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Photonics

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Refraction of waves of photons (light) by a prism

The science of photonics includes the generation, emission, transmission, modulation, signal processing, switching, amplification, detection and sensing of light. The term photonics thereby emphasizes that photons are neither particles nor waves - they are different in that they have both particle and wave nature. It basically covers all technical applications of light over the whole spectrum from ultraviolet over the visible to the near, mid and far infrared. Most applications, however, are in the range of the visible and near infrared light. The term Photonics developed as an outgrowth of the first practical semiconductor light emitters invented in the early 1960s and optical fibers developed in the 1970s.

Contents

[edit] Overview of photonics research

The science of photonics includes investigation of the emission, transmission, amplification, detection, and modulation of light.

Light sources

Light sources that are used in photonics are usually more sophisticated than light bulbs. Commonly used light sources in photonics are semiconductor light sources like Light-Emitting Diodes (LEDs), SuperLuminescent Diodes (SLDs) and Lasers as well as fluorescent lamps, Cathode Ray Tubes (CRTs) and plasma screens. It has to be noted that while Cathode Ray Tubes (CRTs), plasma screens and OLED Displays generate their own light, Liquid Crystal Displays (LCDs) like TFT screens require a backlight which is comprised of either Cold Cathode Fluorescent Lamps (CCFLs) or nowadays more often of LEDs.

Characteristic for research on semiconductor light sources is the frequent use of III-V semiconductors instead of the classical semiconductors like silicon and germanium. This is due to the special properties of III-V semiconductors that allow for the implementation of light emitting devices. Examples for material systems used are gallium arsenide (GaAs) and aluminium gallium arsenide (AlGaAs) or other compound semiconductors. They are also used in conjunction with silicon to produce hybrid silicon lasers.

Transmission media

Light can be transmitted through any transparent medium. Often optical fibers like glass fibers or plastic optical fibers (POFs) are used to guide the light along a desired path. In optical communications optical fibers allow for transmission distances of more than 100 km without amplification depending on the bit rate and modulation format used for transmission. A very advanced research topic within photonics is the investigation and fabrication of special structures and "materials" with engineered optical properties. These include photonic crystals, photonic crystal fibers and metamaterials.

Amplifiers

Optical amplifiers are used to amplify an optical signal. Optical amplifiers used in Optical Communications are Doped Fiber Amplifiers (DFAs), Semiconductor Optical Amplifiers (SOAs), Raman amplifiers and parametric amplifiers. A very advanced research topic on optical amplifiers is the research on Quantum-Dot Semiconductor Optical Amplifiers (QD-SOAs)

Detection

Photodetectors are used to detect light. Photodetectors range from very fast Photodiodes (PDs) for communications applications over medium speed Charge Coupled Devices (CCDs) for digital cameras to very slow solar cells that are used for harvesting energy from the sunlight. There are also many other Photodetectors based on thermal, chemical, quantum, photoelectric and other effects.

Modulation

Modulation of a light source is used to encode information on a light source. Modulation can be achieved by modulating the light source directly. One of the easiest examples is to use a flashlight to send Morse code. This, however, is not very fast but still a viable method to transmit information. Another method is to take the light from a light source and modulate it in an external optical modulator like a Mach-Zehnder Modulator (MZM) or an Electroabsorption Modulator (EAM).

An additional topic covered by modulation research is the modulation format. On-Off Keying (OOK) has been the commonly used modulation format in optical communications. In the last years more advanced modulation formats like Phase-Shift Keying (PSK) or even Orthogonal Frequency-Division Multiplexing (OFDM) have been investigated to counteract effects like dispersion that degrade the quality of the received signal after transmission.

Photonic Systems Research

Photonics also includes research on Photonic Systems. This term is often used for optical communication systems. This area of research focuses on the implementation of photonic systems like high speed photonic networks. This also includes research on Optical regenerators which are used to improve the signal quality of an optical signal.

[edit] History of photonics

The word 'Photonics' appeared in the late 1960s to describe a research field whose goal was to use light to perform functions that traditionally fell within the typical domain of electronics, such as telecommunications, information processing, etc.

Photonics as a field really began in 1960, with the invention of the laser, and the laser diode followed in the 1970s by the development of optical fibers as a medium for transmitting information using light beams, and the Erbium-doped fiber amplifier. These inventions formed the basis for the telecommunications revolution of the late 20th century and provided the infrastructure for the internet.

Historically, the term photonics only came into common use among the scientific community in the 1980s as fiber optic transmission of electronic data was adopted widely by telecommunications network operators (although it had earlier been coined). At that time, the term was adopted widely within Bell Laboratories. Its use was confirmed when the IEEE Lasers and Electro-Optics Society established an archival journal named Photonics Technology Letters at the end of the 1980s.

During the period leading up to the dot-com crash circa 2001, photonics as a field was largely focused on telecommunications. However, photonics covers a huge range of science and technology applications, including: Laser manufacturing, Biological and chemical sensing, Medical diagnostics and therapy, Display technology, Optical computing.

Various non-telecom photonics applications exhibit a strong growth particularly since the dot-com crash, partly because many companies have been looking for new application areas quite successfully. A huge further growth of photonics can be expected for the case that the current development of silicon photonics will be successful.

[edit] Relationship to other fields

Classical optics

Photonics is closely related to optics. However optics preceded the discovery that light is quantized (when the photoelectric effect was explained by Albert Einstein in 1905). The tools of optics are the refracting lens, the reflecting mirror, and various optical components which were known prior to 1900. The key tenets of classical optics, such as Huygens Principle, the Maxwell Equations, and wave equations, do not depend on quantum properties of light.

Modern optics

Photonics is approximately synonymous with quantum optics, quantum electronics, electro-optics, and optoelectronics. However each is used with slightly different connotations by scientific and government communities and in the marketplace. Quantum optics often connotes fundamental research, whereas photonics is used to connote applied research and development.

The term photonics more specifically connotes:

  1. the particle properties of light,
  2. the potential of creating signal processing device technologies using photons,
  3. those quantum optical technologies which are manufacturable and can be low-cost, and
  4. an analogy to electronics.

The term optoelectronics connotes devices or circuits comprising both electrical and optical functions, i.e., a thin-film semiconductor device. The term electro-optics came into earlier use and specifically encompasses nonlinear electrical-optical interactions applied, e.g, as bulk crystal modulators such as the Pockels cell, but also includes advanced imaging sensors typically used for surveillance by civilian or government organizations.

Emerging fields

Photonics also relates to the emerging science of quantum information in those cases where it employs photonic methods. Other emerging fields include opto-atomics in which devices integrate both photonic and atomic devices for applications such as precision timekeeping, navigation, and metrology. Another emerging field is polaritonics which differs with photonics in that the fundamental information carrier is a phonon-polariton, which is a mixture of photons and phonons, and operates in the range of frequencies from 300 gigahertz to approximately 10 terahertz.

[edit] Applications

Aphrodita aculeata, a sea mouse, showing colorful spines, a remarkable example of photonic engineering by a living organism

Applications of photonics are ubiquitous. Included are all areas from a common live to the most advanced science, e.g. light detection, telecommunications, information processing, illumination, metrology, spectroscopy, holography, medicine (surgery, vision correction, endoscopy, health monitoring), military technology, laser material processing, visual art, biophotonics, agriculture, and robotics.

Just as applications of electronics have expanded dramatically since the first transistor was invented in 1948, the unique applications of photonics continue to emerge. Those which are established as economically important applications for semiconductor photonic devices include optical data recording, fiber optic telecommunications, laser printing (based on xerography), displays, and optical pumping of high-power lasers. The potential applications of photonics are virtually unlimited and include chemical synthesis, medical diagnostics, on-chip data communication, laser defense, and fusion energy, to name several interesting additional examples.

[edit] See also

Search Wiktionary Look up photonics in Wiktionary, the free dictionary.
Physics portal

[edit] Sources

[edit] External links

International Optical Societies
National Optical Societies
  • EPIC - The European Photonics Industry Consortium
  • OP-TEC - National Science Foundation's National Center for Optics and Photonics Education
  • Photonics Cluster Netherlands - The Internet Portal of the Dutch Photonics Society
Periodicals
Research Networks
  • EURO-FOS - Europe's Research Network on Photonic Systems
  • ePIXnet - European Network of Excellence on Photonic Integrated Components and Circuits
  • BONE - Building the Future Optical Network in Europe
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