Cf: ulexite and selenite minerals.  If the fused fibers are in direct contact - certainly after being bent during heating - they will leak light into each other.  At least two solutions:

1) Gradient index fibers.  The light never makes it to the surface. The fibers must still pack.  

http://www.pages.drexel.edu/~bel23/HCP.html 
Monodisperse circles hexagonally close pack to 0.9069% density. You lose a little more for fiber-fiber cladding spacing.

2) The fiber preform is a thick low index glass rod tightly fit inside a thin wall high refractive index glass tube.  One end is heated, fused, and drawn to create a remarkable length of thin cladded fiber with the same component size ratio.  These fibers may be bundled and drawn again to become much thinner.  Then bundle and fuse to form the rod. A huge number of exceptionally thin fibers are them suspended in an enveloping high refractive index matrix, never quite touching.  Look up the fabrication of channel plate amplifiers.

http://en.wikipedia.org/wiki/Total_internal_reflection#Derivation_of_evanescent_wave

In very rough terms, the fiber separation for 1/e leakage, 37%, is one wavelength (in the cladding).  Two wavelengths is 1/e^2 or 14%, three is 5%.  Green light is about 0.5 microns. For a cladding 1.5 refractive index, a 2-micron cladding separation is 1/e^[(2)(1.5)/(0.5)] or 0.25% leakage.  Cladding thickness can be thin versus fiber diameter.

The real world is dirty and has footnotes.

How can fiber optic image conduits consist of only fiber core, no cladding?
I'm trying to get the image from Google Books service, in the thumbnail. Reading the address in php via file_get_contents get all the web page of the book while I just want to get the cover image. I know that it can be done via the src tag of html img element but I need the image server side. Is there a way? Thanks

Here the code I've used:

$context = [
    'http' =&gt; [
        'method'=&gt;"GET",
        'header' =&gt; "Accept:image/png\r\nAccept-Language:it-IT,it;q=0.8,en-US;q=0.5,en;q=0.3\r\nCache-Control:max-age=0\r\nConnection:  keep-alive\r\nUser-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:33.0) Gecko/20100101 Firefox/33.0\r\n"
     ]
];
$context = stream_context_create($context);
$result = @file_get_contents($bookThumbnail, false, $context);

