14 Important Optical Power Meter Glossary Terms

Optical Power Meter

A device used to measure the strength of a fiberoptic signal. Optical power meters are often used during fiberoptic installations to ensure that a cable system doesn't exceed its loss budget, at which point the signal from the transmitter would be too weak to use. An optical power meter can also be used to monitor interference and to check cables and transmitters.

Calibration Wavelengths

The colors of light used to set an optical power meter for single mode or multimode fibers. Wavelengths are typically referred to in nanometers, commonly abbreviated as nm, or in microns, abbreviated as m. Most optical power meters have multiple calibration wavelength settings including 850nm, 1310nm and 1550nm. Meters with multiple calibration wavelengths can be used to test different types of light sources.

Coherence Length

The maximum length at which a light source has not exceeded its loss budget. The longer a coherence length, the further the distance from a light source to its fringe visibility. The coherence length of light can be tested with a Michelson interferometer.

Detector head

Photodiodes used by optical power meters to convert an optical signal to a measurable electrical signal. Some "smart" detector heads have built-in microcontrollers for improved accuracy.

Dynamic Range

The range of wavelengths that an optical power meter is capable of accurately reading. A wider dynamic range is generally preferable, as this allows an optical power meter to test a broader spectrum.

Michelson Interferometer

A device for testing the coherence length of light and to split and combine beams of light. Michelson interferometers split a single beam of light into two separate beams, which are then recombined into a composite beam.

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.

Power Range

The range of power readings that an optical power meter is capable of accurately measuring. Most optical power meters have a power range of around 1 milli Watt to 10 nano Watt. Power range is sometimes measured in decibels.

Power Uncertainty

The difference in readings between optical power meters meters and NIST standards due to calibration differences, fiber movement, temperature and various other factors. Power uncertainty can account for a difference in readings between two optical power meters.

Return Loss

A measurement in decibels of signal lost in the transmission of an optical signal between two devices, usually through interference in a fiberoptic line. A high return loss is better than a low return loss, as a high return loss indicates that an acceptable amount of a signal has been transmitted from one device to another. Also known as a reflection loss.


Semiconductors used in an optical power meter to provide readings. Many handheld optical power meters use germanium, gallium arsenide and/or silicon as sensors to provide measurements at different power levels. For instance, silicon is only useful at wavelengths of 850 nm and under. Germanium sensors can be useful for higher power levels but are less sensitive, while gallium arsenide sensors provide dependable readings for single mode fibers. The sensors used in an optical power meter can greatly affect performance and accuracy.

Single-Mode Fiber

Single-mode fiber, most commonly used in fiber optic 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.

Spectral Ripple

Modulation generally caused by high-energy SLED devices. Spectral ripple affects spectral density curve and can be problematic when measuring, testing and using fiberoptic equipment.

Wavelength Range

A measurement of the wavelengths that can be read by an optical power meter. Most newer optical power meters have a wavelength range of around 800 nm to 1650 nm. A wide wavelength range allows an optical power meter to work with a variety of light sources.