Well you don't need a filter, but instead you can use the Auth check method to check if user is logged in or not:
if (Auth::check()) { //Logged in }
In your controller method to make sure the user is logged in, and if he isn't you can do a redirect, like:
return Redirect::to('user/login');
However if you want to use a filter you could use the beforeFilter method in the __construct of your controller, like this:
public function __construct()
{
$this->beforeFilter('auth', array('on' => array('create')));
}