tree-and-branch" systems. The new optically-based networks will be far more reliable more flexible and better adapted to signal switching than conventional CATV networks have been. Although the new networks will be put into place
Crossconnects have been deployed in the exchange and interexchange telephone operating environment over the last decade. They have operated exclusively on DS1 and DS3 inputs. SONET has standardized optical interfaces a new form of tributary multiplexing and extensive operations capabilities. The migration of new SONET based facilities onto existing crossconnects is reviewed.
SONET (Synchronous Optical NETwork) has provided the opportunity to implement standardized next generation optical communications networks. One of the most important aspects of these evolving networks is the ability to survive a catastrophic event. These catastrophic events include loss of communication between sites or the loss of an entire site. This paper will contrast various network survivability solutions with the emphasis on ring networks including operation advantages and disadvantages. An overview of several ring implementations will be discussed including two and four fiber rings concluding with a summary of the various survivability solutions.
When considering today's network and looking ahead towards a complete Synchronous Optical Network (SONET), attention must be given to transitional network functionality to ensure next generation transport network element longevity. The transition will not happen overnight. Initial SONET equipment will satisfy today's transport requirements but must be capable of operating efficiently as SONET equipment in an all SONET networks. Careful consideration of transitional network functionality will ensure cost effective SONET deployment both initially and for the long term. The first requirement of the transitional network is that it be as cost efficient as the existing asynchronous network in transporting DS 1 and D53 signals. Currently, the SONET standard1 specifies five (5) ways to directly map a DS1 into a SONET VT1.5. SONET equipment will be prohibitively complex if required to support all five mappings. This paper addresses DS 1 service transport, and reviews the five DS 1 to VT mappings currently specified in the SONET standard. Network partitioning concerns resulting from multiple DS 1 mapping deployment are discussed. Finally, it is concluded that it is in a (network) provider's best interest to reduce the number of DS 1 mappings deployed in a SONET network to those which satisfy transport requirements of all current and envisioned services. To ensure optimal signal transport characteristics and minimal cost solutions for wideband and voice services in the transmission network, the floating asynchronous mapping provides the best network solution and should be used by all transport equipment not requiring DSO processing.
When a semiconductor laser is coupled to an optical fiber without an isolator sharp intensity noise spikes can occur due to Rayleigh backscatter. It is shown that these spikes can be suppressed by self locking the laser with a discrete reflection of magnitude comparable to Rayleigh backscatter. This approach is of interest for certain low-cost lightwave applications such as the subscriber ioop where the use of optical isolators may not be desirable due to cost constraints.
We present a single fiber system to transmit three wideband HDTV signals over 1 5km distance. This is achieved by the use of frequency-division- multiplexing of frequency modulated baseband signals. A wavelength-divisionmultiplexing technique is also applied to demonstrate a bi-directional transmission system over the same fiber. These systems provide a simple and cost-effective solution for HDTV production applications.
With fiber approaching the subscriber premises much attention is being given to maintenance and repair issues. A novel approach for conducting Fiber Loop Testing on bidirectional single-fiber networks is described. Through the use of the system laser and detector regular maintenance and testing can be carried out in-line without interrupting traffic. Apart from the obvious cost savings other advantages of this approach include the integration of the fiber testing function into the transmission system and the automation of the testing and fault locating process.
The complex nature of the optical distribution system has delayed the ubiquitous deployment of fiber in the local loop. The shared resource approach, using either bus or splitter architectures, ameliorates these limitations. Growth of fiber into the local distribution loop requires new packaging schemes that avoid significant changes to deployment or craft practices. A modular approach is presented that violates neither appearance nor installation practices. The design allows for service upgrade, from POTS to video and BISDN.
With the advent of fiber to the subscriber systems comes the significant challenge of how to power the associated active electronics distributed outdoors in the local ioop. This paper addresses some issues associated with the powering of these systems and presents a network powering architecture which has been developed for this application.
This paper will describe an effort that was undertaken to address the feasibility of providing fiber optic facilities to replace existing copper plant thus enhancing a planned rehabilitation program in the NYNEX corporation. It will focus on the use of passive optic solutions although other architectures were also studied. Real geographical areas typical problems encountered and vendor/telco solutions to these problems will be discussed. Conclusions reached and recommendations made are stated at the end of this study.
Cost optimization of passive optical networks is critical to future deployment of optical fiber in the subscriber loop. This paper presents various design approaches for configuring passive optical networks with a comparative analysis of costeffectiveness.
Wavelength division multiplexing (WDM) permits delivery of a variety of communications services over the same fiber without the need for costly MUX/DEMUX electronics. The versatility of miniature, monolithic imaging systems utilizing multilayer dielectric mirrors is demonstrated, both in single mode and multimode optical propagation environments, as in a three channel WDM for the transmission of bidirectional ISDN telephony signals and wideband television distribution signals on the same fiber without interference.