The present invention introduces a new class of thin doubly collimating light distributing engines for use in a variety of general lighting applications, especially those benefiting from thinness. The saturable absorber structure has a dimension along the first guide axis greater than its dimension along the second guide axis. By using specially designed random basic screen and random master screen, where at least the basic screen is comprised in the document, a moire intensity profile of a chosen shape becomes visible in their superposition, thereby allowing the authentication of the document.