1 、 Principle of optical fiber loss measurement
An optical power meter and light source are used to measure optical fiber or optical fiber equipment loss. The light from the light source is injected into one end of the optical fiber. The received optical power is measured by an optical power meter connected to the other end of the optical fiber. The light source can be a laser or a light-emitting diode (LED) designed as part of the tester or replaced by the light source used in the light wave communication equipment. Because the loss of optical fiber varies with the wavelength of light, the wavelength used by the optical power meter should be the same as that used by the visual communication equipment. If the light wave equipment works at 1310nm wavelength, the light power meter and light source should also be adjusted to 1310nm wavelength for measurement. If the wavelength of lightwave equipment is 1550nm, the soft power meter wavelength and light source should also be adjusted to 1550nm.
2、 Expression of optical power and its loss
1. Expression of optical power
The optical power meter test is used to determine the visual power loss in the optical fiber link. The measurement of optical power is milliwatt (MW), and the more commonly used unit of measure of optical power is DBM. The following describes the conversion relationship between the DBM unit and the MW unit. DBM unit is the logarithm ratio of the measured power to the 1MW reference power
Example:
The optical power of 1MW is equivalent to 0 DBM according to the formula; the visual power of 2MW is equal to 3dbm; the visual power of 5MW is equivalent to 7dBm; the optical power of 10MW is equivalent to 10dBm; the optical power of 0.1MW is identical to the optical power of -10dbm, etc. Examples of the conversion process:
2. Expression of optical power loss
Optical power loss L (optical loss) (DB) is often used to regulate optical fiber's attenuation. Its unit is dB, and the calculation formula is as follows:
For example, determining the optical fiber cable's visual loss in the optical fiber cable takes time and connects the light source to one end of the visual line (input). It is known that the optical output power is 0.1MW. When the optical power meter is connected to the other end of the tested (output) optical cable, the received optical intensity measured by the optical power meter is 0.05mw. Using the above decibel power loss formula, the optical fiber loss can be calculated as follows:
If the optical power is expressed in DBM to following formula can also be used to calculate the visual power loss: as shown in the figure below:
3、 Some supplements to help memory
3dB optical loss is equivalent to 50% optical power loss (LG2 = 0.3); 7dB optical loss is equivalent to 80% optical power loss (lg5 = 0.7); 10dB optical loss is equivalent to 90% optical power loss (LG10 = 1); 20dB optical loss is equivalent to 99% optical power loss (LG100 = 2); 30dB optical loss is equivalent to 99.9% optical power loss (lg1000 = 3).