You handle them every day, but how much do you know about what’s inside?
Here we delve into the key internal components of common open standards-based transceivers, and highlight the ways in which not all transceivers are created equal.
Inside the SFP
The job of an optical transceiver is to convert the electrical signal from a switch or router to an optical signal that can be transmitted and received over fiber optic cable. The optical portion of SFP transceivers built to MSA (multi-source agreement) specifications are laid out as shown below:
Fiber Stub. A strand of fiber cable along which optical signal enters the transceiver. A small fiber stub is optimal to minimize signal attenuation.
Isolator. Shields the transmitted signal from the received signal by reducing EMI (electromagnetic interference) within the transceiver. This improves signal strength in a highly compact form factor.
Focusing Lens. Refocuses the light coming in (or going out) to maximize signal strength.
TOSA and ROSA. The Transmitter and Receiver Optical Sub-Assemblies, or TOSA and ROSA, house all the components that enable data transmission and reception over fiber optic cable. This is where lower-quality manufacturers are very likely to cut corners; using inferior lasers will lower the cost to build, but will burn out much faster, thereby increasing your operational cost overall.
Inside the QSFP28
TOSA MUX and ROSA DEMUX. Unlike 1G and 10G transceivers, 100G transceivers like the QSFP28 use internal WDM technology to achieve higher data rate transmission. The data is channelized into four wavelength “lanes” of 25G each within the transceiver.
Tx and Rx CDR. Higher data rate transceivers are equipped with Clock Data Recovery (CDR) to ensure the transmitted and received signals are synchronized for optimal transmission
Tx EML. The EML is the point at which electrical signal actuates the laser to generate the optical signal.
Micro Controller. The heart of the transceiver, an electrical component akin to a computer’s CPU that controls all transceiver functions. This is another component that can be skimped on in lower-quality transceivers.
TEC Control. A thermoelectric cooler that prevents the transceiver from overheating.
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