OPTI 100H: What is Light?

This is the course page for OPTI 100H: What is Light? or better What is Optics? Simply optics is the study of light, which essentially has three interpretations:

  • Geometrical: light is a ray,
  • Physical: light is a wave, and
  • Quantum: light is both (i.e., wave-particle duality).

We will talk about these three interpretations through the course, while applying it to optics technology, including displays, cameras, lasers, fiber optics, and many other optics technologies. In Optical Sciences we essentially divide the study (research and teaching) into four domains, which are:

  • Optical Engineering: examine and develop different uses of light with instruments like lenses, spectrometers and interferometers; they build the practical devices that put light to use. In this area one works a lot with geometrical optics, but physical optics also plays a role. It is the most applied of the four areas.
  • Image Science: investigates the ways that image quality can be defined, measured and optimized; it touches and improves the visualization of everything from healthy bones to unstable atmosphere to millennia-old geological formations. In this area one works a lot with geometrical optics and physical optics, and there is also some quantum optics. It is the second most applied of the four areas.
  • Photonics: is the science of the dual nature of light, emphasizing that it is both particle and wave at once; it covers the research and application of light from ultraviolet to the infrared. In this area one works a lot with quantum and physical optics, and there is some geometrical optics. It is the second most fundamental of the four areas.
  • Optical Physics: concentrates on the inspection, manipulation and control of electromagnetic radiation in relation to matter, focusing on the discovery and application of new phenomena. Optical physicists use and develop light sources that span the electromagnetic spectrum from microwaves to X-rays. In this area one works a lot with quantum optics, there is some physical optics, and you might use a little geometrical optics. It is the most fundamental of the four areas.

We will touch upon these four areas, especially with visits to active research labs in the College.


How does this course take you on this journey to learn more about optics? Imagine you are looking at your SmartPhone – maybe thinking about how the Giant Magellan Telescope mirrors are being fabricated in the UA’s Richard F. Caris Mirror Lab. So much optics is involved in this – so our journey is done with you simply trying to learn more about these mirrors through your SmartPhone. Here are the optics involved:

  • Eye: light is incident on your retina and then your brain interprets what it is seeing (note that it is conjectured that about 50% of your brain revolves around your visual system – can you think of a better reason to explore optics!).
  • Display: you are looking at the Mirror Lab info on your phone. The display is either OLED or a backlit LED screen. Tons of optics go into making these displays work – from sources to optical layers to color filters.
  • Cameras: visible and infrared cameras exist in bunches on our SmartPhones. They give you all kinds of different formats from wide field of view, telephoto, close-up, and so forth.
  • Proximity sensor: your phone knows when your face is close to screen through optical methods so that it can know to turn off the display.
  • Ambient light sensor: tells you phone how bright to make the display, assists when using the cameras, and so forth.
  • Lidar: stands for light detection and ranging. It typically uses a laser, but it can be any light source used to scan the environment so that ranges to objects in its view.
  • Facial recognition: technology such as dot projectors put an extensive pattern of infrared dots across the illuminated object, and from determination of the sag (i.e., distance away from a plane) each dot is located, the facial recognition device can do an ID check (often called structured illumination).
  • Photolithography: all of the computer chips in your SmartPhone are made with an optical process called photolithography. This process allows for small wire traces (down to 13 nm = 13 x 10-9 m in width) to be made. Without optics there would not be microelectronics. Simply, optics makes technology possible.
  • 5G: fifth generation transmission technology for broadband cellular networks that provides the protocol to take data from your SmartPhone to cell phone towers. The frequency of the light is in the microwave region (between infrared and radio waves, and also often called millimeter-wave), so it is a slight reach to consider this “optics”, but note that a lot of optics professionals work in this area.
  • Fiber-optics: at the cell phone tower, the 5G signal is transferred to a fiber optic network which takes the data with any request to the server that has the information. The fiber optic is comprised of a small inner glass channel (typically around 8 microns = 8 x 10-6 m in diameter) called the core which is embedded in a wider outer glass channel called the cladding. Total internal reflection keeps the pulses of light that represent your data (ones = light pulses and zeros = no light pulses).
  • Lasers: to get these pulses of light into the fiber optics, there are modulated lasers pulsing on and off as required. In a fiber optic the wavelength tends to be 1.5 microns running at a very high repetition rate. The optical signal will be amplified if it has to go a great distance (i.e., over 100 km).
  • Optical switch: to get the signal onto and off the desired fiber, to amplify its signal, and so forth, one uses a switch. Think of this as the ability to transfer a signal from one fiber to another fiber via optical methods while amplifying the signal.
  • Solar power: at the data center where there are servers there is a high demand of electrical power to run the lasers, switches, computers, and many other devices. Thus, they often power them with solar.
  • GMT: at the UA we make the largest precision-made mirrors on the planet including the seven 8.4-meter diameter ones that will comprise the primary mirror for GMT.

Now realize, you have only finished half the journey of the light – photons must now be sent back via fiber optics to a cellphone tower to your phone to your computer chips (made with optics) to your display to your eye. Without optics none of this would be possible, which is why they say the fourth industrial revolution is being led by the photon (the most plentiful fundamental particle, which is the smallest quanta of light).

If you visit all of the links above, you will have barely scratched the field of optics. Optics drives the world around us in this modern age from communications to displays to cameras and to how we make other technologies. In this course we will take the above journey with some segues via lectures, demos, tours, discussions, and a lot of head scratching, saying hmmmmm, and a lot of fun.


I could go on and on! Our students, faculty, staff, and alumni are essentially involved in these technologies, companies, websites, and so forth (well most of them – the bazooka is for fun!). If you find a great site, let me know.