13 Important OTDR Glossary Terms

Optical Time Domain Reflectometer (OTDR)

An optical time domain reflectometer is an optoelectronic device used to detect faults, bends or other similar defects in a length of optical fiber. The OTDR detects such faults by measuring the intensity of light reflected on the fiber and detecting any loss of said light. This device is used to pinpoint damaged areas within the tested length of optical fiber, making it possible to repair problem areas quickly and easily. Testing with an optical time domain reflectometer can take up to three minutes but, conversely, may take as little as ten seconds, depending on the length of fiber tested.

Attenuation Coefficient

Attenuation coefficient refers to the ratio that describes an energy or light beam's decrease in intensity as it passes through a given medium. The coefficient pertains directly to the ease with which the material is penetrated by the beam of energy. A low coefficient indicates that the given medium is close to transparent, while a higher number is indicative of a more opaque material. The attenuation coefficient is often referred to as the linear attenuation coefficient.

Back Scattered Light

Back scatter refers to the reflection of waves or electromagnetic signals from the point at which they originated. Back scattering is used in fiberoptic technology to detect optical faults. The amount of scattering is measured and attenuation is determined using the data collected during this test.

Bend Detection

Bend detection is a method of testing in fiberoptic technology used to detect intrusions, bends or faults in optical fiber. Multiple signals are sent through the fiber at various levels of power in order to notify the user of a decrease in intensity (loss or attenuation).

Central Wavelength

Central wavelength, or CWL, refers to the point between two wavelengths, equidistant from each, wherein transmittance is half of the peak. The distance between the two wavelengths (the midpoint of which is the central wavelength) is termed as the FWHM, or full width at half maximum.

Fiber Link Attenuation

The attenuation of an optical fiber refers to the measurement of the light lost between its initial input and its output. Several issues can cause this loss, including flawed coupling within the fiber, scattering and absorption. Fiber link attenuation serves to limit the distance a signal is able to travel through the fiber before it becomes undetectable.

Fiber To The x (FTTx)

"Fiber To The x" is a collective generic expression that refers to various fiber deployment techniques that are classified by the location at which the fiber ends. The "x" in the acronym is changed to another letter, depending on where the fiber ends in a given situation. In FTTC, or fiber to the curb or cabinet, for example, the fiber most commonly ends approximately 300 yards from the customer's location. In FTTH, or fiber to the home, the fiber terminates at the customer's home or business.

Multimode Fiber

Multimode fiber, usually utilized in communication over short distances, is a type of optical fiber that is manufactured to transmit multiple rays of light (also known as modes) simultaneously. Each mode is carried at a reflection angle slightly different than the ray adjacent to it. In order to accommodate multiple modes at the same time, multimode fiber has a larger core than single-mode fiber.

Optical Density

Optical density, or OD, refers to the blocking specification of a given medium, or filter, and relates specifically to the quality and quantity of electromagnetic energy that is transmitted through it. This is related directly to the attenuation coefficient of a given material. If the value of optical density is high, this is indicative of a low level of transmission. The converse is also true: low optical density value indicates a higher level of transmission.

Propagation Constant

In fiber optics, the propagation constant measures the change in a wave of energy as it is generated and propagates in a specific direction. The quantity of the measured constant can be either current or voltage in a given electromagnetic field.

Single-Mode Fiber

Single-mode fiber, most commonly used in fiberoptic communication over long distances, is a type of optical fiber that is designed to transmit a single ray of light (or mode) at one time. Characterized by its ability to transmit a ray of light with less modal dispersion than multimode fiber, single-mode fiber is capable of preserving the integrity and purity of a light pulse over more lengthy distances.

Wavelength Division Multiplexing (WDM)

In the field of fiberoptic communication, wavelength division multiplexing (abbreviated as WDM) is a type of technology that uses multiplexing to combine multiple data signals onto one optical fiber via the use of different laser light wavelengths. Multiplexing refers specifically to the combining of more than one signal or data stream into a single signal through a shared medium. Wavelength division multiplexing is used to make bidirectional communication possible using a single fiber.