Select2 Multiple fields as array

I am using select2 as my multiple input textbox as follows

<input name="locations[]" class="width_100" id="locations" type="text" placeholder="London, Delhi.." >

My initialisation part in js as follows

    $("#locations").select2({
    minimumInputLength: 3,
    tags: [],
    ajax: {
        url: $('#site').val()+'/ajax/location_search/'+Math.random(),
        dataType: 'json',
        type: "GET",
        quietMillis: 50,
        data: function (term) {
            return {
                term: term
            };
        },
        results: function (data) {
            return {
                results: $.map(data, function (item) {
                    return {
                        text: item.city_name,
                        id: item.city_id
                    }
                })
            };
        }
    }
});

In all other select2 fileds are getting as an array in the backend. But in this I am getting the input as comma separated values like the following

[locations] => Array
    (
        [0] => 17633,35799
    )

The same select2 multiple, but not the ajax one giving the data as array as follows

 [languages] => Array
    (
        [0] => 7
        [1] => 1
    )

Can any one please help to to solve the issue ?