How to choose 100G 2km optical module?

The transmission distance of 100G optical modules is mainly divided into short distance (2km and below), medium distance (2-10km), and long distance (10km and above). At present, among the three distances, medium distance occupies the main market share.

In the face of so many types of optical modules, what are the similarities of 100G 2km optical modules? What‘s the difference? How to choose?

At present, there are 3 types of 100G medium-distance (2km) optical modules, which are:

100GE QSFP28 PSM4 2km (abbreviated in this article: PSM4)

100GE QSFP28 CWDM4 2km (abbreviated in this article: CWDM4)

100GE QSFP28 CLR4 2km (abbreviated in this article: CLR4)

package

From the name, it is not difficult to see that these four models use the same package: QSFP28.

At present, the mainstream package of 100G mid-distance on the market is QSFP28. The packaged optical module is small in size, low in power consumption, and can achieve higher-density wiring.

It can support 4 channels of transmission at the same time, the data rate of each channel is 25Gbit/s, and the transmission rate of 100Gbps can be achieved through 4 channels. It can meet the application requirements of 100G Ethernet (4×25Gbps) and EDR InfiniBand.

Power consumption

In terms of power consumption, due to the use of QSFP28 packaging, the maximum power consumption of the three optical modules is less than 3.5W.

For the energy cost of the data center, most of the operating costs of the data center can be reduced. Improve your organization‘s profitability by reducing energy and operating costs. The low-power design of 100G medium distance (2km) can bring significant cost savings even if the energy consumption is slightly reduced.

We mainly analyze the difference between 100G medium distance (2km) from the following points: transmission mode, application scenarios, price and other aspects.

Transfer method

100GE QSFP28 PSM4 adopts MPO12 optical port because it adopts PSM4 (4-channel parallel) transmission technology.

The MPO connector required for this optical port has a 12-core MPO single-mode ferrule. Compared with other interface connectors, the main features are compact design and more jumper cores.

But the disadvantage is also obvious. As the distance increases, the cost of fiber jumpers increases significantly.

In order to solve the problem of the cost of fiber optic patch cords for medium and long distances, both CWDM4 and CLR4 adopt WDM (wavelength division multiplexing) technology, which can effectively reduce the cost of fiber optic patch cords in medium and long distances by transmitting two fibers at one time.

Therefore, the above two optical modules use dual LC interfaces to realize full-duplex signal transmission, realize the transceiver separation of the optical interface, and reduce the complexity of the optical fiber interface.

Application scenarios

In terms of application scenarios, high-speed optical modules generally need to turn on FEC to ensure stable signal transmission, but turning on FEC will increase the delay of signals.

100GE QSFP28 CLR4 can achieve zero-error transmission of 2km or even 10km (bit error rate 1E-12) without turning on the error correction of FEC. Therefore, CLR4 satisfies scenarios such as high-performance computing and high-frequency trading.

In order to ensure the stability of the optical fiber transmission system, PSM4 and CWDM4 must be used in the optical fiber link with the previous error correction (FEC) function.

Cost

In terms of cost, since the PSM4 internal optical devices only need to use conventional DFB lasers, the price of 100G medium distance (2km) products is relatively cheap.

However, CWDM4 and CLR4 use more expensive WDM DFB lasers, so they are a little more expensive in terms of cost.

Among them, CLR4 is more expensive because of its excellent performance, it can transmit 2km signal without turning on FEC, and it can also be used in ultra-performance computing scenarios.