wp_login_url not working correctly

I'm working on a project where I need to add a custom link to admin menu, and I'm using the following code for it:

$login_url = wp_login_url();
add_options_page('Login', 'Login Page', 'manage_options', 'loop.php?url='.esc_url($login_url).'');

Here's a thing. The above code is adding following URL to menu:

http://example.com/wp-admin/loop.php?url=http:/example.com/wp-login.php

Instead of:

http://example.com/wp-admin/loop.php?url=http://example.com/wp-login.php

What's different?

It's generating the URL with only http:/ instead of http://

I even tried it without esc_url but it's still not working.

Hope you can help :)