如何json_encode包含json字符串元素的数组？输出不应包含反斜杠“\”

For Example

$json_string = '{"employee" : { "name" : "test","id" : "1"}}';

    $array = [
                "center"    => "Mumbai",
                "data"      =>  $json_string
    ];

  //echo json_encode($array,JSON_PRETTY_PRINT);
  //echo json_encode($array,JSON_UNESCAPED_SLASHES);
  echo json_encode($array,JSON_UNESCAPED_UNICODE);
$json_string = '{"employee" : { "