Global InformationOptical power meter information
An optical power meter (OPM) is a device used to measure the power in an optical signal. The term usually refers to a device for testing average power in fiber optic systems. Other general purpose light power measuring devices are usually called radiometers, photometers, laser power meters (can be photodiode sensors or thermopile laser sensors), light meters or lux meters.
A typical optical power meter consists of a calibrated sensor, measuring amplifier and display. The sensor primarily consists of a photodiode selected for the appropriate range of wavelengths and power levels. On the display unit, the measured optical power and set wavelength is displayed. Power meters are calibrated using a traceable calibration standard.
A traditional optical power meter responds to a broad spectrum of light, however, the calibration is wavelength dependent. This is not normally an issue, since the test wavelength is usually known, however, it has a couple of drawbacks. Firstly, the user must set the meter to the correct test wavelength, and secondly, if there are other spurious wavelengths present, then wrong readings will result.
Optical power meters are available as stand-alone bench or handheld instruments or combined with other test functions such as an Optical Light Source (OLS), Visual Fault Locator (VFL), or as sub-system in a larger or modular instrument. Commonly, a power meter on its own is used to measure absolute optical power, or used with a matched light source to measure loss.
When combined with a light source, the instrument is called an Optical Loss Test Set, or OLTS, typically used to measure optical power and end-to-end optical loss. More advanced OLTS may incorporate two or more power meters, and so can measure Optical Return Loss. GR-198, Generic Requirements for Hand-Held Stabilized Light Sources, Optical Power Meters, Reflectance Meters, and Optical Loss Test Sets, discusses OLTS equipment in depth.
Alternatively, an Optical Time Domain Reflectometer (OTDR) can measure optical link loss if its markers are set at the terminus points for which the fiber loss is desired. However, this is an indirect measurement. A single-direction measurement may quite inaccurate if there are multiple fibers in a link, since the back-scatter coefficient is variable between fibers. Accuracy can be increased if a bidirectional average is made. GR-196, Generic Requirements for Optical Time Domain Reflectometer (OTDR) Type Equipment, discusses OTDR equipment in depth.