Types of Optics: A Quick Guide

by Joseph

Everyone has been there. You look up into the sky after it rains and see a beautiful rainbow arching across the sky. But what causes this pattern of colors to form?

After it rains, there are still lots of tiny water droplets suspended in the air. These droplets act like prisms to split the light from the sun into its many colors.

In addition to prisms, there are many different types of optics that we use all the time. Keep reading to find out all about some common optical devices and how they are used.

Some Background on Light

The word optics comes from the Greek optikos meaning to see. This is related to the Greek word for the eye, ops. Nowadays, the word optics refers to anything having to do with light.

This makes sense because we wouldn’t be able to see anything without light. Everything you see, from the screen in front of you to the plants and animals around you, has had a ray of light bounce off of it and hit your eye.

Although people have been studying light for centuries, it remains somewhat of a mystery. When you turn on a lightbulb, the light seems to fill up the room instantly.

However, it travels at a set speed, and this speed can go up or down depending on what the light moves through. Light seems to contradict itself, exhibiting properties of both particles and waves.

Sometimes it moves in straight lines, getting reflected and refracted. But at other times, it interferes with itself and splits into more than one ray.

Visible light is just a part of the electromagnetic spectrum which includes infrared and ultraviolet light. It extends down to radio waves at one end and up to gamma rays at the other.

Types of Optics

There are many different kinds of optics devices that utilize the effects described above.

Whether you’re looking to do some experiments of your own with light or just trying to make your internet faster, there is an optical device for you.


One of the most common optical devices is the lens. They are everywhere, from eyeglasses to the cameras on all of our phones. Lenses serve to focus light at a single point.

When light travels from one medium, like air, to another, like glass, it bends or refracts. When the glass is curved, parallel rays of light can bend in such a way that they meet at one point. This is the focus or focal point.

Man-made lenses have been around for more than 5,000 years and continue to find new and exciting applications today.


Another common optical device is the polarizer. These are mostly used on the surface of the lens of sunglasses and vehicle mirrors. A polarizer is just a material that absorbs or reflects some light while letting the rest through.

Beams of light have a specific orientation depending on their electric field. This is called its polarization. Normally, light is a cacophony of different polarization states.

However, a polarizer picks out one particular orientation and only allows that to pass through. This reduces the overall intensity of the light and makes it easier to control the light later on.

If you have two polarized sunglasses, you can try turning them at different relative angles to see how it affects the light.

Fiber Optics

One of the most profound innovations in the transfer of information in recent years was the discovery of fiber optics.

Normally, when you flip a switch in your house or turn on your computer, electrons flow through a circuit to provide electricity. Since electrons have mass, they are very slow compared to the speed of light.

This is especially important when it comes to internet speed, where large amounts of data have to travel through miles of electric wires.

Fiber optic technology encodes the data onto a beam of light which travels through the cable at some of the fastest speeds possible.


Just like the little droplets of water in a rainbow, prisms split light into many different colors. White light from the sun or from a lightbulb contains all of the colors of light within it.

However, different colors of light have slightly different frequencies. When light enters a prism, it gets refracted at different angles depending on the frequency.

This means that different colors come off at different angles, producing the rainbows we see.

Passive Optics vs. Active Optics

Passive and active are terms used to describe how an optical system is set up. If you have a network of optical devices that uses switches to control where the light goes, this is an active optical network.

However, if you control where the light goes with things like beamsplitters, this is a passive optical network. Both types have advantages and disadvantages depending on how exactly you want to use the network.


Beamsplitters are exactly what they sound like. They split a beam of light into two or more beams. This is different from prisms because the light isn’t split into its constituent colors.

Instead, beamsplitters allow some light to pass through and reflect the rest at right angles. These can consist of two prisms attached together, as in cemented beamsplitters.

Optical Flats

Optical flats are devices that help to determine how flat or smooth some other material is. They consist of a piece of glass that has been polished so much that it becomes extremely flat.

You may think the glass in your mirror is flat, but there are many imperfections that you can’t see. If you need something to be truly flat, you may need an optical flat to compare it with.

Diffraction Gratings

One way in which light shows the properties of a wave as opposed to a particle is with diffraction. Imagine you shine a light through a very small vertical slit of material.

You might expect the light to come out as a single slit. However, if the slit is small enough, it instead comes out as several points of light spread out horizontally.

This happens because the wave part of the light interferes with itself at different places.

If you’re interested in optical devices and how you might use them, you can discover more here.

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