Optical power meter (OPM) is a device used to measure the absolute optical power or the relative length of optical fiber optical power loss in fiber optic systems, similar to the multimeter of electronics. By measuring the optical network transmitter or absolute power, a power meter will be able to evaluate the performance of the light side of the device. In addition, connection loss and continuity can be measured and tested as well as helping to evaluate the quality of the fiber transmission link. A typical optical power meter consists of a calibrated sensor by using a combination of OPM and the steady laser source. A traditional optical power meter responds to a broad spectrum of light, however the calibration is wavelength dependent.
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. Some 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.
Units of the optical power is dbm, the specification of the fiber transceiver or switch the light emitting and receiving optical power, typically light emitting less than 0dbm minimum optical power that can be received by the receiving end is called sensitivity, is able to receive the maximum optical power lessto the sensitivity value of the unit is db (dbm-dbm = db), called dynamic range, the light-emitting power subtracting the receiving sensitivity is permissible fiber attenuation values of the test the actual light emitting power by subtracting the actual received optical powervalue of fiber attenuation (db), the receiver receives the optimum value of the optical power is the maximum optical power that can be received – (dynamic range / 2), but generally not so good due to each of the optical transceiver and the optical modulethe dynamic range is not the same, so the fiber concrete to allow attenuation of the number depends on the actual situation. Generally allowed attenuation is about 15-30dB.
Some manual, only the light emitting power and the transmission distance of the two parameters, and sometimes the attenuation per km of optical fiber transmission distance calculated, mostly 0.5dB/km minimum transmission distance is divided by 0.5, which is able to receive a maximum lightpower, if the received optical power is higher than this value, the optical transceiver may be burned. with maximum transmission distance is divided by 0.5, is the sensitivity, if the received optical power is lower than this value, the link may be unreasonable.
There are two ways for fiber connection. One is fixed connection and the other is active connection. Fixed connection is welding, using special equipment to discharge and melt the optical fiber together. The advantage is low attenuation while disadvantage is inflexible and complicated operation. The other way is active connection. Active connection connect fiber pigtail through connector, usually on ODF. The advantage is simple and flexible operation and disadvantage is high attenuation. Generally speaking, an active connection is equivalent to one kilometer optical fiber attenuation. Fiber attenuation could be evaluated in this way, including fixed and active connection, will attenuate 0.5db optical power per kilometer. If the active connection is very few, the value could be 0.4db. pure fiber doesn’t include active connection, so the value could reduce to 0.3db. the theoretical value of pure fiber is 0.2db/km; for insurance in most case the value is 0.5db.