hardware. Extremely sharp kinks or bends increase the fiber loss and may lead to fiber breakage.

FIBER-OPTIC MEASUREMENTS

Fiber-optic data links operate reliably if fiber-optic component manufacturers and you perform the necessary laboratory and field measurements. Manu- facturers must test how component designs, material properties, and fabrication techniques affect the performance of fiber-optic components. These tests can be categorized as design tests or quality control tests. Design tests are conducted during the develop- ment of a component. Design tests characterize the performance of the component (optical, mechanical, and environmental) in the intended application. Once the performance of the component is characterized, the manufacturer generally only conducts quality control tests. Quality control tests verify that the parts pro- duced are the same as the parts the design tests were conducted on. When manufacturers ship fiber-optic components, they provide quality control data detail- ing the results of measurements performed during or after fabrication of the component.

You, as the installer, should measure some of these parameters upon receipt before installing the component into the fiber-optic data link. These tests determine if the component has been damaged in the shipping process. In addition, you should measure some component parameters after installing or repair- ing fiber-optic components in the field. The values obtained can be compared to the system installation specifications. These measurements determine if the installation or repair process has degraded per- formance of the component and will affect data link operation.

FIELD MEASUREMENTS

Field measurements measure the transmission properties of installed fiber-optic components. You must perform field measurements to evaluate those properties most likely affected by the installation or repair of fiber-optic components or systems.

The discussion on field measurements is limited to optical fiber and optical connection properties. Optical fiber and optical connection field measurements evaluate only the transmission properties affected by component or system installation or repair. Because optical fiber geometrical properties, such as core and cladding diameter and numerical aperture, are not expected to change, there is no need to remeasure these properties. The optical connection properties that are likely to change are connection insertion loss and reflectance and return loss.

Field measurements require rugged, portable test equipment, unlike the sophisticated test equipment used in the laboratory. Field test equipment must pro- vide accurate measurements in extreme environmental conditions. Since electrical power sources may not always be available in the field, test equipment should allow battery operation. In addition, while both fiber ends are available for conducting laboratory measurements, only one fiber end may be readily available for field measurements. Even if both fiber ends are available for field measurements, the fiber ends are normally located some distance apart, thereby requiring two people to perform the measurements.

The main field measurement technique involves optical time domain reflectometry. An optical time domain reflectometer (OTDR) is recommended for conducting field measurements on installed optical fibers or links of 50 meters or more in length. An OTDR requires access to only one fiber end. An OTDR measures the attenuation of installed optical fibers as a function of length. It also identifies and evaluates optical connection losses along a cable link and locates any fiber breaks or faults.

Users also can measure fiber attenuation and cable plant transmission loss, using an optical power meter and a stabilized light source. Use this measurement technique when optical time domain reflectometry is not recommended. Measurements obtained with a stabilized light source and power meter are more accu- rate than those obtained with an OTDR. Measuring fiber attenuation and transmission loss using a power meter and light source requires access to both ends of the fiber or link. An optical loss test set (OLTS) combines the power meter and source functions into one physical unit.

OPTICAL TIME DOMAIN REFLECTOMETRY

You use optical time domain reflectometry to characterize optical fiber and optical connection pro- perties in the field. In optical time domain reflectometry, an OTDR transmits an optical pulse through an installed optical fiber. The OTDR measures the fraction of light that is reflected back. When you compare the amount of light scattered back at different times, the OTDR can determine fiber and connection losses, When several fibers are connected to form an