Fiber Optical Transceivers From Past to Present

The fiber optical transceiver develops from the original 155M to today's 100G, and I want to talk about the high data rate fiber optic transceivers.

When 10G Ethernet line cards first hit the market early in the century, OEMs had several choices of MSAs. Modules such as XFP and XENPAK integrate more signal-conditioning circuitry inside the module, while the enhanced version of SFP, known as SFP+, provides a smaller module in exchange for implementing more circuits on the motherboard or line card. This helped lower costs in two ways. The availability of multiple MSAs gives designers a choice on implementation while still providing the benefits of a common form factor. At the same time, the multiple MSAs allow OEMs to tailor the transceiver solution to the radius of the optical network, the type of fiber (MMF or SMF) employed, and the type of laser used in the transceiver.

And there developed the 40G QSFP and CFP, and 100G CFP transceiver, from CFP to CFP2 to CFP4. The trickiest prediction to make is how the MSA process aids the move to 40G, 100G, and 400G standards. The arrival of 40G, 100G, and 400G follow-ons to 10G Ethernet would take even longer than it has taken over the last decade. For 100G, some OEMs say that the preservation of 10 x 10G and 4 x 25G channels provides too many choices, but 40G Ethernet used 10G channels, so it made sense to offer a choice of channel bandwidth for those transitioning from 40G to 100G Ethernet.

Current multi-mode optics standards for 40GbE and 100GbE optics use multiple 10Gbps lasers, simultaneously transmitting across multiple fiber strands to achieve high data rates. Because of the multi-lane nature of these optics, both 40GbE and 100GbE multi-mode optics use a different style of fiber cabling, known as MPO or MTP cabling. An MPO/MTP cable presents 12 separate strands of multi-mode fiber in a single Ribbon cable. As with 10GbE optics over multi-mode fiber, an OM3 or OM4 grade MMF is needed to be able to cover longer distances (up to 150m).

It seems safe to predict at this point that the 10 x 10G and 4 x 25G channelization methods will coexist in the near term, but that 16 x 25G will be a preferred channelization for 400G Ethernet.

The fiber optical transceiver module will play an important role in the cost of optical networking as the choice of fiber and the choice of laser. Whatever, the development of the fiber transceivers is meeting the requirements in networking.