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How to choose the right cable

March 23, 2022

1. Optical fiber classification

Optical fibers can be divided into single-mode and multi-mode according to the transmission mode of light in them. The core diameter of the multi-mode fiber is 50 or 62.5 μm, and the outer diameter of the cladding is 125 μm, which is denoted as 50/125 μm or 62.5/125 μm. The core diameter of the single-mode fiber is 9 μm, and the outer diameter of the cladding is 125μm, which is expressed as 9/125 μm.

The optical fibers work at short wavelengths of 850 nm, long wavelengths of 1,310 nm and 1,550 nm. Optical fiber loss is generally decreased with the increase of wavelength, 850 nm loss is generally 2.5dB/km, 1.31μm loss is generally 0.35 dB/km, 1.55 μm loss is generally 0.20 dB/km, this is the lowest loss of optical fiber, wavelength 1.65 μm above the loss tends to increase. Due to the absorption of OHˉ (water peak), there are loss peaks in the ranges of 900 ~ 1300 nm and 1340 nm ~ 1520 nm, which could not be fully utilized.


2, single/multi-mode cable

Single-mode fiber transmits only the main mode, that is, the light is transmitted only along the axis of the fiber, completely avoiding dispersion and waste of light energy. In addition, single-mode laser with wavelength of 1310nm or 1550nm is generally used, which is close to the minimum attenuation wavelength of quartz of 1550nm. The transmission distance is shown in Table 3.

Multi Mode Fiber -- multiple modes of light can be transmitted simultaneously. Multi-mode optical fiber transmits the main mode or multiple other modes, and the light will constantly reflect along the edge wall of the fiber, resulting in a lot of dispersion and waste of light energy. The dispersion between the modes is large, which limits the frequency of digital signal transmission and becomes more serious with the increase of the distance. See Table 1 and Table 2 for the transmission distance.

In the high-speed network, in the 10Gb/ S system with 850nm VCSEL as the light source, OM3 fiber can transmit 300m, and OM4 fiber can transmit 550m. The transmission distance of hundreds of meters makes OM3/OM4 multimode fiber widely used in data centers, local area networks, high-performance computing centers and storage area networks. IEEE has proposed parallel solutions for 40Gb/s and 100Gb/s networks using OM3/OM4 multimode fiber.

The parallel system using OM3 fiber can transmit 100m at 40Gb/s and 100Gb/s. Parallel system with OM4 fiber can transmit 150m at 40Gb/s and 100Gb/s. The connection length of 85% data centers will not exceed 100m, and almost 100% will not exceed 150M.

Why can't OM3/OM4 multimode fiber support the same connection lengths in 40Gb/s and 100Gb/s systems as it does in 10Gb/s systems? This is because the VCSEL specification has been relaxed on 40Gb/s and 100Gb/s connections. In order to reduce the system cost, ieee 802.3BA standard relaxed the laser spectrum width requirement, but at the same time paid the price of reducing the system connection length.

Therefore, if you want to choose multi-mode cable should be considered from the following points:

A. In terms of the future development trend, the horizontal wiring network rate needs 1 Gb/s bandwidth to desktop, the backbone network of the building needs to be upgraded to 10 Gb/s bandwidth, and the backbone network of the park needs to be upgraded to 10 Gb/s or 100Gb/s bandwidth. At present, the network application is growing at the rate of about 50% per year. It is expected that gigabit to desktop in the next 5 years will become as common as the current gigabit to desktop. Therefore, it is necessary to have certain foresight on the current system planning, six types of wiring should be considered in the horizontal part, and ten gigabit multi-mode cable should be considered in the main part. Especially now six types of copper cable plus 10 million multi-mode cable and super five types of copper cable plus 10 million multi-mode cable cost of about 10~20% difference, from the perspective of long-term application, such as cost should be considered using six types of copper cable plus 10 million cable.

B. From the perspective of investment, where 10G will not be used in at least 10 years, Wofeng OM1 (ordinary multimode 62.5/125) shall be selected; Because OM3 optical cable uses low-cost VCSEL and 850nm light source equipment, the cost of 10 gigabit transmission is greatly reduced.


3, Our suggestions for the selection of single-mode cable are as follows:

A. From the perspective of transmission distance, if you want to support 10 gigabit transmission in the future, and the distance is far should consider the use of single-mode cable.

B. In terms of cost, zero-water peak fiber provides 50% more bandwidth than single-mode fiber, but the cost is similar.

Conclusion: Single-mode or multi-mode?

Based on the above analysis, we believe that users should from the perspective of application, transmission distance, forward-looking perspective, cost of the above factors, the lowest price to invest in the best performance!