How to send custom data to DataTable server-side processing not from DataTable's filter input?

In my page there is a group of four fields to make custom search of records in the database ; the results will be displayed inside a DataTable which is displayed below these group of fields :

Here is the javascript creation of the DataTable :

<script type="text/javascript">
$(document).ready(function() {

    var j_table = $("#t_list").dataTable( {

        "oLanguage"     : {
                            "sInfoThousands": " ",
                            "sEmptyTable"   : _getText("datatable_resultat_zero", "global"),
                            "sInfo"         : _getText("datatable_zone_statut_info", "global"),
                            "sInfoEmpty"    : "",
                            "sInfoFiltered" : _getText("datatable_zone_statut_filtre", "global"),
                            "sLengthMenu"   : _getText("datatable_zone_nb_affichage", "global"),
                            "sSearch"       : _getText("datatable_zone_filtre", "global"),
                            "sZeroRecords"  : _getText("datatable_resultat_zero", "global"),
                            "oPaginate"     : {
                                                "sPrevious" : _getText("datatable_btn_prcdt", "global"),
                                                "sNext"     : _getText("datatable_btn_svt", "global")
                                              }
                        },

        "sPaginationType"   : "bootstrap",

        "aoColumnDefs": [
                         { "aTargets": [ 3 ], "bSortable": false },
                         { "aTargets": [ 3 ], "bSearchable": false },
                         {
                             "aTargets": [ 3 ],
                             "mRender": function ( data, type, full ) {
                               return '<div style="text-align: center;"><a href="<?php echo site_url('meeting/modif'); ?>/'+data+'" title="Modifier"><button class="btn btn-mini">Detail</button></a></div>';
                             }
                         }
                       ],

        "bServerSide": true,

        "sAjaxSource": "<?php echo site_url('ajax/dataTableListerMeetingNotes'); ?>",

        "sServerMethod": "POST"

    } );

});
</script>

So how to pass the values entered in the four fields to the ajax source of the DataTable when clicking the "Valider" blue button ? And how to collect these data inside the script called by the DataTable's ajax ?