Fitting more functionality into the fiber frame

Sept. 1, 1998

Fitting more functionality into the fiber frame

Sandra McWilliams and Jorge Cano

adc Telecommunications Inc.

The fiber-distribution frame has, for some time, been a centralized management locale for crossconnection. But in today`s highly competitive world of telecommunications, network facility space is at a minimum because of growing service demand. Thus, service providers are on a constant quest for ways to run their operations more efficiently and cost-effectively. For these reasons, fiber-distribution frames increasingly are taking on new functionality for integrating additional optical equipment, allowing service providers to maximize service capacity, quality, and equipment space. Adding equipment elements through the use of integrated modules not only adds functionality to the original frame, it also allows those elements to tie in to the central cable-management scheme and monitoring processes. The result is a complete, centralized fiber solution.

The connector is another piece of the fiber framework changing to tackle the space problem. The use of wavelength-division multiplexing (wdm) and dense wavelength-division multiplexing (dwdm) have increased the amount of equipment in the already-crowded frame. To help alleviate the space problem, a new breed of connectors has arrived to accommodate two fiber connections in the same footprint in which standard SC connectors terminate one fiber. These new connectors also improve performance with low reflectance and insertion loss while providing technician safety.

Improved connector technology and integrated system modules are two ways fiber-optic equipment vendors are ensuring that plenty of bandwidth and service quality fit properly in the frame.

Form meets functionality

There is a move afoot in the industry to evolve network connections into more than just a junction of two cables that has no tangible effect on passing signals. It is now evident that signals can be managed and enhanced with additional services, allowing more flexibility and control in a central location. Fiber-distribution frames are the perfect place for this kind of management. At the frame, service providers can initiate a variety of signal alterations and easily manage connections. For these reasons, the fiber-distribution frame is an ideal point in the optical-transmission network to optimize services to meet the needs of today while also laying the groundwork for emerging services.

Optical components can be integrated, combined, and interconnected or crossconnected through the use of modular connector systems. These value-added systems allow the service provider to install individual modules--an A/B switch, a splitter, or a wdm/dwdm system, etc.--into the frame and have them all interconnected and working in tandem.

Maximizing the limited space in the fiber-distribution frame is the first step in ensuring the capacity to add functionality in the future. Through the use of value-added modules, the network planner can expand and grow the network based on the requirements of a particular facility. In addition, the modules are designed for fast and easy installation, saving labor time and cost.

Using the modular approach in the fiber frame provides solid protection for the individual components, because they are housed inside the frame rather than elsewhere along the fiber run. A centralized fiber frame architecture also allows installers to take advantage of the latest cable-management systems, which help prevent fiber kinks that can lead to costly outages or service degradation. The use of value-added modules in the fiber frame offers a variety of operational advantages, but also allows installation of service enhancement components.

An A/B protection switch, for example, is one optical component that can provide increased effectiveness when used in an integrated fiber-frame module scheme (see Fig. 1). This optical switch provides automatic switching between two fiber lines when a loss of optical signal is detected. It will switch to the alternate path in less than 15 msec. The switch typically is used at the receiving end to switch a transmission to a spare fiber. The switching threshold is set at a low power level to maximize the optical power budget available in the user`s network.

A/B switches also feature dual optical monitors, which allow the user to know immediately if the alternate fiber has lost its optical signal. Upon detecting a signal loss on the alternate fiber, the switch will notify the user automatically. The switch is latching, so it will retain its operational state during a loss of electrical power. An internal microcontroller ensures that a switch does not revert to the opposite state on a power-up, and it will only switch if the alternate fiber is known to be good. An A/B switch can provide additional value in an optical network when it features a manual switch on the front panel that allows the user to force the optical switch to either the A or B position or that allows the switch to operate automatically by monitoring the input fibers.

Splitters also can be added to the frame to segregate part of the optical signal, enabling nonintrusive testing and monitoring or transmission to multiple subscriber locations (see Fig. 2). Splitters are a very common network device and can offer a variety of split ratios. By integrating splitter modules and crossconnecting them into the fiber frame, the user can monitor fiber signals in the central office. For monitoring purposes, the splitter will send a small portion of the signal to monitoring ports, which analyze the signal on a nonintrusive basis.

As subscriber demand continues to increase, network loads inevitably will do the same. As a result, fiber runs at certain frequencies may reach their peak capacity. One obvious way to increase the bandwidth of the fiber system is to run more fiber, but with demanding customers waiting for service, adding more runs is not a time-sensitive option. Running new fiber also is quite cost-prohibitive and, in some instances, logistically impossible.

As an alternative, service providers can simply install a wdm or dwdm system in the frame. A wdm system transmits a second set of signals through the fiber at a different frequency, effectively doubling the capacity of the run. Broadband wdm uses 2-channel wavelength-division multiplexing and demultiplexing to accomplish this capacity increase. Two-channel broadband wdm systems operating at 1310 and 1550 nm have been in use for almost a decade. Most long-haul and interexchange service providers have implemented two-channel upgrades already, but they still require more bandwidth. In broadband wdm systems, the channel spacing is typically 240 nm. These components are equivalent to adding multiple traffic lanes to the highway, without increasing the width of the road.

dwdm systems further increase capacity by allowing many more independent wavelengths to operate over the existing fiber infrastructure. Four, eight, 16, and more independent wavelength channels can quickly be added to dramatically increase information capacity and make the best use of fiber`s large potential bandwidth. In dwdm systems, the channel spacing is typically 1.6 nm or less. As a result of these narrow channels, the laser transmitters for use with dwdms have to operate at specific narrow wavelengths. Due to relatively recent improvements in semiconductor laser technology and wavelength stabilization, suitable lasers for dwdm systems are now readily available.

Continuing the highway analogy, the use of dwdm systems allows providers to add up to 32 or more lanes to existing roads. While this capacity increase is extremely large, it does require everyone to drive much narrower, but available, vehicles.

To be compatible with fiber-optic amplifiers, all of these additional wavelengths in dwdm systems are in the 1530- to 1565-nm wavelength range. This further adds to the benefits of dwdm systems because fiber-optic amplifiers can amplify all the channels at once without the need for optic-to-electric and electric-to-optic conversion of each individual channel. dwdm is clearly the best and most cost-effective option for increasing network capacity for the long term. Again, dwdm systems are just one of many value-added components that can be included in the fiber-frame architecture to create a more feature-packed, efficient service offering from a centrally maintained and managed location.

Connecting with the right fit

All of the additional functionality, service points, and management elements integrated into the centralized fiber-distribution frame are making facility space an ever scarcer commodity. In addition, the development of dwdm and its increased fiber capacity has made high-performance, quality termination points a must. For these reasons, the importance of fiber-optic connectors has increased. Ensuring high performance and handling ever-increasing numbers of fibers have presented network planners and service providers with a critical challenge.

Higher fiber counts require creative solutions to minimize the floor-space cost of the fiber-termination equipment. Past solutions have included adding more terminations to existing hardware. This approach provides higher terminations but reduces fiber cable management. A new breed of connector, half the size of today`s SC connector, replacing two fiber connections with only one, offers an alternative approach. While providing higher-termination density, these small-form-factor connectors also use a smaller-diameter cable. An example of this new breed, called the LX.5 connector, will be introduced at this month`s National Fiber Optic Engineers Conference in Orlando, FL (see Fig. 3). Combining the smaller cable and increased termination density with frames that already provide good cable management will ensure ease-of-use well into the future. Expanded carrying capacity translates to a demand for higher levels of network performance in all system components.

Framework fidelity

The fiber-distribution frame, long treated as a place that fiber simply passes through, should be used as a valuable, centralized location for managing and enhancing fiber-based service. By integrating value-added modules and using new, smaller connectors that maximize fiber-termination density and quality, carriers can solve some of their most pressing problems: lack of facility space and requirements for improved system quality.

With the module strategy, no decision a service provider makes is final. New service features, capacity, or testing capabilities can be added or exchanged by simply unplugging an old module and sliding in a new one. Service providers benefit from the ease of implementation plus the centralized monitoring and visibility afforded by having a complete fiber solution in the frame.

In the highly competitive world of telecommunications, any solution that maximizes system performance capability while reducing operational costs is an advantage. To achieve this advantage, the fiber-distribution frame is the right fit. u

Sandra McWilliams is program manager, fiber-optic products, and Jorge Cano is product manager, fiber-optic products, for adc Telecommunications` Broadband Connectivity Group, Minnetonka, MN. They can be reached at [email protected] and [email protected], respectively.

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