Often people working in optics and photonics confuse geometric optics with wave optics, but they aren’t the same thing! Geometric optics treats the propagation of light in terms of “rays”, where each ray travels in a straight line. But in wave optics, we consider the propagation of light in terms of electromagnetic waves.
Since light has a dual nature, both geometric optics and wave optics are relevant and incredibly useful in their own way. Geometric optics is most relevant when light reacts with objects several times larger than the light’s wavelength. It’s when light interacts with very small objects— smaller than you can see with your naked eyes— that the wave characteristics come into the foreground.
The path of light in geometrical optics is determined by the laws of reflection and refraction at the interface between different media. Wave optics predicts interference and diffraction, two important concepts that geometric optics can’t explain.
This article is the first of a series on “Avoid Optical Pitfalls”. Each article will look at a topic that is often confused, and provide a brief, easy-to-understand explanation of the key foundational concepts involved.
Wave optics enable us to understand why light separates into colors on a soap bubble.