File Upload $_FILES getting empty value

<form id="UploadForm" method="post" enctype="multipart/form-data">
<input type="file" id="upload" name="upload" >
</form>

unction uploadimg(){
		$.ajax({
			url:"uploadImg.php",
			data:{},
			success:function(response){
				console.log(response);
				if(response=="success"){
					alert("Image Uploaded Successfully");
				}
				else if(response=="Invalid"){
					alert("Invalid File Type");
				}
				else{
					alert("Image Not Uploaded");
				}
			}
		});
	}

$allowedExts = array("gif", "jpeg", "jpg", "png");
	//$temp = explode(".", $_FILES["upload"]["name"]); //image
	//$extension = end($temp);
	echo $_FILES["upload"]["name"];
	$ext=pathinfo($_FILES["upload"]["name"],PATHINFO_EXTENSION);
	echo "--------------------".$ext."-------------------------";
	$src="";
	if ((($_FILES["upload"]["type"] == "image/gif")
	|| ($_FILES["upload"]["type"] == "image/jpeg")
	|| ($_FILES["upload"]["type"] == "image/jpg")
	|| ($_FILES["upload"]["type"] == "image/pjpeg")
	|| ($_FILES["upload"]["type"] == "image/x-png")
	|| ($_FILES["upload"]["type"] == "image/png"))
	&& in_array($extension, $allowedExts)) {
		$filename = $_SESSION['username']. $_FILES['upload']['name'];
		move_uploaded_file($_FILES['upload']['tmp_name'],"upload/". $filename);
		//Update Query
		
		$query="update js_basic_details set image='".$filename."' where email_id='".$_SESSION['username']."'";
		if(mysql_query($query))
			return "success";
		else
			return "Error";
	}
	else{
		echo "Invalid";
	}