A replaceable modular opto-mechanical unit includes a light source in the form of, for example, a laser assembly; an optical modulator assembly which modulates light from the light source; and a lens located in a light path between the light source and the optical modulator assembly. The lens focuses the light from said light source toward a center of the optical modulator assembly. The unit further includes a base adapted to removably support the light source, the optical modulator assembly and the lens in an optically aligned manner. The base is further adapted to be removably attached onto a receiving structure of a printer, such that an attachment of the base having the optically aligned light source, optical modulator assembly, and lens supported thereon, permits light from the optical modulator assembly to be focussed onto an optical element of the printer.