As you may already know, conventional fiber made of silica glass can "only" carry information 31% slower than the speed of light in a vacuum. This is approximately 200,000Km/s instead of around 300,000Km/s.
A research team at the University of Southampton (UK) have developed and produced prototypes of a new type of fiber with a hollow core. Their prototype can carry information at 99.7% of the speed of light in a vacuum!
However one of the main downside of their current prototype is the significantly higher attenuation compared to traditional fiber (3.5dB/Km versus 0.3dB/Km) which makes it impracticable for anything other than short-hop applications. This particular issue can probably be enhanced in future prototypes.
More details can be found here: http://phys.org/news/2013-03-fiber-cable-capable-light-in-vacuum-throughput.html