Photonics

Summary

Photonics is a rapidly emerging field that uses the quantum interpretation that light has both wave and particle aspects that generate, detect, and modify it. Photonics covers the full range of the electromagnetic spectrum, but most applications are in the visible and infrared. Photonic systems are replacing electricity in the transmission, reception, and amplification of telecommunication information. Photonic applications include lasers, photovoltaic solar cells, sensors, detectors, and quantum computers.

Definition and Basic Principles

Photonics is the application of the scientific idea that electromagnetic radiation in all its forms, from radio waves to cosmic rays, exhibits wave and particle behavior. However, these different behaviors cannot be observed simultaneously. Which is observed depends on the physical arrangement at the time of detection. Since this radical idea was presented, science has come to accept this dualism, and photonics is the practical use of this wave-particle duality in instruments and measurement methodologies. Light traveling from source to destination follows the rules of wave motion, but at its emission and reception points it behaves as a particle. Particles emit light energy in localized bundles called photons, and photons transfer their energy when they interact with other particles.

Photonics uses this property to develop instruments sensitive to the interaction of photons with particles in the transmission, detection, and modulation of light. Two properties of light enable it to replace electricity in applications involving information technology and power transmission. Light travels at the fastest speed possible in nature, and through the use of optical waveguides in fiber-optic material, there is almost no loss in the signal.

Background and History

In 1905, Albert Einstein expanded German physicist Max Planck's idea of quantized energy units to explain the photoelectric effect. It was known that certain metals could produce an electric current (photocurrent) when radiated by light energy. The classical understanding posits that if there were sufficient intensity of the light, it would provide enough energy to free bound electrons in the metal's atoms and produce electric current. Einstein realized that instead of a wave of diffuse intensity interacting with the metal's electrons, a local bundle of light carrying one quantum of energy could release the electron if its energy exceeded the energy holding the electron in the atom. This bundle of light was named a photon, and the reaction was viewed as a particle-particle effect instead of a wave-particle interaction.

Soon afterward, other phenomena such as Compton scattering, X-ray production, pair creation, and annihilation were interpreted successfully using a photon model of light. Light retains its wavelike properties as it travels through space. It assumes its photon or particle-like behavior only when it interacts with matter in a detector or at a target.

How It Works

Generation and Emission. An atom's electrons are placed in excited energy states, and as they drop to lower states, photons are emitted. In lasers, light amplification is achieved through stimulated emission in which electrons are excited to a higher-energy state and emit the same photon when they drop in energy. This produces a coherent source of light at a particular frequency.

Transmission. Transmission is the process of sending and receiving a signal from one point to another. In photonics, the signal is sent over an optical fiber waveguide to ensure the integrity of the signal. A transmitted signal may be altered by digitization or modulation in coding for security or error control.

Modulation.Modulation is the varying of any time-input signal (carrier wave) by an accompanying signal (modulating wave) to produce some information that can be processed. In photonics, the two types of modulations are digital and analog. In digital modulation of a laser diode, the output signal is zero when the input current (bias) is at the minimum (threshold) frequency. When the input frequency is greater than the threshold, a constant positive value is produced by the output. In analog modulation, the output signal varies in step with the input frequency.

Signal Processing.Signal processing represents the operations performed on input waveforms that provide amplification, coding, and information. The inputs are either analog or digital representations of time-varying quantities. In photonics, the modulation of a light signal determines the type of processing performed.

Switching. Fiber-optical switches are useful in redirecting the optical signal in an optical network. A two-position switch reroutes a signal to one of two output channels. Factors determining the efficiency of a two-position switch include speed, reproducibility, and cross-talk. Speeds of a few milliseconds are possible with electromechanical switches. Reproducibility provides the same intensity in the signal every time a switch is made. Cross-talk measures how uncoupled one output channel is from the other in a multichannel optical system.

Amplification. There exists an array of optical amplifiers to increase the signal. Optical communications use fiber optic and semiconductor amplifiers. For research, there are Raman and quantum-dot amplifiers.

Photodetection and Sensing. Photodetectors are devices that take light radiation and directly convert it to electrical signals varying the electric current or voltage to replicate the changes in the input light source. In one type, electrons are emitted from the surface of a metal using the photoelectric effect. Photodiodes and photomultipliers operate under this effect. Another type is made of junctions of semiconductors. Electrons or electron holes (positive current) are emitted on the device's absorption of radiant energy. The p-n junction photodiode, the PIN photodiode, and the avalanche photodiode work under this property. Most fiber-optic communication systems employ a PIN or an avalanche photodiode. The effectiveness of a photodetector is measured by the ratio of the output electric current (I) over the input optical power (P).

Applications and Products

Fiber Optics. This includes all the various technologies that use transparent materials to transmit light waves. A traditional fiber-optic cable consists of a bundle of glass threads, each of which can transmit messages in light waves that have been modulated in some fashion. The advantages of transmitting electrons through conducting wire include their travel at the speed of light, less signal loss due to optical waveguides, and greater bandwidth. The data can be transmitted digitally, and the fiber-optic materials are typically lighter than metal cable lines. Fiber optics is used most heavily for local-area networks in data and telecommunications.

The heavy reliance on fiber-optic technology makes necessary the continual development of more efficient optical-fiber materials with ever-increasing switching speeds and more bandwidth to accommodate users' increasing video demands.

Quantum Optics. The peculiar properties of quantum systems using photons make them candidates for quantum computing devices. Through superposition, the basic q-bit state can simultaneously be more than one value. This can lead to properties of a computing system that can perform certain tasks such as code breaking faster and more efficiently than existing binary computers. Using photons that can be polarized into two states, an optical computer can be designed to take advantage of these light quanta. Whether such systems will ever have the stability to serve as computational devices and have the speed and low power consumption of the electronic computers commonly used remains an active research question.

Telecommunications. Optical telecommunication devices send coded information from one location to another through optical fibers. The astonishing growth of the Internet and the ever-increasing demands for more information delivered faster with more efficiency have spurred the development of optical transmission networks. There are optical networks underneath the Earth's oceans and extensive ground-based systems connecting continental communication systems.

Holography.Holography is used optically to store, retrieve, and process information. Its ability to project three-dimensional (3-D) images has allowed for such videos to be more accessible for public viewing. The use of holograms in data storage inside crystals or photopolymers has increased the amount of memory that can be encoded in these structures. Holographic devices are used as security scanners in assessing the contents of packages, determining the authenticity of art, and examining material structures.

Micro-optics. Microphotonics uses the properties of certain materials to reduce light to microscopic size so that it can be used in optical networking applications. Light waves are confined to move in materials because of total internal reflection using wave guides. The materials have a high index of refraction decreasing the critical angle. This enhances the total reflection capabilities. A photonic crystal has several reflections inside the material. Optical waveguides, optical microcavities, and waveguide gratings represent different materials and geometries.

Biophotonics. Biophotonics encompasses all the various interactions of light with biological systems. It refers especially to the effect of photons (quanta of light) on cells, tissues, and organisms. These interactions include emission, detection, absorption, reflection, modification, and creation of radiation from living tissue and materials produced from biological organisms. Areas of application include medicine, agriculture, and environmental science.

Medicine. Medical uses for photonic technologies include laser surgery, vision correction, and endoscopic examinations.

Laser surgery uses laser light to remove diseased tissue or to treat bleeding blood vessels. Lasers are also extensively used in correcting problems in human vision. Laser-assisted in situ keratomileusis (LASIK) is a technique that uses a microkeratome laser to cut flaps in the cornea and remove excess tissue to correct myopia (near-sightedness). An alternative procedure is photorefractive keratectomy (PRK), which uses an excimer laser to reshape the corneal surface. Other optical uses of lasers include removing cataracts and reducing excess ocular pressure to treat glaucoma.

Using a fiber-optic flexible tube and a suitable light source, a physician can obtain visual images of internal organs without more invasive surgery or high-energy X-rays.

Military. Photonic devices have found use in military operations in terms of sensors, particularly infrared. Through the use of light-emitting diodes (LEDs) and lasers, photonics technologies are developed for infantry soldiers on the battlefield and field officers. This technology is also utilized in diverse areas such as navigation, search and rescue, mine laying, and detection. Applications range from an optical scope that enables soldiers to see around obstacles during night operations using a flexible fiber-optic tube to weapons such as low-, medium-, and high-power lasers in the millimeter (microwave) wavelength region.

Careers and Course Work

Photonics is a multidisciplinary field. It has roots in physics through classical optics and quantum theory. The explosion in the applications has been driven by the use of engineering to develop instruments and devices using the particular properties of photons for transmitting, sensing, and detecting.

Career paths include optical engineering, illumination engineering, and optoelectronics. Numerous universities in the United States offer degree programs or conduct research in photonics. Many community colleges offer associate's degrees for careers as laser technicians. The basic undergraduate major would be physics with some emphasis in optics. A typical master's or doctoral program would concentrate on physics and quantum optics or optical engineering with research in lasers or photonics.

The number of industries using photonics technology is growing. Photonics is prevalent in telecommunications, medicine, industrial manufacturing, energy, lighting, remote sensing, security, and defense. Job titles include research physicist, optical engineer, light-show director, laser-manufacturing technician, industrial laser technician, medical laser technician, and fiber-optic packaging and manufacturing engineer.

Social Context and Future Prospects

The photonics industry is important in the ever-growing use of handheld devices for voice, video, and data. The job growth in photonics is anticipated to be in the design and manufacture of display screens for television sets, computer monitors, mobile phones, handheld video-game systems, personal digital assistants, navigation systems, electronic book readers, and electronic tablets such as the iPad. These systems have traditionally used semiconductor light sources such as light-emitting and superluminescent diodes (LEDs and SLDs), fluorescent lamps, and cathode ray tubes (CRTs). Plasma display panels (PDPs) and liquid crystal displays (LCDs) are in great demand. Green photonics develops organic light-emitting diodes (OLEDs) and light-emitting polymers (LEPs).

The design and development of media such as glass or plastic fibers for transmission is another career path in photonics. There is a need for engineers to develop new photonic crystals, photonic crystal fibers, and metal surfaces (nanoplasmonics).

There is also demand for better photodetectors that range from very fast photodiodes (PDs) for communications to charge-coupled devices (CCDs) for digital cameras to solar cells that are used to collect solar energy.

Bibliography

Cvijetic, Milorad. Optical Transmission: Systems Engineering. Artech, 2004.

Hecht, Jeff. Beam: The Race to Make the Laser. Oxford University Press, 2023

Keiser, Gerd. Fiber Optic Communications. Springer Nature Singapore, 2022.

Longdell, Jevon. “Quantum Information: Entanglement on Ice.” Nature 469.7331 (2011): 475–76.

Menzel, Ralf. Photonics: Linear and Nonlinear Interactions of Laser Light and Matter. 2nd ed. Springer, 2007.

Shtykov, Vitaliy V., and Sergey Smolskiy. Introduction to Quantum Electronics and Nonlinear Optics. Springer, 2020.

"What Is Photonics?" Photonics, www.photonics.com/Articles/What‗Is‗Photonics/a65926. Accessed 15 May 2024.

"What Is Photonics?" Synopsis, www.synopsys.com/glossary/what-is-photonics.html. Accessed 12 Jan. 2022.