Ray-optics is commonly used to describe electromagnetic propagation in optical frequencies, yet students have a rather blurred idea and develop a lot of misconceptions about what an optical ray actually is. Most students tend to think of a ray as something similar to a “laser ray” that is transmitted from a starting point to a destination following either a straight-line route or, regarding waveguides, a “zig-zag” route through successive internal reflections. Another common misconception is that, within a waveguide, any totally reflected ray is sustainable and can support signal transmission. Yet, ray-optics is a convenient tool when it comes to an easier approach to fiber-optic phenomena compared to that with the electromagnetic theory.

The article describes a two-hour lecture (in the framework of a course on Optical Communications) whose objective was two-fold: First an attempt was made to present the analogies between ray-optics and electromagnetic theory regarding propagation in optical waveguides with the aim students to comprehend what an optical ray actually is and how the ray-optic considerations are associated with the electromagnetic ones. Core phenomena in that presentation are the reflection, refraction and total reflection as well as propagation through a slab waveguide. Second, the simplicity of ray-optics is utilized to illustrate basic facts of modal and chromatic dispersion in fibers despite the fact that the latter is commonly described through electromagnetic considerations that, however, students find it difficult to comprehend.

The above approach was applied in a two-teaching-hour lecture in the framework of the “Optical Communications” course at the Electrical & Electronic Engineering Educators Dept., School for Pedagogical & Technological Education (ASPETE), Athens, Greece. Given that ASPETE’s graduates have the option to be employed as teachers at technological high schools, they will most probably have to present fiber-optics essentials to their pupils.

The overall procedure was evaluated by means of a short questionnaire, distributed to the students, that should be answered by means of a 5-grade Likert scale. Students’ answers were a strong indication that the above described approach was generally successful.

Future implementations of the described approach may include the use of gaming tools such as Kahoot.

Keywords: Engineering Education, Electrical Engineering Education, Optical waveguides, Optical fibers, Ray optics, Electromagnetics.