Optical module transmission distance

Analysis of the transmission distance of the optical module, the optical module used with the single-mode fiber has a long transmission distance. The optical module used with multimode optical fiber has short transmission distance. Let's take a look at the calculation method of the transmission distance of the optical module.

Optical module transmission distance

Optical power unit conversion

Mastering the conversion method of optical power units is the basis for calculating the transmission distance of optical modules. Only after mastering this knowledge point can we continue to discuss.

The so-called optical power refers to the work done by light in unit time. The power we often see in the specifications of optical modules refers to optical power. Optical power units are often expressed in milliwatts (mw) and decibels in milliwatts (dBm). The conversion relationship between the two is: 0dBm=1mw. The decibel milliwatt less than 1mw is a negative value.

There are two simple formulas for the conversion between the two:

Premise: 0dBm=1mw

Formula 1: Add 10 to the left = multiply 10 to the right

So 0+10dBm=1 X 10mw ie 10dBm=10mw

How many milliwatts is 20dBm?

The calculation method is: 0+10dBm+10dBm=1 X 10mw X 10mw⇒20dBm=100mw

So 30dBm=1000mw(1w) 40dBM=10w

-50dBm=0dBm-10-10-10-10-10=1mw/10/10/10/10/10=0.00001mw

Formula 2: Add 3 to the left = multiply 2 to the right

3dBm=2mw

How many milliwatts is 9dBm?

The calculation method is: 0+3dBm+3dBm+3dBm=1 X 2mw X 2mw X 2mw⇒9dBm=8mw

So 40+3dBM=10*2w, that is, 43dBm=20w.

The above two formulas are conversion rules summarized by scientists, which are very practical.

Calculation method of fiber loss

During the transmission process, light enters from one end of the optical fiber and then emits from the other end. During the entire transmission process, optical fiber loss, that is, optical fiber attenuation, will inevitably occur. Factors affecting fiber loss can be divided into fiber internal loss and fiber external loss. The specific principles have been studied in previous articles, so I won’t go into details here. The calculation method of fiber loss can be calculated by means of fiber attenuation spectrum.

Single-mode fiber and multimode fiber cause different losses in different wavelength ranges. Single-mode fiber and G1 multimode fiber have lower fiber loss in the wavelength range of 1300nm and 1500nm. Multimode fiber has low fiber loss in the wavelength range of 850nm. Therefore, the working wavelength of most single-mode fiber optic modules is around 1300nm, and the working wavelength of multimode fiber optic modules is around 850nm. In general, in the same wavelength band, the loss of single-mode fiber is lower than that of multi-mode fiber. This also explains why the optical module used with single-mode fiber has a longer transmission distance.

Calculation of working distance of optical module

When the optical module is connected to the optical fiber, it needs to receive the light transmitted by the optical fiber. Understand the problem that light will cause attenuation during transmission. So whether the attenuated light energy can be received by the optical module? It becomes the key to restrict the working distance of the optical module. At this time, the calculation principle of the working distance of the optical module has surfaced. We take the power of the incoming light minus the power loss during optical fiber transmission to get the output power at the output end, and then compare this power value with the minimum acceptable power in the optical module specification to calculate the optical module effective transmission distance.