Magento: Ajax update using Json Array

<script>
    $j(document).ready(function(){
        $j("#serial_id, #sticker_number").blur(function(){
            var sticker_number = $j('#sticker_number').val();
            var serial_id = $j('#serial_id').val();
            
            if(!isNaN($j.trim(sticker_number)) && !isNaN($j.trim(serial_id))){
                
                $j.ajax({
                    type: "POST",
                    url: '<?php echo $this->getUrl('warranty/index/getProductName'); ?>',
                    data: {'sticker_number':sticker_number,'serial_id':serial_id},
                    beforeSend: function(){
                        $j('#loding_img').show();
                    },
                    success: function(data) {
                        $j('#product_id').val(data.product_id);
                        $j('#pro_name').val(data.product_name);
                        $j('#product_message').html(data.message);
                        $j('#loding_img').hide();
                    }
                });
            }
        });
    });
</script>

public function getProductNameAction(){
		
    $_reponse = array();
    
    if((isset($_POST['sticker_number']) && !empty($_POST['sticker_number'])) && (isset($_POST['serial_id']) && !empty($_POST['serial_id']))){
        $getProductName = Mage::getModel('warranty/warranty')->getCollection()
                        ->addFieldToFilter('sticker_number', $_POST['sticker_number'])
                        ->addFieldToFilter('serial_number', $_POST['serial_id'])
                        ->getFirstItem();
        
        if($getProductName->getWarrantyId()){
            $obj = Mage::getModel('catalog/product');
            $_product = $obj->load($getProductName->getProductId());
            if($_product->getId()){
                $_reponse['message'] = "<span style='color: #3d6611'>You are registering for : "."<strong>".$_product->getName()."</strong>";
                $_reponse['product_id'] = $_product->getId();
                $_reponse['product_name'] = $_product->getName();
            }else{
                $_reponse['message'] = "<span style='color: #eb340a'>Entered Sticker Number  Or Serial Number is invalid. Please Recheck the combination and try again";
            }
            
        }else{
            $_reponse['message'] = "<span style='color: #eb340a'>Entered Sticker Number  Or Serial Number is invalid. Please Recheck the combination and try again";
        }
    }
    $this->getResponse()->setHeader('Content-type', 'application/json');
    $this->getResponse()->setBody(Mage::helper('core')->jsonEncode($_reponse));
    
}