It’s no exaggeration, there would be no optical communication without optical modules!

Over the past 100 years, human beings have developed from simple telegraph communications to today's 5G communications, and life has undergone tremendous changes. Live broadcasting, VR/AR, ultra-high-definition video conferencing, telemedicine, autonomous driving, and smart homes are becoming more and more widespread. All of these require high-speed data transmission.

Because high-speed signals attenuate rapidly in copper cables and cannot be transmitted over long distances, and because the transmission frequency of light is more than 1,000 times higher than that of radio signals, the transmission rate of information is effectively increased; therefore, optical fiber has gradually become the mainstream transmission medium.

In computers, storage devices, and switches, data is processed and transmitted in the form of electrical signals. So, how do we convert electrical signals into optical signals and enter optical fibers? Or how do we convert optical signals in optical fibers into electrical signals and connect them to communication systems?

Thus, the optical module - the magician of the communication industry, came into being! It realizes the photoelectric conversion.

1. The status of optical modules

Since its birth, optical modules have always had an unshakable status in the industry! The leaders in the communications industry commented:

“Without optical modules, there is no optical communication.”

"Optical modules are required for all 5G bearer technologies."

"No matter which 5G bearer standard and technology is used, it is ultimately inseparable from the support of optical modules. Long-distance, low-cost, high-speed optical modules are the key elements to achieve low-cost and wide coverage of 5G."

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2. Functions of optical modules

An optical module usually consists of an optical transmitting component (including a laser), an optical receiving component (including a detector), a driving circuit, and an optoelectronic interface. The structure is shown in the figure below.

Schematic diagram of optical module structure (SFP+ package) (Picture from the optical module white paper)

In optical communications, the transmission and reception of information are achieved by optical modules:

• At the transmitting end, the optical module completes the electrical/optical conversion.
• Light is transmitted in optical fibers.
• At the receiving end, the optical module realizes optical/electrical conversion.

3. Development of optical modules

Optical modules are the basic building blocks of the 5G network physical layer and are widely used in wireless and transmission equipment. For 5G bearer, 25/50/100 Gb/s high-speed optical modules will be gradually introduced in the fronthaul, midhaul and backhaul access layers, and N×100/200/400 Gb/s high-speed optical modules will be introduced in the backhaul aggregation and core layers.

The development trend and technical route of optical modules are shown in the figure below.

The following is an introduction to the three main features of optical modules.

(1) Packaging

The determination of packaging standards enables optical modules produced by various manufacturers to be compatible and interoperable.

The packaging form is the most important feature of the optical module. With the development of optoelectronic devices, the bandwidth of devices and chips has gradually increased. With the increase in the bandwidth of devices and chips, along with the development of photonic integration technology, optical modules have also achieved higher-speed transmission and smaller packaging.

The figure below shows the development of optical module packaging.

(2) Transmission rate

High-speed data transmission makes various 5G applications possible.

The transmission rate refers to the number of bits transmitted per second, measured in Mb/s or Gb/s. The optical module has gradually increased from the early 155 Mb/s to: 622 Mb/s, 1.25 Gb/s, 2.5 Gb/s, 10 Gb/s, 25, 50, 100 Gb/s, 200 Gb/s, 400 Gb/s, and 800 Gb/s.

To achieve a higher rate, there are usually three solutions:

(3) Transmission distance

In the field of optical communications, faster and farther has always been the unremitting pursuit of communications people.

In the early stage, the transmission distance of optical modules mainly included SR (100 m), LR (10 km), ER (40 km), and ZR (80 km). With the construction of data center networks, two transmission distances, DR (500 m) and FR (2 km), were further derived for more cost-effective wiring. The common transmission distances of optical modules are as follows:

The higher the rate, the shorter the transmission distance. If the distance exceeds the above limit, you can use an optical fiber amplifier such as EDFA (Erbium Doped Fiber Amplifier) ​​to amplify the weak optical signal to make it transmit farther; or use a coherent optical module for transmission. Of course, both are not cheap and require additional costs.

With the advent of the 5G era and the popularization of the Internet of Things, the information generated has exploded, which has put forward higher transmission performance requirements for the physical layer of the entire communication system. As an important component, optical modules will continue to contribute to the development of communications!