FTTH and alternatives

Main difference: Singlemode fiber has a lower power loss characteristic than multimode fiber, which means light can travel longer distances through it than it can through multimode fiber. Not surprising, the optics required to drive singlemode fiber are way more expensive, especially considering any varying circumstances.

When to use each: Both singlemode and modern multimode fiber can handle 10G speeds. The most important thing to consider is the distance requirement. Within a data center, it's typical to use multimode which can get you 300-400 meters. If you have very long runs or are connecting over longer distance, single mode can get you 10km, 40km, 80km, and even farther - you just need to use the appropriate optic for the distance required, and again, the prices go up accordingly.

Compatibility issues: They are not compatible. You cannot mix multimode and singlemode fiber between two endpoints. The optics are not compatible either.

There's a lot more to say about fiber, in general, but I hope this answers your immediate question.

It all really depends on your requirements and current setup. That being said, here are some of the main ones.

Active

Pros:

1. Active can fit a lot more wavelengths (colors) onto a single fiber pair. The pro being, the composite signal that is sent over a single fiber pair can carry more bandwidth than a passive of the same size could, in turn you don't need as much physical fiber between your two sites (this really only applies if you require that much bandwidth). This is advantageous when distance is a problem because it allows you to get more out of a single leased fiber pair as opposed to passive - see here.

2. Active setups grant you more control over your optical network, you can dynamically re-tune wavelengths without dropping connections (it's transparent to whatever is riding on that wavelength).

3. Scalability - Active can be easier to scale as your network grows (you can fit more wavelengths on the fiber, see above), but again - we're talking seriously big iron. I'll dig into it a bit more below.

Cons:

1. EXPENSIVE - Active DWDM setups are extremely expensive in comparison to passive, so as ytti mentioned, if your distance requirements aren't unreasonable this is not the route to go.

2. Setup/Configuration - Depending on your vendor, configuration can be a serious undertaking, and require a solid understanding of optical networks. There are many more components in active builds.

Passive

Pros:

1. Inexpensive (in comparison to active) - As mentioned above, less components are required, and less engineering time is required.

2. INITIAL Setup - Because of the colored optics there isn't a need to tune wavelengths for all of your connections. It's a matter of matching your colored optics and plugging it.

Cons:

1. Scalability - Not only are you limited to colored optics, and thus less wavelengths on the transport fiber as you grow you would be require to have more passive devices. Furthermore, with the more passive devices you have the more difficult it can be to manage, you'll have to start managing the same wavelength on multiple passive devices and they could be serving different purposes on each depending on your setup.

2. Control - If you need to change a wavelength or connection for whatever reason, you're option is limited to taking it out of service and disconnecting the physical cabling as the wavelength is tied to the optic.

Hope this helps.