@link to another package inside of a package-info.java

you have to import the used Package so javadoc knows the the namespace you are refering to.

package-info.java should look link this:

import package.subpackage.ClassnameYouWantToLink;
/**
* {@link ClassnameYouWantToLink}
*/

if you don't want to import the package you need the full quallified package-Name infront of the ClassName:

/**
* {@link package.subpackage.ClassnameYouWantToLink}
*/