Industry Information

The rapid expansion of optical fiber networks, including data services measured by data volume or bandwidth, shows that optical fiber transmission technology is and will continue to be an important part of network systems in the future. Network designers are becoming more and more satisfied with optical fiber solutions, because the use of optical fiber solutions can achieve a more flexible network architecture and other advantages, such as EMI (electromagnetic interference) elasticity and data security. Optical fiber transceivers play a very important role in these optical fiber connections. When designing optical fiber transceivers, three aspects need to be considered: environmental conditions, electrical conditions and optical performance.

What is optical transceiver?

Fiber optic transceiver is an independent component for transmitting and receiving signals. Typically, it is inserted into a device that provides one or more transceiver module slots, such as a router or network interface card. The transmitter receives electrical input and converts it into optical output from a laser diode or LED. The light from the transmitter is coupled to the optical fiber through the connector and transmitted through the optical cable equipment. Then, the light from the end of the optical fiber is coupled to the receiver, in which the detector converts the light into an electrical signal, and then adjusts it appropriately for use by the receiving device. There are a full range of optical transceivers in the telecommunications market, such as SFP transceivers, sfp+ transceivers (such as sfp-10g-sr shown in the figure below), 40g qsfp+, 100g CFP, etc.

Design considerations

Compared with copper wire solutions, optical fiber links can indeed handle higher data rates over longer distances, which promotes the wider use of optical fiber transceivers. When designing optical fiber transceiver, the following aspects should be considered.

Environmental conditions

One challenge comes from external weather - especially bad weather at high or exposed heights. These components must operate in a wider temperature range under extreme environmental conditions. The second environmental issue related to the design of fiber-optic transceivers is the motherboard environment, which includes the power consumption and heat dissipation characteristics of the system.

A major advantage of optical fiber transceivers is the relatively low electrical power requirements. However, this low power consumption does not completely mean that thermal design can be ignored when assembling the host configuration. Adequate ventilation or airflow shall be included to help dissipate the heat energy discharged from the module. Part of this requirement is met by a standardized SFP cage installed on the motherboard, which can also be used as a thermal conduit. When the host is operating at its maximum design temperature, the housing temperature reported by the digital monitor interface (DMI) is the final test of the effectiveness of the thermal design of the entire system.

Electrical conditions

In essence, optical fiber transceiver is an electrical device. In order to maintain the error free performance of data passing through the module, the power supply of the module must be stable and noise free. More importantly, the power supply that drives the transceiver must be properly filtered. Typical filters are specified in the multi-source protocol (MSA), which guides the original design of these transceivers. One such design in sff-8431 specification is shown below.

optical performance

Optical performance is measured by bit error rate or BER. The problem in designing optical transceivers is that the optical parameters of the transmitter and receiver must be controlled so that any possible attenuation of optical signals along the optical fiber will not lead to poor BER performance. The related main parameter is the BER of the complete link. That is, the starting point of the link is the electrical signal source driving the transmitter. Finally, the electrical signal is received by the receiver and interpreted by the circuit in the host. For those communication links using optical transceivers, the main goal is to ensure BER performance at different link distances and wide interoperability with third-party transceivers from different suppliers.