Edit Relationship to Other Fields

Photonics is the science of generating, controlling, and detecting photons, particularly in the visible and near infra-red spectrum, but also extending to the ultraviolet (0.2 - 0.35 µm wavelength), long-wave infrared (8 - 12 µm wavelength), and far-infrared/THz portion of the spectrum (e.g., 2-4 THz corresponding to 75-150 µm wavelength) where today quantum cascade lasers are being actively developed. Photonics is an outgrowth of the first practical semiconductor light emitters invented in the early 1960s at General Electric, MIT Lincoln Laboratory, IBM, and RCA and made practical by Zhores Alferov and Dmitri Z. Garbuzov and collaborators working at the Ioffe Physico-Technical Institute and almost simultaneously by Izuo Hayashi and Mort Panish working at Bell Telephone Laboratories.

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] Relationship to other fields

[edit] 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.

[edit] 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 eponymously 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.

[edit] 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] Overview of photonics research

Refraction of waves of photons (light) by a prism

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

Photonic devices include optoelectronic devices such as lasers and photodetectors, as well as optical fiber, photonic crystals, planar waveguides, and other passive optical elements.

Applications of photonics include 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.

[edit] History of photonics

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] Applications of Photonics

Aphrodita aculeata (Sea mouse), showing colourful spines, a remarkable example of photonic engineering by a living organism.

· Consumer Equipment: Barcode scanner, printer, CD/DVD/Blu-ray devices, remote control devices

· Telecommunications: Optical fiber communications , Optical Down converter to Microwave

· Medicine: correction of poor eyesight, laser surgery, surgical endoscopy, tattoo removal

· Industrial manufacturing: the use of lasers for welding, drilling, cutting, and various kinds of surface modification

· Construction: laser levelling, laser rangefinding, smart structures

· Aviation: photonic gyroscopes lacking any moving parts

· Military: IR sensors, command and control, navigation, search and rescue, mine laying and detection

· Entertainment: laser shows, beam effects, holographic art

· Information processing

· Metrology: time and frequency measurements, rangefinding

· Photonic computing: clock distribution and communication between computers, circuit boards, or within optoelectronic integrated circuits; in the future: quantum computing

[edit] Periodicals

· Photonics Spectra

· Laser Focus World

· Optics & Photonics Focus

· Nature Photonics

· Photonics news

· Industrial Laser Solutions

[edit] Sources

What is Photonics?archived copyBBC News: Sea mouse promises bright futureedit

/ Physics portal

BiophotonicsHolographyMicrophotonicsNano-opticsOpticsPhotonic crystalPhotonic crystal fiber

· Quantum optics

Photonic crystals are periodic optical (nano)structures that are designed to affect the motion of photons in a similar way that periodicity of a semiconductor crystal affects the motion of electrons. Photonic crystals occur in nature and in various forms have been studied by science for the last 100 years.

[hide]
· 1 Introduction
· 2 Naturally occurring photonic crystals
· 3 History of photonic crystals
· 4 Fabrication challenges
· 5 Computing photonic band structure
· 6 Applications
· 7 See also
· 8 References
· 9 External links

[edit] Introduction

Photonic crystals are composed of periodic dielectric or metallo-dielectric (nano)structures that affect the propagation of electromagnetic waves (EM) in the same way as the periodic potential in a semiconductor crystal affects the electron motion by defining allowed and forbidden electronic energy bands. Essentially, photonic crystals contain regularly repeating internal regions of high and low dielectric constant. Photons (behaving as waves) propagate through this structure - or not - depending on their wavelength. Wavelengths of light (stream of photons) that are allowed to travel are known as modes. Disallowed bands of wavelengths are called photonic band gaps. This gives rise to distinct optical phenomena such as inhibition of spontaneous emission, high-reflecting omni-directional mirrors and low-loss-waveguiding, amongst others.

Since the basic physical phenomenon is based on diffraction, the periodicity of the photonic crystal structure has to be of the same length-scale as half the wavelength of the EM waves i.e. ~200 nm (blue) to 350 nm (red) for photonic crystals operating in the visible part of the spectrum - the repeating regions of high and low dielectric constants have to be of this dimension. This makes the fabrication of optical photonic crystals cumbersome and complex.

[edit] Naturally occurring photonic crystals

A prominent example of a photonic crystal is the naturally occurring gemstone opal. Its play of colours is essentially a photonic crystal phenomenon based on Bragg diffraction of light on the crystal's lattice planes. Another well-known photonic crystal is found on the wings of some butterflies such as those of genus Morpho.[1][2]

[edit] History of photonic crystals

Although photonic crystals have been studied in one form or another since 1887, the term “photonic crystal” was first used over 100 years later, after Eli Yablonovitch and Sajeev John published two milestone papers on photonic crystals in 1987.[3][4]

Before 1987, one-dimensional photonic crystals in the form of periodic multi-layers dielectric stacks (such as the Bragg mirror) were studied extensively. Lord Rayleigh started their study in 1887[5], by showing that such systems have a one-dimensional photonic band-gap, a spectral range of large reflectivity, known as a stop-band. Today, such structures are used in a diverse range of applications; from reflective coatings to enhancing the efficiency of LEDs to highly reflective mirrors in certain laser cavities (see, for example, VCSEL). A detailed theoretical study of one-dimensional optical structures was performed by Bykov[6], who was the first to investigate the effect of a photonic band-gap on the spontaneous emission from atoms and molecules embedded within the photonic structure. Bykov also speculated as to what could happen if two- or three-dimensional periodic optical structures were used.[7] However, these ideas did not take off until after the publication of two milestone papers in 1987 by Yablonovitch and John. Both these papers concerned high dimensional periodic optical structures – photonic crystals. Yablonovitch’s main motivation was to engineer the photonic density of states, in order to control the spontaneous emission of materials embedded within the photonic crystal; John’s idea was to use photonic crystals to affect the localisation and control of light.

After 1987, the number of research papers concerning photonic crystal began to grow exponentially. However, due to the difficulty of actually fabricating these structures at optical scales (see Fabrication Challenges), early studies were either theoretical or in the microwave regime, where photonic crystals can be built on the far more readily accessible centimetre scale. (This fact is due to a property of the electromagnetic fields known as scale invariance – in essence, the electromagnetic fields, as the solutions to Maxwell's equations, has no natural length scale, and so solutions for centimetre scale structure at microwave frequencies are the same as for nanometre scale structures at optical frequencies.) By 1991, Yablonovitch had demonstrated the first three-dimensional photonic band-gap in the microwave regime.[8]

In 1996, Thomas Krauss made the first demonstration of a two-dimensional photonic crystal at optical wavelengths.[9] This opened up the way for photonic crystals to be fabricated in semiconductor materials by borrowing the methods used in the semiconductor industry. Today, such techniques use photonic crystal slabs, which are two dimensional photonic crystals “etched” into slabs of semiconductor; total internal reflection confines light to the slab, and allows photonic crystal effects, such as engineering the photonic dispersion to be used in the slab. Research is underway around the world to use photonic crystal slabs in integrated computer chips, in order to improve the optical processing of communications both on-chip and between chips.

Although such techniques are still to mature into commercial applications, two-dimensional photonic crystals have found commercial use in the form of photonic crystal fibres (otherwise known as holey fibres, because of the air holes that run through them). Photonic crystal fibres where first developed by Philip Russell in 1998, and can be designed to possess enhanced properties over (normal) optical fibres.

The study of three-dimensional photonic crystals has proceeded more slowly then their two-dimensional counterparts. This is because of the increased difficulty in fabrication; there was no inheritance of readily applicable techniques from the semiconductor industry for fabricators of three-dimensional photonic crystals to draw on. Attempts have been made, however, to adapt some of the same techniques, and quite advanced examples have been demonstrated[10], for example in the construction of "woodpile" structures constructed on a planar layer-by-layer basis. Another strand of research has been to try and construct three-dimensional photonic structures from self-assembly – essentially allowing a mixture of dielectric nano-spheres to settle from solution into three-dimensionally periodic structures possessing photonic band-gaps.

[edit] Fabrication challenges

The major challenge for higher dimensional photonic crystals is in fabrication of these structures, with sufficient precision to prevent scattering losses blurring the crystal properties and with processes that can be robustly mass produced. One promising method of fabrication for two-dimensionally periodic photonic crystals is a photonic-crystal fiber, such as a "holey fiber". Using fiber draw techniques developed for communications fiber it meets these two requirements, and photonic crystal fibres are commercially available. Another promising method for developing two-dimensional photonic crystals is the so-called photonic crystal slab. These structures consist of a slab of material (such as silicon) which can be patterned using techniques borrowed from the semiconductor industry. Such chips offer the potential to combine photonic processing with electronic processing on a single chip.

For three dimensional photonic crystals various techniques[11] have been used including photolithography and etching techniques similar to those used for integrated circuits. Some of these techniques are already commercially available like Nanoscribe's Direct Laser Writing system.[12] To circumvent nanotechnological methods with their complex machinery, alternate approaches have been followed to grow photonic crystals as self-assembled structures from colloidal crystals.

[edit] Computing photonic band structure