by  Fayre Fan (edited by Alan J Weissberger)

Introduction: 

The fiber optic transceiver is the core component of optical communications.  It is used to realize optical-to-electrical conversion. The transmitter converts the electrical signal into an optical signal, while the receiver does the reverse – it converts the optical signal into an electrical signal.

Increasingly, fiber optics is being used for the transport of 5G signals to and from the edge of the carrier’s wide area network. Optical transceivers are the basic component of 5G backhaul, midhaul and fronthaul.   Their cost accounts for 50%~70% of the total 5G network costs.  

Low cost is the key appeal of the 5G optical transceivers. The industry has carried out extensive research on 5G optical module technology, and currently, there are many solutions.

Increasing demands for 5G transceivers: low cost is the key to 5G optical module:

The growth of optical modules in the 5G network mainly comes from three factors:

• More base stations are needed in the high-frequency band.
• Larger bandwidth is required for high-speed rates.
• More connections are required for added midhaul transmission links.

Global top suppliers of 5G base stations include Huawei (China), Ericson (Sweden), Nokia (Finland), ZTE (China), and Samsung (Korea). China is the largest 5G market, which has captured about 74% of the market, followed by Korea and Europe.  

The development of the global 5G network market stimulates the increasing demand for 5G optical transceivers. According to the forecast data from Lightcounting,  the global market share of 5G fronthaul transceivers will reach 657/632/593 million dollars in 2022~2024. 5G midhaul and backhaul transceivers will reach 242/245/247 million dollars respectively. Therefore, reducing cost is a key objective of 5G transceiver development.  Here’s an illustration of backhaul, midhaul and fronthaul:

5G fronthaul -demand for 25G BiDi transceiver:

In the 4G fronthaul network, the most commonly used transceivers are single-mode 10G duplex transceivers. 5G network has higher requirements for the data rate and optical interface of transceivers. In consideration of saving fiber resources and maintaining high-precision synchronization of uplink and downlink, the simplex bi-directional (BiDi) transceiver allowing data transmitting and receiving over one single fiber, is superior to duplex transceivers. Moreover, considering the 5G download rate is at least 10 times higher than that of the 4G network, the 25 Gbit/s data rate is also necessary for the 5G fronthaul transceivers. Taken together, 25G BiDi transceivers are needed for 5G fronthaul networks.

Optical Transceivers for 5G Front-Haul

5G midhaul and backhaul – demand for 50G/100G/200G/400G transceivers:

The 5G midhaul and backhaul are mainly carried through the metro access layer, convergence layer, and core layer. For the access layer, 50G/100G transceivers are commonly used. For example, 50G PAM4 transceiver is a cost-effective solution for 5G midhaul and backhaul.  It is based on 25G optical components and PAM4 (Pulse Amplitude Modulation 4-level) modulation. For the convergence layer and core layer, 100G/200G/400Gb/s DWDM transceivers are mainly used. And low-cost coherent 100G/200G/400G transceivers are welcomed, which mainly use QAM (Quadrature Amplitude Modulation) modulation and DSP (Digital Signal Processing) technology.

Optical Transceivers for 5G Mid-Haul/Back-Haul

Technological innovations of 5G transceivers:

Optical transceiver-related technology mainly includes packaging technology and optoelectronic components technology. 

In terms of packaging technology, 5G transceivers can adopt existing mature packaging technologies. For example, since 25G BiDi has a similar optical structure to that of 10G BiDi, the common TO-CAN (transistor-outline-can) package can be used to save cost.

The most vital technological innovation aims at optoelectronic components technology. The technological innovation of optoelectronic devices mainly aims at these goals: function expansion, data rate increase, and cost reduction. 

Function expansion innovation of laser chips example: industrial-grade laser chips no longer require temperature control devices, the laser chip used in the non-airtight environment no longer requires the expensive airtight package, the laser chip with a small divergence angle no longer requires an expensive non-spherical lens,  anti-reflection laser chips no longer require isolators, etc. Those technologies simplify the packaging of the optical module, also providing higher reliability and lower cost.

Data rate increase innovation includes example: the 50G PAM4 optical module uses a 25G baud rate laser/detector, and an electrical chip with high linearity. Compared with the 25G NRZ (non-return to zero) optical module, it allows for higher bandwidth. 

Cost reduction innovation example: coherent 100G transceiver, it reduces the cost on the premise of meeting the transmission distance requirement within 200km.

Ultimately, the key technologies of 5G optical modules are mainly reflected in the innovation of optoelectronic chips. The specific technologies include:

• Industrial temperature grade high-speed laser chip technology
• High linearity 25G baud rate DFB chip and EML chip technology
• Low-cost 25G wavelength tunable laser chip technology
• Low-cost coherent 100G/200G/400G optical transceiver technology

For example, Marvell  and OE Solutions recently announced a collaboration to deliver the industry’s first production-ready 100G QSFP-DD optical modules optimized for 5G backhaul and Metro Access applications.

In conclusion,  5G optical transceivers will play a more important role in the entire optical module market compared with the 4G era.  Technological innovation will be the main driver to realize the low-cost 5G optical modules.

References:

https://www.researchreportsworld.com/global-5g-base-station-sales-market-21017689

https://www.3coptics.com/News/9.html