为什么("2011/7/11")用json_encode显示器输出该日期("2011\/7\/11")？

如何转换"2011\/7\/11"为"2011/7/11"？

$data_go = '2011/7/11';
$ddmmyyy='([1-9][\d]{3})[- \/.]([0-1][\d])[- \/.]([0-3][\d])';
            if(preg_match("/$ddmmyyy$/", $data_go)) {
            $year = substr($data_go,0,4);
            $month = substr($data_go,5,2);
            $day = substr($data_go,8,2);
            $j2g = $this->convert_date->JalaliToGregorian($year, $month, $day);
             $ok = $j2g[0]."/".$j2g[1]."/".$j2g[2];
            }else {
              return FALSE;
            }
echo json_encode($ok); // output "2011\/7\/11"