Talk about one-strand fiber links at full-duplex

I suppose that you are talking about WDM (Wavelength-division multiplexing) using SFP. The bandwith available for a single strand of fibre is bounded only by the money : quoting a figure from a telecom vendor 80*40Gb on a fiber for a transport network dwdm device.
Using cisco as a reference , i find that the maximum bandwith available for non-telco dwdm is 1G ( 10G coming ). The advantage for the provider is that using DWDM it doubles the available optic fiber for connections. For the consumer , there is no advantage nor any disadvantage , since it is 'transparent'.

The two solution already mentioned (DWDM & single-core-SFPs) are both methods of getting multiple signals down a single strand of fiber.

As Haakon said, single-core-SFPs work in pairs and just replaces your normal SFP/GBIC modules in standard network equipment. And as cavver said, DWDM is another method. DWDM though is more complex, requires separate pieces of equipment and is much more expensive.

The advantages are that you can get more data down the same infrastructure allow you to double (at least) your bandwidth. [DWDM gear can carry multiple signals (160+ channels) over a single piece of fiber and can intermix data and voice traffic.]

The disadvantages are you may sacrifice the distance the signal can travel and of course you increase your risk. If a single strand is cut, twice as much is impacted.

The advantages of CWDM

CWDM - Coarse Wavelength Division Multiplexing

DWDM - Dense Wavelength Division Multiplexing

DWDM undoubtedly is principal technology in the field of today optical applications, but its high price make a lot of off hand operators quite hesitant . Is it possible to enjoy a lower cost WDM technology? Faced with this demand, CWDM came into being.

CWDM is a low-cost WDM transmission technology for MAN access layer. In principle, CWDM use optical multiplexer making different wavelengths light signals multiplex to a single fiber for transmission, at the receiving end of the link, with an optical demultiplexer making the mixed signal in the optical fiber decompose into different wavelengths signal, connected to the appropriate receiving equipment.

The most important advantage of CWDM is low-cost equipment. In addition, another advantage of CWDM is to reduce network operating costs. Since CWDM devices are small, low power consumption, easy maintenance and power supply, it can use the 220V AC power. Because of its wavelength is relatively small, so the board back up to a small amount.  8-wave CWDM devices have no special requirements for optical fiber, G.652, G.653, G.655 fiber can be used, also can make use of existing fiber optic cable. CWDM systems can significantly improve the optical fiber transmission capacity and improve the utilization of optical fiber for optical fiber.

CWDM has good flexibility and scalability. Using CWDM technology can open the business for the user in one day or several hours, but also with the increasing business volume, you can insert a new OTU board for capacity expansion. Improve the quality of service. Using CWDM system in the MAN can make it possible to restore the optical layer. Optical layer recovery is more economic than the much-layer recovery. Taking into account to optical layer recovery is independent of the business and rate, then some of its original structure without protection system (such as Gigabit Ethernet), we can use CWDM to be protected. As the advantages of CWDM technology, the CWDM get more and more applications in the telecommunications, broadcasting, enterprise network, campus network and other areas.

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