Sending file parameters with AJAX request

Question

I have a form, which has several input types. I am saving the form with AJAX:

function save_form_data(){
    $.ajax({
                url:"path/to/file.php",
                method:"POST",
                dataType:'json',
                data: $("#options_form").serializeArray(),
                success:function(returnObj){
                console.log(returnObj);
                }
           });
}

I am using this function on submit function of jQuery.

$('#options_form').submit(function(event){
    console.log('submitted');
    event.preventDefault();
    save_theme_options();
});

But, the problem that I face is I am not able to get the files uploaded in the form using AJAX request. I try to print $_FILES, but results in an empty array.

How do I solve this issue?