How to protect my laravel project source code?

Depends on what you mean by protecting.

A properly set up hosting will never display the php source code.

You really can't protect the source code from someone who has direct access to the server. At least not if you expect to have good performance on the site.

I want to encrypt Source code. like " zend guard" . I want a free/opensource alternative

I would not recommend it since it will slow down your site, however that is up to you to make that trade off.

It's much better to host it on a server only you have access to.

I don't think there are any free alternatives at least not any found in the few minutes.

Read this article on protecting you php source code

https://www.phpclasses.org/blog/package/9574/post/1-PHP-Source-Code-Protection-Solutions.html