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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, 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 such as a NIST 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. Sometimes optical power meters are combined with a different test function such as an Optical Light Source (OLS) or Visual Fault Locator (VFL), or may be a sub-system in a much larger instrument. When combined with a light source, the instrument is usually called an Optical Loss Test Set. Optical Loss Test Sets (OLTS) are available in dedicated hand held instruments and platform-based modules to suit various network architectures and test requirements. They are used to measure optical power and power loss, and reflectance and reflected power loss. The products may also be used as optical sources or optical power meters, or to measure optical return loss or event reflectance. Three types of equipment can be used to measure optical power loss: #''Component equipment'' - Optical Power Meters (OPMs) and Stabilized Light Sources (SLSs) are packaged separately, but when used together they can provide a measurement of end-to-end optical attenuation over an optical path. Such component equipment can also be used for other measurements. #''Integrated test set'' - When an SLS and OPM are packaged in one unit, it is called an integrated test set. Traditionally, an integrated test set is usually called an OLTS. (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. #An ''Optical Time Domain Reflectometer (OTDR)'' can be used to measure optical link loss if its markers are set at the terminus points for which the fiber loss is desired. The accuracy of such a measurement can be increased if the measurement is made as a bidirectional average of the fiber. (GR-196, ) ''Generic Requirements for Optical Time Domain Reflectometer (OTDR) Type Equipment'', discusses OTDR equipment in depth. == Sensors == The major semiconductor sensor types are Silicon (Si), Germanium (Ge) and Indium Gallium Arsenide (InGaAs). Additionally, these may be used with attenuating elements for high optical power testing, or wavelength selective elements so they only respond to particular wavelengths. These all operate in a similar type of circuit, however in addition to their basic wavelength response characteristics, each one has some other particular characteristics: * Si detectors tend to saturate at relatively low power levels, and they are only useful in the visible and 850 nm bands. * Ge detectors saturate at the highest power levels, but have poor low power performance, poor general linearity over the entire power range, and are generally temperature sensitive. They are only marginally accurate for "1550 nm" testing, due to a combination of temperature and wavelength affecting responsivity at e.g. 1580 nm, however they provide useful performance over the commonly used 850 / 1300 / 1550 nm wavelength bands, so they are extensively deployed where lower accuracy is acceptable. Other limitations include: non-linearity at low power levels, and poor responsivity uniformity across the detector area. * InGaAs detectors saturate at intermediate levels. They offer generally good performance, but are often very wavelength sensitive around 850 nm. So they are largely used for singlemode fiber testing at 1270 - 1650 nm. An important part of an optical power meter sensor, is the fiber optic connector interface. Careful optical design is required to avoid significant accuracy problems when used with the wide variety of fiber types and connectors typically encountered. Another important component, is the sensor input amplifier. This needs very careful design to avoid significant performance degradation over a wide range of conditions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Optical power meter」の詳細全文を読む スポンサード リンク
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