codeigniter non latin characters ajax call

I have a textarea and a button where i send the text via ajax to the database to post it.

However when i post non-latin characters... it wont get them and it returns blank... if the text is in latin characters it works fine...

my js code

$.ajax({

                type: "POST",

                url: www+"controller/postText",

                dataType: 'json',

                data: {

                    input       : input.val(),

                },

                success: function(data) {

                    return data;

                }

            });

my php code

public function postText(){



    $input = isset($_POST["input"]) ? trim($_POST["input"]) : "";



    echo $input;

    return false;

}