Recent advances in information and communication technologies allow the development of tools for educational purposes, promoting changes in the educational paradigm. Nowadays there are lots of digital learning objects stored on numerous repositories with the possibility of being shared among the e-learning community. A learning object is an entity of learning content that can be used several times in different courses or in different situations. In order to be useful, a learning object must be modular, accessible, interoperable and reusable. However, less attention is usually paid to their effectiveness for learning, which can only be assessed by means of the student engagement and the later evaluation results. Student engagement is one of most important factors that affect teaching and student motivation to learn. Computer-based animation and visualization are powerful and motivationally attractive education techniques, which can simplify the presentation of the conceptual frameworks and schematic overviews, thereby enhancing learning. Indeed the teaching of most Engineering disciplines implies the combination of visual animated objects and high interactivity. Those resources require considerable computing time and so it is not possible to access shared servers through Internet, e.g. they must be executed on the user’s PC locally. To this end, several technologies such as Java and Flash are available. Java is usually employed when you need speed or have a very complex simulation. However, Flash has more advantages for e-learning applications. It can be executed on more machines (Flash player has more than a 95% penetration among Internet users), requires a smaller plug-in, allow vector graphics and their user-friendly graphics tools provide an easier way to program 2D and 3D animations using the last version of the powerful programming language called Action Script 3.0. In this paper, several digital learning objects for the explanation of different optical modulation concepts are shown. More specifically, simulation models for the optical response of a laser diode, Mach-Zehnder and electroabsorption modulators were implemented. The interactive Flash animations focus on the influence of the bias point (voltage or current), the dynamic margin with emphasis on clipping and inversion effects, the extinction ratio, the modulation index, as well as a comparison between digital vs. analogue modulation, and direct vs. external modulation.