How to open file in PHP that has unicode characters in its name?

For example I have a filename like this - проба.xml and I am unable to open it from PHP script.

If I setup php script to be in utf-8 than all the text in script is utf-8 thus when I pass this to file_get_contents:

$fname = "проба.xml";
file_get_contents($fname);

I get error that file does not exist. The reason for this is that in Windows (XP) all file names with non-latin characters are unicode (UTF-16). OK so I tried this:

$fname = "проба.xml";
$res = mb_convert_encoding($fname,'UTF-8','UTF-16');
file_get_contents($res);

But the error persists since file_get_contents can not accept unicode strings...

Any suggestions?