Getting passed value in controller from view, codeigniter

I have written the following codes for my view, javascript and controller.

Whenever a user clicks on the delete button in the view, it will call the function named "remove_image". Then, the image name (fullpath) will be passed over to the delete_banner (controller).

The value of fullpath is dynamic it can be in the following format "assets/images/banner3.jpg" and "banner4.jpg".

Th problem I am facing is that, when the fullpath is "assets/images/banner3.jpg" and I var_dump the value of $image_name in the delete_banner controller, it only returns "assets" instead of "assets/images/banner3.jpg".

The link written in html and php looks something like this:

<a href="<?php echo base_url().'backendBanner/delete_banner/'.$banner['banner_path']; ?>">

Code for the button in view to call the function

<td>
      <a onclick="return remove_image($(this));" rel="<?php echo $banner['banner_path']; ?>"><input type="button" class="btn btn-danger" value="Delete"></a>
</td>

Code for the function In this function, $banner['banner_path'] is equal to fullpath

<script>
            function remove_image(img)
            {
                if(confirm('<?php echo lang('confirm_remove_image');?>'))
                {
                    var fullpath  = img.attr('rel');
                    alert(fullpath);
                    window.location="<?php echo base_url().'backendBanner/delete_banner/'; ?>" + fullpath;
                }
            }
        </script>

Controller

public function delete_banner($image_name)
    {
        var_dump($image_name);
    }