Q&A in Fiber Optical Communication

Q: When choosing an SFP transceiver, is it necessary to consider the OS rating of a single mode fiber? Or is it enough to know the cable length?

A: In short, no - it doesn't matter. What matters is your distance requirements (the cable length you mentioned).

The OS rating of single mode fiber should have no bearing on your choice of optical transceivers.

Both OS1 and OS2 will work with the most popular single mode transceivers (most of which use wavelengths around 1310nm and 1550nm). This includes 1000Base-LX/LX10/EX/LH/ZX and it is the transceiver which larger determines the distance the signal will propagate, not the fiber.

The main difference in OS1 and OS2 is the construction of the cable, although OS2 may specify cable with a lower attenuation specification (depending on when and under which standards it was manufactured).

Just remember SR(Short Reach) transceiver works with multi-mode fiber (50 or 62.5 micron), LR/ER(Long Reach) optic transceiver works with single-mode fiber (9 micron).

Q: Why the optical transceivers are labeled with DOM?

If fiber optic transceiver supports digital optical monitoring (DOM), and the platform (i.e. switch/router) also supports it as this will allow you to determine things like low/high power levels.

Q: What are the advantages and disadvantages of using 10GBase-T vs. SFP+ Direct Attach Cable(dac) to interconnect devices where distance is not a determining factor?

A: Broadly speaking SFP+ DAC is, ignoring distance:

Cheaper at the adapter side.
Lower power and latency.
Gives added flexibility if you need to move to fiber later.
Flexibility of SFP+ cages. If you ever need fiber connections, all you need is change optics. With fixed 10GBase-T ports, that is what you're stuck with...
B: 10GBase-T on the other hand is:

Cheaper at the connector side - patch leads being cheaper than SFP+ direct attach cables.
Somewhat easier to work with physically - SFP+ DACs tend to be a bit thick, bulky and can be a pain to route through cable management in my experience, though to an extent this depends on type (passive vs. active) and manufacturer.
More flexible in that the same cable plant can be used for 10/100/1000.
I've been watching the field for a while, and it doesn't seem like there's consensus on the "best" option yet - networking, server and adapter vendors seem to be hedging their bets.

For what it's worth, we went with SFP+ DAC in a top-of-rack configuration, largely due to the ability to mix copper/fiber on the same device. Whether this is applicable for your environment will depend on the number of ports and nature of the network you're building.

One final point, if you do some reading on this, finding objective, unbiased opinion is hard - a lot of the commentary and claims are by people with vested financial interest in encouraging one or other option. As an example, compare and contrast.

Hope the above explanations will help you further understanding the issues in fiber optical communication.