- urlencode: documentation ( source)
<?php
$calendar_id = urlencode('japanese__ja@holiday.calendar.google.com');
$url = 'https://calendar.google.com/calendar/ical/'.$calendar_id.'/public/full.ics';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$result = curl_exec($ch);
curl_close($ch);