When screening reduction inside a fibers optic link, some fundamental principles should be kept in thoughts all the time.

1.The screening wavelength must usually be identical as the functioning wavelength. Because optical fibers reduction varies with mild wavelength, you will get incorrect result if your measuring wavelength is different from the specific functioning wavelength. For example, if a system is developed for 1550nm but you test it with 1310nm mild resource and power meter, the result will not be correct.

2.The screening mild resource must be identical as the intended functioning lightwave equipment mild source. If the system is developed for a LED source, Optical coupler you must test it with a LED source. If the system is developed for multimode laser light, you must use a multimode laser mild resource for testing. This is also true for one mode laser mild source.

Fiber optic equipment utilized inside a reduction testing

In a fundamental reduction screening setup, four sorts of test equipment are needed. They are the mild source, the power meter, the reference patch cables and the adapter (mating sleeve).

Here are some considerations when choosing your equipment.

The mild resource must have identical wavelength as the working equipment, proper mode (multimode or one mode, must be same as the working equipment), sort (LED or laser, same as the working equipment) and proper connector.

The power meter must have identical wavelength as the mild source, proper connector and calibrated.

The reference patch cables must be top quality with know loss Optical coupler , proper connectors and be identical sort as the fibers plant being tested.

The adapter (mating sleeve) must be with top quality ceramic sleeves and be proper sort (FC, SC, LC, etc).

Understanding dB (decibel) in fibers optic reduction testing

As in any power measurement, fibers optic mild power measurement unit can be expressed in milliwatt (mW), but a more handy unit is dB(decibel).

Decibel (dB) is most often utilized in electronics testing. It is the ratio in between two levels. One degree is the input and the other degree is the output. The ratio is calculated in logarithmic as explained below.

For power measurement, dB is defined as: dB = ten x log(output power/input power)

So for example, after a fibers link, the output mild power degree gets 50% of its input, the reduction on the link will be 10log(0.5)= -3 dB.

Since dB is really a ratio, it has no absolute units. So from above measurement sample, we have no concept on the specific power, may it be 0.1 mW or 1 mW.

That is why we have an additional unit dBm. It is the ratio on the measured power to 1mW of reference power. It is defined as: dBm = 10xlog(measured power/1mW)

So for example, a 0.1mW mild power expressed in dBm will be 10xlog(0.1mW/1mW)=-10 dBm.

From above we know that dBm is a absolute unit, we know specifically how numerous mW it is.