Tried everything possible.. here is final piece of working code. Hope it helps someone who is looking for it.
<?
$url='https://www.googleapis.com/plus/v1/people/116599978027440206136?fields=image%2Furl&key=MY_API_KEY&fields=image';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_PROXYPORT, 3128);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
$response = curl_exec($ch);
curl_close($ch);
$d = json_decode($response);
$avatar_url = $d->{'image'}->{'url'};
echo $avatar_url;
?>