AJAX call PHPExcel output file is empty - php

Question

I start with this code:
index.html:
$("button").click(function(){
$.ajax({
type: "POST",
url: "htmltable_to_excel/savexls.php",
cache: false,
data: JSON.stringify({'name': 'test'}),
dataType: 'text',
contentType: 'text/plain',
async: false,
success: function(result)
{
alert(result);
//window.open("htmltable_to_excel/savexls.php",'_blank');
}
});
savexls.php:
$val = file_get_contents('php://input');
$json = json_decode($val, true);
echo $json['name'];
It is return 'test'. AJAX call seems good.
I have code for created xlsx via PHPExcel:
savexls.php:
require_once 'PHPExcel.php';
$val = file_get_contents('php://input');
$json = json_decode($val, true);
$objPHPExcel = new PHPExcel();
$objPHPExcel->setActiveSheetIndex(0);
$objPHPExcel->getActiveSheet()->setCellValue('A1', $json['name']);
// Redirect output to a client’s web browser (Excel2007)
$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
ob_clean();
header('Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet; charset=utf-8');
header('Content-Disposition: attachment;filename="01simple.xlsx"');
header('Cache-Control: max-age=0');
// If you're serving to IE 9, then the following may be needed
// header('Cache-Control: max-age=1');
// If you're serving to IE over SSL, then the following may be needed
header ('Expires: Mon, 26 Jul 1997 05:00:00 GMT'); // Date in the past
header ('Last-Modified: '.gmdate('D, d M Y H:i:s').' GMT'); // always modified
header ('Cache-Control: cache, must-revalidate'); // HTTP/1.1
header ('Pragma: public'); // HTTP/1.0
$objWriter->save('php://output');
But when I open the created xlsx file cell is empty. I forgetting something here? What could be the problem? Does anyone have an idea? Thanks!