Optical engineering is the engineering discipline that focuses on the design of equipment and devices that function by using light. It is based on the science of optics, a field of physics that studies the properties and behaviors of visible light and its two nearest neighbors on the electromagnetic spectrum, infrared and ultraviolet. The practice of optical engineering is ancient, and the use of mirrors, shaped and polished crystals, or containers of clear water for purposes such as magnification or focusing sunlight to start fires is more than 2,000 years old. In modern times, this field is important to a very wide array of technologies, including optical instruments such as microscopes and binoculars, lasers, and many commonly used electronic and communication devices.
Some practical applications of optics can be done using a model of electromagnetic radiation based on classical physics. This is because the predictions of modern quantum mechanics diverge noticeably from classical mechanics only at the atomic or subatomic scale or under extremely unusual conditions such as near-absolute zero temperatures. Many modern optical technologies are based on how individual photons interact with atoms and particles, where the predictions of classical mechanics cease to be a useful approximation of reality, and so the science of quantum optics is necessary to understand and master these phenomena. Materials science is also important knowledge for optical engineering.
The design of many devices that use light to view or analyze objects involves optical engineering. Viewing instruments such as binoculars, telescopes, and microscopes use lenses and mirrors to magnify images, while corrective lenses for eyeglasses and contact lenses refract incoming light to compensate for defects in the wearer's vision. Thus, their creation demands considerable scientific knowledge of how these optical components will affect incoming light. Successful optical lens design requires understanding of both how a lens' composition, structure, and shape will affect the functioning of an optical device, and how a lens' shape and materials will affect factors such as the device's mass, size, and distribution of weight, as well as its ability to operate in different conditions.
The design of devices called spectrometers cannot be done without optical engineering. A spectrometer uses the properties of incoming photons to discover information about the chemical composition or other traits of the matter that the light has been emitted by or interacted with. Spectrometers exist in a wide array of different types and are enormously important to modern science and industry, in applications ranging from identifying the composition of minerals to quality control in the metalworking industry to studying the motion of other galaxies.
Optical engineering is likewise essential to fiber-optic technology, which transmits information through cables using pulses of light instead of electricity. Optical fibers are flexible materials that can be used as waveguides, materials that can guide the direction of light. They guide light as it travels by taking advantage of a phenomenon called total internal reflection, which keeps the light channeled down the core of the fiber. The design of optical fibers requires an understanding of how light is refracted as it moves through different media, along with the refractive qualities of different materials. Fiber-optics are essential to modern communication technologies, such as telephones, high-speed Internet, and cable television, due to their enormous capacity.
The design of lasers, which produce narrow beams of coherent light, also relies heavily on optical engineering. Lasers work by energetically exciting a material, called a gain medium, until it begins releasing energy in the form of photons. Designing a working laser involves knowledge of both the quantum properties of light and of different materials that can be used as gain media in order to create photons with the qualities necessary for the laser's intended use and of how optical equipment such as lenses and mirrors can focus that light. Laser technology is widely used in modern life. It is the basis for optical disk media formats such as CDs and DVDs, the detection technology LIDAR (light detection and ranging), and in many industrial applications.