Optical transceivers – turning data into light
The traffic rules of fiber optic communication
In the first article of our series on WDM, Getting on the road with dark fiber, we compared a fiber optic network to a powerful multi-lane expressway, capable of transporting traffic between various sites. And just as we have traffic rules for driving, different traffic rules are needed to transport our optical traffic. These are called protocols. Below, we describe the three key protocols for storage, data and voice, respectively.
Fibre Channel, or FC: A high-speed network technology primarily used to connect computer data storage to servers. Fibre Channel is mainly used in storage area networks in enterprise storage. FC networks are known as a fabric because they operate in unison as one big switch. Fibre Channel typically runs on optical fiber cables within and between data centers.
Ethernet: Networking technologies mainly used for connecting a number of computer systems to form a local area network, with protocols to control the passing of information and to avoid simultaneous transmission by two or more systems.
Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH): SDH is a standard technology for synchronous data transmission on optical media. It is the international equivalent of SONET, which is used in the US and Canada. Both technologies provide faster and less expensive network interconnection than traditional plesiochronous digital hierarchy (PDH) equipment.
From electricity to light (and back again)
To transport all this traffic over a network, whether it be FC, Ethernet or SONET/SDH, a component called an optical transceiver is needed.
Transceivers are wavelength-specific lasers that convert electrical data signals from data switches into optical signals. These signals can then be transmitted over the optical fiber. Each data stream is converted to a signal with a unique wavelength, meaning that it is effectively a unique light color. The signals can be wideband 850nm, 1310nm or 1550nm, or narrow band CWDM or DWDM wavelengths.
Due to the physical properties of light, no channel can interfere with the next – they are completely separated from each other. Each channel is transparent to the speed and type of data, meaning that any mix of SAN, WAN, voice and video services can be transported simultaneously over a single fiber or fiber pair in a WDM system.
Typically, the size of an optical transceiver determines how far the traffic can travel. It also has a value that defines the amount of optical power available to successfully transmit signals over a distance of optical fiber. We will come back to this so-called optical power budget in our next article.
Transceiver form factors
A form factor specifies the physical dimensions of the transceiver – its shape and size. The size varies depending on speeds and protocols, and over time has tended to get bigger with increasing line speeds. In general, manufacturers design according to the multisource agreement (MSA). This is a standard for ensuring that the same form-factor transceivers from different vendors are compatible in size and function, ensuring interoperability.