An Optical Loss Test Set (OLTS) is an instrument used to verify the performance and quality of fiber-optic networks across various applications and industries. It plays a fundamental role in field testing, often being employed more frequently than other tools such as the Optical Time Domain Reflectometer (OTDR). This preference stems from the fact that an OLTS performs what is known as Tier 1 testing, a mandatory step in fiber certification, whereas OTDRs conduct Tier 2 tests, which are not always required. Typically, Tier 1 testing with an OLTS must be completed before any Tier 2 testing is undertaken. The Tier 1 test measures critical parameters like insertion loss, cable length, and polarity, all of which can be efficiently performed by a technician using an OLTS.
Primary Functions of an OLTS
The core purpose of an OLTS is to provide the most accurate measurement of a fiber link’s total insertion loss. This is achieved by placing a stable light source at one end of the link and a calibrated optical power meter at the opposite end. The power meter precisely measures the amount of light arriving after traveling through the fiber. This method is mandated by key industry standards, which refer to this procedure as Tier 1 testing. By conducting this test, technicians can assess the overall health of a fiber-optic network. It reveals the cumulative loss introduced by connectors, splices, and the fiber itself, helping to evaluate network efficiency and identify potential performance issues.
How OLTS Testing Works
An OLTS test involves a light source that emits a continuous light signal at specific wavelengths into one end of the fiber. At the far end, the power meter’s detector measures the optical power at those same wavelengths. By comparing the power transmitted with the power received, the total light lost (insertion loss) over the link is determined. Industry standards define strict insertion loss limits for different fiber types and applications. The result from an OLTS is compared against these limits to determine if the link passes or fails. While basic light source and power meter combinations can measure loss, a dedicated OLTS integrates additional features that streamline testing. These include capabilities for duplex testing, pre-programmed loss limits, bidirectional operation, and integrated length measurement. The length measurement feature is particularly important because performance limits for a link are often based on both a maximum length and a total loss budget.
Industry Applications
OLTS equipment is utilized in numerous industries that rely on fiber-optic infrastructure. It is a staple in telecommunications for maintaining the networks that carry data, voice, and video signals. Within data centers, where high-speed connectivity is critical, OLTS is used to ensure fiber links are operating optimally. Enterprise networks, industrial automation systems, and research facilities also employ OLTS to monitor performance and ensure reliable, uninterrupted service delivery across their extensive fiber installations.
Benefits and Considerations
The principal advantage of using an OLTS is its accuracy in determining a fiber link’s total end-to-end loss, which is the primary criterion for standards-based certification. Additionally, it can measure the link’s length and, in some configurations, optical return loss. This data is invaluable for verifying installation quality and pinpointing segments that may degrade network performance.
One operational consideration is that the standard OLTS test requires access to both ends of the fiber link, often necessitating two technicians for efficient operation. This can pose a logistical challenge in situations with limited personnel, though the accuracy gained from dual-ended testing is generally considered worth the effort. It is also important to recognize the scope of an OLTS. It is designed for Tier 1 certification—measuring total loss—but it cannot identify the precise location of a fault within the cable. Locating specific faults, such as a poor splice or a bend, requires Tier 2 testing with an OTDR, which analyzes backscattered light to map the fiber and isolate events. Thus, OLTS and OTDR are complementary tools in a complete fiber characterization strategy.
