Classification and Usage of Optical Modules

Optical module, as an important part of fiber optic communication, is an optoelectronic device that realizes the functions of photoelectric conversion and electro-optical conversion in the process of optical signal transmission. The main key parameters of the optical module are transmission rate, package form, working wavelength, transmission distance, and working temperature, etc.

1. Classification of Optical Modules

1.1 Package Form

Optical modules are divided into the following common types according to the package form: SFP, SFP+, SFP28, QSFP+, QSFP28, and QSFP-DD.

• The SFP optical module is an upgraded version of GBIC with a maximum rate of 4.25G, characterized by small size and hot-swappable.
• The SFP+ optical module is an enhanced version of the SFP with a transmission rate of 10Gbps for 8.5G Fiber Channel and 10G Ethernet applications.
• The SFP28 optical module has a transmission rate of 25Gbps, and it has the advantages of lower power consumption, higher port density, and hot-swappable support.
• The QSFP+ optical module has a transmission rate of 40Gbps, supports MPO fiber connectors and LC fiber connectors, features a small size, and is hot-pluggable.
• The QSFP28 optical module uses four 25Gbit/s channels in parallel with a transmission rate of 100Gbps to meet 100G Ethernet applications.
• The QSFP-DD optical module has rates of 200Gbps and 400Gbps.

1.2 Transmission Rate

The common transmission rates are 1Gb/s, 10Gb/s, 25Gb/s, 40Gb/s, 100Gb/s and 400Gb/s. According to the different transmission rates, the optical modules can be categorized into 1G optical modules, 10G optical modules, 25 optical modules, 40G optical modules, 100G optical modules, 400G optical modules and so on.

1.3 Transmission Distance

According to the transmission distance, optical modules can be divided into short distance, medium distance, and long distance, the transmission distance of short-distance optical modules is 2km and below, the transmission distance of medium-distance optical modules is between 10-20km, while the long-distance optical modules is more than 30km.

1.4 Transmission Mode

Optical modules can be categorized into three types: simplex optical modules, half-duplex optical modules, and full-duplex optical modules according to the supported data transmission methods. A simplex optical module only supports data transmission in the same direction, such as the TV station can send signals to the audience, but the audience cannot send signals to the TV station; a half-duplex optical module supports data transmission in both directions but does not support data transmission in both directions at the same time, such as walkie-talkies can support each other to talk, but does not support simultaneous speech; full-duplex optical module supports data transmission in both directions at the same time Full-duplex optical modules support data transmission in both directions at the same time, such as cell phones can support both sides to talk at the same time.

1.5 Center Wavelength

According to the center wavelength, the different optical modules can be divided into ordinary optical modules and color optical modules. The center wavelengths of ordinary optical modules are 850nm, 1310nm, and 1550nm, while the center wavelengths of color optical modules are CWDM wavelengths and DWDM wavelengths, of which the CWDM wavelengths range from 1270 to 1610nm, and the DWDM wavelengths range from 1525 to 1565nm or 1570 to 1610nm.

2. How to select the right optical module?

There are many types of optical modules on the market with varying quality. If you choose an inappropriate optical module, it will result in network delay, network instability, and other problems. Therefore, it’s vital to choose the appropriate optical module. When purchasing optical modules, the following points are the key factors to consider.

2.1 Transmission Distance

The transmission distance supported by different optical modules is different. The transmission distance of multi-mode optical modules is much shorter and cheaper than that of single-mode optical modules.

2.2 Transmission Modes

Optical modules have three main data transmission modes: simplex, half-duplex, and full duplex. Simplex transmission supports data transmission in one direction only; half-duplex transmission allows data transmission in both directions, but only in one direction at a certain moment; and full-duplex transmission allows data to be transmitted in both directions at the same time. It is best to choose an optical module that supports full-duplex transmission.

2.3 Transmission Media

Copper and fiber optic cables are currently the two most widely used transmission media, so some optical modules are designed with electrical ports, and some optical modules are designed with optical ports. Generally speaking, optical-port optical modules are commonly used in 10G and 40G Ethernet transmission applications, while electrical-port optical modules are used in 100 Gigabit and Gigabit Ethernet applications, and the transmission distance of optical-port optical modules is generally farther than that of electrical-port optical modules.

2.4 Heat Resistance

The working environment temperature of the optical module should not be too high, if it exceeds the temperature that the optical module can withstand, it is likely to have link failure. Therefore, the heat-resistant optical module should be selected.

2.5 Compatibility

Optical module equipment manufacturers will have their equipment to varying degrees of encryption, which is what we call compatibility. Their brand of modules can only be used in their equipment above, other brands of optical modules cannot match their equipment. Compatibility vendors need to adapt different compatibility on the optical module, it is particularly important to be able to perfectly solve the adaptation problem.

2.6 Price

Now more and more suppliers are limited to choosing compatible optical modules, the quality of which can be fully comparable to the original optical module, but the price is very competitive, which can help save a lot of cost.

The above points are the mostly consider factors when choosing optical modules. In addition, you also need to consider the operating wavelength, operating rate after-sales service, and so on.

3. Instruction for the use of optical modules

The correct installation of optical modules is very important, which directly affects the performance of the communication system. The following are the steps and precautions for the installation of optical modules:

3.1 Electrostatic Discharge (ESD) protection measure

Whether indoors or outdoors, ESD protection measures must be taken when using optical modules. Make sure to wear antistatic gloves or antistatic bracelets, and then touch the optical module with your hands.

3.2 Pick-and-place operation

It is strictly prohibited to touch the gold finger of the optical module when picking up the optical module. It must be held gently to prevent the optical module from being pressed and knocked. If the optical module is accidentally bumped when picking up and placing, it is recommended that the optical module is no longer used.

3.3 Plugging and unplugging methods

• Press the optical module down firmly until it locks into place with a slight vibration or a "pop" sound.
• Close the puller ring after insertion.
• Pull gently on the puller ring to confirm the optical module is securely installed at the bottom if it doesn't come out.

3.4 Installation or removal of fiber optic patch cords:

• Fix the pull ring of the module before inserting the fiber optic patch cord.
• Use a dust cap when the fiber optic patch cord is not in use to prevent contamination during docking.
• Insert the fiber optic patch cord into the optical module.

3.5 Faulty optical module cleaning

If optical modules or fiber optic cables have not been used for a long time and do not have dust caps, they must be cleaned before reuse. Optical modules are cleaned using cotton swabs, while fiber optic ports are cleaned using fiber polishing paper.

Through this article, we've gained a richer comprehension of the classification and practical applications of optical modules.

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