Optical time-domain reflectometers (OTDRs) are used on fiber-optic installations to measure the accuracy of fusion splices and locate breaks or damage to optical fibers. As its name implies, an OTDR performs optical-fiber evaluation in the time domain, which translates to distance, when the speed of the light inside the fiber is known. By using a trace--that is, sending a lightwave and measuring a return signal in much the same way that radar sends an RF pulse and measures the return--an OTDR can produce an array of measurement information, including fiber attenuation, splice and connector loss, reflectance, fiber length, and break location.
Every fiber-optic cable requires testing to ensure the transmitted light signal at one end of the fiber is properly propagated to the other end. One important factor to consider when testing a fiber span is the attenuation of the light signal as it propagates through the fiber. Although this measurement can be taken with an optical source and a power meter, this method produces only an overall measurement, with no information about the spatial distribution of the losses.
An OTDR provides additional information such as how well distributed the loss is along the entire span, whether there is unacceptable loss at any given point, or if there is a break in the span and where the break is located. The OTDR provides a signal level versus distance plot, which is useful for calculating individual fault or event location, characterization, loss, reflectance, fiber attenuation, total length, and even optical return loss.
One more benefit of an OTDR is that since it operates like a radar and the transmitter and receiver are found on the same instrument, access to only one end of a fiber span is necessary to test a link.
OTDRs are a large part of a steadily growing market. The improvements made to OTDRs make up the most significant technological trend in the test-equipment space, according to a recent report, U.S. Fiber-Optic Test Equipment Market, published by Frost & Sullivan, a California-based telecommunications market research firm.
The introduction of the mini-OTDR is thought to be the most important product development within the fiber-optic test-equipment industry in recent history. Frost & Sullivan's research indicates the mini-OTDR is being hailed as the "only field instrument that a technician will need." The traditional bench unit requires a trained technician to operate. The mini-OTDR, a portable handheld unit that features simple single-button testing and built-in data analysis, eliminates much of the training associated with the traditional OTDR. These devices are fueling the OTDR market and, in turn, promoting a healthy fiber-optic test-equipment market.
"The fiber-optic test-equipment market is growing at a brisk rate and OTDRs are an indispensable tool in modern fiber implementations," says Shekar Gopalan, a consultant analyst with the test and measurement group at Frost & Sullivan. "A recent study of ours predicts the world market size of OTDRs is expected to be approximately $70 million in 1999, growing steadily over the next five years. The market, comprised of about 20 vendors, is constantly evolving with new equipment being introduced periodically."
That sits pretty well with vendors like Quebec's EXFO Electro Optical Engineering, which attributes market growth to what it calls the "democratization" of the OTDR as a general-purpose tool. The company believes OTDRs will play an increasingly central role in outside-plant testing. Attributes of accessibility and ease-of-operation are spreading the use of OTDRs to every level of the industry.
"There's a new trend toward OTDRs at nontraditional wavelengths, such as 1625 nm for L-band and supervisory channel testing, 1410 nm for testing around the water peak on new fiber technologies, and an interest for many other wavelengths," says Stephane Duquet, product manager for OTDRs in EXFO's outside-plant division. "This trend is being driven by the opening of multiple WDM [wavelength-division multiplexing] windows and the need to investigate them thoroughly. Therefore, today's singlemode OTDR test sets have to be able to handle not only two, but at least three or four different wavelengths."
Duquet also agrees that smaller size is becoming a popular attribute for OTDRs but cautions there are two sides to everything. While basic mini-OTDRs offer good optical performance, there is usually a compromise on features such as memory or software packages to make the product more affordable and simple to use. On the other hand, more-sophisticated OTDRs are offered in compact, modular platforms that can host two or three test modules, including automated loss test sets or optical switches. These higher-end units provide maximum flexibility and upgradability as well as more complex analysis software, including the support of off-the-shelf PC software.
"In the benchtop market, OTDRs are now being sold in completely modular systems that combine multiple OTDRs with other test modules to answer today's manufacturing needs," says Duquet. "For example, multiple OTDR wavelengths enabling the creation of the fiber-attenuation profile. Also, rack-mounted modular systems can be packaged as remote fiber test systems to perform monitoring on the live network."
Features seem to be making the difference in who succeeds in the OTDR vendor market and who loses ground. Desirable features, says Frost & Sullivan's Gopalan, include high accuracy and compatibility with external software applications such as spreadsheets, databases, and statistical-quality programs.
"Other features desirable in an OTDR include gpib/lan [general-purpose interface bus/local-area- network] interfaces, graphical displays, menu-based features, portability, reliability, software control, and even touchscreen controls," says Gopalan. "Additionally, the products must be upgradable and scalable with emerging technologies and measurements. Emerging applications such as WDM and DWDM [dense WDM] call for enhanced capabilities in OTDRs. Increasing WDM and DWDM implementations in telecommunications applications in the next three to five years is expected to fuel the growth of this market. Another driver is the rapidly increasing implementation of fiber-based LAN applications such as packet-over-SONET [Syn chronous Optical Network]."
The OTDR market is becoming highly competitive among about two dozen manufacturers, including several globally strong contenders, including Wavetek Wandel Golter mann (WWG--Eningen, Ger many). WWG predicts a continued demand for optical test platforms with common hardware and software.
"This enables the user to mix and match test configurations according to the application and, more importantly, spread his capital investment over time," says Russell Taws, product manager at WWG. "As network operators and providers look for ways to improve quality-of-service, reduce mean time to repair, and warrant service-level agreements, test solutions with a simple upgrade path from an instrument to a remote fiber test system will be favored."
A competitive market also means a wider variety of needs to fulfill and a broader variety of products offered. Ultimately, that will result in increased choice and quality for the OTDR users. The pressure is on the vendors to offer products that fill the needs of even the most demanding customers.
According to Gopalan, there are several ways for vendors to gain an advantage over the competition. Manufacturers need to establish excellent relationships with clients and develop strategic alliances for joint development of test products to meet client needs. A focus on evolving WDM/DWDM applications will help, especially in the LAN and networking industries' mass markets.
"Active participation in industry forums, such as the Optical Networking Forum and Institute of Electrical and Electronics Engineers stand ards com mittees, is important," says Gop alan. "Companies should strive to develop equipment with open-architecture platforms, preferably modular with software-driven applications that enable the product to be scalable and preserve user investments for a longer period. Lastly, a key requirement is for vendors to offer a high level of applications support to the OTDR user community."
Lastly, as with so many other telecommunications products, manufacturer and distributor relationships are very important. A high level of interaction with clients in the form of demonstrations, presentations, and trials is required to promote confidence and loyalty. In a competitive, ever-evolving OTDR market, the best product may come down to the oldest of market strategies--going that extra mile for the customer.