Photonics Glossary

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. Among the elements of photonics explored at the College of Optical Sciences are the following:


Telepresence refers to a set of technologies that allow a person to feel as if they were present, to give the appearance of being present or to have an effect, via telerobotics, at a place other than their true location. Dynamic holography is one approach towards realizing telepresence.


All-optical switching generally refers to a switch that spatially redirects a stream of information that is carried on a light beam. An AOS is often a device where one beam of light, the control beam, is directed into a material whose characteristics are altered, which in turn affects a second beam of light, the signal beam. Through such means it may be possible to create optical transistors that function at much higher speeds than their electrical counterparts.


Electroactive adaptive eyewear provides the user with additional context specific information via pop-up displays or adjusts its optical power based on the user’s needs. A simple example of electroactive adaptive eyewear is electroactive bifocals, where the focusing power of the lens is changed by applying a voltage to liquid crystals that are part of the lens, so that the user can either read or see at a distance without having to switch glasses.


This branch of technology involves components, devices and systems that operate by modification of the optical properties of a material by the application of an electric field. Thus, it concerns the interaction between the electromagnetic (optical) and the electrical (electronic) states of materials. Electro-optic materials include lithium niobate and electro-optic polymers, which have been subject to significant development over the last decade and have potential for integration with silicon photonics.


A fiber laser or fibre laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium and thulium. They are related to doped fiber amplifiers, which provide light amplification without lasing. Fiber nonlinearities, such as stimulated Raman scattering or four-wave mixing, can also provide gain and thus can serve to provide gain for a fiber laser.


Integrated optics technology aims at constructing so-called integrated optical devices or photonic integrated circuits, which contain multiple optical components that are combined to fulfill some more or less complex functions. In most cases, integrated optic devices use optical waveguides to direct light around the device, in much the same way that conductors direct electrons around a semiconductor chip.


Heterogeneous integration refers to the process of combining several different materials on the same integration platform in order to achieve a high-performance photonic integrated circuit. Heterogenous integration is often needed in photonics, since among the prevalent photon materials only semiconductors such as indium phosphide are capable of performing all required functions. An example of heterogeneous integration would be the bonding of a III-V semiconductor laser to a silicon photonic circuit, since a laser cannot be made directly in silicon.


Semiconductor lasers are lasers based on semiconductor gain media, where optical gain is usually achieved by stimulated emission at an interband transition under conditions of a high carrier density in the conduction band. Semiconductor lasers see widespread use as they can often be efficiently electrically pumped. Conventional uses of semiconductor lasers in consumer electronics (DVD players) and optical communications generally do not require power higher than 1-5 milliwatts. Recently, research at OSC and elsewhere has led to the development of semiconductor-based laser systems with powers in the 1W to 1kW level, and these are referred to as high-power semiconductor lasers.


This is the trapping of light inside an optical material by refracting and reflecting the light at critical angles; in a photovoltaic device or optical detector, trapped light will travel further in the material, greatly increasing the probability of absorption and hence the probability of producing charge carriers and hence photocurrent.


Nanophotonics studies the behavior of light on the nanometer scale. It is considered as a branch of photonics that deals with the interaction of light with particles or substances at deeply subwavelength length scales. It also refers to nanoscale devices that are being developed to manage light generation, propagation and detection at these scales.


Nonlinear photonics concerns the propagation of light in photonics structures, such as optical waveguides, in the presence of significant nonlinear optical effects such as second harmonic generation, difference frequency mixing, four-wave mixing, self-phase modulation, stimulated Raman scattering and a host of other phenomena that derive from a nonlinear response of a medium to applied optical and electrical fields.


A magneto-optic effect is any one of a number of phenomena in which an electromagnetic wave propagates through a medium that has been altered by the presence of a quasistatic magnetic field. The most commonly used and observed magneto-optic effect is Faraday rotation, wherein the polarization direction of a light beam traversing a medium is rotated due to the presence of a magnetic field applied along the direction of light propagation. The Faraday effect is nonreciprocal, which means that reflected light that passes back through the medium will have its polarization angle rotated in the same direction as upon its forward traversal, leading to the use of the Faraday effect for the realization of optical isolators.


Optical communications concerns the transmission of information with light, most commonly through the use of optical fiber, which is the communications background of the Internet. Information is imparted to the light by modulating its amplitude, phase and other properties. An optical network is a series of communications links arrayed in such a way as to allow information to be directed to and among a number of potential destinations.


A photovoltaic system (informally, PV system) is an arrangement of components designed to supply usable electric power, using the sun (or, less commonly, other light sources) as the power source. Fundamentally, photovoltaic systems involve the use of semiconductor materials that convert incident solar radiation to electrical power.


Polymer waveguides are optical waveguides that are based on polymers (sometimes known as plastics), rather than conventional glass, oxide or semiconductor materials. Polymer waveguides have the advantage of generally being quite low-cost, and they have unique properties such as flexibility and moldability that present new opportunities for optical waveguides.


Silicon photonics is the study and application of photonic systems that use silicon as an optical medium. Silicon is valued for photonics since it has low optical loss at telecommunications wavelengths, a high refractive index that enables the design of ultracompact optical circuitry and, ultimately, the ability to take advantage of the tremendous silicon manufacturing technology base and potentially integrate electronics with photonics.


Optoelectronics is the study and application of electronic devices that source, detect and control light, and it is usually considered a subfield of photonics. In this context, light often includes invisible forms of radiation, such as ultraviolet and infrared, in addition to visible light. Optoelectronic devices are electrical-to-optical or optical-to-electrical transducers or instruments that use such devices in their operation. Optoelectronics is based on the quantum mechanical effects of light on electronic materials, especially semiconductors, sometimes in the presence of electric fields.


A typical solar concentrator uses lenses, called Fresnel lenses, that take a large area of sunlight and direct it towards a specific spot by bending the rays of light and focusing them. A Fresnel lens is capable of collecting and focusing enough sunlight to burn combustible materials and melt asphalt.


A solid-state laser is a laser that uses a gain medium that is a solid, rather than a liquid as in dye lasers or a gas as in gas lasers. Semiconductor-based lasers are also in the solid state, but they are often considered to be in a separate class from solid-state lasers due to their ability to be electrically pumped.